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Thermal decomposition reactions of cotton fabric treated with piperazine-phosphonates derivatives as a flame retardant
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Thermal decomposition reactions of cotton fabric treated with piperazine-phosphonates derivatives as a flame retardant Thach-Mien Nguyen a , SeChin Chang a,∗ , Brian Condon a , Tina P Thomas b , Parastoo Azadi b a b
United States Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans, LA 70124, United States Complex Carbohydrate Research Center, 315 Riverbend Road, Athens, GA 30602, United States
a r t i c l e
i n f o
Article history: Received 15 January 2014 Received in revised form 1 August 2014 Accepted 16 August 2014 Available online xxx Keywords: Piperazine-phosphonates derivative Cotton fabric ATR-IR TGA–FTIR Py-GC/MS
a b s t r a c t There has been a great scientific interest in exploring the great potential of the piperazine-phosphonates in flame retardant (FR) application on cotton fabric by investigating the thermal decomposition of cotton fabric treated with them. This research tries to understand the mode of action of the two piperazine-phosphonates derivatives on cotton fabric. The investigation proceeds by preparing Tetraethyl piperazine-1,4-diyldiphosphonate (TEPP) and Diethyl 4-methyl piperazin-1-ylphosphoramidate (DEPP), engrafting them on cotton fabric and studying their mechanism of thermal degradation on fabric. In studying the mechanism, we learned the chemical functional groups of the chemicals on the surface of the treated fabrics and of the evolved gases produced thermogravimetrically and pyrolytically by using different analytical techniques such as attenuated total reflection infrared (ATR-IR), thermogravimetric analysis–Fourier transform infrared (TGA–FTIR) spectroscopy and pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS). The experiment’s results showed some distinctive details in the thermal degradation of the fabric when applied with these additives. Published by Elsevier B.V.
1. Introduction In textile researches, scientists often performed experiments to study the properties of textile products by using different analytical techniques. To evaluate the burning behavior and to measure the fire hazard parameters for the fabrics, techniques such as vertical and 45 degree angle fabric strip tests, limiting oxygen index and combustion calorimetry have been used [1–4]. Furthermore, differential scanning calorimetry and thermogravimetric analysis have also been used as important tools for understanding thermal properties of textiles materials, e.g., physical and chemical degradation temperatures, endo- and exothermic characteristics of these transitions and any associated weight losses [5]. While none of the above techniques provides the full details of the pyrolysis process and the formation of the resulting products, there have been reported several scientific studies that deal with the application of analytical pyrolysis or thermal degradation to cotton fabrics or fibers in general, including the identification of volatile pyrolysis products from using Py-GC and Py-GC/MS [6–8]. In addition, gas product formation studied by TGA–FTIR has improved the understanding of the mechanism of cotton and flame retardants cotton fabrics [9,10].
∗ Corresponding author. Tel.: +1 504 286 4487; fax: +1 504 286 4390. E-mail address: [email protected] (S. Chang).
It has been reported that piperazine-phosphonate, flame retardant additives are very effective on different polymeric systems including cotton fabrics [1,3,11–13]. Although this chemistry has been well developed and is widely available, still more serious work is needed to study their mode of action. It is only until recently that textile [3] and non-textile literatures has published the studies and their results regarding piperazine-phosphonates applied to cellulose acetate and their thermal decomposition and interaction with other compounds of non-flame retardant piperazine derivatives [14–16]. In this research, the aim is to prepare two piperazine-phosphonate derivatives and then apply them on cotton fabric. In order to understand their thermal degradation, the ATR-IR, TGA–FTIR and Py-GC/MS techniques were used to study the control and treated cotton fabrics. 2. Experimental 2.1. Materials All purchased chemicals for the experiments came from Aldrich and were used in their original forms except tetrahydrofuran (THF) and acetonitrile (CH3 CN). These solvents were dried using the Solvent Purification System from Innovative Technology. All reactions were conducted under nitrogen and were monitored by silica gel 60 F254 thin layer chromatography (TLC) from EMD. Cotton fabric
http://dx.doi.org/10.1016/j.jaap.2014.08.006 0165-2370/Published by Elsevier B.V.
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from 100% cotton cellulose was obtained as twill fabric with the weight of 258 g/m2 (from Testfabrics, Inc., Style 423). This fabric was desized (starches removed), bleached and was cleared of all resins and finishes. 2.2. Synthesis (Scheme 1. See Supporting information for NMR data) 2.2.1. Synthesis of TEPP To a solution of piperazine (5.0 gm, 58 mmol) in 150 mL of dry CH3 CN, potassium carbonate (16.0 gm, 116 mmol) was added, and the mixture was cooled to 0 ◦ C. Next, a solution of diethyl chlorophosphate (16.7 mL, 116 mmol) in 130 mL of dry CH3 CN was slowly added by an addition funnel to the above mixture, while stirring under nitrogen. After the addition, the reaction was allowed to warm up to room temperature and monitored by TLC using 10% methanol/ethyl Acetate as an eluent and iodine as the staining reagent. When the reaction was completed, a white solid was filtered off and the filtered solution was evaporated to give a white solid as product in 96% yield with no purification needed. Scheme 1. 2.2.2. Synthesis of DEPP This compound was synthesized following the published literature [17]. In this reaction, DEPP was prepared by an elegant method employing the reaction of 1-amino-4-methyl piperazine with diethyl chlorophosphate in the presence of triethylamine. At the end of the reaction, a white solid was filtered off. The removal of the solvent gave yellowish oil as product in 82% yield with no purification required. 2.3. Fabric treatment A required quantity of each chemical was dissolved in a minimum quantity of water (for TEPP) or 30% aqueous isopropanol (w/v) (for DEPP). Next, each solution was poured into a shallow container that contains the twill fabric samples laying flat. The fabrics were then soaked in these solutions for 1 h. After that, they were subjected to a padder (Birch Bros. Southern, Inc.) at 10 psi (or 0.689 bar), then a drying oven (model LTF 146491, Mathis U.S.A., Inc) at 100 ◦ C for 5 min and finally a curing oven (model LTE 18795, Mathis U.S.A., Inc) at 165 ◦ C for 5 min. Upon being taken out of the curing oven, the fabrics were immediately stored in a desiccator for cooling down. All samples were weighed before and after the treatment and the values were fitted to Eq. (1) to obtain add-on percents (or addon levels):
add-on(%)=
(weightafter drying − weightbefore treatment ) weightbefore treatment
×100
(1)
2.4. Instrumentation 2.4.1. ATR-IR and TGA/FTIR The functional groups on the fabrics were examined by a Bruker Platinum Alpha ATR-IR spectrometer, A220/D01 prior to the thermal degradation. These experiments were set to collect 34 interferograms at a resolution of four wavenumbers in the range of 4000–600 cm−1 . At the end, the spectra were analyzed using the Opus software and later reconstructed using OriginLab 9 software. The TGA–FTIR experiment was conducted by a TA Instruments Q500 thermogravimetric analyzer and a Bruker Tensor-27 spectrometer. In this experiment, 5–8 mg of each sample was heated between 20 and 550 ◦ C in the thermogravimetric analyzer at a rate of 10 ◦ C/min and under a nitrogen flow rate of 60 mL/min. The resulted volatile decomposition products then traveled through a
