- Email: [email protected]
Synthesis and flame retardant properties of cyclophosphazene derivatives containing boron
Accepted Manuscript Synthesis and flame retardant properties of cyclophosphazene derivatives containing boron Lianghui Ai, Shanshan Chen, Jinming Zeng, Ping Liu, Weishi Liu, Yonghong Pan, Dongfa Liu PII:
S0141-3910(18)30248-9
DOI:
10.1016/j.polymdegradstab.2018.07.026
Reference:
PDST 8610
To appear in:
Polymer Degradation and Stability
Received Date: 16 May 2018 Revised Date:
23 July 2018
Accepted Date: 29 July 2018
Please cite this article as: Ai L, Chen S, Zeng J, Liu P, Liu W, Pan Y, Liu D, Synthesis and flame retardant properties of cyclophosphazene derivatives containing boron, Polymer Degradation and Stability (2018), doi: 10.1016/j.polymdegradstab.2018.07.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Synthesis and Flame Retardant Properties of Cyclophosphazene Derivatives Containing Boron Lianghui Aia, Shanshan Chena, Jinming Zenga, Ping Liua ∗, Weishi Liua,b, Yonghong Panc,*, Dongfa Liuc State Key Laboratory of Luminescent Materials and Devices, Research Institute of Materials Science, South China University of Technology, Guangzhou 510640, China b Guangzhou Shine Polymer Technology Co., Ltd., Guangzhou 511400, China c Guangzhou Institute of Quality Supervision Test, Guangzhou 510110, China
RI PT
a
SC
Abstract: An organic compound hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B), containing phosphorus, nitrogen, and boron, was synthesized and
M AN U
characterized. Its flame retardant properties in epoxy resin (EP) were investigated. The results showed that the limiting oxygen index (LOI) value of EP/7%CP-6B reached 32.3% and a UL 94 V-0 rating was attained. When 7 wt.% CP-6B was added, the peak heat release rate (pk-HRR), total heat release (THR), average effective heat combustion
TE D
(av-EHC), average mass loss rate (av-MLR), average CO yield, and average CO2 yield of EP decreased. In addition, the flame-retardant mechanism was investigated using
EP
Laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), energy dispersive X-ray (EDX),
AC C
and Pyrolysis-gas chromatography mass spectrometry (PY-GC-MS). The results revealed that CP-6B was an efficient flame retardant acting in the gas and condensed phases simultaneously.
Keywords: cyclophosphazene derivatives; boron; epoxy resin; flame retardant mechanism
* Corresponding author. Tel.: +86 20 87111686. E-mail address: [email protected] (P. Liu).
ACCEPTED MANUSCRIPT 1. Introduction Over the past few decades, organic halogen-based flame retardants have been widely used due to their low dosage and high flame retardant efficiency [1]. However,
RI PT
these retardants easily produce large amount of smoke and toxic corrosive gases during the burning [2-6]. Therefore, in recent years, the European Union has restricted the use of organic halogen-based flame retardants, such as brominated diphenyl oxide [7,8].
SC
Therefore, more attention is being devoted to the development of organic halogen-free
M AN U
flame retardants [9-12].
Organic phosphorus-containing flame retardants decompose at lower temperatures to produce metaphosphoric acid, which is strong dehydrating agent [13,14]. Although organic phosphorus-containing flame retardants can promote polymer dehydration,
TE D
carbonization, and reduce the condensed phase temperature as well as dilute the oxygen concentration [15-17], high amount of phosphorus is needed to achieve a significant flame retardant effect. This has a negative impact on the materials [18-21]. Organic
EP
nitrogen-containing flame retardants in the combustion can produce a large number of
AC C
non-flammable gases, such as ammonia [22,23]. Non-combustible gases can dilute the oxygen in the air as well as the combustible gases produced through the decomposition of materials. In general, nitrogen-containing flame retardants are not used alone due to the limitations of the nitrogen content [24,25]. Cyclotriphosphazene derivatives have been widely used as flame retardants due to their good thermal stability. However, the efficiency of these flame retardants is not high due to the lower phosphorus content [26-29]. The flame retardants based on hexaphenoxy-cyclotriphosphazene have been
ACCEPTED MANUSCRIPT reported [30-33]. They increase the flame retardant efficiency by adding phosphorus. However, cyclophosphazene derivatives containing boron are rarely reported. Inorganic boron flame retardants have nontoxic stable properties [34-36], but inorganic boron
RI PT
flame retardants have poor compatibility with resins. Organic boron flame retardants have characteristics of low toxicity, no dripping, and smoke suppression [37-40]. In our previous work, a triazine derivative containing boric acid, 2, 4, 6-tris (4-boronic-2-
M AN U
properties of the compound were studied.
SC
thiophene)-1, 3, 5- triazine (3TT-3BA), was synthesized [41,42] and the flame retardant
Epoxy resin (EP) is a very important thermosetting resin and is widely used in diverse areas [43-48]. However, its flammability limits the wider application [49], such as structural materials for electronic equipment, aircraft, terrestrial vehicles [51-53]. In
TE D
this paper, in order to develop a novel organic flame retardant containing boron, phosphorus, and nitrogen, the cyclotriphosphazene derivative called hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B) was synthesized. Using EP as the research
EP
system, the flame retardant properties and related flame retardant mechanism of CP-6B
AC C
were investigated.
2. Experimental section 2.1 Materials
Hexachlorocyclotriphosphazene (HCCP, 99%), 4-Bromophenol (98%), triisopropyl
borate (99%), and n-Butyllithium solution (n-BuLi, 2.5 M in hexane) were obtained from the Beijing HWRK Chem Co., Ltd. Diaminodiphenylmethane (DDM, 99%) was purchased from the Shanghai Macklin Biochemical Technology Co., Ltd. Epoxy resin
ACCEPTED MANUSCRIPT (EP, E-44) with an epoxide equivalent weight of 210–240 g/equiv was supplied by the Xiya Reagent Co., Ltd., China. Tetrahydrofuran (THF), dichloromethane, petroleum ether, acetone, hydrochloric acid (HCl), and sodium hydroxide (NaOH) were purchased
RI PT
from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). 2.2 Synthesis
SC
Scheme 1 shows the synthesis route of CP-6B.
M AN U
Scheme 1. Synthesis route of CP-6B.
2.2.1 Synthesis of Hexakis (4-bromo-phenoxy)-cyclophosphazene (CP-6Br) The compounds 4-Bromophenol (11.94 g, 69.02 mmol) and NaOH (3.11 g, 77.75
TE D
mmol) were dissolved in anhydrous THF (120 mL). The mixture was stirred at reflux for 2 h under nitrogen atmosphere. HCCP (3 g, 8.63 mmol) was dissolved in anhydrous THF (30 mL), added dropwise to the system, and then stirred at reflux for 24 h under
EP
nitrogen atmosphere. The reaction mixture was cooled to room temperature.
AC C
Subsequently, the crude product was obtained by filtration and rotary evaporation. The crude product was purified by a silica gel column with dichloromethane/petroleum ether (1:3, v/v) as the eluant. A white crystal was obtained at a yield of 90.5%. 1H NMR (600 MHz, DMSO-d6, ppm): δ 6.84 (d, 12H), 7.46 (d, 12H) (Fig. S1). 13C NMR (150 MHz, DMSO-d6, ppm): δ 118.42, 123.12, 133.16, 149.16 (Fig. S2).
31
P NMR
(243 MHz, DMSO-d6): δ 8.76 (s, 3P) (Fig. S3). HRMS (ESI) m/z: calcd. for C36H24Br6N3O6P3 (M+H+): 1167.5995; found, 1167.5994 (Fig. S4). FTIR (KBr, cm−1):
ACCEPTED MANUSCRIPT 3085 (Ar-H), 1600 and 1500 (aromatic ring), 1259 (P3N3), 1208 (P=N), 1165 (P-O-C), 961 (P-O-Ph), 887 (P-N), 834 (-C6H4-), 554 (C-Br) (Fig. S5). 2.2.2 Hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B)
RI PT
In a 250 mL round bottom flask, CP-6Br (5 g, 4.28 mmol) was dissolved in anhydrous THF (125 mL), continuously evacuated, and filled with nitrogen three times to ensure an anhydrous, oxygen-free system. The system was cooled to −78 °C using
SC
dry ice/acetone. Then n-BuLi (15.42 mL, 38.55 mmol) was added dropwise. The
M AN U
mixture was stirred at −78 °C for 2 h. The triisopropyl borate (11.87 mL, 51.44 mmol) was then slowly added and the reaction was stirred at −78 °C for 2 h. Then the mixture returned to room temperature and was stirred overnight. THF was removed by rotary evaporation, resulting in a pale yellow solid. The solid was dissolved in water (100 mL),
TE D
and diluted HCl was dropped. The hydrolysis reaction was carried out for 1 h. Subsequently, the solid was filtered and washed with water twice; then it was washed with dichloromethane twice to obtain a white solid at a yield of 70.4%. 1H NMR (600
C NMR (150 MHz, DMSO-d6, ppm): δ 119.95, 130.22, 136.25, 152.09 (Fig. S7). 31P
AC C
13
EP
MHz, DMSO-d6, ppm): δ 6.87 (d, 12H), 7.73 (d, 12H), 8.04 (s, 12H, -OH) (Fig. S6).
NMR (243 MHz, DMSO-d6): δ 9.07 (s, 3P) (Fig. S8). 11B NMR (193 MHz, DMSO-d6, ppm): δ 1.30 (s, 6B) (Fig. S9). FTIR (KBr, cm−1): 3415 (-OH), 1600 and 1500 (aromatic ring), 1350 (B-O), 1259 (P3N3), 1208 (P=N), 1165 (P-O-C), 961 (P-O-Ph), 887 (P-N), 842 (-C6H4-), 760 and 659 (B-C) (Fig. S10). The average particle size (D50): 71.69 um. (Fig. S12 and Table S1) 2.3 Preparation of samples
ACCEPTED MANUSCRIPT Different weights of CP-6B were added to the EP. Table 1 shows the weight ratios of the EP/CP-6B. The mixture was stirred at 80 °C. Then the curing agent DDM was added. The mixture was poured into molds and cured at 80 °C for 2 h, 120 °C for 2 h,
RI PT
and 150 °C for 2 h. Finally, the samples were slowly cooled to room temperature.
SC
Table 1. The weight ratios of the EP samples.
1
M AN U
2.4 Characterization
H NMR spectra were recorded using a Bruker AVANCE-600 MHz NMR
spectrometer (Billerica, MA, USA).
13
C NMR spectra were recorded at 150 MHz.
NMR spectra were recorded at 243 MHz and
31
P
11
B NMR spectra were recorded at 193
TE D
MHz using the same instrument. Fourier Transform Infrared (FTIR) spectra were recorded using a Nicolet 6700 FTIR spectrometer (Madison, WI, USA). Mass spectrometry was performed using a Bruker Agilent 1290 mass spectrometer. The
EP
particle size was tested using a BT-9300S Laser Particle Size Analyzer.
AC C
Thermogravimetric analysis (TG) was performed using a Netzsch 209 F3 thermal analyzer (Selb, Germany) at a heating rate of 10 °C/min under nitrogen atmosphere. Differential scanning calorimetry (DSC) was performed using a Netzsch 204 F1 analyzer at a heating rate of 10 °C/min under nitrogen atmosphere. The limiting oxygen index (LOI) was tested using a Fire Testing Technology (FTT, East Grinstead, UK) instrument, according to ASTM D2863. The dimensions of each sample were 80 mm × 10 mm × 4 mm. Vertical burning (UL 94) tests were performed
ACCEPTED MANUSCRIPT with a FTT UL 94 instrument by using samples with dimensions of 125 mm × 12.7 mm × 3.2 mm, according to the ASTM 3801 guidelines. The burning grades were classified as either V-0, V-1, V-2, or no rating (NR), depending on the self-extinguishing time and
RI PT
dripping. Cone calorimeter (Cone) tests were performed using a FTT instrument according to ISO-5660 guidelines, with an incident flux of 50 kW/m2. The dimensions of the samples were 100 mm × 100 mm × 3 mm.
SC
The images of the residual chars from the cone calorimeter tests were examined
M AN U
using scanning electron microscopy (SEM; Carl Zeiss, Germany) at an accelerating voltage of 10 kV. The elemental analysis of the residual chars from cone calorimeter test was analyzed with an energy dispersive X-ray (EDX).
Laser Raman spectroscopy (LRS) was performed using a laser Raman
TE D
spectrometer (Renishawin Via, Renishaw). X-ray diffraction (XRD) patterns were recorded using a MERCURY CCD X-ray diffractometer (D/max-III, Japan). Pyrolysis-Gas Chromatography Mass Spectrometry (PY-GC-MS) was recorded using a
EP
Pyrolysis-Gas Chromatography Mass Spectrometry (GCMS-QP 2010 plus, Japan).
AC C
The impact strengths were measured with a ZCJ 1320 impact testing machine (Guangdong, China) for which the sample dimensions were 80 mm ×10 mm × 4 mm. 3. Results and discussion 3.1 Thermogravimetric (TG) and differential thermal gravity (DTG) Fig. 1 shows the TG and DTG of CP-6B in nitrogen (a) and air (b). Their thermal decomposition data are summarized in Table 2. The TG curve of CP-6B showed two weight loss stages under nitrogen atmosphere. The first weight loss of CP-6B at about
ACCEPTED MANUSCRIPT 154.2 °C mainly involved conversion of boric acid to boroxine. The second decomposition (350–500 °C) mainly involved degradation of boroxine and CP-6B, which formed B-O-C char [41,42,54,55]. The residual char yield of CP-6B was 34.9%.
RI PT
The TG curve of CP-6B showed three weight loss stages under air atmosphere. The first degradation stage occurred at 154.5 °C, and the second degradation stage occurred at 396.7 °C. This result was consistent with the results under nitrogen atmosphere. The
SC
third degradation stage occurred at 559.2 °C, and the residual char yield of CP-6B was
M AN U
48.0%. This was further oxidation to form a more stable structure.
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
TE D
Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen.
Fig. 2 shows the TG (a) and DTG (b) curves of the pure EP and EP/CP-6B. Their
EP
thermal decomposition data are summarized in Table 3. The pure EP had only one
AC C
decomposition stage and reached the maximum decomposition rate at 395.7 °C. Its residual char yield at 800 °C (W800°C) was 9.7%. When the CP-6B was added, EP/CP-6B exhibited two weight loss stages and correspondingly two differential DTG peaks can be observed. The first stage was in the temperature range of 350 °C–450 °C, corresponding to a strong DTG peak (Tmax1). The decomposition temperatures of the EP/CP-6B were lower than that of pure EP. The reason for this observation was that CP-6B promoted decomposition of EP prior to forming the initial carbon layer
ACCEPTED MANUSCRIPT containing B-O-C. Subsequently, the second stage was in the temperature range of 500 °C–600 °C, corresponding to a small and blunt DTG peak (Tmax2). This was due to the destruction of the initial carbon layer to form a new carbon layer with higher oxygen
RI PT
stability. When the CP-6B was loaded, the residue at 800 °C was higher than that of pure EP. These results indicated that CP-6B promoted the formation of a protective char
SC
and acted as a flame retardant.
