- Email: [email protected]
Exfoliation of layered zirconium phosphate nanoplatelets by melt compounding
Materials and Design 122 (2017) 247–254
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Exfoliation of layered zirconium phosphate nanoplatelets by melt compounding Lei Chen a,b, Dazhi Sun a,⁎, Jin Li b, Guangdao Zhu c a Shenzhen Key Laboratory of Nanoimprint Technology, Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, People's Republic of China b Department of Materials Science, Fudan University, Shanghai 200433, People's Republic of China c Huaian Nylon Chemical Fibre Co., Ltd., Huaian, Jiangshu 223400, People's Republic of China
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• ZrP nanoplatelets with various sizes were successfully exfoliated by the presented melt compounding method. • This fabrication method could be used to prepare polymer nanocomposites with exfoliated ZrP nanoplatelets in a large scale. • The improvement of modulus of elasticity of ZrP/POE-g-MA was attributed to the well-exfoliated nanoplatelets. • The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by diglycolamine.
a r t i c l e
i n f o
Article history: Received 10 January 2017 Received in revised form 6 March 2017 Accepted 7 March 2017 Available online 07 March 2017 Keywords: Zirconium phosphate nanoplatelets Exfoliation Melt compounding method Polymer nanocomposite Maleic anhydride grafted polymer
a b s t r a c t A melt compounding method to achieve the exfoliation of layered zirconium phosphate (ZrP) nanoplatelets was presented in this work. ZrP nanoplatelets were first intercalated by diglycolamine (DGA) to increase the interlayer distance and functionality. In the next melt compounding process, the cyclic anhydrides of maleic anhydride grafted polyolefin elastomers (POE-g-MA) reacted with the hydroxyls in DGA-ZrP. Subsequently, the long polyolefin chains of POE-g-MA intercalated into the interlayer of ZrP smoothly and exfoliated the nanoplatelets successfully. ZrP nanoplatelets with various sizes were fully exfoliated in POE-g-MA matrices. The modulus of elasticity of POE-g-MA was improved by the incorporation of ZrP nanoplatelets and further increased if the nanoplatelets are exfoliated. The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by DGA and then exfoliated, especially for the smaller nanoplatelets. Our work provides a general method to prepare polymer nanocomposites containing exfoliated ZrP nanoplatelets in a large scale. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction
⁎ Corresponding author. E-mail address: [email protected] (D. Sun).
http://dx.doi.org/10.1016/j.matdes.2017.03.026 0264-1275/© 2017 Elsevier Ltd. All rights reserved.
Adding synthetic or natural nanoscale inorganic compounds into polymeric materials is a well-known technique to improve various properties of the organic matrices, such as mechanical strength [1–11], flame retardancy [12–18], barrier properties [18–24],
248
L. Chen et al. / Materials and Design 122 (2017) 247–254
dimensional stability [25–28], and so on. Such prepared polymer nanocomposites can be distinguished into three types, depending on the dimension of the incorporated nanoparticles, i.e. 0-dimensional (0D) spherical/quasi-spherical nanoparticles, 1-dimensional (1D) nanorods/ nanotubes/nanowires and 2-dimensional (2D) nanoplatelets/nanosheets [29,30]. Among all the potential nanocomposite additives, clay and layered silicates have been widely investigated probably because they are easily available and their intercalation chemistry has been studied for a long time [29–32]. Clays have several advantages, such as high ion exchange capacity, high aspect ratio and inexpensiveness, thereby resulting in high potential for large-scale commercial uses. But the main drawback of clays is that they are produced via purification and modification of the mined clay. It is extremely difficult to achieve 100% purity, narrow particle size distribution and controlled aspect ratio for clays, which affect the mechanical properties of polymer nanocomposites directly [11,33,34]. Compared with clay, synthetic zirconium phosphate (Zr(HPO4)2·H2O, ZrP) nanoplatelets have a much higher ion exchange capacity (6 times higher than clay), and their size and aspect ratio can be controlled by varying reaction time and reactant concentrations [35–38]. Furthermore, the size distribution of ZrP nanoplatelets has been found to be quite narrow, thus suitable for fundamental study of nanofiller effect on the properties of the host polymers. Moreover, ZrP