transfer line to reach the gas cell of the FTIR spectrometer. Although the TGA experiment investigated the thermal degradation of the samples from 20 to 600 ◦ C, the FTIR experiment examined the gaseous products released during the main degradation ranging from 100 to 500 ◦ C. Both transfer line and gas cell were maintained at 200 ◦ C. When the evolved gases reached the gas cell, they were analyzed by a liquid-nitrogen cooled MCT detector which is equipped with ZnSe window. The gas components were then recorded as the absorption peaks in the 4000–600 cm−1 region at a resolution of four wavenumbers. This data was obtained at every 5 degree increment along TGA heating profile and there was a 30 s delay between the timed measurements for the FTIR. When the experiment was completed, the data was analyzed using an Opus software which measures the intensity of the absorption band (representing the functional groups) as a function of temperature. For analytical purposes, an OriginLab 9 software was utilized to retain the three dimensional images of the FTIR spectra. 2.4.2. Py-GC–MS About 0.4–0.6 mg of each sample was weighed and pyrolyzed using a pyrolyzer at 480 ◦ C. The residues were then analyzed using Agilent Technologies gas chromatograph mass spectrometer. During the experiment, the interface temperature was maintained at 280 ◦ C and the carrier gas helium was used at a flow rate of 1 mL/min. Also, the column temperature was ramped from 50–280 ◦ C (with 5 ◦ C/min) and then maintained at 280 ◦ C for 5 min. To avoid overloading the column, the split ratio was preset at 50:1; this ratio was carefully controlled so that results from the chromatography could still be quantified. For each sample, three repetitive trials were performed and the resulting chromatograms were manually integrated. In addition, all cellulose derived peaks were carefully interpreted. 3. Results and discussion 3.1. Fabric treatment As the result of this treatment, the concentrations achieved for TEPP and DEPP on the fabrics were 19 and 18 wt%, respectively. Samples of the treated fabrics TEPP-19 and DEPP-18 and the control fabric were characterized instrumentally. 3.2. Functional groups present on the surface of treated fabrics before thermal decomposition It is widely known that flame retardants can alter the process of pyrolysis of the fabrics. To understand how the alteration happens, it is important to gain knowledge of the chemical components on the treated fabrics before the pyrolysis. In this experiment, the Infrared spectroscopy using ATR was employed to examine the functional groups on the surface of the control as well as the treated fabrics. The results are shown in Fig. 1. Although the data were collected in a wide range, much of the differences can be observed between 1500 and 700 cm−1 . As seen in Fig. 1, TEPP-19 and DEPP-18 do have something in common: the peak characteristics of P O and O P O at around 1240–1228 cm−1 and 820–790 cm−1 , respectively [18a,b]. The lower frequency observed for P O in DEPP-18 suggests, however, that this is likely due to the hydrogen bond formed between the NH group and the P O [19a]. Upon a more thorough inspection of the two spectra, their differences are revealed by their signature peaks. The spectroscopic feature at 972 cm−1 is found for TEPP-19, which corresponds to the asymmetric vibration of P N C group in which the alkyl is not CH3 or C2 H5 [18c]. At lower frequency, P N absorption for TEPP-19 is shown at 772 cm−1 ; this may be due to the attachment of two N-bonded CH2 groups [19b]. In the range
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Scheme 1. Synthesis of tetraethyl piperazine-1,4-diyldiphosphonate (TEPP) and diethyl 4-methyl piperazin-1-ylphosphoramidate (DEPP).
0.20
100
unburned control unburned 19 % TEPP unburned 18 % DEPP
νP-N-C
80
unburned control
0.15 νP-N-C νP-O
0.10
60
C
C
165, 247°C ; 34%
40
νP=O
control
0.05
νP-O
C
0.00 1500 1400 1300 1200 1100 1000
140, 250°C ; 22%
TEPP-19
20
DEPP-18 320°C; 3%
0
900
800
700
wavenumber (cm-1)
0
100
200
300
400
500
600
Fig. 2. Degradation thermograms in nitrogen for the control, TEPP-19 and DEPP-18.
Fig. 1. ATR-IR spectrum (expanded region) for the control, TEPP-19 and DEPP-18 before pyrolysis.
820–790 cm−1 , O P O peak of DEPP-18 becomes broad and less intense; this may be ascribed to the perturbation from N (C)2 group attached to the NH which links to P [20]. From the above analysis, it is evident that both chemicals remain intact during the treatment process for the fabrics.
3.3. Gas products during thermal decomposition The mass loss curves for the control and treated fabrics are shown in Fig. 2. In addition, the onset temperature or the beginning of major weight loss and char residue (%) in nitrogen atmosphere is displayed. As seen in Fig. 2, the treated fabrics have lower onset temperature and yield higher char residue when compared with the control. The earlier decomposition of both compounds TEPP and DEPP causes smaller mass loss at around 165 and 140 ◦ C on TEPP19 and DEPP-18, respectively. While more TEPP decomposes than DEPP, less material or cotton fabric is degraded in TEPP-19 sample. As a result, TEPP-19 provides more char at 600 ◦ C when compared with DEPP-18. By coupling with TGA, FTIR can detect the real-time gaseous products released in the pyrolysis process. During the experiment, the FTIR data are plotted one on top of the other with a total of 80 scans to form a 3D spectrum in which the evolution of gas products is shown as a function of both wavenumber and temperature.
Typical spectra output from this experiment for TEPP-19 and DEPP-18 as well as the control are shown in Fig. 3. During the pyrolysis, the gases released from the untreated fabric (Fig. 3a) are mainly hydrocarbon OH (∼3300–3000 cm−1 ); hydrocarbon CH2 , CH3 (∼3014–2600 cm−1 ); CO2 (∼2360–2310 and 710 cm−1 ); CO (∼2185–2100 cm−1 ); water vapor (∼4000–3500 and 1800–1500 cm−1 ); some hydrocarbon C O (∼1850–1600 cm−1 ) and C O H deformation, C O C, C H, C C and C C (∼1500–900 cm−1 ) [10,21]. They are the products of the reduction of cellulose molecule, the appearance of free radicals, oxidation, dehydration, decarboxylation, decarbonylation and decomposition of cellulose to tarry pyrolyzate-containing levoglucosan, which vaporizes and then decomposes at later time or higher temperature. As shown in Fig. 3, it is obvious that all three profiles share several common features, such as the water vapor, hydrocarbon OH, CO2 , CO, hydrocarbon C H, C C C C gases . . . When comparing the evolution profiles for TEPP-19 and DEPP-18, it is noticeable that they do possess two similar characteristics: C O of EtOH (1271, ∼1040–970 cm−1 ) and P O C2 H5 (730–690 cm−1 ) [18c,22,23] (See Supporting information for expanded regions). Besides these common features, they reveal their differences in other signature peaks. Around 1774–1695 cm−1 , while TEPP-19 appears normal for moisture fingerprint region, DEPP-18 seems to contain other functional groups. In general, for organophosphorous compounds, this is presumably the region of absorption for P( O) OH [19c]. Moreover, in DEPP-18, this region extends
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a)
b)
c)
Fig. 3. Volatiles released out during pyrolysis of the control (a), TEPP-19 (b) and DEPP-18 (c).