M AN U
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen atmosphere.
TE D
Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
3.2 Limiting oxygen index (LOI) and vertical burning
AC C
EP
Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B.
LOI and UL 94 tests were used to study the flame retardant properties of materials.
Table 4 lists the LOI values and UL 94 ratings of pure EP and EP/CP-6B. Pure EP was easy to burn, accompanied by dripping. Thus, pure EP could not pass the UL-94 test. When 1 wt.% CP-6B was added, the LOI value of EP/1%CP-6B reached 29.6%, and the UL-94 rating reached V-1 without dripping. With the increase in the CP-6B mass fraction, the LOI values of EP/3%CP-6B, EP/5%CP-6B and EP/7%CP-6B reached
ACCEPTED MANUSCRIPT 30.8%, 31.4%, and 32.3%, respectively, and their UL-94 rating reached to V-0. CP-6B promoted EP to form carbon layers, which could isolate oxygen and prevent dripping. These results showed that CP-6B had a flame retardant effect. When 10 wt.% CP-6B
RI PT
was added, EP passed the UL-94 rating as well, but its LOI value was only 28.6%. Fig. 3 shows digital images of EP/CP-6B after UL 94 tests. Pure EP burned completely. When CP-6B was added, EP/CP-6B was not completely decomposed. Fig. 4 shows the
SC
digital images of pure EP and EP/CP-6B after LOI tests. Pure EP had almost no residue.
M AN U
With the increase of CP-6B content, the residue content of the sample gradually increased. The addition of CP-6B could extend the carbon layer cover around the EP, isolate the oxygen, and prevent heat exchange, which helped in preventing dripping. When 10 wt.% CP-6B was added, the increase in residual carbon was no longer obvious.
TE D
The reason was that the release of gases increased when 10 wt.% CP-6B was added, the char layer was easily destroyed, which deteriorated the flame retardant effect.
AC C
EP
Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests.
3.3 Cone calorimeter tests
Table 5. Typical cone test parameters for pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT Cone calorimeter is a useful method for evaluating fire behaviors of the composite materials. In general, the combustion parameters used in this method include time to ignition (TTI), peak heat release rate (pk-HRR), heat release rate (HRR), total heat
RI PT
release (THR), average effective heat combustion (av-EHC), fire performance index (FPI), fire growth index (FGI), average mass loss rate (av-MLR), average CO yield (av-COY), and average CO2 yield (av-CO2Y). The combustion parameters are
SC
summarized in Table 5.
M AN U
The effective heat combustion (EHC) reflects the degree of combustion of volatile gas in the gas phase, which is useful for analysis of the flame-retardation mechanism. Table 5 lists the av-EHC values of pure EP and EP/CP-6B. The av-EHC value of EP/CP-6B was lower than that of pure EP. When 7 wt.% CP-6B was incorporated, the
TE D
av-EHC of the sample decreased from 23.8 MJ/kg to 18.7 MJ/kg. The CP-6B promoted EP to form dense carbon layer and inhibited internal resin decomposition. At the same time, the decomposition of CP-6B produced non-flammable gases, which could dilute
EP
the oxygen and combustible gases produced through the decomposition of EP. When 10
AC C
wt.% CP-6B was incorporated, the av-EHC increased again. This was caused by the destruction of the char layer, which caused the internal resin to release more combustible gases. The FPI and FGI are important parameters for evaluating fire hazard. Table 4 lists the FPI values of pure EP and EP/CP-6B. The FPI value of EP/CP-6B was higher than that of pure EP, and the FGI value of EP/CP-6B was lower than that of pure EP. This indicated that the addition of CP-6B could reduce the risk of fire. The FPI value of EP/7%CP-6B was almost 1.8 times higher than that of pure EP, which implied
ACCEPTED MANUSCRIPT that CP-6B could increase the time available to people for escaping in the event of a full-scale fire. Moreover, the FGI value of EP/7%CP-6B was only about 27.7% of the corresponding value of pure EP, which meant that CP-6B could effectively reduce the
RI PT
risk of fire and the combustion intensity of EP. Before addition of CP-6B, the av-COY and av-CO2Y contents of pure EP were 0.013 kg/kg and 0.209 kg/kg, respectively. When CP-6B was added, the amounts of av-COY and av-CO2Y of EP/CP-6B were
SC
lower than those in pure EP. These results indicated that CP-6B promoted the formation
M AN U
of dense and intumescent carbon layers, which inhibited heat exchange and insulated oxygen.
Fig. 5 shows the HRR (a) and THR (b) curves of pure EP and EP/CP-6B. The HRR of pure EP peaked at 95 s, and the pk-HRR of pure EP was 1026 kW/m2. When 7 wt.%
TE D
CP-6B was added to the sample, the HRR of the sample peaked at 120 s, and the pk-HRR of EP/7%CP-6B was 359 kW/m2. The THR of pure EP was the highest, and its value was 83 MJ/m2. With the increased CP-6B mass fraction, the THR decreased
EP
gradually. When 7 wt.% CP-6B was loaded, the THR decreased to 54 MJ/m2. The
AC C
CP-6B could promote EP dehydration, carbonization, and reduced the condensed phase temperature. This could suppress the decomposition of EP and reduce HRR and HRR of EP. When 10 wt.% CP-6B was added, the HRR and THR increased. Excessive gases were released by CP-6B, the char layer developed cracks and holes. The char layer of EP/10%CP-6B could not effectively isolate oxygen and combustion heat.
Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests.
RI PT
The mass loss rate (MLR) expresses the rate of mass loss during the combustion of materials, which can be used to clarify the flame-retardation mechanism in the condensed phase. Fig. 6 shows the mass loss curves of pure EP and EP/CP-6B as
SC
functions of time. Table 5 lists the av-MLR values and the residual char yields of pure
M AN U
EP and EP/CP-6B after cone calorimeter. When 7 wt.% CP-6B was added, the av-MLR was the minimum and the residual char yield reached 22.6%. This was because the char layer and the non-flammable gases had a protective effect on EP. However, when 10 wt.% CP-6B was added, the increase in residual carbon was not obvious. The destroyed
TE D
char layer could not effectively inhibit the decomposition of EP, so the residual carbon was not significantly improved.
EP
Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B,
AC C
(c)EP/3%CP-6B, (d)EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B.
Fig. 7 shows digital photographs of the residual chars after the cone calorimeter
tests. The pure EP burned completely, with almost no carbon residue. However, after adding the CP-6B, the residual chars became intumescent and hard. These results are consistent with the digital images of the LOI tests. This indicated that the CP-6B was active in the condensed phase. However, when 10 wt.% CP-6B was added, excessive
ACCEPTED MANUSCRIPT gases were released by CP-6B, the char layer was easily damaged, and the carbon layer developed cracks. Therefore, the heat resistance of cracked char layer decreased, which deteriorated the flame-retardant effect. This was the reason for the decline in LOI and
RI PT
cone calorimeter data as well. 3.4 SEM
Fig. 8 shows the SEM micrographs of the residual of pure EP and EP/CP-6B after
SC
the cone calorimeter tests. The residual chars of pure EP were fragmented, loose and
M AN U
porous, and could barely play any protective role. However, the residual chars of EP/1%CP-6B and EP/3%CP-6B were continuous and dense, with a few small holes. The residual chars of EP/5%CP-6B and EP/7%CP-6B were very dense, compact, and continuous without any holes. The dense carbon layer can play a protective role by
TE D
isolating oxygen and preventing heat exchange. The residual chars of EP/10%CP-6B had some fragments and holes. Therefore, excessive CP-6B caused destruction of the
EP
carbon layer. The results were consistent with those of LOI tests and cone calorimeter.
AC C
Fig. 8. SEM images of residual chars of (a) pure EP (×200), (b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200), (e) EP/7%CP-6B (×200), and (f) EP/10%CP-6B (×200).
3.5 Flame-retardation mechanism 3.5.1 XRD Fig. 9 shows the XRD pattern of the residual chars of pure EP and EP/7%CP-6B.
ACCEPTED MANUSCRIPT The residual char of EP/7%CP-6B exhibited two obvious sharp diffraction peaks at 2θ = 24.5° and 39.8°, which corresponded to BPO4. BPO4 may be generated during the combustion formation. It is considered to contribute to the flame-retardant properties of
RI PT
the material.
SC
Fig. 9. XRD patterns of residual samples.
M AN U
3.5.2 Morphologies of pure EP and EP/7%CP-6B at different temperatures Fig. 10 shows digital photographs of pure EP and EP/7%CP-6B maintained at various temperatures for 15 min in a muffle furnace. The pure EP began to decompose on the surface at 350 °C and began to expand at 400 °C, and combusted completely at
TE D
650 °C. There was little residual char in the crucible. By contrast, the EP/7%CP-6B retained its shape at 400 °C. At 450 °C, EP/7%CP-6B began to swell on the surface and formed a dense and hard carbon layer. When it maintained at 650 °C for 15 min, the
EP
amount of residual char from EP/7%CP-6B was still as high as 4.30 wt.%. These results
AC C
indicated that pure EP could not form a protective carbon layer without CP-6B, and therefore, it underwent thermal degradation easily. When the CP-6B was added to EP, the thermal stability of EP improved.
Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at various temperatures for 15 min in a muffle furnace.
ACCEPTED MANUSCRIPT 3.5.3 FTIR spectra of pure EP and EP/7%CP-6B
Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for
and (d) EP/7%CP-6B residual char.
RI PT
15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B;
SC
Fig. 11 shows the FTIR spectra of pure EP and EP/7%CP-6B after being
M AN U
maintained at 650 °C for 15 min in a muffle furnace. Pure EP was completely decomposed, and the carbon residue of pure EP had almost no absorption peaks. However, there were many absorption peaks after the decomposition of EP/7%CP-6B. The peak at 1460 cm−1 corresponded to the stretching vibration of B-O-C. The
TE D
absorption peak at 1104 cm−1 corresponded to the stretching vibration peak of P-O. The absorption peak at 942 cm−1 corresponded to the symmetrical stretching vibration peak of O-B-O. The absorption peak at 632 cm−1 corresponded to the bending vibration of
EP
B-O-B. This indicated that the EP/CP-6B was not completely degraded, and it was
AC C
protected by the formed carbon layer. The FTIR results indicated that BPO4 was present in the carbon residue of EP/CP-6B. These results were consistent with the XRD results. 3.5.4 EDX
The elemental analysis of the residual chars from cone calorimeter test was
investigated by EDX. As shown in Table 6, EP/7%CP-6B sample contained phosphorus. This
indicated
the
formation
of
phosphorus-containing
chemical
structure.
EP/7%CP-6B sample showed higher oxygen contents compared with the pure EP
ACCEPTED MANUSCRIPT sample. According to the XRD and FTIR results of the char residue, B-O-C, P-O, and O-B-O structures were formed during combustion. The residue char of EP/7%CP-6B contained BPO4. EP/7% CP-6B formed high thermal-oxidative stability carbon layer
RI PT
under heating and sufficient oxygen. It protected the underlying material from further oxidative decomposition.
M AN U
SC
Table 6. Elemental analysis of the residual char.
3.5.5 LRS
Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
TE D
calorimeter tests.
In general, Raman spectroscopy is used to research the graphitic structure of char
EP
residues. Fig. 12 shows the Raman spectra of the residual chars of pure EP and
AC C
EP/7%CP-6B after the cone calorimeter tests. D and G bands were present in both spectra. The D band at about 1364 cm−1 belonged to disordered graphite or glassy carbon, and the G band at approximately 1614 cm−1 represented a graphic structure, which was related to the vibration of carbon atoms in the graphite layer. The ratio of the integrated intensities of D to G bands (ID/IG) could be used to indicate the degree of graphite structural integrity and the degree of graphitization. The ID/IG value of the char residue of EP/7%CP-6B (2.47) was lower than that of pure EP (2.64). This indicated
ACCEPTED MANUSCRIPT that the degree of graphitization of the residual char of EP/7%CP-6B was higher than that of pure EP. This result illustrated that the intumescent carbon layer had a higher
RI PT
degree of graphitization.
Scheme 2. The decomposition model of CP-6B.
SC
Scheme 2 is the decomposition model of CP-6B. During the combustion process,
M AN U
the boric acid first formed boroxine [41,42,54,55], continued to decompose to generate free radicals and ions. Finally, metaphosphoric acid, phosphoric acid and boric acid were produced. The resulting metaphosphoric acid could promote EP dehydration, carbonization. Phosphoric acid and boric acid formed BPO4 at high temperature [56].
TE D
3.5.6 PY-GC-MS
EP
Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b).
AC C
To investigate the gas-phase flame-retardation mechanism, Pyrolysis-Gas Chromatography Mass Spectrometry was performed to identify the decomposed volatiles. Fig. 13 shows the PY-GC-MS results of EP and EP/7%CP-6B at 450 and 700 °C. At 450 °C, few gas phase volatiles generated from EP and EP/7%CP-6B were observed. The relative intensity of the gas-phase volatiles from EP/7%CP-6B was higher than that from pure EP. It was indicated that CP-6B promoted the decomposition of EP at this stage. However, at 700 °C, pure EP generated a large amount of vapor
ACCEPTED MANUSCRIPT volatiles, and the amount and intensity of EP/7%CP-6B vapor volatiles were considerably lower than those of pure EP. The decomposition of pure EP was very intense and thorough. This indicated that the presence of the CP-6B inhibited the
RI PT
decomposition of EP. This result was consistent with the results of TG and cone calorimeter.
Table 7 lists the assignment of peaks in the mass spectrum of EP, and Table 8 lists
SC
the assignment of peaks in the mass spectrum of EP/7%CP-6B. The number of
M AN U
gas-phase volatiles generated from pure EP was significantly higher than that generated from EP/7%CP-6B. The gas phase volatiles generated from pure EP included hydrocarbons, ketones and molecules containing epoxy groups. In the process of combustion decomposition, EP produced many active free radicals, of which
TE D
H· and ·OH, and H· and ·OH continued to promote the decomposition of EP and accelerate its combustion. The gas-phase volatiles generated owing to the decomposition EP/7%CP-6B were alcohols, phenols, and ammonia, and these
EP
substances were produced at 450 °C. This indicated that CP-6B promoted the
AC C
decomposition of EP/CP-6B to produce small-molecule radicals. These free radicals could capture H· and ·OH during the decomposition of EP; produce stable alcohols, phenols and ammonia; and promote flame-retardation in the gas-phase.
Table 7. Assignment of peaks in PY-GC-MS results of pure EP.
Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B.
ACCEPTED MANUSCRIPT 3.7 Mechanical properties
RI PT
Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
Table 9. Mechanical properties of pure EP and EP/CP-6B.