nanoplatelets have also been found to improve the flame retardancy of the polymer matrices mainly through catalytic carbonization effect, rather than physical effects, by forming a highperformance carbonaceous char on the sample surface [13]. In preparing polymer nanocomposites containing layered nanoplatelets, intercalation and exfoliation have always been the two most critical steps. In general, inorganic nanoplatelets cannot be easily dispersed in most polymers due to their preferred face-to-face stacking in agglomerated tactoids. Dispersion of the tactoids into discrete monolayers is further hindered by the intrinsic incompatibility of hydrophilic layered inorganic compounds and hydrophobic engineering plastics. Effective intercalation has been shown to be essential for the preparation of fully exfoliated polymer nanocomposites with greatly improved modulus and barrier properties [39–43]. In the past two decades, the most traditional and popular approach is to intercalate the nanoplatelets by organic amines to produce polymer–compatible nanoplatelets. There are three methods to prepare polymer nanocomposites, i.e. intercalation of a suitable monomer followed by polymerization, polymer intercalation from solution, and direct polymer melt compounding [3]. Among them, direct polymer melt compounding is the most attractive because of its low cost, high productivity and compatibility with current polymer processing techniques. It uses widespread and conventional equipments in the plastic industry with high producing rates. Up till now, a few exfoliated nanocomposites with clay were successfully prepared by melt compounding method, such as PP/clay [4], PA6/clay [44,45], and EVA/clay [46] composites. The intercalated-exfoliated type of PA6/ZrP nanocomposites have also been prepared whereas PET/ZrP, PP/ZrP and EVA/ZrP compounds appear to be micro-composites [12]. To the best of our knowledge, no
exfoliated nanocomposites with ZrP nanoplatelets have been successfully prepared by melt compounding method. Hence, the objective of this study is to develop a viable melt compounding method for achieving full exfoliation of layered zirconium phosphate nanoplatelets. This was done using a two-step process: in the first, ZrP nanoplatelets were intercalated by diglycolamine. Secondly, the intercalated ZrP nanoplatelets were mixed with maleic anhydride grafted polymer (polymer-g-MA) matrices using a mixer rheometer. To demonstrate the validity of this method, ZrP nanoplatelets with different sizes were prepared. The usefulness of polymer-g-MA to exfoliate layered ZrP nanoplatelets was monitored using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscope. To study the effect of ZrP nanoplatelets on the mechanical property of polymer-g-MA matrices, the tensile properties of the ZrP/polymer-gMA nanocomposites were also tested and discussed. 2. Experimental section 2.1. Materials Zirconyl chloride (ZrOCl2·8H2O, 98%, Aladdin Industrial Co., Ltd), phosphoric acid (85%, Tianjin Yongda Chemical Reagent Co., Ltd), and diglycolamine (DGA, Aladdin Industrial Co., Ltd) were used as received. Maleic anhydride grafted polyolefin elastomer (POE-g-MA, 1801B, Guangzhou Haosu Chemical Co., Ltd) was chosen as the polymer-gMA to exfoliate ZrP nanoplatelets. The chemical structure of POE-gMA was shown in Fig. 1. Table 1 The abbreviations of all the samples in this work. The abbreviation of sample
The description of sample
ZrP Refl3MZrP
Zirconium phosphate nanoplatelets ZrP synthesized by refluxing method in the condition of 3.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 3.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 6.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 9.0 mol/L H3PO4 Zirconium phosphate intercalated by diglycolamine (DGA) Refl3MZrP intercalated by diglycolamine 3MZrP intercalated by diglycolamine 6MZrP intercalated by diglycolamine 9MZrP intercalated by diglycolamine Maleic anhydride grafted polyolefin elastomer The compounds of ZrP with POE-g-MA The compounds of Refl3MZrP with POE-g-MA
3MZrP 6MZrP 9MZrP DGA-ZrP DGA-Refl3MZrP DGA-3MZrP DGA-6MZrP DGA-9MZrP POE-g-MA ZrP/POE-g-MA Refl3MZrP/POE-g-MA or R3M/MA DGA-Refl3MZrP/POE-g-MA or DGA-R3M/MA 3MZrP/POE-g-MA or 3M/MA DGA-3MZrP/POE-g-MA or DGA-3M/MA 6MZrP/POE-g-MA or 6M/MA DGA-6MZrP/POE-g-MA or DGA-6M/MA 9MZrP/POE-g-MA or 9M/MA DGA-9MZrP/POE-g-MA or DGA-9M/MA POE-g-MA-1 POE-g-MA-2 POE-g-MA-3
Fig. 1. The chemical structure of POE-g-MA: a) the details of the structure of POE-g-MA, b) the simplified version of POE-g-MA.