further down to 1633 cm−1 . In many phosphoramidates and similar materials, P NH2 exhibits its deformation absorption in the region 1650–1550 cm−1 [18b]. There are two separate peaks in the overall range 1186–990 cm−1 for DEPP-18, which are identified as being in some way related to the CH2 and/or C O H deformation similar to those of the untreated fabric [10,21]. At around 1040–1000 cm−1 , P O P asymmetric vibration appears for TEPP-19 while P N and NH2 absorptions are seen for DEPP18 at ∼993–900 and 823 cm−1 , respectively [18c,d,e]. In addition, the characteristic absorption for H2 C CH2 from 940–900 cm−1 is detected for TEPP-19 [24] (See Supporting information for expanded region). Although the vibration of CH2 and CH3 both asymmetric and symmetric in both spectra appear almost at the same region (3014–2674 cm−1 for TEPP-19 and 3029–2821 cm−1 for DEPP-18), it is clear that DEPP-18 has more processes running in parallel and consecutively during its thermal decomposition than TEPP-19. Among the three profiles, it is obvious that without the additives, more materials from the fabric are decomposed and that this decomposition process takes place at later time. Furthermore, between the treated fabrics, the decomposition of TEPP-19, which produces less gas products, occurs earlier than that of DEPP-18. It is obvious that TGA data is supported by FTIR data. Since more cotton fabric is decomposed in DEPP-18 sample during the thermal degradation, its gas profile bears some resemblance to the gas profile of the control.
3.4. Gas products from pyrolysis process While TGA can best provide the changes in onset of degradation and char residue of the fabrics at desired temperatures, Py-GC/MS can further assist the characterization of the actual decomposition of the treated fabrics thanks to its ability to detect the chemical fragments formed during the degradation process. This process combines with the gas chromatography for the separation of pyrolyzed products and mass spectrometry for the identification of volatile compounds. The identified thermal decomposition products then help contribute to the understanding of the pyrolysis pathway. The chromatograms for the control and treated fabrics as well as probable species formed from this experiment are presented in Fig. 4 and Tables 1–3. Additionally, same work was also carried out for each chemical and the results are summarized in Tables 4 and 5. As seen in Fig. 4a and from Table 3, the chromatogram of the untreated fabric comprises of several different species such as aldehydes, ketones, furans, furfural and nucleoglucosan which are similar to those reported in literature [7]. In fact, there are almost 50 different compounds formed after the breakdown of levoglucosan besides the normally seen gases, i.e., hydrogen, methane, acetylene, carbon monoxide, ethylene, ethane, carbon dioxide [25]. When cotton fabric is treated with phosphorus, nitrogen and/or halogen containing FRs, the numbers of gas products are reduced [8].
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Fig. 4. Total ion chromatograms for control twill (a), TEPP-19 (b) and DEPP-18 (c) pyrolysis products.
In this study, the chromatograms of treated fabrics (Fig. 4b and c) seem to contain less peaks than the untreated one. Triethyl phosphate, tetraethyl pyrophosphate and 1-methyl piperazine were detected for TEPP-19 and DEPP-18, not to mention other evolved gases released by three fabrics. In general, there still remains
a number of unknown compounds which could not be recognized by the MS library in each chromatogram. Considering the effect of two FRs on the pyrolysis process, the production of volatiles shows some differences between the treated fabrics. In addition to the common species, 2-cyclopentanedione, 3-methyl
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a)
b)
Scheme 2. Proposed mode of action of TEPP (a) and DEPP (b).
Table 1 Major peaks of control twill with retention time and probable species by pyrolysis.
Table 2 Major peaks of TEPP-19 with retention time and probable species by pyrolysis.
Peak
Retention time (min)
Compound detected
Peak
Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2.466 3.513 4.136 5.03 5.737 7.901 8.37 9.565 12.86 14.185 15.587 16.248 17.196 29.638 30.902
2-Propanone,1-hydroxy 1,4-Pentadien,3-one Propanoic acid,2-oxo-,methyl ester Furfural Furan,2-propyl 2,5-Furandione,dihydro,3-methylene 2-Furancarboxaldehyde,5-methyl Oxazolidine,2,2-diethyl,3-methyl Levoglucosenone 4H-pyran,4-one,3,5-dihydroxy-6-methyl 4H-pyran,4-one,3,5-dihydroxy-2-methyl 1,4:3,6-Dianhydro ␣-d-glucopyranose 5-Hydroxymethylfurfural d-Allose/-d-glucopyranose 1,6-Anhydro, -d-glucopyranose
1 2 3 4 5 6 7
5.001 5.707 5.821 6.232 6.894 8.376 10.362
8 9 10
12.941 13.573 16.017
11 12 13
16.61 25.481 24.1–26.503
Furfural Furan,2-propyl 2(3H)-furanone-5-methyl 4-Cyclopentene-1,3-dione Ethanone,1-(2-Furanyl) 2-Furancarboxaldehyde,5-methyl 1,2-Cyclopentanedione, 3-methyl or methyl cyclopentenolone Levoglucosenone Triethyl phosphate 1,4:3,6-Dianhydro-␣-dglucooyranose 5-Hydroxymethylfurfural Tetraethyl pyrophosphate 1,6-Anhydro, -d-glucopyranose
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Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11 12 13
4.965 5.693 5.8 6.2 6.877 8.329 13.04 13.465 13.8 15.11 15.799 16.512 24.1–26.23
Furfural Furan,2-propyl 2(3H)-furanone-5-methyl 4-Cyclopentene-1,3-dione Ethanone,1-(2-furanyl) 2-Furancarboxaldehyde,5-methyl Levoglucosenone Triethyl phosphate 1-Methylpiperazine 4H-pyran-4-one, 3,5-dihydroxy-2-methyl 1,4:3,6-Fianhydro-␣-d-glucooyranose 5-Hydroxymethylfurfural 1,6-Anhydro, -d-glucopyranose
Table 4 Major peaks of TEPP with retention time and probable species by pyrolysis. Peak
Retention time (min)
Compound detected
1 2 3 4
7.99 10.554 14.123 25.98
N-ethylpiperazine Piperazine, 1,4,-diethyl Triethyl phosphate Tetraethyl pyrophosphate
7
3.5. Possible mechanisms for thermal decomposition of the fabrics Data from the TGA–FTIR and Py-GC/MS reveal that the first step of decomposition of untreated fabric is the depolymerization of the cellulose polymer to form various anhydrosugar derivatives and to release some water and CO2 . In treated fabrics, this process can be changed by the presence of FRs due to their catalytic action (Scheme 2). It is clearly that much less water, CO2 and compounds from breaking down of cellulose polymer released in both treated fabrics. TEPP and DEPP may decompose by hydrolysis or elimination to release ethanol, phosphate esters, ethylene and the acidic derivatives which may catalyze the formation of char. In case of DEPP-18, besides the formation of the acidic intermediate, phosphoramidate and ethanol, the hydrolysis may also result in the cleavage of N N bond to release the piperazine derivative. It is reported that piperazine-NH containing compound can cleave at N N bond to release a piperazine species [14]. The newly formed piperazine derivative is further broken down to nitrogen containing derivatives. These might be the main reasons for the appearance of more different functional groups in the evolution profile of gas products for DEPP-18 (by TGA–FTIR) and different piperazine derivatives observed from the pyrolysis for DEPP chemical (by Py-GC/MS). 4. Conclusion