SC
Owing to the high structural strength and excellent sealing performance of EP, it is
M AN U
widely used in electronic devices [57,58]. Therefore, the mechanical properties of EP are crucial as well [59,60]. The glass transition temperatures of pure EP and EP/CP-6B were measured using DSC, as shown in Fig. 14. All EP materials had only one Tg in the DSC thermograms. When CP-6B was added, the Tg values decreased. Table 9 lists the
TE D
mechanical properties of pure EP and EP/CP-6B. When 3 wt.% CP-6B was added, the impact energy, impact strength, and toughness of EP increased from 0.31 J to 0.55 J, 7.7 kJ·m−2 to 13.8 kJ·m−2, and 76.4 J·m−2 to 138.0 J·m−2, respectively. It attributed the crack
EP
pinning mechanism [61]. EP was easy to crack. When CP-6B was added, CP-6B could
AC C
consume deformation work and prevent crack propagation. This effect enhanced the fracture toughness of EP. When 10 wt.% CP-6B was added, the mechanical properties of EP deteriorated severely. This indicated that excess CP-6B could degrade the mechanical properties of EP. 4. Conclusions An organic compound containing a phosphazene ring and a phenylboronic acid group, namely, hexakis (4-boronic acid-phenoxy) cyclophosphazene (CP-6B), was
ACCEPTED MANUSCRIPT synthesized. CP-6B can decompose nonflammable gases and promote the formation of a dense and hard intumescent carbon layer in EP. When 7 wt.% CP-6B was added, the LOI value reached 32.3%, and the UL 94 V-0 rating was attained; pk-HRR decreased
RI PT
from 1026 kW/m2 to 359 kW/m2; THR decreased from 83 MJ/m2 to 54 MJ/m2; av-EHC decreased from 23.8 MJ/kg to 18.7 MJ/kg. Furthermore, the FPI value of EP/7%CP-6B was almost 1.8 times higher than that of pure EP; FGI value of EP/7%CP-6B was only
SC
about 27.7% that of pure EP; and av-MLR, av-COY, and av-CO2Y of EP decreased.
phosphorus and nitrogen.
Acknowledgements
M AN U
Therefore, CP-6B can induce the synergistic flame-retardant effect of boron,
TE D
This research was financially supported by the NSFC (Grant Nos. 20674022, 20774031, and 21074039), the Natural Science Foundation of Guangdong (Grant Nos. 2010A090100001, 2014A030313241, 2014B090901068, and 2016A010103003), the
EP
Natural Science Foundation of Guangzhou (Grant Nos. 201604010034), and the
AC C
Ministry of Education of the People’s Republic of China (Grant No. 20090172110011).
References
[1] Z.M. Zhu, Y.J. Xu, W. Liao, S.M. Xu, Y.Z. Wang, Highly Flame Retardant Expanded Polystyrene Foams from Phosphorus-Nitrogen-Silicon Synergistic Adhesives, Ind. Eng. Chem. Res. 56 (2017) 4649–4658. [2] J.H. Zhang, Q.H. Kong, L.W. Yang, D.Y. Wang, Few layered Co(OH)2 ultrathin
ACCEPTED MANUSCRIPT nanosheet-based polyurethane nanocomposites with reduced fire hazard: from eco-friendly flame retardance to sustainable recycling, Green Chem. 18 (2016) 3066–3074.
RI PT
[3] C. Shunthirasingham, N. Alexandrou, K.A. Brice, H. Dryfhout-Clark, K. Su, C. Shin, R. Park, A. Pajda, R. Noronha, H. Hung, Temporal trends of halogenated flame
Sci.: Processes Impacts 20 (2018) 469–479.
SC
retardants in the atmosphere of the Canadian Great Lakes Basin (2005-2014), Environ.
M AN U
[4] K. Wenelska, E. Mijowska, Preparation, Thermal Conductivity, and Thermal Stability of Flame Retardant Polyethylene with a exfoliated MoS2/MxOy. New J. Chem. 41 (2017) 13287–13292.
[5] T.T. Xu, P. Li, S.Y. Wu, L.L. Lei, D.F. He, Tris(2-chloroethyl) phosphate (TCEP)
TE D
and tris (2-chloropropyl) phosphate (TCPP) induce locomotor deficits and dopaminergic degeneration in Caenorhabditis elegans. Toxicol. Res. 6 (2017) 63–72. [6] Y.Z. Feng, C.G. He, Y.F. Wen, Y.S. Ye, X.P. Zhou, X.L. Xie, Y.W. Mai, Improving
EP
thermal and flame retardant properties of epoxy resin by functionalized graphene
AC C
containing phosphorous, nitrogen and silicon elements. Composites: Part A 103 (2017) 74–83.
[7] Y.L. Jia, Y. Lu, G.X. Zhang, Y.J. Liang, F.X. Zhang, Facile synthesis of an eco-friendly nitrogen-phosphorus ammonium salt to enhance the durability and flame retardancy of cotton. J. Mater. Chem. A 5 (2017) 9970–9981. [8] A. Ballesteros-Gómez, B.J. De, P.E. Leonards, A novel brominated triazine-based flame retardant (TTBP-TAZ) in plastic consumer products and indoor dust. Environ. Sci.
ACCEPTED MANUSCRIPT Technol. 48 (2014) 4468–4474. [9] H.Z. Wang, H. Niu, J.Y. Dong, Inherently flame retardant polypropylene copolymer. Polymer 126 (2017) 109–115.
RI PT
[10] E. Palacios, P. Leret, M.D. Mata, J.F. Fernández, A.D. Aza, M.A. Rodríguez, F. Rubio-Marcos, Self-Forming 3D Core-Shell Ceramic Nanostructures for Halogen-Free Flame Retardant Materials. ACS Appl. Mater. Interfaces 8 (2016) 9462–9471.
SC
[11] S.A. Isarov, P.W. Lee, J.H. Towslee, K.M. Hoffman, R.D. Davis, J.M. Maia, J.K.
(2016) 504–514.
M AN U
Pokorski, DNA as a flame retardant additive for low-density polyethylene. Polymer 97
[12] S. Dev, P.N. Shah, Y.P. Zhang, D. Ryan, C.J. Hansen, Y. Lee, Synthesis and mechanical properties of flame retardant vinyl ester resin for structural composites.
TE D
Polymer 133 (2017) 20–29.
[13] Y. Zhang, B. Yu, B.B. Wang, K.M. Liew, L. Song, C.M. Wang, Y. Hu, Highly Effective P-P synergy of a Novel DOPO-based Flame Retardant for Epoxy Resin. Ind.
EP
Eng. Chem. Res. 56 (2017) 1245–1255.
AC C
[14] L.J. Qian, F.F. Feng, S. Tang, Bi-phase flame-retardant effect of hexa-phenoxycyclotriphosphazene on rigid polyurethane foams containing expandable graphite. Polymer 55 (2014) 95–101. [15] M.J. Chen, Z.B. Shao, X.L. Wang, L. Chen, Y.Z. Wang, Halogen-Free FlameRetardant Flexible Polyurethane Foam with a Novel Nitrogen-Phosphorus Flame Retardant. Ind. Eng. Chem. Res. 51 (2012) 9769–9776. [16] L. Liu, Z.Z. Wang, X.Y. Xu, Melamine amino trimethylene phosphate as a novel
ACCEPTED MANUSCRIPT flame retardant for rigid polyurethane foams with improved flame retardant, mechanical and thermal properties. J. Appl. Polym. Sci. 134 (2017) 45234–45235. [17] Q.Q. Luo, Y.C. Yuan, C.L. Dong, H.H. Huang, S.M. Liu, J.Q. Zhao, Highly
RI PT
Effective Flame Retardancy of a Novel DPPA-Based Curing Agent for DGEBA Epoxy Resin. Ind. Eng. Chem. Res. 55 (2016) 10880–10888.
[18] Y.Z. Feng, C.G. He, Y.F. Wen, Y.S. Ye, X.P. Zhou, X.L. Xie, Y.W. Mai, Superior
SC
flame retardancy and smoke suppression of epoxy-based composites with phosphorus/
M AN U
nitrogen co-doped graphene. J. Hazard. Mater 346 (2018) 140–151.
[19] R.K. Jian, P. Wang, W.S. Duan, L. Xia, X.L. Zheng, A facile method to flame-retard epoxy resin with maintained mechanical properties through a novel P/N/S-containing flame retardant of tautomerization. Mater. Lett. 204 (2017) 77–80.
TE D
[20] D. Xiao, Z. Li, U. Gohs, U. Wagenknecht, B. Voit, D.Y. Wang, Functionalized allylamine polyphosphate as a novel multifunctional highly efficient fire retardant for polypropylene. Polym. Chem. 8 (2017) 6309–6318.
EP
[21] J. Jing, Y. Zhang, X.L. Tang, Y. Zhou, X.N. Li, B.K. Kandola, Z.P. Fang, Layer by
AC C
layer deposition of polyethylenimine and bio-based polyphosphate on ammonium polyphosphate: A novel hybrid for simultaneously improving the flame retardancy and toughness of polylactic acid. Polymer 108 (2017) 361–371. [22] D.J. Liao, Q.K. Xu, R.W. McCabe, H.V. Babu, X.P. Hu, N. Pan, D.Y. Wang, T.R. Hull,
Ferrocene-Based
Nonphosphorus
Copolymer:
Synthesis,
High-charring
Mechanism, and Its Application in Fire Retardant Epoxy Resin. Ind. Eng. Chem. Res. 56 (2017) 12630–12643.
ACCEPTED MANUSCRIPT [23] H.Y. Ding, K. Huang, S.H. Li, L. Xu, J.L. Xia, M. Li, Synthesis of a novel phosphorus and nitrogen-containing bio-based polyol and its application in flame retardant polyurethane foam. J. Anal. Appl. Pyrolysis 128 (2017) 102–113.
RI PT
[24] B. Zhao, D.Y. Liu, W.J. Liang, F. Li, J.S. Wang, Y.Q. Liu, Bi-phase flame-retardant actions of water-blown rigid polyurethane foam containing diethyl-N, N-bis (2hydroxyethyl) phosphoramide and expandable graphite. J. Anal. Appl. Pyrolysis 124
SC
(2017) 247–255.
M AN U
[25] B. Tawiah, B. Yu, W.Y. Cheung, S.Y. Chan, W. Yang, B. Fei, Synthesis and application of synergistic azo-boron-BPA/polydopamine as efficient flame retardant for poly(lactic acid). Polym. Degrad. Stab. 152 (2018) 64–74.
[26] M.J. Xu, K. Ma, D.W. Jiang, J.X. Zhang, M. Zhao, X.K. Guo, Q. Shao, E. Wujcik,
TE D
B. Li, Z.H. Guo, Hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene chain extender for preparing high-performance flame retardant polyamide 6 composites. Polymer 146 (2018) 63–72.
EP
[27] B. Zhao, W.J. Liang, J.S. Wang, F. Li, Y.Q. Liu, Synthesis of a novel
AC C
bridged-cyclotriphosphazene flame retardant and its application in epoxy resin. Polym. Degrad. Stab. 133 (2016) 162–173. [28] J.Z. Xu, Z.M. He, W.H. Wu, H.Y. Ma, J.X. Xie, H.Q. Qu, Y.H. Jiao, Study of thermal properties of flame retardant epoxy resin treated with hexakis [p(hydroxymethyl) phenoxy]cyclotriphosphazene. J Therm Anal Calorim 114 (2013) 1341–1350. [29] H. Liu, X.D. Wang, D.Z. Wu, Novel cyclotriphosphazene-based epoxy compound
ACCEPTED MANUSCRIPT and its application in halogen-free epoxy thermosetting systems: Synthesis, curing behaviors, and flame retardancy. Polym. Degrad. Stab. 103 (2014) 96–112. [30] L.J. Qian, L.J. Ye, G.Z. Xu, J. Liu, J.Q. Guo, The non-halogen flame retardant based
on a novel
compound with phosphaphenanthrene and
RI PT
epoxy resin
cyclotriphosphazene double functional groups. Polym. Degrad. Stab. 96 (2011) 1118–1124.
SC
[31] M. Pan, R. Huang, T.T. Wang, D.Y. Huang, J.X. Mu, C.L. Zhang, Preparation and
M AN U
properties of epoxy resin composites containing hexaphenoxycyclotriphosphazene. High. Perform. Polym. 26 (2014) 114–121.
[32] R. Yang, W.T. Hu, L. Xu, Y. Song, J.C. Li, Synthesis, mechanical properties and fire behaviors of rigid polyurethane foam with a reactive flame retardant containing
TE D
phosphazene and phosphate. Polym. Degrad. Stab. 122 (2015) 102–109. [33] L.J. Qian, L.J. Ye, Y. Qiu, S.R. Qu, Thermal degradation behavior of the compound containing phosphaphenanthrene and phosphazene groups and its flame retardant
EP
mechanism on epoxy resin. Polymer 52 (2011) 5486–5493.
AC C
[34] X.S. Wang, H.C. Pang, W.D. Chen, Y. Lin, L.S. Zong, G.L. Ning, Controllable Fabrication of Zinc Borate Hierarchical Nanostructure on Brucite Surface for Enhanced Mechanical Properties and Flame Retardant Behaviors. ACS Appl. Mater. Interfaces 6 (2014) 7223–7235.
[35] S. Tang, L.J. Qian, Y. Qiu, Y.P. Dong, High-performance flame retardant epoxy resin based on a bi-group molecule containing phosphaphenanthrene and borate groups. Polym. Degrad. Stab. 153 (2018) 210–219.
ACCEPTED MANUSCRIPT [36] Q.H. Zhang, G.Q. Chen, T.L. Xing, Silk flame retardant finish by ternary silica sol containing boron and nitrogen. Appl. Surf. Sci. 421 (2017) 52–60. [37] S.M. Unlu, U. Tayfun, B. Yildirim, M. Dogan, Effect of boron compounds on fire
RI PT
protection properties of epoxy based intumescent coating. Fire Mater. 41 (2016) 17–28. [38] H.Q. Peng, Y.Z. Wang, Effects of Boric Acid on Flame Retardancy of Intumescent Flame-Retardant Polypropylene Systems Containing a Caged Bicyclic Phosphate. ACS
SC
Sym Ser 1013 (2009) 225–248.
M AN U
[39] G. Guo, J. Sun, C. Zhao, Y. Liu, C.M. Liu, Phosphorus-containing polymers from THPS. VII. Synthesis of phosphorus-containing trialkynes and their metal-free 1, 3dipolar cycloaddition reaction with azidated soybean-oil. Green Chem. 18 (2016) 1278–1286.
TE D
[40] S. Yang, Q.X. Zhang, Y.F. Hu, Synthesis of a novel flame retardant containing phosphorus, nitrogen and boron and its application in flame-retardant epoxy resin. Polym. Degrad. Stab. 133 (2016) 358–366.