POE-g-MA-4
The compounds of DGA-Refl3MZrP with POE-g-MA The compounds of 3MZrP with POE-g-MA The compounds of DGA-3MZrP with POE-g-MA The compounds of 6MZrP with POE-g-MA The compounds of DGA-6MZrP with POE-g-MA The compounds of 9MZrP with POE-g-MA The compounds of DGA-9MZrP with POE-g-MA POE-g-MA prepared in the same melt compounding conditions with the samples of Refl3MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 3MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 6MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 9MZrP series
L. Chen et al. / Materials and Design 122 (2017) 247–254 Table 2 Melt compounding processing conditions used in this study. Sample
Melt compounding processing conditions
Refl3MZrP series 3MZrP series
Mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 10 min Mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 15 min The 1st stage, mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 15 min; The 2nd stage, mixing temp.: 190 °C, rotor speed: 50 rpm and mixing time: 4 min The 1st stage, mixing temp.: 190 °C, rotor speed: 50 rpm and mixing time: 12 min; The 2nd stage, mixing temp.: 195 °C, rotor speed: 50 rpm and mixing time: 7 min
6MZrP series
9MZrP series
2.2. Preparation of ZrP Zirconium phosphate nanoplatelets with different sizes were prepared by the refluxing and hydrothermal methods [38]. In a typical refluxing method, a sample of 500.0 g ZrOCl2·8H2O was refluxed with 5 L 3.0 M (3.0 mol/L) H3PO4 in a 10 L double layer glass jacketed pilot plant reactor at 100 °C for 24 h. After the reaction, the product was washed by deionized water and collected by centrifugation five times. Then, the ZrP nanoplatelets were dried at 70 °C for 24 h. The dried ZrP nanoplatelets were ground into fine powders in an agate mortar. The final products were identified as Refl3MZrP. In the hydrothermal method, a sample of 20.0 g ZrOCl2·8H2O was mixed with 100.0 mL 3.0/6.0/ 9.0 M H3PO4 and sealed into a Teflon-lined pressure vessel and heated at 200 °C for 24 h. After the reaction, the products were treated by the same procedure as described in refluxing method. The final products were identified as 3MZrP, 6MZrP and 9MZrP, respectively.
249
2.3. Exfoliation of ZrP Firstly, four pristine ZrP samples were completely intercalated by DGA under the action of 45 kHz ultrasonic for 8 h in solution. After the reaction, the intercalated ZrP samples were washed by ethyl alcohol and collected by centrifugation five times. Then, the intercalated ZrP samples were dried at 70 °C for 24 h and ground into fine powders in an agate mortar. The intercalated ZrP samples were identified as DGARefl3MZrP, DGA-3MZrP, DGA-6MZrP and DGA-9MZrP, respectively. Finally, the intercalated ZrP samples were mixed with POE-g-MA matrices in a Harpro mixer rheometer (RM-200C, Harbin Harpro Electric Technology Co., Ltd). The mass ratio of ZrP nanoplatelets and POE-gMA matrices was 1/19. Because ZrP nanoplatelets would increase the weight by 50% if they were completely intercalated by DGA, DGA-ZrP/ POE-g-MA (1.5/19), ZrP/POE-g-MA (1/19) and pure POE-g-MA were prepared for the melt compounding experiments. Four series of samples, i.e. Refl3MZrP series, 3MZrP series, 6MZrP series and 9MZrP series, were prepared in this study. Refl3MZrP series contain three samples, i.e. Refl3MZrP/POE-g-MA compounds (R3M/MA, 1.5 g/28.5 g), DGARefl3MZrP/POE-g-MA compounds (DGA-R3M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-g-MA-1, 30 g). 3MZrP series also contain three samples, i.e. 3MZrP/POE-g-MA compounds (3 M/MA, 1.5 g/28.5 g), DGA-3MZrP/POE-g-MA compounds (DGA-3 M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-g-MA-2, 30 g). Similarly, 6MZrP series contain three samples: 6MZrP/POE-g-MA compounds (6 M/MA, 1.5 g/28.5 g), DGA-6MZrP/POE-g-MA compounds (DGA-6 M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-gMA-3, 30 g). In the same way, 9MZrP series contain three samples: 9MZrP/POE-g-MA compounds (9 M/MA, 1.5 g/28.5 g), DGA-9MZrP/ POE-g-MA compounds (DGA-9 M/MA, 2.25 g/28.5 g) and pure POE-gMA matrices (POE-g-MA-4, 30 g). The descriptions of abbreviations of
Fig. 2. SEM images of ZrP nanoplatelets with different size: a) Refl3MZrP; b) 3MZrP; c) 6MZrP; d) 9MZrP.