Table 5 Major peaks of DEPP with retention time and probable species by pyrolysis. Peak
Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11
2.09 4.917 5.591 5.82 7.278 7.391 8.112 9.273 10.499 14.336 16.809
Ethanamine, N-ethyl,N-methyl Pirazine,methyl Piperazine,1,4-dimethyl Piperazine,1-methyl Piperazine,ethyl Piperazine,2,3-dimethyl Piperazine,1,2,4-trimethyl 1-Amino,4-methylpiperazine Piperazine,1,4-diethyl Triethyl phosphate Phosphoric acid, diethyl ester
(or may be methyl cyclopentenolone) and tetraethyl pyrophosphate are detected for TEPP-19 while 1-methylpiperazine and 4H-pyran-4-one, 3,5-dihydroxy-2-methyl are seen for DEPP-18. Among these four compounds, 2-cyclopentanedione, 3-methyl (or may be methyl cyclopentenolone) and 4H-pyran-4-one, 3,5dihydroxy-2-methyl come from the secondary decomposition of anhydrous sugars [21] while tetraethyl pyrophosphate and 1methylpiperazine are the products of the decomposition of TEPP and DEPP, respectively. Additional Py-GC/MS studies on each chemical provide more insights into their own breakdown. With these details, possible pyrolysis pathways and byproducts which may influence the decomposition of the treated fabrics can be elucidated. From Tables 4 and 5, besides triethyl phosphate which is common pyrolysis product for both chemicals, tetraethyl pyrophosphate which was seen in TEPP-19 was detected again for TEPP. Though both FRs bearing the same ethyl phosphonate group, only TEPP can generate this latter compound. Overall, the results from pyrolysis for TEPP and DEPP show some piperazine and nitrogen containing derivatives. It is known that piperazine has been detected as a byproduct during pyrolysis of piperazine containing molecules [14,15,26]. As the results, the appearance of the piperazine and nitrogen containing derivatives is likely from the secondary pyrolysis of the piperazine moiety; that may have dissociated from the mother compounds during the first stage of the decomposition.
By employing ATR-IR, TGA–FTIR and Py-GC/MS techniques, extensive experiment is performed to investigate the mechanism of the thermal degradation for the control cotton fabric and the cotton fabrics treated with flame retardants, TEPP and DEPP. The results showed that: the treatment process does not decompose the two flame retardants; most main products are enhanced when the residence time is increased; the control generates more gas products that all come out at later time; most evolved gases from the control are flammable substances which are products of the depolymerization of cotton cellulose; both treated fabrics release ethanol, phosphate esters, acidic intermediates, with or without ethylene and nitrogen derivatives and maybe some products from cotton cellulose; more activities are observed for DEPP-18 compared with TEPP-19. Acknowledgements This study was financed by the U.S. Department of Agriculture. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jaap.2014.08.006. References [1] T.D. Nguyen, S. Chang, B.D. Condon, R.P. Slopek, Synthesis of a novel flame retardant containing phosphorus–nitrogen and comparison of application on cotton fabric, Fibers Polym. 133 (2012) 963. [2] R.E. Lyon, R.N. Walters, Pyrolysis combustion flow calorimetry, J. Anal. Appl. Pyrol. 71 (2004) 27. [3] S. Chang, B. Condon, T.M. Nguyen, E. Graves, J. Smith, Antiflammable properties of capable phosphorus–nitrogen containing triazine derivatives on cotton, in: A.B. Morgan, C.A. Wilkie, G.L. Nelson (Eds.), Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science, ACS Symposium Series 1118, American Chemical Society, Washington, DC, 2013, pp. 123–137. [4] P. Bajaj, Heat and flame protection, in: A.R. Horrocks, S.C. Anand (Eds.), Handbook of Technical Textiles, Woodhead Publishing Limited and CRC Press LLC, Florida, USA and Cambridge, UK, 2000, pp. 223–263. [5] S.F. Ibrahim, E.S. El-Amoudy, K.E. Shady, Thermal analysis and characterization of some cellulosic fabrics dyed by a new natural dye and mordanted with different mordants, Int. J. Chem. 3 (2011) 40.
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[16] S. Gann, L. Mauclaire, P. Rupper, V. Salimova, T.T. Tran, Thermal degradation of cellulose acetare in presence of bis-phosphoramidates, J. Anal. Appl. Pyrol. 90 (2011) 33. [17] T.D. Nguyen, S. Chang, B.D. Condon, S.M. Uchimiya, C. Fortier, Development of an environmentally friendly halogen-free flame retardant for cotton, Polym. Adv. Technol. 23 (2012) 1555. [18] R.R. Shagidullin, A.V. Chernova, V.S. Vinogradova, F.S. Mukhametow, Atlas of IR Spectra of Organophosphorus Compounds, Nauka and Kluwer Academic, Moscow and Boston, 1990, pp. 180–181 ((a) pp. 180–181; (b) p 9 (Table 2); (c) p. 5 (Table 1); (d) pp. 302–303; (e) pp. 250–251). [19] L.J. Bellamy, The Infra-red Spectra of Complex Molecules Vol. 1, Chapman and Hall, London and New York, 1975 ((a) pp. 348–351; (b) p. 361; (c) p. 357). [20] R.A. Chittenden, L.C. Thomas, Characteristic infra-red absorption frequencies of organo-phosphorus compounds-VI, Spectrochim. Acta 22 (1966) 1449. [21] D.K. Shen, S. Gu, The mechanism for thermal decomposition of cellulose and its main products, Bioresour. Technol. 100 (2009) 6496. [22] J.M. Garrigues, A. Pe’rez-Ponce, S. Garrigues, M. de la Guardia, Direct determination of ethanol and methanol in liquid samples by means of vapor phase-Fourier transform infrared spectrometry, Vib. Spectrosc. 15 (1997) 219. [23] J. Arana, J.M. Dona-Rodri’guez, C. Garriga i Cabo, O. Gonza’lez-Di’az, J.A. Herrera-Melia’n, J. Pe’rez-Pena, FTIR study of gas-phase alcohols photocatalytic degradation with TiO2 and AC-TiO2 , Appl. Catal., B: Environ. 53 (2004) 221. [24] E.T. Kaljuvee, E.R. Kuusik, Evolved gas analysis at thermal treatment of oil shales by TG-FTIR, in: Proceedings of the International Conference on Oil Shale: “Recent Trends In Oil Shale”, 2006 November 7–9, Amman, Jordan, 2006. [25] I.R. Hardin, Y.L. Hsieh, Thermal conditions and pyrolysis products in flammability test, Text. Chem. Color 17 (1985) 41. [26] E.L. Wittbecker, W.S. Spliethoff, C.R. Stine, Polyurethane analog of the polyester, polyethylene terephthalate, J. Appl. Polym. Sci. 9 (1965) 213.