EP
[41] T. Zhang, W.S. Liu, M.X. Wang, P. Liu, Y.H. Pan, D.F. Liu, Synthesis of a
AC C
boron/nitrogen-containing compound based on triazine and boronic acid and its flame retardant effect on epoxy resin. High. Perform. Polym. 29 (2016) 1–11. [42] T. Zhang, W.S. Liu, M.X. Wang, P. Liu, Y.H. Pan, D.F. Liu, Synergistic effect of an aromatic boronic acid derivative and magnesium hydroxide on the flame retarding of epoxy resin. Polym. Degrad. Stab. 130 (2016) 257–263. [43] S. Wang, S.Q. Ma, C.X. Xu, Y. Liu, J.Y. Dai, Z.B. Wang, X.Q. Liu, J. Chen, X.B. Shen, J.J. Wei, J. Zhu, Vanillin-Derived High-Performance Flame Retardant Epoxy
ACCEPTED MANUSCRIPT Resins: Facile Synthesis and Properties. Macromolecules 50 (2017) 1892–1901. [44] M. Rajaei, D.Y. Wang, D. Bhattacharyya, Combined effects of ammonium polyphosphate and talc on the fire and mechanical properties of epoxy/glass fabric
RI PT
composites. Compos Part B Eng 113 (2017) 381–390. [45] X. Wang, S. Zhou, W.W. Guo, P.L. Wang, W.Y. Xing, L. Song, Y. Hu, Renewable
ACS Sustainable Chem. Eng. 5 (2017) 3409–3416.
SC
Cardanol-Based Phosphate as a Flame Retardant Toughening Agent for Epoxy Resins.
M AN U
[46] Y. Tan, Z.B. Shao, X.F. Chen, J.W. Long, L. Chen, Y.Z. Wang, Novel Multifunctional Organic-Inorganic Hybrid Curing Agent with High Flame-Retardant Efficiency for Epoxy Resin. ACS Appl. Mater. Interfaces 7 (2015) 17919–17928. [47] Y.C. Li, J. Schulz, S. Mannen, C. Delhom, B. Condon, S. Chang, M. Zammarano,
TE D
J.C. Grunlan, Flame retardant behavior of polyelectrolyte-clay thin film assemblies on cotton fabric. Acs Nano 4 (2010) 3325–3337. [48] J.W. Gu, C.B. Liang, X.M. Zhao, B. Gan, H. Qiu, Y.Q. Guo, X.T. Yang, Q.Y. Zhang,
EP
D.Y. Wang, Highly thermally conductive flame-retardant epoxy nanocomposites with
AC C
reduced ignitability and excellent electrical conductivities. Compos. Sci. Technol. 139 (2017) 83–89.
[49] S.L. Qiu, X. Wang, B. Yu, X.M. Feng, X.W. Mu, R.K.K. Yuen, Y. Hu, Flame-retardant-wrapped polyphosphazene nanotubes: A novel strategy for enhancing the flame retardancy and smoke toxicity suppression of epoxy resins. J. Hazard. Mater. 325 (2017) 327–339. [50] E.N. Kalali, X. Wang, D.Y. Wang, Multifunctional intercalation in layered double
ACCEPTED MANUSCRIPT hydroxide: toward multifunctional nanohybrids for epoxy resin. J. Mater. Chem. A 4 (2016) 2147–2157. [51] T.T. Ma, C.G. Guo, Synergistic effect between melamine cyanurate and a novel
RI PT
flame retardant curing agent containing a caged bicyclic phosphate on flame retardancy and thermal behavior of epoxy resins. J. Anal. Appl. Pyrolysis 124 (2017) 239–246.
[52] X.D. He, W.C. Zhang, R.J. Yang, The Characterization of DOPO/MMT
SC
Nanocompound and its Effect on Flame Retardancy of Epoxy Resin. Compos A-Appl
M AN U
Sci Manuf 98 (2017) 124–135.
[53] S. Yang, J. Wang, S.Q. Huo, L.F. Cheng, M. Wang, Preparation and flame retardancy of an intumescent flame-retardant epoxy resin system constructed by multiple flame-retardant compositions containing phosphorus and nitrogen heterocycle.
TE D
Polym. Degrad. Stab. 119 (2015) 251–259.
[54] V. Benin, S. Durganala, A.B. Morgan, Synthesis and flame retardant testing of new
1180–1190.
EP
boronated and phosphonated aromatic compounds. J. Mater. Chem. 22 (2012)
AC C
[55] V. Benin, B. Gardelle, A.B. Morgan, Heat release of polyurethanes containing potential flame retardants based on boron and phosphorus chemistries, Polym. Degrad. Stab. 106 (2014) 108–121. [56] X. Liu, Y. Zhou, H. Peng, J.W. Hao, Catalyzing charring effect of solid acid boron phosphate on dipentaerythritol during the thermal degradation and combustion. Polym. Degrad. Stab. 119 (2015) 242–250. [57] J.L. Wang, C. Ma, P.L. Wang, S.L. Qiu, W. Cai, Y. Hu, Ultra-low phosphorus
ACCEPTED MANUSCRIPT loading to achieve the superior flame retardancy of epoxy resin. Polym. Degrad. Stab. 149 (2018) 119–128. [58] P. Wang, L. Xia, R.K. Jian, Y.F. Ai, X.L. Zheng, G.L. Chen, J.S. Wang,
RI PT
Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance. Polym. Degrad. Stab. 149 (2018) 69–77.
SC
[59] X.L. Fu, X. Wang, W.Y. Xing, P. Zhang, L. Song, Y. Hu, Two-dimensional
M AN U
cardanol-derived zirconium phosphate hybrid as flame retardant and smoke suppressant for epoxy resin. Polym. Degrad. Stab. 151 (2018) 172–180.
[60] S.Q. Huo, J. Wang, S. Yang, B. Zhang, X. Chen, Q.L. Wu, L.F. Yang, Synthesis of a novel reactive flame retardant containing phosphaphenanthrene and piperidine groups
TE D
and its application in epoxy resin. Polym. Degrad. Stab. 146 (2017) 250–259. [61] Y.L. Liang, R.A. Pearson, The toughening mechanism in hybrid epoxy-silica-
AC C
EP
rubber nanocomposites (HESRNs). Polymer 51 (2010) 4880–4890.
ACCEPTED MANUSCRIPT
Caption Scheme 1. Synthesis route of CP-6B. Scheme 2. The decomposition guess model of CP-6B.
RI PT
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
atmosphere. Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
SC
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen
M AN U
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests. Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests. Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B, (c)
TE D
EP/3%CP-6B, (d) EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B. Fig. 8. SEM images of residual chars of (a) pure EP (×200), (b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200), (e) EP/7%CP-6B (×200), and (f)
EP
EP/10%CP-6B (×200).
AC C
Fig. 9. XRD patterns of residual samples. Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at various temperatures for 15 min in a muffle furnace. Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for 15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B; and (d) EP/7%CP-6B residual char. Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
ACCEPTED MANUSCRIPT calorimeter tests. Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b). Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
RI PT
Table 1. The weight ratios of the EP samples. Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen. Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
SC
Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B.
M AN U
Table 5. Typical cone test parameters for pure EP and EP/CP-6B. Table 6. Elemental analysis of the residual char.
Table 7. Assignment of peaks in PY-GC-MS results of pure EP. Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B.
AC C
EP
TE D
Table 9. Mechanical properties of pure EP and EP/CP-6B.
AC C
EP
TE D
M AN U
SC
Scheme 1. Synthesis route of CP-6B.
RI PT
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Scheme 2. The decomposition model of CP-6B.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
RI PT
ACCEPTED MANUSCRIPT
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen
AC C
EP
TE D
M AN U
SC
atmosphere.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B,
AC C
EP
TE D
M AN U
(c)EP/3%CP-6B, (d)EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 8. SEM images of residual chars of (a) pure EP (×200),
M AN U
(b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200),
AC C
EP
TE D
(e) EP/7%CP-6B (×200), and (f) EP/10%CP-6B (×200).
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 9. XRD patterns of residual samples.
RI PT
ACCEPTED MANUSCRIPT
Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at
AC C
EP
TE D
M AN U
SC
various temperatures for 15 min in a muffle furnace.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for
M AN U
15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B;
AC C
EP
TE D
and (d) EP/7%CP-6B residual char.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
calorimeter tests.
SC
Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b).
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT Table 1. The weight ratios of the EP samples. E-44 (g)
DDM (g)
CP-6B (g)
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
100 100 100 100 100 100
25 25 25 25 25 25
0 1.25 3.75 6.25 8.75 12.5
AC C
EP
TE D
M AN U
SC
RI PT
Samples
ACCEPTED MANUSCRIPT Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen. Tonseta(°C)
Tmax1b(°C)
Tmax2(°C)
Tmax3(°C)
W800 °Cc(%)
Nitrogen
142.3
154.2
394.5
–
34.9
Air
149.5
154.5
396.7
559.2
48.0
Initial temperature at 5% mass loss; bTemperature at the maximum mass loss rate;
c
Residual char yield at 800 °C.
AC C
EP
TE D
M AN U
SC
RI PT
a
ACCEPTED MANUSCRIPT Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
EP
TE D
M AN U
SC
Residual char yield at 800 °C.
AC C
c
RI PT
Samples Tonseta(°C) Tmax1b(°C) Tmax2(°C) W800 °Cc(%) EP 318.9 395.7 – 9.7 EP/1%CP-6B 275.1 384.5 524.4 16.6 EP/3%CP-6B 279.5 388.8 522.4 18.0 EP/5%CP-6B 289.2 390.8 520.8 20.3 EP/7%CP-6B 299.1 388.4 523.6 22.3 EP/10%CP-6B 292.6 387.6 518.8 24.1 a b Initial temperature at 5% mass loss; Temperature at the maximum mass loss rate;
ACCEPTED MANUSCRIPT Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B. UL-94 (3.2 mm)a
Dripping
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
22.8 ± 0.2 29.6 ± 0.2 30.8 ± 0.2 31.4 ± 0.2 32.3 ± 0.2 28.6 ± 0.2
NR V-1 V-0 V-0 V-0 V-0
Yes No No No No No
NR=no rating
RI PT
LOI (%)
AC C
EP
TE D
M AN U
SC
a
Samples
ACCEPTED MANUSCRIPT Table 5. Typical cone test parameters for pure EP and EP/CP-6B. Residual
pk-HRR
THR
av-EHC
FPI
FGI
av-COY
av-CO2Y
av-MLR
(s)
(kW/m2)
(MJ/m2)
(MJ/kg)
(s·m2/kW)
kW/(m2·K)
(kg/kg)
(kg/kg)
(g/s)
EP
36 ± 2
1026 ± 19
83 ± 3
23.8 ± 0.3
0.04
10.80
0.013
0.209
0.76
6.8
EP/1%CP-6B
33 ± 2
709 ± 14
78 ± 4
22.2 ± 0.3
0.05
6.17
0.011
0.188
0.63
11.8
EP/3%CP-6B
30 ± 2
599 ± 16
74 ± 3
20.9 ± 0.3
0.05
5.99
0.011
0.182
0.53
14.6
EP/5%CP-6B
28 ± 2
446 ± 15
58 ± 3
19.8 ± 0.3
0.06
3.71
0.009
0.141
0.40
19.8
EP/7%CP-6B
26 ± 2
359 ± 13
54 ± 3
18.7 ± 0.3
0.07
2.99
0.012
0.175
0.38
22.6
EP/10%CP-6B
27 ± 2
471 ± 18
60 ± 4
19.5 ± 0.3
0.06
3.49
0.011
0.142
0.39
23.0
SC M AN U TE D EP AC C
Samples
RI PT
TTI
char yield(%)
ACCEPTED MANUSCRIPT Table 6. Elemental analysis of the residual char. Sample
C 83.89 65.47
P 0 2.26
AC C
EP
TE D
M AN U
SC
RI PT
EP EP/7%CP-6B
Element composition (wt.%) O N 13.33 2.77 25.05 7.21
ACCEPTED MANUSCRIPT
Peak
Retain Time (min)
m/z
1
1.558
44
13
7.375
2
3.608
92
14
7.817
3
6.758
106
15
8.308
4
7.983
108
5
11.100
164
6
1.767
58
M AN U
Table 7. Assignment of peaks in PY-GC-MS results of pure EP.
7
1.892
98
8
2.525
TE D
EP 78
AC C
9
m/z
RI PT 134
108
16
8.900
132
17
9.225
132
18
9.925
146
19
10.367 135
20
10.900 144
5.058
106
21
11.267
148
5.208
106
22
11.567
160
11
5.550
104
23
11.975
146
12
6.117
120
24
12.408 158
10
Structure
118
SC
Structure
Retain Peak Time (min)
ACCEPTED MANUSCRIPT Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B. m/z
1.758
89
f
13.008
148
b
3.650
92
g
19.583
184
c
6.800
106
h
20.908
278
d
8.125
108
i
15.100
210
e
11.958
134
j
17.525
210
SC
a
Structure
M AN U
m/z
EP AC C
Structure
RI PT
Peak
Retain Time (min)
TE D
Peak
Retain Time (min)
ACCEPTED MANUSCRIPT Table 9. Mechanical properties of pure EP and EP/CP-6B. Toughness (J·m−2) 76.4 121.3 138.0 94.4 77.5 60.6
AC C
EP
TE D
M AN U
SC
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
Impact strength (kJ·m−2) 7.7 12.1 13.8 9.5 7.8 6.1
RI PT
Impact energy (J) 0.31 0.49 0.55 0.38 0.31 0.24
Samples
ACCEPTED MANUSCRIPT
SC
RI PT
Graphical Abstracts
CP-6B can decompose nonflammable gases and promote the formation of a dense
AC C
EP
TE D
M AN U
and hard intumescent carbon layer in EP.
ACCEPTED MANUSCRIPT
Highlights The compound CP-6B contains boron, phosphorus and nitrogen, and CP-6B can play a synergistic flame-retardant effect. The low loading of CP-6B can achieve good flame retardant performance and
RI PT
less damage to mechanical properties. The CP-6B can promote the formation of a dense and hard intumescent carbon
AC C
EP
TE D
M AN U
SC
layer in EP.