250
L. Chen et al. / Materials and Design 122 (2017) 247–254
Fig. 3. The comparison of XRD patterns of ZrP nanoplatelets and corresponding ZrP/POE-g-MA compounds.
all the samples were summarized in Table 1. The melt compounding processing conditions were shown in Table 2. 2.4. Characterizations X-ray diffraction (XRD) measurements were made directly from ZrP powders, DGA-ZrP powders, ZrP/POE-g-MA bulk, DGA-ZrP/POE-g-MA bulk and pure POE-g-MA bulk. All XRD patterns were obtained for 2θ in the range from 2 to 70°, with a step interval of 0.02° in a X-ray diffractometer (XRD Smartlab, Rigaku Co., Ltd) using the Cu-Kα radiation source at λ = 0.15418 nm. The morphology of these samples was imaged using a scanning electron microscope (SEM VEGA 3 LMH, Tescan Co., Ltd). The infrared spectra of ZrP/POE-g-MA bulk, DGA-ZrP/POE-gMA bulk and pure POE-g-MA bulk were detected by a Fourier transform infrared spectroscopy (FTIR Spectrum TWO, PerkinElmer Co., Ltd). To prepare samples for mechanical testing, all the melt-mixed compounds were dried at 70 °C for 24 h firstly. Then they were granulated by a plastic crusher (MTLS 160, Mitex automatic machine Co., Ltd). All tensile testing specimens (ASTM D638 Type V) were injection molded by Haake Minijet II microinjection molding machine under the same injection molding processing conditions. The injection molding processing conditions were 185 °C of melt temperature, 55 °C of mold temperature, 490 bar of injection pressure, 3 s of injection time, 490 bar of packing pressure and 15 s of packing time. All specimens were kept in a sealed desiccator under vacuum for 24 h before mechanical property measurements were performed. Tensile testing was performed on an Instron Legend 2367 testing system with 1 kN load cell at a crosshead speed of 20 mm/min for modulus of elasticity. To improve accuracy, an Instron strain gauge extensometer (10 mm gauge) was used. The data values were reported with an average from five measurements.
3. Results and discussion ZrP nanoplatelets were first prepared via the refluxing and hydrothermal methods. It is anticipated that the crystallinity and the size of ZrP nanoplatelets will increase with increasing the concentration of phosphoric acid. Furthermore, compared with the refluxing method, the hydrothermal method can produce ZrP nanoplatelets with larger size in the same concentration of phosphoric acid [38]. This is validated by the SEM images of Refl3MZrP, 3MZrP, 6MZrP and 9MZrP shown in Fig. 2. The SEM images show that the length dimensions of the prepared
Fig. 4. The FTIR spectra of ZrP nanoplatelets and ZrP/POE-g-MA compounds.
L. Chen et al. / Materials and Design 122 (2017) 247–254
251
Scheme 1. The esterification of POE-g-MA with DGA-ZrP.