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Thermal decomposition reactions of cotton fabric treated with piperazine-phosphonates derivatives as a flame retardant Thach-Mien Nguyen a , SeChin Chang a,∗ , Brian Condon a , Tina P Thomas b , Parastoo Azadi b a b
United States Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans, LA 70124, United States Complex Carbohydrate Research Center, 315 Riverbend Road, Athens, GA 30602, United States
a r t i c l e
i n f o
Article history: Received 15 January 2014 Received in revised form 1 August 2014 Accepted 16 August 2014 Available online xxx Keywords: Piperazine-phosphonates derivative Cotton fabric ATR-IR TGA–FTIR Py-GC/MS
a b s t r a c t There has been a great scientific interest in exploring the great potential of the piperazine-phosphonates in flame retardant (FR) application on cotton fabric by investigating the thermal decomposition of cotton fabric treated with them. This research tries to understand the mode of action of the two piperazine-phosphonates derivatives on cotton fabric. The investigation proceeds by preparing Tetraethyl piperazine-1,4-diyldiphosphonate (TEPP) and Diethyl 4-methyl piperazin-1-ylphosphoramidate (DEPP), engrafting them on cotton fabric and studying their mechanism of thermal degradation on fabric. In studying the mechanism, we learned the chemical functional groups of the chemicals on the surface of the treated fabrics and of the evolved gases produced thermogravimetrically and pyrolytically by using different analytical techniques such as attenuated total reflection infrared (ATR-IR), thermogravimetric analysis–Fourier transform infrared (TGA–FTIR) spectroscopy and pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS). The experiment’s results showed some distinctive details in the thermal degradation of the fabric when applied with these additives. Published by Elsevier B.V.
1. Introduction In textile researches, scientists often performed experiments to study the properties of textile products by using different analytical techniques. To evaluate the burning behavior and to measure the fire hazard parameters for the fabrics, techniques such as vertical and 45 degree angle fabric strip tests, limiting oxygen index and combustion calorimetry have been used [1–4]. Furthermore, differential scanning calorimetry and thermogravimetric analysis have also been used as important tools for understanding thermal properties of textiles materials, e.g., physical and chemical degradation temperatures, endo- and exothermic characteristics of these transitions and any associated weight losses [5]. While none of the above techniques provides the full details of the pyrolysis process and the formation of the resulting products, there have been reported several scientific studies that deal with the application of analytical pyrolysis or thermal degradation to cotton fabrics or fibers in general, including the identification of volatile pyrolysis products from using Py-GC and Py-GC/MS [6–8]. In addition, gas product formation studied by TGA–FTIR has improved the understanding of the mechanism of cotton and flame retardants cotton fabrics [9,10].
∗ Corresponding author. Tel.: +1 504 286 4487; fax: +1 504 286 4390. E-mail address: [email protected] (S. Chang).
It has been reported that piperazine-phosphonate, flame retardant additives are very effective on different polymeric systems including cotton fabrics [1,3,11–13]. Although this chemistry has been well developed and is widely available, still more serious work is needed to study their mode of action. It is only until recently that textile [3] and non-textile literatures has published the studies and their results regarding piperazine-phosphonates applied to cellulose acetate and their thermal decomposition and interaction with other compounds of non-flame retardant piperazine derivatives [14–16]. In this research, the aim is to prepare two piperazine-phosphonate derivatives and then apply them on cotton fabric. In order to understand their thermal degradation, the ATR-IR, TGA–FTIR and Py-GC/MS techniques were used to study the control and treated cotton fabrics. 2. Experimental 2.1. Materials All purchased chemicals for the experiments came from Aldrich and were used in their original forms except tetrahydrofuran (THF) and acetonitrile (CH3 CN). These solvents were dried using the Solvent Purification System from Innovative Technology. All reactions were conducted under nitrogen and were monitored by silica gel 60 F254 thin layer chromatography (TLC) from EMD. Cotton fabric
http://dx.doi.org/10.1016/j.jaap.2014.08.006 0165-2370/Published by Elsevier B.V.