S0141-3910(18)30248-9
DOI:
10.1016/j.polymdegradstab.2018.07.026
Reference:
PDST 8610
To appear in:
Polymer Degradation and Stability
Received Date: 16 May 2018 Revised Date:
23 July 2018
Accepted Date: 29 July 2018
Please cite this article as: Ai L, Chen S, Zeng J, Liu P, Liu W, Pan Y, Liu D, Synthesis and flame retardant properties of cyclophosphazene derivatives containing boron, Polymer Degradation and Stability (2018), doi: 10.1016/j.polymdegradstab.2018.07.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Synthesis and Flame Retardant Properties of Cyclophosphazene Derivatives Containing Boron Lianghui Aia, Shanshan Chena, Jinming Zenga, Ping Liua ∗, Weishi Liua,b, Yonghong Panc,*, Dongfa Liuc State Key Laboratory of Luminescent Materials and Devices, Research Institute of Materials Science, South China University of Technology, Guangzhou 510640, China b Guangzhou Shine Polymer Technology Co., Ltd., Guangzhou 511400, China c Guangzhou Institute of Quality Supervision Test, Guangzhou 510110, China
RI PT
a
SC
Abstract: An organic compound hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B), containing phosphorus, nitrogen, and boron, was synthesized and
M AN U
characterized. Its flame retardant properties in epoxy resin (EP) were investigated. The results showed that the limiting oxygen index (LOI) value of EP/7%CP-6B reached 32.3% and a UL 94 V-0 rating was attained. When 7 wt.% CP-6B was added, the peak heat release rate (pk-HRR), total heat release (THR), average effective heat combustion
TE D
(av-EHC), average mass loss rate (av-MLR), average CO yield, and average CO2 yield of EP decreased. In addition, the flame-retardant mechanism was investigated using
EP
Laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), energy dispersive X-ray (EDX),
AC C
and Pyrolysis-gas chromatography mass spectrometry (PY-GC-MS). The results revealed that CP-6B was an efficient flame retardant acting in the gas and condensed phases simultaneously.
Keywords: cyclophosphazene derivatives; boron; epoxy resin; flame retardant mechanism
* Corresponding author. Tel.: +86 20 87111686. E-mail address: [email protected] (P. Liu).
ACCEPTED MANUSCRIPT 1. Introduction Over the past few decades, organic halogen-based flame retardants have been widely used due to their low dosage and high flame retardant efficiency [1]. However,
RI PT
these retardants easily produce large amount of smoke and toxic corrosive gases during the burning [2-6]. Therefore, in recent years, the European Union has restricted the use of organic halogen-based flame retardants, such as brominated diphenyl oxide [7,8].
SC
Therefore, more attention is being devoted to the development of organic halogen-free
M AN U
flame retardants [9-12].
Organic phosphorus-containing flame retardants decompose at lower temperatures to produce metaphosphoric acid, which is strong dehydrating agent [13,14]. Although organic phosphorus-containing flame retardants can promote polymer dehydration,
TE D
carbonization, and reduce the condensed phase temperature as well as dilute the oxygen concentration [15-17], high amount of phosphorus is needed to achieve a significant flame retardant effect. This has a negative impact on the materials [18-21]. Organic
EP
nitrogen-containing flame retardants in the combustion can produce a large number of
AC C
non-flammable gases, such as ammonia [22,23]. Non-combustible gases can dilute the oxygen in the air as well as the combustible gases produced through the decomposition of materials. In general, nitrogen-containing flame retardants are not used alone due to the limitations of the nitrogen content [24,25]. Cyclotriphosphazene derivatives have been widely used as flame retardants due to their good thermal stability. However, the efficiency of these flame retardants is not high due to the lower phosphorus content [26-29]. The flame retardants based on hexaphenoxy-cyclotriphosphazene have been
ACCEPTED MANUSCRIPT reported [30-33]. They increase the flame retardant efficiency by adding phosphorus. However, cyclophosphazene derivatives containing boron are rarely reported. Inorganic boron flame retardants have nontoxic stable properties [34-36], but inorganic boron
RI PT
flame retardants have poor compatibility with resins. Organic boron flame retardants have characteristics of low toxicity, no dripping, and smoke suppression [37-40]. In our previous work, a triazine derivative containing boric acid, 2, 4, 6-tris (4-boronic-2-
M AN U
properties of the compound were studied.
SC
thiophene)-1, 3, 5- triazine (3TT-3BA), was synthesized [41,42] and the flame retardant
Epoxy resin (EP) is a very important thermosetting resin and is widely used in diverse areas [43-48]. However, its flammability limits the wider application [49], such as structural materials for electronic equipment, aircraft, terrestrial vehicles [51-53]. In
TE D
this paper, in order to develop a novel organic flame retardant containing boron, phosphorus, and nitrogen, the cyclotriphosphazene derivative called hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B) was synthesized. Using EP as the research
EP
system, the flame retardant properties and related flame retardant mechanism of CP-6B
AC C
were investigated.
2. Experimental section 2.1 Materials
Hexachlorocyclotriphosphazene (HCCP, 99%), 4-Bromophenol (98%), triisopropyl
borate (99%), and n-Butyllithium solution (n-BuLi, 2.5 M in hexane) were obtained from the Beijing HWRK Chem Co., Ltd. Diaminodiphenylmethane (DDM, 99%) was purchased from the Shanghai Macklin Biochemical Technology Co., Ltd. Epoxy resin
ACCEPTED MANUSCRIPT (EP, E-44) with an epoxide equivalent weight of 210–240 g/equiv was supplied by the Xiya Reagent Co., Ltd., China. Tetrahydrofuran (THF), dichloromethane, petroleum ether, acetone, hydrochloric acid (HCl), and sodium hydroxide (NaOH) were purchased
RI PT
from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). 2.2 Synthesis
SC
Scheme 1 shows the synthesis route of CP-6B.
M AN U
Scheme 1. Synthesis route of CP-6B.
2.2.1 Synthesis of Hexakis (4-bromo-phenoxy)-cyclophosphazene (CP-6Br) The compounds 4-Bromophenol (11.94 g, 69.02 mmol) and NaOH (3.11 g, 77.75
TE D
mmol) were dissolved in anhydrous THF (120 mL). The mixture was stirred at reflux for 2 h under nitrogen atmosphere. HCCP (3 g, 8.63 mmol) was dissolved in anhydrous THF (30 mL), added dropwise to the system, and then stirred at reflux for 24 h under
EP
nitrogen atmosphere. The reaction mixture was cooled to room temperature.
AC C
Subsequently, the crude product was obtained by filtration and rotary evaporation. The crude product was purified by a silica gel column with dichloromethane/petroleum ether (1:3, v/v) as the eluant. A white crystal was obtained at a yield of 90.5%. 1H NMR (600 MHz, DMSO-d6, ppm): δ 6.84 (d, 12H), 7.46 (d, 12H) (Fig. S1). 13C NMR (150 MHz, DMSO-d6, ppm): δ 118.42, 123.12, 133.16, 149.16 (Fig. S2).
31
P NMR
(243 MHz, DMSO-d6): δ 8.76 (s, 3P) (Fig. S3). HRMS (ESI) m/z: calcd. for C36H24Br6N3O6P3 (M+H+): 1167.5995; found, 1167.5994 (Fig. S4). FTIR (KBr, cm−1):
ACCEPTED MANUSCRIPT 3085 (Ar-H), 1600 and 1500 (aromatic ring), 1259 (P3N3), 1208 (P=N), 1165 (P-O-C), 961 (P-O-Ph), 887 (P-N), 834 (-C6H4-), 554 (C-Br) (Fig. S5). 2.2.2 Hexakis (4-boronic acid-phenoxy)-cyclophosphazene (CP-6B)
RI PT
In a 250 mL round bottom flask, CP-6Br (5 g, 4.28 mmol) was dissolved in anhydrous THF (125 mL), continuously evacuated, and filled with nitrogen three times to ensure an anhydrous, oxygen-free system. The system was cooled to −78 °C using
SC
dry ice/acetone. Then n-BuLi (15.42 mL, 38.55 mmol) was added dropwise. The
M AN U
mixture was stirred at −78 °C for 2 h. The triisopropyl borate (11.87 mL, 51.44 mmol) was then slowly added and the reaction was stirred at −78 °C for 2 h. Then the mixture returned to room temperature and was stirred overnight. THF was removed by rotary evaporation, resulting in a pale yellow solid. The solid was dissolved in water (100 mL),
TE D
and diluted HCl was dropped. The hydrolysis reaction was carried out for 1 h. Subsequently, the solid was filtered and washed with water twice; then it was washed with dichloromethane twice to obtain a white solid at a yield of 70.4%. 1H NMR (600
C NMR (150 MHz, DMSO-d6, ppm): δ 119.95, 130.22, 136.25, 152.09 (Fig. S7). 31P
AC C
13
EP
MHz, DMSO-d6, ppm): δ 6.87 (d, 12H), 7.73 (d, 12H), 8.04 (s, 12H, -OH) (Fig. S6).
NMR (243 MHz, DMSO-d6): δ 9.07 (s, 3P) (Fig. S8). 11B NMR (193 MHz, DMSO-d6, ppm): δ 1.30 (s, 6B) (Fig. S9). FTIR (KBr, cm−1): 3415 (-OH), 1600 and 1500 (aromatic ring), 1350 (B-O), 1259 (P3N3), 1208 (P=N), 1165 (P-O-C), 961 (P-O-Ph), 887 (P-N), 842 (-C6H4-), 760 and 659 (B-C) (Fig. S10). The average particle size (D50): 71.69 um. (Fig. S12 and Table S1) 2.3 Preparation of samples
ACCEPTED MANUSCRIPT Different weights of CP-6B were added to the EP. Table 1 shows the weight ratios of the EP/CP-6B. The mixture was stirred at 80 °C. Then the curing agent DDM was added. The mixture was poured into molds and cured at 80 °C for 2 h, 120 °C for 2 h,
RI PT
and 150 °C for 2 h. Finally, the samples were slowly cooled to room temperature.
SC
Table 1. The weight ratios of the EP samples.
1
M AN U
2.4 Characterization
H NMR spectra were recorded using a Bruker AVANCE-600 MHz NMR
spectrometer (Billerica, MA, USA).
13
C NMR spectra were recorded at 150 MHz.
NMR spectra were recorded at 243 MHz and
31
P
11
B NMR spectra were recorded at 193
TE D
MHz using the same instrument. Fourier Transform Infrared (FTIR) spectra were recorded using a Nicolet 6700 FTIR spectrometer (Madison, WI, USA). Mass spectrometry was performed using a Bruker Agilent 1290 mass spectrometer. The
EP
particle size was tested using a BT-9300S Laser Particle Size Analyzer.
AC C
Thermogravimetric analysis (TG) was performed using a Netzsch 209 F3 thermal analyzer (Selb, Germany) at a heating rate of 10 °C/min under nitrogen atmosphere. Differential scanning calorimetry (DSC) was performed using a Netzsch 204 F1 analyzer at a heating rate of 10 °C/min under nitrogen atmosphere. The limiting oxygen index (LOI) was tested using a Fire Testing Technology (FTT, East Grinstead, UK) instrument, according to ASTM D2863. The dimensions of each sample were 80 mm × 10 mm × 4 mm. Vertical burning (UL 94) tests were performed
ACCEPTED MANUSCRIPT with a FTT UL 94 instrument by using samples with dimensions of 125 mm × 12.7 mm × 3.2 mm, according to the ASTM 3801 guidelines. The burning grades were classified as either V-0, V-1, V-2, or no rating (NR), depending on the self-extinguishing time and
RI PT
dripping. Cone calorimeter (Cone) tests were performed using a FTT instrument according to ISO-5660 guidelines, with an incident flux of 50 kW/m2. The dimensions of the samples were 100 mm × 100 mm × 3 mm.
SC
The images of the residual chars from the cone calorimeter tests were examined
M AN U
using scanning electron microscopy (SEM; Carl Zeiss, Germany) at an accelerating voltage of 10 kV. The elemental analysis of the residual chars from cone calorimeter test was analyzed with an energy dispersive X-ray (EDX).
Laser Raman spectroscopy (LRS) was performed using a laser Raman
TE D
spectrometer (Renishawin Via, Renishaw). X-ray diffraction (XRD) patterns were recorded using a MERCURY CCD X-ray diffractometer (D/max-III, Japan). Pyrolysis-Gas Chromatography Mass Spectrometry (PY-GC-MS) was recorded using a
EP
Pyrolysis-Gas Chromatography Mass Spectrometry (GCMS-QP 2010 plus, Japan).
AC C
The impact strengths were measured with a ZCJ 1320 impact testing machine (Guangdong, China) for which the sample dimensions were 80 mm ×10 mm × 4 mm. 3. Results and discussion 3.1 Thermogravimetric (TG) and differential thermal gravity (DTG) Fig. 1 shows the TG and DTG of CP-6B in nitrogen (a) and air (b). Their thermal decomposition data are summarized in Table 2. The TG curve of CP-6B showed two weight loss stages under nitrogen atmosphere. The first weight loss of CP-6B at about
ACCEPTED MANUSCRIPT 154.2 °C mainly involved conversion of boric acid to boroxine. The second decomposition (350–500 °C) mainly involved degradation of boroxine and CP-6B, which formed B-O-C char [41,42,54,55]. The residual char yield of CP-6B was 34.9%.
RI PT
The TG curve of CP-6B showed three weight loss stages under air atmosphere. The first degradation stage occurred at 154.5 °C, and the second degradation stage occurred at 396.7 °C. This result was consistent with the results under nitrogen atmosphere. The
SC
third degradation stage occurred at 559.2 °C, and the residual char yield of CP-6B was
M AN U
48.0%. This was further oxidation to form a more stable structure.
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
TE D
Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen.
Fig. 2 shows the TG (a) and DTG (b) curves of the pure EP and EP/CP-6B. Their
EP
thermal decomposition data are summarized in Table 3. The pure EP had only one
AC C
decomposition stage and reached the maximum decomposition rate at 395.7 °C. Its residual char yield at 800 °C (W800°C) was 9.7%. When the CP-6B was added, EP/CP-6B exhibited two weight loss stages and correspondingly two differential DTG peaks can be observed. The first stage was in the temperature range of 350 °C–450 °C, corresponding to a strong DTG peak (Tmax1). The decomposition temperatures of the EP/CP-6B were lower than that of pure EP. The reason for this observation was that CP-6B promoted decomposition of EP prior to forming the initial carbon layer
ACCEPTED MANUSCRIPT containing B-O-C. Subsequently, the second stage was in the temperature range of 500 °C–600 °C, corresponding to a small and blunt DTG peak (Tmax2). This was due to the destruction of the initial carbon layer to form a new carbon layer with higher oxygen
RI PT
stability. When the CP-6B was loaded, the residue at 800 °C was higher than that of pure EP. These results indicated that CP-6B promoted the formation of a protective char
SC
and acted as a flame retardant.
M AN U
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen atmosphere.
TE D
Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
3.2 Limiting oxygen index (LOI) and vertical burning
AC C
EP
Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B.
LOI and UL 94 tests were used to study the flame retardant properties of materials.