ZrP nanoplatelets are 50–100 nm of Refl3MZrP, 250–500 nm of 3MZrP, 350–800 nm of 6MZrP and 500–1200 nm of 9MZrP, respectively. ZrP nanoplatelets with size variations are ideal for studying the size effect on the exfoliation and mechanical properties of nanoplatelets in polymer matrices. The XRD patterns of ZrP powders, DGA-ZrP powders, ZrP/POE-g-MA bulk, DGA-ZrP/POE-g-MA bulk and pure POE-g-MA bulk are presented in Fig. 3. For instance, Fig. 3a shows the XRD patterns of Refl3MZrP series. The first peak (2θ = 11.56°) in the XRD pattern of Refl3MZrP nanoplatelets is the crystal face of ⟨002〉, which corresponds to the 7.7 Å interlayer distance. And the other peaks at 2θ of 19.78°, 25.02° and 34.08° reveal the crystal faces of ⟨110〉, ⟨112〉 and ⟨215〉, respectively. The relatively broad peaks in the XRD pattern indicate that the crystallinity of Refl3MZrP nanoplatelets is relatively low. Furthermore, the peaks in the XRD patterns of ZrP nanoplatelets become narrower with the increase of the concentration of phosphoric acid during the synthesis, which indicate the improving crystallinity of ZrP nanoplatelets. This results is consistent with Sun L. Y. et al.'s work [38]. The first peaks of the XRD patterns of 3MZrP, 6MZrP and 9MZrP nanoplatelets appear at 2θ of 11.6°, 11.68° and 11.7°,respectively, corresponding to the same interlayer distance (d002 = 7.6 Å) of these ZrP nanoplatelets with different size. However, the interlayer distances of DGA-3MZrP, DGA-6MZrP and DGA-9MZrP nanoplatelets have some difference, which can be shown by the positions of the first peaks of these three corresponding XRD patterns. After the intercalation of DGA, the first peaks of DGA-3MZrP, DGA-6MZrP and DGA-9MZrP nanoplatelets shift from 7.6 Å to 17.3 Å (2θ = 5.12°), 18.4 Å (2θ = 4.8°) and 20.5 Å (2θ = 4.32°), respectively. Compared with Refl3MZrP, Refl3MZrP/POE-g-MA and POE-g-MA-1, the XRD pattern of Refl3MZrP/POE-g-MA contains the peaks from the XRD patterns of both pristine Refl3MZrP nanoplatelets and pure POEg-MA, which indicates that POE-g-MA has no effect on the crystal structure of Refl3MZrP nanoplatelets and that POE-g-MA cannot exfoliate pristine Refl3MZrP nanoplatelets in melt compounding process directly. The first peak at 2θ of 4.46° in the XRD pattern of DGA-Refl3MZrP nanoplatelets corresponds to the intercalated interlayer distance of 19.8 Å. The increment of interlayer distance of Refl3MZrP nanoplatelets is 12.1 Å which is larger than the length of DGA with approximate 8.5 Å. Therefore, no peak at 2θ of 11.56° indicates that Refl3MZrP nanoplatelets were fully intercalated by DGA. The peaks in the XRD pattern of DGA-Refl3MZrP/POE-g-MA appear at the same angles with the XRD pattern of POE-g-MA, which are totally different with the XRD pattern of DGA-Refl3MZrP nanoplatelets, indicating that the Refl3MZrP
nanoplatelets can be successfully exfoliated by POE-g-MA in melt compounding process if they were intercalated by DGA first. Similarly, Fig. 3b–3d present the XRD patterns of 3MZrP series, 6MZrP series and 9MZrP series, respectively, which shows the same exfoliation results with Refl3MZrP series. It is also noted that POE-g-MA can completely exfoliate ZrP nanoplatelets to monolayers if the nanoplatelets were intercalated by DGA first regardless of the size of ZrP nanoplatelets. In the intercalating process, DGA molecules insert into the interlayer of ZrP nanoplatelets by the acid-base reaction between amine groups and hydroxyl groups on ZrP nanoplatelets, which lowers the surface energy of the inorganic nanoplatelets and improves the wetting with the polymer matrices. Furthermore, the interlayer distance of ZrP nanoplatelets increases from 7.6 Å to around 19 Å. Subsequently, with an aid of shearing force during the melt mixing, the maleic anhydride groups of POE-g-MA react with diglycolamine of DGA-ZrP in a high temperature condition. The acylation of maleic anhydride groups with diglycolamine has two forms, esterification and amidation. In order to understand the reaction mechanism further, the infrared spectra of 6MZrP nanoplatelets, DGA-6MZrP nanoplatelets, pure POE-g-MA, 6MZrP/POE-g-MA compounds and DGA-6MZrP/POE-g-MA compounds were detected by FTIR, as shown in Fig. 4. It was found that two bands at 1857 cm− 1 and 1781 cm− 1 have appeared in the infrared spectra of both pure POE-g-MA and