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from 100% cotton cellulose was obtained as twill fabric with the weight of 258 g/m2 (from Testfabrics, Inc., Style 423). This fabric was desized (starches removed), bleached and was cleared of all resins and finishes. 2.2. Synthesis (Scheme 1. See Supporting information for NMR data) 2.2.1. Synthesis of TEPP To a solution of piperazine (5.0 gm, 58 mmol) in 150 mL of dry CH3 CN, potassium carbonate (16.0 gm, 116 mmol) was added, and the mixture was cooled to 0 ◦ C. Next, a solution of diethyl chlorophosphate (16.7 mL, 116 mmol) in 130 mL of dry CH3 CN was slowly added by an addition funnel to the above mixture, while stirring under nitrogen. After the addition, the reaction was allowed to warm up to room temperature and monitored by TLC using 10% methanol/ethyl Acetate as an eluent and iodine as the staining reagent. When the reaction was completed, a white solid was filtered off and the filtered solution was evaporated to give a white solid as product in 96% yield with no purification needed. Scheme 1. 2.2.2. Synthesis of DEPP This compound was synthesized following the published literature [17]. In this reaction, DEPP was prepared by an elegant method employing the reaction of 1-amino-4-methyl piperazine with diethyl chlorophosphate in the presence of triethylamine. At the end of the reaction, a white solid was filtered off. The removal of the solvent gave yellowish oil as product in 82% yield with no purification required. 2.3. Fabric treatment A required quantity of each chemical was dissolved in a minimum quantity of water (for TEPP) or 30% aqueous isopropanol (w/v) (for DEPP). Next, each solution was poured into a shallow container that contains the twill fabric samples laying flat. The fabrics were then soaked in these solutions for 1 h. After that, they were subjected to a padder (Birch Bros. Southern, Inc.) at 10 psi (or 0.689 bar), then a drying oven (model LTF 146491, Mathis U.S.A., Inc) at 100 ◦ C for 5 min and finally a curing oven (model LTE 18795, Mathis U.S.A., Inc) at 165 ◦ C for 5 min. Upon being taken out of the curing oven, the fabrics were immediately stored in a desiccator for cooling down. All samples were weighed before and after the treatment and the values were fitted to Eq. (1) to obtain add-on percents (or addon levels):
add-on(%)=
(weightafter drying − weightbefore treatment ) weightbefore treatment
×100
(1)
2.4. Instrumentation 2.4.1. ATR-IR and TGA/FTIR The functional groups on the fabrics were examined by a Bruker Platinum Alpha ATR-IR spectrometer, A220/D01 prior to the thermal degradation. These experiments were set to collect 34 interferograms at a resolution of four wavenumbers in the range of 4000–600 cm−1 . At the end, the spectra were analyzed using the Opus software and later reconstructed using OriginLab 9 software. The TGA–FTIR experiment was conducted by a TA Instruments Q500 thermogravimetric analyzer and a Bruker Tensor-27 spectrometer. In this experiment, 5–8 mg of each sample was heated between 20 and 550 ◦ C in the thermogravimetric analyzer at a rate of 10 ◦ C/min and under a nitrogen flow rate of 60 mL/min. The resulted volatile decomposition products then traveled through a
transfer line to reach the gas cell of the FTIR spectrometer. Although the TGA experiment investigated the thermal degradation of the samples from 20 to 600 ◦ C, the FTIR experiment examined the gaseous products released during the main degradation ranging from 100 to 500 ◦ C. Both transfer line and gas cell were maintained at 200 ◦ C. When the evolved gases reached the gas cell, they were analyzed by a liquid-nitrogen cooled MCT detector which is equipped with ZnSe window. The gas components were then recorded as the absorption peaks in the 4000–600 cm−1 region at a resolution of four wavenumbers. This data was obtained at every 5 degree increment along TGA heating profile and there was a 30 s delay between the timed measurements for the FTIR. When the experiment was completed, the data was analyzed using an Opus software which measures the intensity of the absorption band (representing the functional groups) as a function of temperature. For analytical purposes, an OriginLab 9 software was utilized to retain the three dimensional images of the FTIR spectra. 2.4.2. Py-GC–MS About 0.4–0.6 mg of each sample was weighed and pyrolyzed using a pyrolyzer at 480 ◦ C. The residues were then analyzed using Agilent Technologies gas chromatograph mass spectrometer. During the experiment, the interface temperature was maintained at 280 ◦ C and the carrier gas helium was used at a flow rate of 1 mL/min. Also, the column temperature was ramped from 50–280 ◦ C (with 5 ◦ C/min) and then maintained at 280 ◦ C for 5 min. To avoid overloading the column, the split ratio was preset at 50:1; this ratio was carefully controlled so that results from the chromatography could still be quantified. For each sample, three repetitive trials were performed and the resulting chromatograms were manually integrated. In addition, all cellulose derived peaks were carefully interpreted. 3. Results and discussion 3.1. Fabric treatment As the result of this treatment, the concentrations achieved for TEPP and DEPP on the fabrics were 19 and 18 wt%, respectively. Samples of the treated fabrics TEPP-19 and DEPP-18 and the control fabric were characterized instrumentally. 3.2. Functional groups present on the surface of treated fabrics before thermal decomposition It is widely known that flame retardants can alter the process of pyrolysis of the fabrics. To understand how the alteration happens, it is important to gain knowledge of the chemical components on the treated fabrics before the pyrolysis. In this experiment, the Infrared spectroscopy using ATR was employed to examine the functional groups on the surface of the control as well as the treated fabrics. The results are shown in Fig. 1. Although the data were collected in a wide range, much of the differences can be observed between 1500 and 700 cm−1 . As seen in Fig. 1, TEPP-19 and DEPP-18 do have something in common: the peak characteristics of P O and O P O at around 1240–1228 cm−1 and 820–790 cm−1 , respectively [18a,b]. The lower frequency observed for P O in DEPP-18 suggests, however, that this is likely due to the hydrogen bond formed between the NH group and the P O [19a]. Upon a more thorough inspection of the two spectra, their differences are revealed by their signature peaks. The spectroscopic feature at 972 cm−1 is found for TEPP-19, which corresponds to the asymmetric vibration of P N C group in which the alkyl is not CH3 or C2 H5 [18c]. At lower frequency, P N absorption for TEPP-19 is shown at 772 cm−1 ; this may be due to the attachment of two N-bonded CH2 groups [19b]. In the range
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Scheme 1. Synthesis of tetraethyl piperazine-1,4-diyldiphosphonate (TEPP) and diethyl 4-methyl piperazin-1-ylphosphoramidate (DEPP).
0.20
100
unburned control unburned 19 % TEPP unburned 18 % DEPP
νP-N-C
80
unburned control
0.15 νP-N-C νP-O
0.10
60
C
C
165, 247°C ; 34%
40
νP=O
control
0.05
νP-O
C
0.00 1500 1400 1300 1200 1100 1000
140, 250°C ; 22%
TEPP-19
20
DEPP-18 320°C; 3%
0
900
800
700
wavenumber (cm-1)
0
100
200
300
400
500
600
Fig. 2. Degradation thermograms in nitrogen for the control, TEPP-19 and DEPP-18.
Fig. 1. ATR-IR spectrum (expanded region) for the control, TEPP-19 and DEPP-18 before pyrolysis.
820–790 cm−1 , O P O peak of DEPP-18 becomes broad and less intense; this may be ascribed to the perturbation from N (C)2 group attached to the NH which links to P [20]. From the above analysis, it is evident that both chemicals remain intact during the treatment process for the fabrics.
3.3. Gas products during thermal decomposition The mass loss curves for the control and treated fabrics are shown in Fig. 2. In addition, the onset temperature or the beginning of major weight loss and char residue (%) in nitrogen atmosphere is displayed. As seen in Fig. 2, the treated fabrics have lower onset temperature and yield higher char residue when compared with the control. The earlier decomposition of both compounds TEPP and DEPP causes smaller mass loss at around 165 and 140 ◦ C on TEPP19 and DEPP-18, respectively. While more TEPP decomposes than DEPP, less material or cotton fabric is degraded in TEPP-19 sample. As a result, TEPP-19 provides more char at 600 ◦ C when compared with DEPP-18. By coupling with TGA, FTIR can detect the real-time gaseous products released in the pyrolysis process. During the experiment, the FTIR data are plotted one on top of the other with a total of 80 scans to form a 3D spectrum in which the evolution of gas products is shown as a function of both wavenumber and temperature.