Table 4 lists the LOI values and UL 94 ratings of pure EP and EP/CP-6B. Pure EP was easy to burn, accompanied by dripping. Thus, pure EP could not pass the UL-94 test. When 1 wt.% CP-6B was added, the LOI value of EP/1%CP-6B reached 29.6%, and the UL-94 rating reached V-1 without dripping. With the increase in the CP-6B mass fraction, the LOI values of EP/3%CP-6B, EP/5%CP-6B and EP/7%CP-6B reached
ACCEPTED MANUSCRIPT 30.8%, 31.4%, and 32.3%, respectively, and their UL-94 rating reached to V-0. CP-6B promoted EP to form carbon layers, which could isolate oxygen and prevent dripping. These results showed that CP-6B had a flame retardant effect. When 10 wt.% CP-6B
RI PT
was added, EP passed the UL-94 rating as well, but its LOI value was only 28.6%. Fig. 3 shows digital images of EP/CP-6B after UL 94 tests. Pure EP burned completely. When CP-6B was added, EP/CP-6B was not completely decomposed. Fig. 4 shows the
SC
digital images of pure EP and EP/CP-6B after LOI tests. Pure EP had almost no residue.
M AN U
With the increase of CP-6B content, the residue content of the sample gradually increased. The addition of CP-6B could extend the carbon layer cover around the EP, isolate the oxygen, and prevent heat exchange, which helped in preventing dripping. When 10 wt.% CP-6B was added, the increase in residual carbon was no longer obvious.
TE D
The reason was that the release of gases increased when 10 wt.% CP-6B was added, the char layer was easily destroyed, which deteriorated the flame retardant effect.
AC C
EP
Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests.
3.3 Cone calorimeter tests
Table 5. Typical cone test parameters for pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT Cone calorimeter is a useful method for evaluating fire behaviors of the composite materials. In general, the combustion parameters used in this method include time to ignition (TTI), peak heat release rate (pk-HRR), heat release rate (HRR), total heat
RI PT
release (THR), average effective heat combustion (av-EHC), fire performance index (FPI), fire growth index (FGI), average mass loss rate (av-MLR), average CO yield (av-COY), and average CO2 yield (av-CO2Y). The combustion parameters are
SC
summarized in Table 5.
M AN U
The effective heat combustion (EHC) reflects the degree of combustion of volatile gas in the gas phase, which is useful for analysis of the flame-retardation mechanism. Table 5 lists the av-EHC values of pure EP and EP/CP-6B. The av-EHC value of EP/CP-6B was lower than that of pure EP. When 7 wt.% CP-6B was incorporated, the
TE D
av-EHC of the sample decreased from 23.8 MJ/kg to 18.7 MJ/kg. The CP-6B promoted EP to form dense carbon layer and inhibited internal resin decomposition. At the same time, the decomposition of CP-6B produced non-flammable gases, which could dilute
EP
the oxygen and combustible gases produced through the decomposition of EP. When 10
AC C
wt.% CP-6B was incorporated, the av-EHC increased again. This was caused by the destruction of the char layer, which caused the internal resin to release more combustible gases. The FPI and FGI are important parameters for evaluating fire hazard. Table 4 lists the FPI values of pure EP and EP/CP-6B. The FPI value of EP/CP-6B was higher than that of pure EP, and the FGI value of EP/CP-6B was lower than that of pure EP. This indicated that the addition of CP-6B could reduce the risk of fire. The FPI value of EP/7%CP-6B was almost 1.8 times higher than that of pure EP, which implied
ACCEPTED MANUSCRIPT that CP-6B could increase the time available to people for escaping in the event of a full-scale fire. Moreover, the FGI value of EP/7%CP-6B was only about 27.7% of the corresponding value of pure EP, which meant that CP-6B could effectively reduce the
RI PT
risk of fire and the combustion intensity of EP. Before addition of CP-6B, the av-COY and av-CO2Y contents of pure EP were 0.013 kg/kg and 0.209 kg/kg, respectively. When CP-6B was added, the amounts of av-COY and av-CO2Y of EP/CP-6B were
SC
lower than those in pure EP. These results indicated that CP-6B promoted the formation
M AN U
of dense and intumescent carbon layers, which inhibited heat exchange and insulated oxygen.
Fig. 5 shows the HRR (a) and THR (b) curves of pure EP and EP/CP-6B. The HRR of pure EP peaked at 95 s, and the pk-HRR of pure EP was 1026 kW/m2. When 7 wt.%
TE D
CP-6B was added to the sample, the HRR of the sample peaked at 120 s, and the pk-HRR of EP/7%CP-6B was 359 kW/m2. The THR of pure EP was the highest, and its value was 83 MJ/m2. With the increased CP-6B mass fraction, the THR decreased
EP
gradually. When 7 wt.% CP-6B was loaded, the THR decreased to 54 MJ/m2. The
AC C
CP-6B could promote EP dehydration, carbonization, and reduced the condensed phase temperature. This could suppress the decomposition of EP and reduce HRR and HRR of EP. When 10 wt.% CP-6B was added, the HRR and THR increased. Excessive gases were released by CP-6B, the char layer developed cracks and holes. The char layer of EP/10%CP-6B could not effectively isolate oxygen and combustion heat.
Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests.
RI PT
The mass loss rate (MLR) expresses the rate of mass loss during the combustion of materials, which can be used to clarify the flame-retardation mechanism in the condensed phase. Fig. 6 shows the mass loss curves of pure EP and EP/CP-6B as
SC
functions of time. Table 5 lists the av-MLR values and the residual char yields of pure
M AN U
EP and EP/CP-6B after cone calorimeter. When 7 wt.% CP-6B was added, the av-MLR was the minimum and the residual char yield reached 22.6%. This was because the char layer and the non-flammable gases had a protective effect on EP. However, when 10 wt.% CP-6B was added, the increase in residual carbon was not obvious. The destroyed
TE D
char layer could not effectively inhibit the decomposition of EP, so the residual carbon was not significantly improved.
EP
Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B,
AC C
(c)EP/3%CP-6B, (d)EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B.
Fig. 7 shows digital photographs of the residual chars after the cone calorimeter
tests. The pure EP burned completely, with almost no carbon residue. However, after adding the CP-6B, the residual chars became intumescent and hard. These results are consistent with the digital images of the LOI tests. This indicated that the CP-6B was active in the condensed phase. However, when 10 wt.% CP-6B was added, excessive
ACCEPTED MANUSCRIPT gases were released by CP-6B, the char layer was easily damaged, and the carbon layer developed cracks. Therefore, the heat resistance of cracked char layer decreased, which deteriorated the flame-retardant effect. This was the reason for the decline in LOI and
RI PT
cone calorimeter data as well. 3.4 SEM
Fig. 8 shows the SEM micrographs of the residual of pure EP and EP/CP-6B after
SC
the cone calorimeter tests. The residual chars of pure EP were fragmented, loose and
M AN U
porous, and could barely play any protective role. However, the residual chars of EP/1%CP-6B and EP/3%CP-6B were continuous and dense, with a few small holes. The residual chars of EP/5%CP-6B and EP/7%CP-6B were very dense, compact, and continuous without any holes. The dense carbon layer can play a protective role by
TE D
isolating oxygen and preventing heat exchange. The residual chars of EP/10%CP-6B had some fragments and holes. Therefore, excessive CP-6B caused destruction of the
EP
carbon layer. The results were consistent with those of LOI tests and cone calorimeter.
AC C
Fig. 8. SEM images of residual chars of (a) pure EP (×200), (b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200), (e) EP/7%CP-6B (×200), and (f) EP/10%CP-6B (×200).
3.5 Flame-retardation mechanism 3.5.1 XRD Fig. 9 shows the XRD pattern of the residual chars of pure EP and EP/7%CP-6B.
ACCEPTED MANUSCRIPT The residual char of EP/7%CP-6B exhibited two obvious sharp diffraction peaks at 2θ = 24.5° and 39.8°, which corresponded to BPO4. BPO4 may be generated during the combustion formation. It is considered to contribute to the flame-retardant properties of
RI PT
the material.
SC
Fig. 9. XRD patterns of residual samples.
M AN U
3.5.2 Morphologies of pure EP and EP/7%CP-6B at different temperatures Fig. 10 shows digital photographs of pure EP and EP/7%CP-6B maintained at various temperatures for 15 min in a muffle furnace. The pure EP began to decompose on the surface at 350 °C and began to expand at 400 °C, and combusted completely at
TE D
650 °C. There was little residual char in the crucible. By contrast, the EP/7%CP-6B retained its shape at 400 °C. At 450 °C, EP/7%CP-6B began to swell on the surface and formed a dense and hard carbon layer. When it maintained at 650 °C for 15 min, the
EP
amount of residual char from EP/7%CP-6B was still as high as 4.30 wt.%. These results
AC C
indicated that pure EP could not form a protective carbon layer without CP-6B, and therefore, it underwent thermal degradation easily. When the CP-6B was added to EP, the thermal stability of EP improved.
Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at various temperatures for 15 min in a muffle furnace.
ACCEPTED MANUSCRIPT 3.5.3 FTIR spectra of pure EP and EP/7%CP-6B
Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for
and (d) EP/7%CP-6B residual char.
RI PT
15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B;
SC
Fig. 11 shows the FTIR spectra of pure EP and EP/7%CP-6B after being
M AN U
maintained at 650 °C for 15 min in a muffle furnace. Pure EP was completely decomposed, and the carbon residue of pure EP had almost no absorption peaks. However, there were many absorption peaks after the decomposition of EP/7%CP-6B. The peak at 1460 cm−1 corresponded to the stretching vibration of B-O-C. The
TE D
absorption peak at 1104 cm−1 corresponded to the stretching vibration peak of P-O. The absorption peak at 942 cm−1 corresponded to the symmetrical stretching vibration peak of O-B-O. The absorption peak at 632 cm−1 corresponded to the bending vibration of
EP
B-O-B. This indicated that the EP/CP-6B was not completely degraded, and it was
AC C
protected by the formed carbon layer. The FTIR results indicated that BPO4 was present in the carbon residue of EP/CP-6B. These results were consistent with the XRD results. 3.5.4 EDX
The elemental analysis of the residual chars from cone calorimeter test was
investigated by EDX. As shown in Table 6, EP/7%CP-6B sample contained phosphorus. This
indicated
the
formation
of
phosphorus-containing
chemical
structure.
EP/7%CP-6B sample showed higher oxygen contents compared with the pure EP
ACCEPTED MANUSCRIPT sample. According to the XRD and FTIR results of the char residue, B-O-C, P-O, and O-B-O structures were formed during combustion. The residue char of EP/7%CP-6B contained BPO4. EP/7% CP-6B formed high thermal-oxidative stability carbon layer
RI PT
under heating and sufficient oxygen. It protected the underlying material from further oxidative decomposition.
M AN U
SC
Table 6. Elemental analysis of the residual char.
3.5.5 LRS
Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
TE D
calorimeter tests.
In general, Raman spectroscopy is used to research the graphitic structure of char
EP
residues. Fig. 12 shows the Raman spectra of the residual chars of pure EP and
AC C
EP/7%CP-6B after the cone calorimeter tests. D and G bands were present in both spectra. The D band at about 1364 cm−1 belonged to disordered graphite or glassy carbon, and the G band at approximately 1614 cm−1 represented a graphic structure, which was related to the vibration of carbon atoms in the graphite layer. The ratio of the integrated intensities of D to G bands (ID/IG) could be used to indicate the degree of graphite structural integrity and the degree of graphitization. The ID/IG value of the char residue of EP/7%CP-6B (2.47) was lower than that of pure EP (2.64). This indicated
ACCEPTED MANUSCRIPT that the degree of graphitization of the residual char of EP/7%CP-6B was higher than that of pure EP. This result illustrated that the intumescent carbon layer had a higher
RI PT
degree of graphitization.
Scheme 2. The decomposition model of CP-6B.
SC
Scheme 2 is the decomposition model of CP-6B. During the combustion process,
M AN U
the boric acid first formed boroxine [41,42,54,55], continued to decompose to generate free radicals and ions. Finally, metaphosphoric acid, phosphoric acid and boric acid were produced. The resulting metaphosphoric acid could promote EP dehydration, carbonization. Phosphoric acid and boric acid formed BPO4 at high temperature [56].
TE D
3.5.6 PY-GC-MS
EP
Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b).
AC C
To investigate the gas-phase flame-retardation mechanism, Pyrolysis-Gas Chromatography Mass Spectrometry was performed to identify the decomposed volatiles. Fig. 13 shows the PY-GC-MS results of EP and EP/7%CP-6B at 450 and 700 °C. At 450 °C, few gas phase volatiles generated from EP and EP/7%CP-6B were observed. The relative intensity of the gas-phase volatiles from EP/7%CP-6B was higher than that from pure EP. It was indicated that CP-6B promoted the decomposition of EP at this stage. However, at 700 °C, pure EP generated a large amount of vapor
ACCEPTED MANUSCRIPT volatiles, and the amount and intensity of EP/7%CP-6B vapor volatiles were considerably lower than those of pure EP. The decomposition of pure EP was very intense and thorough. This indicated that the presence of the CP-6B inhibited the
RI PT
decomposition of EP. This result was consistent with the results of TG and cone calorimeter.
Table 7 lists the assignment of peaks in the mass spectrum of EP, and Table 8 lists
SC
the assignment of peaks in the mass spectrum of EP/7%CP-6B. The number of
M AN U
gas-phase volatiles generated from pure EP was significantly higher than that generated from EP/7%CP-6B. The gas phase volatiles generated from pure EP included hydrocarbons, ketones and molecules containing epoxy groups. In the process of combustion decomposition, EP produced many active free radicals, of which
TE D
H· and ·OH, and H· and ·OH continued to promote the decomposition of EP and accelerate its combustion. The gas-phase volatiles generated owing to the decomposition EP/7%CP-6B were alcohols, phenols, and ammonia, and these
EP
substances were produced at 450 °C. This indicated that CP-6B promoted the
AC C
decomposition of EP/CP-6B to produce small-molecule radicals. These free radicals could capture H· and ·OH during the decomposition of EP; produce stable alcohols, phenols and ammonia; and promote flame-retardation in the gas-phase.
Table 7. Assignment of peaks in PY-GC-MS results of pure EP.
Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B.
ACCEPTED MANUSCRIPT 3.7 Mechanical properties
RI PT
Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
Table 9. Mechanical properties of pure EP and EP/CP-6B.