the 6MZrP/POE-g-MA compounds, but they did not appear in the infrared spectrum of DGA-6MZrP/POE-g-MA compounds. The bands at 1857 cm−1 and 1781 cm−1 corresponded to the antisymmetric and symmetric stretch of C_O of cyclic anhydride, respectively [47]. This result indicated that POE-g-MA reacted with DGA-ZrP nanoplatelets in the melt compounding process and cyclic anhydride groups of POE-g-MA have reacted completely. The C\\O bond of cyclic anhydride was broken and reacted with the hydroxyl of DGA by the reaction of esterification, which was proved by the band at 1771 cm− 1 which has appeared in the infrared spectra of DGA6MZrP/POE-g-MA compounds. The band at 1771 cm−1 corresponded to the stretch of C_O of ester. Furthermore, there was no peak at the bands from 1680 cm−1 to 1630 cm− 1, which corresponded to the stretch of C_O of amide. The above phenomena indicate that in the melt compounding process, the acylation of maleic anhydride groups of POE-g-MA with diglycolamine of DGA-ZrP happened in the form of esterification only. The details of the chemical reaction are shown in Scheme 1. Because of the increasing interlayer distance of ZrP nanoplatelets, the cyclic anhydrides of POE-g-MA react with the hydroxyls of DGA-ZrP in the melt compounding process. Subsequently, the long polyolefin chains of POE-g-MA intercalate into the interlayer
Fig. 5. The scheme of the exfoliation of ZrP by POE-g-MA.
252
L. Chen et al. / Materials and Design 122 (2017) 247–254
Fig. 6. The SEM images of ZrP/POE-g-MA compounds: a) 9MZrP/POE-g-MA, b) DGA-9MZrP/POE-g-MA.
of ZrP nanoplatelets smoothly and finally exfoliate ZrP nanoplatelets, as shown in Fig. 5. Fig. 6 shows the selected SEM images of 9MZrP/POE-g-MA compounds and DGA-9MZrP/POE-g-MA compounds, respectively. ZrP nanoplatelets could be seen easily in the SEM image of 9MZrP/POE-g-
MA compounds. In the case of ZrP/POE-g-MA compounds, the POE-gMA matrices were unable to intercalate into the interlayer of ZrP nanoplatelets, a phase-separated composite was obtained, and the properties would be in the same range as those for traditional microcomposites [22,29,48]. In contrast to 9MZrP/POE-g-MA
Fig. 7. The tensile testing results of ZrP/POE-g-MA systems: a) the modulus of elasticity of ZrP/POE-g-MA systems, b) the tensile behavior of Refl3MZrP/POE-g-MA compounds, c) the tensile behavior of 6MZrP/POE-g-MA compounds.
L. Chen et al. / Materials and Design 122 (2017) 247–254
compounds, ZrP nanoplatelets were invisible in DGA-9MZrP/POE-g-MA compounds. Only some ZrP monolayers wrapped by POE-g-MA could be identified in the edge, which proves the successful exfoliation of ZrP nanoplatelets in the case of DGA-ZrP/POE-g-MA compounds. Fig. 7a shows the average of modulus of elasticity of ZrP/POE-MA systems. The corresponding black lines denote the error bars of the average of modulus elasticity of all materials. Due to different melt compounding processing conditions of these 4 groups of experiments, the modulus of elasticity of each pure POE-g-MA sample was different from any other pure POE-g-MA sample's modulus of elasticity as well, as presented in Fig. 7a. The testing results indicate that the modulus of elasticity of POE-g-MA matrices increased due to the filling of pristine ZrP nanoplatelets in the case of Refl3MZrP, 3MZrP and 6MZrP. In particular, the modulus of elasticity of POE-g-MA matrices with 3MZrP further improved if the nanoplatelets were exfoliated. Among all the prepared ZrP samples, 9MZrP nanoplatelets with the largest size are different from others. The modulus of elasticity of POE-g-MA matrices decreased with the filling of pristine 9MZrP nanoplatelets but increased significantly if 9MZrP nanoplatelets were first intercalated by DGA. When the pristine inorganic ZrP nanoplatelets fill into organic POE-g-MA matrices, the nanoplatelets will stack into agglomerated tactoids. Due to the agglomeration of nanoplatelets, the stress defects will be formed in ZrP/POE-g-MA compounds, which have negative effects on the mechanical property of polymer compounds. The stress defects are related to the size and volume of the agglomerated tactoids, and the concentration of the pristine ZrP nanoplatelets accounts for the same mass ratio of 5 wt% in each group of our experiments, therefore the size of the agglomerated tactoids is the main reason for the