Typical spectra output from this experiment for TEPP-19 and DEPP-18 as well as the control are shown in Fig. 3. During the pyrolysis, the gases released from the untreated fabric (Fig. 3a) are mainly hydrocarbon OH (∼3300–3000 cm−1 ); hydrocarbon CH2 , CH3 (∼3014–2600 cm−1 ); CO2 (∼2360–2310 and 710 cm−1 ); CO (∼2185–2100 cm−1 ); water vapor (∼4000–3500 and 1800–1500 cm−1 ); some hydrocarbon C O (∼1850–1600 cm−1 ) and C O H deformation, C O C, C H, C C and C C (∼1500–900 cm−1 ) [10,21]. They are the products of the reduction of cellulose molecule, the appearance of free radicals, oxidation, dehydration, decarboxylation, decarbonylation and decomposition of cellulose to tarry pyrolyzate-containing levoglucosan, which vaporizes and then decomposes at later time or higher temperature. As shown in Fig. 3, it is obvious that all three profiles share several common features, such as the water vapor, hydrocarbon OH, CO2 , CO, hydrocarbon C H, C C C C gases . . . When comparing the evolution profiles for TEPP-19 and DEPP-18, it is noticeable that they do possess two similar characteristics: C O of EtOH (1271, ∼1040–970 cm−1 ) and P O C2 H5 (730–690 cm−1 ) [18c,22,23] (See Supporting information for expanded regions). Besides these common features, they reveal their differences in other signature peaks. Around 1774–1695 cm−1 , while TEPP-19 appears normal for moisture fingerprint region, DEPP-18 seems to contain other functional groups. In general, for organophosphorous compounds, this is presumably the region of absorption for P( O) OH [19c]. Moreover, in DEPP-18, this region extends
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a)
b)
c)
Fig. 3. Volatiles released out during pyrolysis of the control (a), TEPP-19 (b) and DEPP-18 (c).
further down to 1633 cm−1 . In many phosphoramidates and similar materials, P NH2 exhibits its deformation absorption in the region 1650–1550 cm−1 [18b]. There are two separate peaks in the overall range 1186–990 cm−1 for DEPP-18, which are identified as being in some way related to the CH2 and/or C O H deformation similar to those of the untreated fabric [10,21]. At around 1040–1000 cm−1 , P O P asymmetric vibration appears for TEPP-19 while P N and NH2 absorptions are seen for DEPP18 at ∼993–900 and 823 cm−1 , respectively [18c,d,e]. In addition, the characteristic absorption for H2 C CH2 from 940–900 cm−1 is detected for TEPP-19 [24] (See Supporting information for expanded region). Although the vibration of CH2 and CH3 both asymmetric and symmetric in both spectra appear almost at the same region (3014–2674 cm−1 for TEPP-19 and 3029–2821 cm−1 for DEPP-18), it is clear that DEPP-18 has more processes running in parallel and consecutively during its thermal decomposition than TEPP-19. Among the three profiles, it is obvious that without the additives, more materials from the fabric are decomposed and that this decomposition process takes place at later time. Furthermore, between the treated fabrics, the decomposition of TEPP-19, which produces less gas products, occurs earlier than that of DEPP-18. It is obvious that TGA data is supported by FTIR data. Since more cotton fabric is decomposed in DEPP-18 sample during the thermal degradation, its gas profile bears some resemblance to the gas profile of the control.
3.4. Gas products from pyrolysis process While TGA can best provide the changes in onset of degradation and char residue of the fabrics at desired temperatures, Py-GC/MS can further assist the characterization of the actual decomposition of the treated fabrics thanks to its ability to detect the chemical fragments formed during the degradation process. This process combines with the gas chromatography for the separation of pyrolyzed products and mass spectrometry for the identification of volatile compounds. The identified thermal decomposition products then help contribute to the understanding of the pyrolysis pathway. The chromatograms for the control and treated fabrics as well as probable species formed from this experiment are presented in Fig. 4 and Tables 1–3. Additionally, same work was also carried out for each chemical and the results are summarized in Tables 4 and 5. As seen in Fig. 4a and from Table 3, the chromatogram of the untreated fabric comprises of several different species such as aldehydes, ketones, furans, furfural and nucleoglucosan which are similar to those reported in literature [7]. In fact, there are almost 50 different compounds formed after the breakdown of levoglucosan besides the normally seen gases, i.e., hydrogen, methane, acetylene, carbon monoxide, ethylene, ethane, carbon dioxide [25]. When cotton fabric is treated with phosphorus, nitrogen and/or halogen containing FRs, the numbers of gas products are reduced [8].
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Fig. 4. Total ion chromatograms for control twill (a), TEPP-19 (b) and DEPP-18 (c) pyrolysis products.
In this study, the chromatograms of treated fabrics (Fig. 4b and c) seem to contain less peaks than the untreated one. Triethyl phosphate, tetraethyl pyrophosphate and 1-methyl piperazine were detected for TEPP-19 and DEPP-18, not to mention other evolved gases released by three fabrics. In general, there still remains
a number of unknown compounds which could not be recognized by the MS library in each chromatogram. Considering the effect of two FRs on the pyrolysis process, the production of volatiles shows some differences between the treated fabrics. In addition to the common species, 2-cyclopentanedione, 3-methyl
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a)
b)
Scheme 2. Proposed mode of action of TEPP (a) and DEPP (b).
Table 1 Major peaks of control twill with retention time and probable species by pyrolysis.
Table 2 Major peaks of TEPP-19 with retention time and probable species by pyrolysis.