SC
Owing to the high structural strength and excellent sealing performance of EP, it is
M AN U
widely used in electronic devices [57,58]. Therefore, the mechanical properties of EP are crucial as well [59,60]. The glass transition temperatures of pure EP and EP/CP-6B were measured using DSC, as shown in Fig. 14. All EP materials had only one Tg in the DSC thermograms. When CP-6B was added, the Tg values decreased. Table 9 lists the
TE D
mechanical properties of pure EP and EP/CP-6B. When 3 wt.% CP-6B was added, the impact energy, impact strength, and toughness of EP increased from 0.31 J to 0.55 J, 7.7 kJ·m−2 to 13.8 kJ·m−2, and 76.4 J·m−2 to 138.0 J·m−2, respectively. It attributed the crack
EP
pinning mechanism [61]. EP was easy to crack. When CP-6B was added, CP-6B could
AC C
consume deformation work and prevent crack propagation. This effect enhanced the fracture toughness of EP. When 10 wt.% CP-6B was added, the mechanical properties of EP deteriorated severely. This indicated that excess CP-6B could degrade the mechanical properties of EP. 4. Conclusions An organic compound containing a phosphazene ring and a phenylboronic acid group, namely, hexakis (4-boronic acid-phenoxy) cyclophosphazene (CP-6B), was
ACCEPTED MANUSCRIPT synthesized. CP-6B can decompose nonflammable gases and promote the formation of a dense and hard intumescent carbon layer in EP. When 7 wt.% CP-6B was added, the LOI value reached 32.3%, and the UL 94 V-0 rating was attained; pk-HRR decreased
RI PT
from 1026 kW/m2 to 359 kW/m2; THR decreased from 83 MJ/m2 to 54 MJ/m2; av-EHC decreased from 23.8 MJ/kg to 18.7 MJ/kg. Furthermore, the FPI value of EP/7%CP-6B was almost 1.8 times higher than that of pure EP; FGI value of EP/7%CP-6B was only
SC
about 27.7% that of pure EP; and av-MLR, av-COY, and av-CO2Y of EP decreased.
phosphorus and nitrogen.
Acknowledgements
M AN U
Therefore, CP-6B can induce the synergistic flame-retardant effect of boron,
TE D
This research was financially supported by the NSFC (Grant Nos. 20674022, 20774031, and 21074039), the Natural Science Foundation of Guangdong (Grant Nos. 2010A090100001, 2014A030313241, 2014B090901068, and 2016A010103003), the
EP
Natural Science Foundation of Guangzhou (Grant Nos. 201604010034), and the
AC C
Ministry of Education of the People’s Republic of China (Grant No. 20090172110011).
References
[1] Z.M. Zhu, Y.J. Xu, W. Liao, S.M. Xu, Y.Z. Wang, Highly Flame Retardant Expanded Polystyrene Foams from Phosphorus-Nitrogen-Silicon Synergistic Adhesives, Ind. Eng. Chem. Res. 56 (2017) 4649–4658. [2] J.H. Zhang, Q.H. Kong, L.W. Yang, D.Y. Wang, Few layered Co(OH)2 ultrathin
ACCEPTED MANUSCRIPT nanosheet-based polyurethane nanocomposites with reduced fire hazard: from eco-friendly flame retardance to sustainable recycling, Green Chem. 18 (2016) 3066–3074.
RI PT
[3] C. Shunthirasingham, N. Alexandrou, K.A. Brice, H. Dryfhout-Clark, K. Su, C. Shin, R. Park, A. Pajda, R. Noronha, H. Hung, Temporal trends of halogenated flame
Sci.: Processes Impacts 20 (2018) 469–479.
SC
retardants in the atmosphere of the Canadian Great Lakes Basin (2005-2014), Environ.
M AN U
[4] K. Wenelska, E. Mijowska, Preparation, Thermal Conductivity, and Thermal Stability of Flame Retardant Polyethylene with a exfoliated MoS2/MxOy. New J. Chem. 41 (2017) 13287–13292.
[5] T.T. Xu, P. Li, S.Y. Wu, L.L. Lei, D.F. He, Tris(2-chloroethyl) phosphate (TCEP)
TE D
and tris (2-chloropropyl) phosphate (TCPP) induce locomotor deficits and dopaminergic degeneration in Caenorhabditis elegans. Toxicol. Res. 6 (2017) 63–72. [6] Y.Z. Feng, C.G. He, Y.F. Wen, Y.S. Ye, X.P. Zhou, X.L. Xie, Y.W. Mai, Improving
EP
thermal and flame retardant properties of epoxy resin by functionalized graphene
AC C
containing phosphorous, nitrogen and silicon elements. Composites: Part A 103 (2017) 74–83.
[7] Y.L. Jia, Y. Lu, G.X. Zhang, Y.J. Liang, F.X. Zhang, Facile synthesis of an eco-friendly nitrogen-phosphorus ammonium salt to enhance the durability and flame retardancy of cotton. J. Mater. Chem. A 5 (2017) 9970–9981. [8] A. Ballesteros-Gómez, B.J. De, P.E. Leonards, A novel brominated triazine-based flame retardant (TTBP-TAZ) in plastic consumer products and indoor dust. Environ. Sci.
ACCEPTED MANUSCRIPT Technol. 48 (2014) 4468–4474. [9] H.Z. Wang, H. Niu, J.Y. Dong, Inherently flame retardant polypropylene copolymer. Polymer 126 (2017) 109–115.
RI PT
[10] E. Palacios, P. Leret, M.D. Mata, J.F. Fernández, A.D. Aza, M.A. Rodríguez, F. Rubio-Marcos, Self-Forming 3D Core-Shell Ceramic Nanostructures for Halogen-Free Flame Retardant Materials. ACS Appl. Mater. Interfaces 8 (2016) 9462–9471.
SC
[11] S.A. Isarov, P.W. Lee, J.H. Towslee, K.M. Hoffman, R.D. Davis, J.M. Maia, J.K.
(2016) 504–514.
M AN U
Pokorski, DNA as a flame retardant additive for low-density polyethylene. Polymer 97
[12] S. Dev, P.N. Shah, Y.P. Zhang, D. Ryan, C.J. Hansen, Y. Lee, Synthesis and mechanical properties of flame retardant vinyl ester resin for structural composites.
TE D
Polymer 133 (2017) 20–29.
[13] Y. Zhang, B. Yu, B.B. Wang, K.M. Liew, L. Song, C.M. Wang, Y. Hu, Highly Effective P-P synergy of a Novel DOPO-based Flame Retardant for Epoxy Resin. Ind.
EP
Eng. Chem. Res. 56 (2017) 1245–1255.
AC C
[14] L.J. Qian, F.F. Feng, S. Tang, Bi-phase flame-retardant effect of hexa-phenoxycyclotriphosphazene on rigid polyurethane foams containing expandable graphite. Polymer 55 (2014) 95–101. [15] M.J. Chen, Z.B. Shao, X.L. Wang, L. Chen, Y.Z. Wang, Halogen-Free FlameRetardant Flexible Polyurethane Foam with a Novel Nitrogen-Phosphorus Flame Retardant. Ind. Eng. Chem. Res. 51 (2012) 9769–9776. [16] L. Liu, Z.Z. Wang, X.Y. Xu, Melamine amino trimethylene phosphate as a novel
ACCEPTED MANUSCRIPT flame retardant for rigid polyurethane foams with improved flame retardant, mechanical and thermal properties. J. Appl. Polym. Sci. 134 (2017) 45234–45235. [17] Q.Q. Luo, Y.C. Yuan, C.L. Dong, H.H. Huang, S.M. Liu, J.Q. Zhao, Highly
RI PT
Effective Flame Retardancy of a Novel DPPA-Based Curing Agent for DGEBA Epoxy Resin. Ind. Eng. Chem. Res. 55 (2016) 10880–10888.
[18] Y.Z. Feng, C.G. He, Y.F. Wen, Y.S. Ye, X.P. Zhou, X.L. Xie, Y.W. Mai, Superior
SC
flame retardancy and smoke suppression of epoxy-based composites with phosphorus/
M AN U
nitrogen co-doped graphene. J. Hazard. Mater 346 (2018) 140–151.
[19] R.K. Jian, P. Wang, W.S. Duan, L. Xia, X.L. Zheng, A facile method to flame-retard epoxy resin with maintained mechanical properties through a novel P/N/S-containing flame retardant of tautomerization. Mater. Lett. 204 (2017) 77–80.
TE D
[20] D. Xiao, Z. Li, U. Gohs, U. Wagenknecht, B. Voit, D.Y. Wang, Functionalized allylamine polyphosphate as a novel multifunctional highly efficient fire retardant for polypropylene. Polym. Chem. 8 (2017) 6309–6318.
EP
[21] J. Jing, Y. Zhang, X.L. Tang, Y. Zhou, X.N. Li, B.K. Kandola, Z.P. Fang, Layer by
AC C
layer deposition of polyethylenimine and bio-based polyphosphate on ammonium polyphosphate: A novel hybrid for simultaneously improving the flame retardancy and toughness of polylactic acid. Polymer 108 (2017) 361–371. [22] D.J. Liao, Q.K. Xu, R.W. McCabe, H.V. Babu, X.P. Hu, N. Pan, D.Y. Wang, T.R. Hull,
Ferrocene-Based
Nonphosphorus
Copolymer:
Synthesis,
High-charring
Mechanism, and Its Application in Fire Retardant Epoxy Resin. Ind. Eng. Chem. Res. 56 (2017) 12630–12643.
ACCEPTED MANUSCRIPT [23] H.Y. Ding, K. Huang, S.H. Li, L. Xu, J.L. Xia, M. Li, Synthesis of a novel phosphorus and nitrogen-containing bio-based polyol and its application in flame retardant polyurethane foam. J. Anal. Appl. Pyrolysis 128 (2017) 102–113.
RI PT
[24] B. Zhao, D.Y. Liu, W.J. Liang, F. Li, J.S. Wang, Y.Q. Liu, Bi-phase flame-retardant actions of water-blown rigid polyurethane foam containing diethyl-N, N-bis (2hydroxyethyl) phosphoramide and expandable graphite. J. Anal. Appl. Pyrolysis 124
SC
(2017) 247–255.
M AN U
[25] B. Tawiah, B. Yu, W.Y. Cheung, S.Y. Chan, W. Yang, B. Fei, Synthesis and application of synergistic azo-boron-BPA/polydopamine as efficient flame retardant for poly(lactic acid). Polym. Degrad. Stab. 152 (2018) 64–74.
[26] M.J. Xu, K. Ma, D.W. Jiang, J.X. Zhang, M. Zhao, X.K. Guo, Q. Shao, E. Wujcik,
TE D
B. Li, Z.H. Guo, Hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene chain extender for preparing high-performance flame retardant polyamide 6 composites. Polymer 146 (2018) 63–72.
EP
[27] B. Zhao, W.J. Liang, J.S. Wang, F. Li, Y.Q. Liu, Synthesis of a novel
AC C
bridged-cyclotriphosphazene flame retardant and its application in epoxy resin. Polym. Degrad. Stab. 133 (2016) 162–173. [28] J.Z. Xu, Z.M. He, W.H. Wu, H.Y. Ma, J.X. Xie, H.Q. Qu, Y.H. Jiao, Study of thermal properties of flame retardant epoxy resin treated with hexakis [p(hydroxymethyl) phenoxy]cyclotriphosphazene. J Therm Anal Calorim 114 (2013) 1341–1350. [29] H. Liu, X.D. Wang, D.Z. Wu, Novel cyclotriphosphazene-based epoxy compound
ACCEPTED MANUSCRIPT and its application in halogen-free epoxy thermosetting systems: Synthesis, curing behaviors, and flame retardancy. Polym. Degrad. Stab. 103 (2014) 96–112. [30] L.J. Qian, L.J. Ye, G.Z. Xu, J. Liu, J.Q. Guo, The non-halogen flame retardant based
on a novel
compound with phosphaphenanthrene and
RI PT
epoxy resin
cyclotriphosphazene double functional groups. Polym. Degrad. Stab. 96 (2011) 1118–1124.
SC
[31] M. Pan, R. Huang, T.T. Wang, D.Y. Huang, J.X. Mu, C.L. Zhang, Preparation and
M AN U
properties of epoxy resin composites containing hexaphenoxycyclotriphosphazene. High. Perform. Polym. 26 (2014) 114–121.
[32] R. Yang, W.T. Hu, L. Xu, Y. Song, J.C. Li, Synthesis, mechanical properties and fire behaviors of rigid polyurethane foam with a reactive flame retardant containing
TE D
phosphazene and phosphate. Polym. Degrad. Stab. 122 (2015) 102–109. [33] L.J. Qian, L.J. Ye, Y. Qiu, S.R. Qu, Thermal degradation behavior of the compound containing phosphaphenanthrene and phosphazene groups and its flame retardant
EP
mechanism on epoxy resin. Polymer 52 (2011) 5486–5493.
AC C
[34] X.S. Wang, H.C. Pang, W.D. Chen, Y. Lin, L.S. Zong, G.L. Ning, Controllable Fabrication of Zinc Borate Hierarchical Nanostructure on Brucite Surface for Enhanced Mechanical Properties and Flame Retardant Behaviors. ACS Appl. Mater. Interfaces 6 (2014) 7223–7235.
[35] S. Tang, L.J. Qian, Y. Qiu, Y.P. Dong, High-performance flame retardant epoxy resin based on a bi-group molecule containing phosphaphenanthrene and borate groups. Polym. Degrad. Stab. 153 (2018) 210–219.
ACCEPTED MANUSCRIPT [36] Q.H. Zhang, G.Q. Chen, T.L. Xing, Silk flame retardant finish by ternary silica sol containing boron and nitrogen. Appl. Surf. Sci. 421 (2017) 52–60. [37] S.M. Unlu, U. Tayfun, B. Yildirim, M. Dogan, Effect of boron compounds on fire
RI PT
protection properties of epoxy based intumescent coating. Fire Mater. 41 (2016) 17–28. [38] H.Q. Peng, Y.Z. Wang, Effects of Boric Acid on Flame Retardancy of Intumescent Flame-Retardant Polypropylene Systems Containing a Caged Bicyclic Phosphate. ACS
SC
Sym Ser 1013 (2009) 225–248.
M AN U
[39] G. Guo, J. Sun, C. Zhao, Y. Liu, C.M. Liu, Phosphorus-containing polymers from THPS. VII. Synthesis of phosphorus-containing trialkynes and their metal-free 1, 3dipolar cycloaddition reaction with azidated soybean-oil. Green Chem. 18 (2016) 1278–1286.
TE D
[40] S. Yang, Q.X. Zhang, Y.F. Hu, Synthesis of a novel flame retardant containing phosphorus, nitrogen and boron and its application in flame-retardant epoxy resin. Polym. Degrad. Stab. 133 (2016) 358–366.
EP
[41] T. Zhang, W.S. Liu, M.X. Wang, P. Liu, Y.H. Pan, D.F. Liu, Synthesis of a
AC C
boron/nitrogen-containing compound based on triazine and boronic acid and its flame retardant effect on epoxy resin. High. Perform. Polym. 29 (2016) 1–11. [42] T. Zhang, W.S. Liu, M.X. Wang, P. Liu, Y.H. Pan, D.F. Liu, Synergistic effect of an aromatic boronic acid derivative and magnesium hydroxide on the flame retarding of epoxy resin. Polym. Degrad. Stab. 130 (2016) 257–263. [43] S. Wang, S.Q. Ma, C.X. Xu, Y. Liu, J.Y. Dai, Z.B. Wang, X.Q. Liu, J. Chen, X.B. Shen, J.J. Wei, J. Zhu, Vanillin-Derived High-Performance Flame Retardant Epoxy
ACCEPTED MANUSCRIPT Resins: Facile Synthesis and Properties. Macromolecules 50 (2017) 1892–1901. [44] M. Rajaei, D.Y. Wang, D. Bhattacharyya, Combined effects of ammonium polyphosphate and talc on the fire and mechanical properties of epoxy/glass fabric
RI PT
composites. Compos Part B Eng 113 (2017) 381–390. [45] X. Wang, S. Zhou, W.W. Guo, P.L. Wang, W.Y. Xing, L. Song, Y. Hu, Renewable
ACS Sustainable Chem. Eng. 5 (2017) 3409–3416.