Peak
Retention time (min)
Compound detected
Peak
Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2.466 3.513 4.136 5.03 5.737 7.901 8.37 9.565 12.86 14.185 15.587 16.248 17.196 29.638 30.902
2-Propanone,1-hydroxy 1,4-Pentadien,3-one Propanoic acid,2-oxo-,methyl ester Furfural Furan,2-propyl 2,5-Furandione,dihydro,3-methylene 2-Furancarboxaldehyde,5-methyl Oxazolidine,2,2-diethyl,3-methyl Levoglucosenone 4H-pyran,4-one,3,5-dihydroxy-6-methyl 4H-pyran,4-one,3,5-dihydroxy-2-methyl 1,4:3,6-Dianhydro ␣-d-glucopyranose 5-Hydroxymethylfurfural d-Allose/-d-glucopyranose 1,6-Anhydro, -d-glucopyranose
1 2 3 4 5 6 7
5.001 5.707 5.821 6.232 6.894 8.376 10.362
8 9 10
12.941 13.573 16.017
11 12 13
16.61 25.481 24.1–26.503
Furfural Furan,2-propyl 2(3H)-furanone-5-methyl 4-Cyclopentene-1,3-dione Ethanone,1-(2-Furanyl) 2-Furancarboxaldehyde,5-methyl 1,2-Cyclopentanedione, 3-methyl or methyl cyclopentenolone Levoglucosenone Triethyl phosphate 1,4:3,6-Dianhydro-␣-dglucooyranose 5-Hydroxymethylfurfural Tetraethyl pyrophosphate 1,6-Anhydro, -d-glucopyranose
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Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11 12 13
4.965 5.693 5.8 6.2 6.877 8.329 13.04 13.465 13.8 15.11 15.799 16.512 24.1–26.23
Furfural Furan,2-propyl 2(3H)-furanone-5-methyl 4-Cyclopentene-1,3-dione Ethanone,1-(2-furanyl) 2-Furancarboxaldehyde,5-methyl Levoglucosenone Triethyl phosphate 1-Methylpiperazine 4H-pyran-4-one, 3,5-dihydroxy-2-methyl 1,4:3,6-Fianhydro-␣-d-glucooyranose 5-Hydroxymethylfurfural 1,6-Anhydro, -d-glucopyranose
Table 4 Major peaks of TEPP with retention time and probable species by pyrolysis. Peak
Retention time (min)
Compound detected
1 2 3 4
7.99 10.554 14.123 25.98
N-ethylpiperazine Piperazine, 1,4,-diethyl Triethyl phosphate Tetraethyl pyrophosphate
7
3.5. Possible mechanisms for thermal decomposition of the fabrics Data from the TGA–FTIR and Py-GC/MS reveal that the first step of decomposition of untreated fabric is the depolymerization of the cellulose polymer to form various anhydrosugar derivatives and to release some water and CO2 . In treated fabrics, this process can be changed by the presence of FRs due to their catalytic action (Scheme 2). It is clearly that much less water, CO2 and compounds from breaking down of cellulose polymer released in both treated fabrics. TEPP and DEPP may decompose by hydrolysis or elimination to release ethanol, phosphate esters, ethylene and the acidic derivatives which may catalyze the formation of char. In case of DEPP-18, besides the formation of the acidic intermediate, phosphoramidate and ethanol, the hydrolysis may also result in the cleavage of N N bond to release the piperazine derivative. It is reported that piperazine-NH containing compound can cleave at N N bond to release a piperazine species [14]. The newly formed piperazine derivative is further broken down to nitrogen containing derivatives. These might be the main reasons for the appearance of more different functional groups in the evolution profile of gas products for DEPP-18 (by TGA–FTIR) and different piperazine derivatives observed from the pyrolysis for DEPP chemical (by Py-GC/MS). 4. Conclusion
Table 5 Major peaks of DEPP with retention time and probable species by pyrolysis. Peak
Retention time (min)
Compound detected
1 2 3 4 5 6 7 8 9 10 11
2.09 4.917 5.591 5.82 7.278 7.391 8.112 9.273 10.499 14.336 16.809
Ethanamine, N-ethyl,N-methyl Pirazine,methyl Piperazine,1,4-dimethyl Piperazine,1-methyl Piperazine,ethyl Piperazine,2,3-dimethyl Piperazine,1,2,4-trimethyl 1-Amino,4-methylpiperazine Piperazine,1,4-diethyl Triethyl phosphate Phosphoric acid, diethyl ester
(or may be methyl cyclopentenolone) and tetraethyl pyrophosphate are detected for TEPP-19 while 1-methylpiperazine and 4H-pyran-4-one, 3,5-dihydroxy-2-methyl are seen for DEPP-18. Among these four compounds, 2-cyclopentanedione, 3-methyl (or may be methyl cyclopentenolone) and 4H-pyran-4-one, 3,5dihydroxy-2-methyl come from the secondary decomposition of anhydrous sugars [21] while tetraethyl pyrophosphate and 1methylpiperazine are the products of the decomposition of TEPP and DEPP, respectively. Additional Py-GC/MS studies on each chemical provide more insights into their own breakdown. With these details, possible pyrolysis pathways and byproducts which may influence the decomposition of the treated fabrics can be elucidated. From Tables 4 and 5, besides triethyl phosphate which is common pyrolysis product for both chemicals, tetraethyl pyrophosphate which was seen in TEPP-19 was detected again for TEPP. Though both FRs bearing the same ethyl phosphonate group, only TEPP can generate this latter compound. Overall, the results from pyrolysis for TEPP and DEPP show some piperazine and nitrogen containing derivatives. It is known that piperazine has been detected as a byproduct during pyrolysis of piperazine containing molecules [14,15,26]. As the results, the appearance of the piperazine and nitrogen containing derivatives is likely from the secondary pyrolysis of the piperazine moiety; that may have dissociated from the mother compounds during the first stage of the decomposition.
By employing ATR-IR, TGA–FTIR and Py-GC/MS techniques, extensive experiment is performed to investigate the mechanism of the thermal degradation for the control cotton fabric and the cotton fabrics treated with flame retardants, TEPP and DEPP. The results showed that: the treatment process does not decompose the two flame retardants; most main products are enhanced when the residence time is increased; the control generates more gas products that all come out at later time; most evolved gases from the control are flammable substances which are products of the depolymerization of cotton cellulose; both treated fabrics release ethanol, phosphate esters, acidic intermediates, with or without ethylene and nitrogen derivatives and maybe some products from cotton cellulose; more activities are observed for DEPP-18 compared with TEPP-19. Acknowledgements This study was financed by the U.S. Department of Agriculture. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jaap.2014.08.006. References [1] T.D. Nguyen, S. Chang, B.D. Condon, R.P. Slopek, Synthesis of a novel flame retardant containing phosphorus–nitrogen and comparison of application on cotton fabric, Fibers Polym. 133 (2012) 963. [2] R.E. Lyon, R.N. Walters, Pyrolysis combustion flow calorimetry, J. Anal. Appl. Pyrol. 71 (2004) 27. [3] S. Chang, B. Condon, T.M. Nguyen, E. Graves, J. Smith, Antiflammable properties of capable phosphorus–nitrogen containing triazine derivatives on cotton, in: A.B. Morgan, C.A. Wilkie, G.L. Nelson (Eds.), Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science, ACS Symposium Series 1118, American Chemical Society, Washington, DC, 2013, pp. 123–137. [4] P. Bajaj, Heat and flame protection, in: A.R. Horrocks, S.C. Anand (Eds.), Handbook of Technical Textiles, Woodhead Publishing Limited and CRC Press LLC, Florida, USA and Cambridge, UK, 2000, pp. 223–263. [5] S.F. Ibrahim, E.S. El-Amoudy, K.E. Shady, Thermal analysis and characterization of some cellulosic fabrics dyed by a new natural dye and mordanted with different mordants, Int. J. Chem. 3 (2011) 40.
Please cite this article in press as: T.-M. Nguyen, et al., Thermal decomposition reactions of cotton fabric treated with piperazinephosphonates derivatives as a flame retardant, J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.08.006
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Please cite this article in press as: T.-M. Nguyen, et al., Thermal decomposition reactions of cotton fabric treated with piperazinephosphonates derivatives as a flame retardant, J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.08.006