SC
Cardanol-Based Phosphate as a Flame Retardant Toughening Agent for Epoxy Resins.
M AN U
[46] Y. Tan, Z.B. Shao, X.F. Chen, J.W. Long, L. Chen, Y.Z. Wang, Novel Multifunctional Organic-Inorganic Hybrid Curing Agent with High Flame-Retardant Efficiency for Epoxy Resin. ACS Appl. Mater. Interfaces 7 (2015) 17919–17928. [47] Y.C. Li, J. Schulz, S. Mannen, C. Delhom, B. Condon, S. Chang, M. Zammarano,
TE D
J.C. Grunlan, Flame retardant behavior of polyelectrolyte-clay thin film assemblies on cotton fabric. Acs Nano 4 (2010) 3325–3337. [48] J.W. Gu, C.B. Liang, X.M. Zhao, B. Gan, H. Qiu, Y.Q. Guo, X.T. Yang, Q.Y. Zhang,
EP
D.Y. Wang, Highly thermally conductive flame-retardant epoxy nanocomposites with
AC C
reduced ignitability and excellent electrical conductivities. Compos. Sci. Technol. 139 (2017) 83–89.
[49] S.L. Qiu, X. Wang, B. Yu, X.M. Feng, X.W. Mu, R.K.K. Yuen, Y. Hu, Flame-retardant-wrapped polyphosphazene nanotubes: A novel strategy for enhancing the flame retardancy and smoke toxicity suppression of epoxy resins. J. Hazard. Mater. 325 (2017) 327–339. [50] E.N. Kalali, X. Wang, D.Y. Wang, Multifunctional intercalation in layered double
ACCEPTED MANUSCRIPT hydroxide: toward multifunctional nanohybrids for epoxy resin. J. Mater. Chem. A 4 (2016) 2147–2157. [51] T.T. Ma, C.G. Guo, Synergistic effect between melamine cyanurate and a novel
RI PT
flame retardant curing agent containing a caged bicyclic phosphate on flame retardancy and thermal behavior of epoxy resins. J. Anal. Appl. Pyrolysis 124 (2017) 239–246.
[52] X.D. He, W.C. Zhang, R.J. Yang, The Characterization of DOPO/MMT
SC
Nanocompound and its Effect on Flame Retardancy of Epoxy Resin. Compos A-Appl
M AN U
Sci Manuf 98 (2017) 124–135.
[53] S. Yang, J. Wang, S.Q. Huo, L.F. Cheng, M. Wang, Preparation and flame retardancy of an intumescent flame-retardant epoxy resin system constructed by multiple flame-retardant compositions containing phosphorus and nitrogen heterocycle.
TE D
Polym. Degrad. Stab. 119 (2015) 251–259.
[54] V. Benin, S. Durganala, A.B. Morgan, Synthesis and flame retardant testing of new
1180–1190.
EP
boronated and phosphonated aromatic compounds. J. Mater. Chem. 22 (2012)
AC C
[55] V. Benin, B. Gardelle, A.B. Morgan, Heat release of polyurethanes containing potential flame retardants based on boron and phosphorus chemistries, Polym. Degrad. Stab. 106 (2014) 108–121. [56] X. Liu, Y. Zhou, H. Peng, J.W. Hao, Catalyzing charring effect of solid acid boron phosphate on dipentaerythritol during the thermal degradation and combustion. Polym. Degrad. Stab. 119 (2015) 242–250. [57] J.L. Wang, C. Ma, P.L. Wang, S.L. Qiu, W. Cai, Y. Hu, Ultra-low phosphorus
ACCEPTED MANUSCRIPT loading to achieve the superior flame retardancy of epoxy resin. Polym. Degrad. Stab. 149 (2018) 119–128. [58] P. Wang, L. Xia, R.K. Jian, Y.F. Ai, X.L. Zheng, G.L. Chen, J.S. Wang,
RI PT
Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance. Polym. Degrad. Stab. 149 (2018) 69–77.
SC
[59] X.L. Fu, X. Wang, W.Y. Xing, P. Zhang, L. Song, Y. Hu, Two-dimensional
M AN U
cardanol-derived zirconium phosphate hybrid as flame retardant and smoke suppressant for epoxy resin. Polym. Degrad. Stab. 151 (2018) 172–180.
[60] S.Q. Huo, J. Wang, S. Yang, B. Zhang, X. Chen, Q.L. Wu, L.F. Yang, Synthesis of a novel reactive flame retardant containing phosphaphenanthrene and piperidine groups
TE D
and its application in epoxy resin. Polym. Degrad. Stab. 146 (2017) 250–259. [61] Y.L. Liang, R.A. Pearson, The toughening mechanism in hybrid epoxy-silica-
AC C
EP
rubber nanocomposites (HESRNs). Polymer 51 (2010) 4880–4890.
ACCEPTED MANUSCRIPT
Caption Scheme 1. Synthesis route of CP-6B. Scheme 2. The decomposition guess model of CP-6B.
RI PT
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
atmosphere. Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
SC
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen
M AN U
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests. Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests. Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B, (c)
TE D
EP/3%CP-6B, (d) EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B. Fig. 8. SEM images of residual chars of (a) pure EP (×200), (b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200), (e) EP/7%CP-6B (×200), and (f)
EP
EP/10%CP-6B (×200).
AC C
Fig. 9. XRD patterns of residual samples. Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at various temperatures for 15 min in a muffle furnace. Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for 15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B; and (d) EP/7%CP-6B residual char. Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
ACCEPTED MANUSCRIPT calorimeter tests. Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b). Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
RI PT
Table 1. The weight ratios of the EP samples. Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen. Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
SC
Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B.
M AN U
Table 5. Typical cone test parameters for pure EP and EP/CP-6B. Table 6. Elemental analysis of the residual char.
Table 7. Assignment of peaks in PY-GC-MS results of pure EP. Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B.
AC C
EP
TE D
Table 9. Mechanical properties of pure EP and EP/CP-6B.
AC C
EP
TE D
M AN U
SC
Scheme 1. Synthesis route of CP-6B.
RI PT
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Scheme 2. The decomposition model of CP-6B.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 1. TG and DTG of CP-6B in nitrogen (a) and air (b).
RI PT
ACCEPTED MANUSCRIPT
Fig. 2. TG (a) and DTG (b) curves for pure EP and EP/CP-6B under nitrogen
AC C
EP
TE D
M AN U
SC
atmosphere.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 3. Digital images of EP/CP-6B after UL 94 tests.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 4. Digital images of pure EP and EP/CP-6B after LOI tests.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 5. HRR (a) and THR (b) curves of pure EP and EP/CP-6B.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 6. Mass loss curves of pure EP and EP/CP-6B from cone tests.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 7. Digital photographs of residual chars of (a) pure EP, (b) EP/1%CP-6B,
AC C
EP
TE D
M AN U
(c)EP/3%CP-6B, (d)EP/5%CP-6B, (e) EP/7%CP-6B, and (f) EP/10%CP-6B.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 8. SEM images of residual chars of (a) pure EP (×200),
M AN U
(b) EP/1%CP-6B (×200), (c) EP/3%CP-6B (×200), (d) EP/5%CP-6B (×200),
AC C
EP
TE D
(e) EP/7%CP-6B (×200), and (f) EP/10%CP-6B (×200).
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 9. XRD patterns of residual samples.
RI PT
ACCEPTED MANUSCRIPT
Fig. 10. Digital photographs of pure EP and EP/7%CP-6B after being maintained at
AC C
EP
TE D
M AN U
SC
various temperatures for 15 min in a muffle furnace.
RI PT
ACCEPTED MANUSCRIPT
SC
Fig. 11. FTIR spectra of pure EP and EP/7%CP-6B after being maintained at 650 °C for
M AN U
15 min in a muffle furnace: (a) pure EP; (b) pure EP residual char; (c) EP/7%CP-6B;
AC C
EP
TE D
and (d) EP/7%CP-6B residual char.
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
calorimeter tests.
SC
Fig. 12. Raman spectra of residual chars of pure EP (a) and EP/7%CP-6B (b) after cone
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 13. PY-GC-MS of EP and EP/7%CP-6B at 450 °C (a) and 700 °C (b).
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
Fig. 14. DSC curves and Tg of pure EP and EP/CP-6B.
ACCEPTED MANUSCRIPT Table 1. The weight ratios of the EP samples. E-44 (g)
DDM (g)
CP-6B (g)
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
100 100 100 100 100 100
25 25 25 25 25 25
0 1.25 3.75 6.25 8.75 12.5
AC C
EP
TE D
M AN U
SC
RI PT
Samples
ACCEPTED MANUSCRIPT Table 2. Thermal decomposition characteristics of CP-6B in air and nitrogen. Tonseta(°C)
Tmax1b(°C)
Tmax2(°C)
Tmax3(°C)
W800 °Cc(%)
Nitrogen
142.3
154.2
394.5
–
34.9
Air
149.5
154.5
396.7
559.2
48.0
Initial temperature at 5% mass loss; bTemperature at the maximum mass loss rate;
c
Residual char yield at 800 °C.
AC C
EP
TE D
M AN U
SC
RI PT
a
ACCEPTED MANUSCRIPT Table 3. Thermal decomposition characteristics of pure EP and EP/CP-6B.
EP
TE D
M AN U
SC
Residual char yield at 800 °C.
AC C
c
RI PT
Samples Tonseta(°C) Tmax1b(°C) Tmax2(°C) W800 °Cc(%) EP 318.9 395.7 – 9.7 EP/1%CP-6B 275.1 384.5 524.4 16.6 EP/3%CP-6B 279.5 388.8 522.4 18.0 EP/5%CP-6B 289.2 390.8 520.8 20.3 EP/7%CP-6B 299.1 388.4 523.6 22.3 EP/10%CP-6B 292.6 387.6 518.8 24.1 a b Initial temperature at 5% mass loss; Temperature at the maximum mass loss rate;
ACCEPTED MANUSCRIPT Table 4. LOI values and UL 94 ratings of pure EP and EP/CP-6B. UL-94 (3.2 mm)a
Dripping
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
22.8 ± 0.2 29.6 ± 0.2 30.8 ± 0.2 31.4 ± 0.2 32.3 ± 0.2 28.6 ± 0.2
NR V-1 V-0 V-0 V-0 V-0
Yes No No No No No
NR=no rating
RI PT
LOI (%)
AC C
EP
TE D
M AN U
SC
a
Samples
ACCEPTED MANUSCRIPT Table 5. Typical cone test parameters for pure EP and EP/CP-6B. Residual
pk-HRR
THR
av-EHC
FPI
FGI
av-COY
av-CO2Y
av-MLR
(s)
(kW/m2)
(MJ/m2)
(MJ/kg)
(s·m2/kW)
kW/(m2·K)
(kg/kg)
(kg/kg)
(g/s)
EP
36 ± 2
1026 ± 19
83 ± 3
23.8 ± 0.3
0.04
10.80
0.013
0.209
0.76
6.8
EP/1%CP-6B
33 ± 2
709 ± 14
78 ± 4
22.2 ± 0.3
0.05
6.17
0.011
0.188
0.63
11.8
EP/3%CP-6B
30 ± 2
599 ± 16
74 ± 3
20.9 ± 0.3
0.05
5.99
0.011
0.182
0.53
14.6
EP/5%CP-6B
28 ± 2
446 ± 15
58 ± 3
19.8 ± 0.3
0.06
3.71
0.009
0.141
0.40
19.8
EP/7%CP-6B
26 ± 2
359 ± 13
54 ± 3
18.7 ± 0.3
0.07
2.99
0.012
0.175
0.38
22.6
EP/10%CP-6B
27 ± 2
471 ± 18
60 ± 4
19.5 ± 0.3
0.06
3.49
0.011
0.142
0.39
23.0
SC M AN U TE D EP AC C
Samples
RI PT
TTI
char yield(%)
ACCEPTED MANUSCRIPT Table 6. Elemental analysis of the residual char. Sample
C 83.89 65.47
P 0 2.26
AC C
EP
TE D
M AN U
SC
RI PT
EP EP/7%CP-6B
Element composition (wt.%) O N 13.33 2.77 25.05 7.21
ACCEPTED MANUSCRIPT
Peak
Retain Time (min)
m/z
1
1.558
44
13
7.375
2
3.608
92
14
7.817
3
6.758
106
15
8.308
4
7.983
108
5
11.100
164
6
1.767
58
M AN U
Table 7. Assignment of peaks in PY-GC-MS results of pure EP.
7
1.892
98
8
2.525
TE D
EP 78
AC C
9
m/z
RI PT 134
108
16
8.900
132
17
9.225
132
18
9.925
146
19
10.367 135
20
10.900 144
5.058
106
21
11.267
148
5.208
106
22
11.567
160
11
5.550
104
23
11.975
146
12
6.117
120
24
12.408 158
10
Structure
118
SC
Structure
Retain Peak Time (min)
ACCEPTED MANUSCRIPT Table 8. Assignment of peaks in PY-GC-MS results of EP/7%CP-6B. m/z
1.758
89
f
13.008
148
b
3.650
92
g
19.583
184
c
6.800
106
h
20.908
278
d
8.125
108
i
15.100
210
e
11.958
134
j
17.525
210
SC
a
Structure
M AN U
m/z
EP AC C
Structure
RI PT
Peak
Retain Time (min)
TE D
Peak
Retain Time (min)
ACCEPTED MANUSCRIPT Table 9. Mechanical properties of pure EP and EP/CP-6B. Toughness (J·m−2) 76.4 121.3 138.0 94.4 77.5 60.6
AC C
EP
TE D
M AN U
SC
EP EP/1%CP-6B EP/3%CP-6B EP/5%CP-6B EP/7%CP-6B EP/10%CP-6B
Impact strength (kJ·m−2) 7.7 12.1 13.8 9.5 7.8 6.1
RI PT
Impact energy (J) 0.31 0.49 0.55 0.38 0.31 0.24
Samples
ACCEPTED MANUSCRIPT
SC
RI PT
Graphical Abstracts
CP-6B can decompose nonflammable gases and promote the formation of a dense
AC C
EP
TE D
M AN U
and hard intumescent carbon layer in EP.
ACCEPTED MANUSCRIPT
Highlights The compound CP-6B contains boron, phosphorus and nitrogen, and CP-6B can play a synergistic flame-retardant effect. The low loading of CP-6B can achieve good flame retardant performance and
RI PT
less damage to mechanical properties. The CP-6B can promote the formation of a dense and hard intumescent carbon
AC C
EP
TE D
M AN U
SC
layer in EP.