observed stress defects. With the increase of the size of nanoplatelets, the stress defects increase and reduce the mechanical property of polymer compounds as in the case of 9MZrP with the largest size in this study. The observed modulus of elasticity of POE-g-MA decreased with addition of the pristine 9MZrP nanoplatelets. However, after intercalated by DGA, DGA-9MZrP nanoplatelets became compatible with POE-g-MA matrices and were completely exfoliated and dispersed well during the melt compounding process, resulting in an obvious improvement of the modulus of elasticity of the polymer matrices. The tensile stress-strain curves of Refl3MZrP/POE-g-MA compounds and 6MZrP/POE-g-MA compounds are shown in Fig. 7b and c, respectively. By comparison with the curves of POE-g-MA and ZrP/POE-gMA compounds, it was found that the filled nanoplatelets made the polymer matrices brittle, while the yield strength increased and the elongation at break decreased at the same time. By comparison with the curves of ZrP/POE-g-MA and DGA-ZrP/POE-g-MA compounds, it was found that the elongation at break of DGA-ZrP/POE-g-MA compounds all increased due to the intercalation of ZrP nanoplatelets by DGA. Normally, the filled nanoplatelets could increase the strength but decrease the ductility of polymer compounds. However, in the case of Refl3MZrP nanoplatelets with the smallest size, the strength and ductility of DGA-Refl3MZrP/POE-g-MA compounds were larger than the pure POE-g-MA, which is mainly due to the fact that the DGA-Refl3MZrP nanoplatelets are completely exfoliated and associated with POE-gMA by the strong covalent bonding. Furthermore, the small size of the Refl3MZrP nanoplatelets of less than 100 nm would results in smaller stress defects in the polymer matrices as compared to other larger nanoplatelets, which is also attributed to the improved mechanical performance. 4. Conclusions Layered zirconium phosphate nanoplatelets were completely exfoliated by melt compounding methods in two steps. Firstly, ZrP nanoplatelets were intercalated by DGA. Then, due to the esterification reaction between the cyclic anhydrides of POE-g-MA and hydroxyls of DGA-ZrP nanoplatelets, DGA-ZrP nanoplatelets were completely exfoliated by POE-g-MA in the melt compounding process, regardless of the
253
size of the nanoplatelets. The modulus of elasticity of POE-g-MA matrices increased due to the filling of ZrP nanoplatelets of various sizes and improved further if the nanoplatelets were exfoliated. Furthermore, the ductility of ZrP/POE-g-MA compounds will become better if ZrP nanoplatelets were first intercalated by DGA especially for the Refl3MZrP nanoplatelets with the smallest size. Maleic anhydride grafted polymers are a class of compatilizers used in polymer processing, therefore, by utilizing our melt compounding method, layered zirconium phosphate nanoplatelets can be exfoliated and dispersed well in different polymer matrices, which is very suitable for the industrial applications. Moreover, this melt compounding method is also of great potential in producing masterbatches of high-concentration nanoplatelets for further polymer nanocomposite processing. Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding sources This work was supported by the start-up fundings from Southern University of Science and Technology (SUSTech) and “The Recruitment Program of Global Youth Experts of China”, the Foundation of Shenzhen Science and Technology Innovation Committee (Grant no.: ZDSYS20140509142721431, JCYJ20160315164631204, and KQTD20140630110339343), and National Natural Science Foundation of China (NSFC Grant no.: 21306077). Acknowledgment We are grateful to Ms. Sixia Hu, the engineer of the Materials Characterization Center in SUSTech, for her support in XRD measurements and Mr. Huaisong Yong for valuable discussions. References [1] Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito, Mechanical properties of nylon 6-clay hybrid, J. Mater. Res. 8 (1993) 1185–1189. [2] R.A. Damiani, J.F. Junior, J.R. Silvano, Influence of the injection molding process on the mechanical properties of (PA6/GF/MMT) nanocomposite, Polym. Compos. 36 (2) (2015) 237–244. [3] H. Wang, C.C. Zeng, M. Elkovitch, L.J. Lee, K.W. Koelling, Processing and properties of polymeric nano-composites, Polym. Eng. Sci. 41 (2001) 2036–2046. [4] M. Kato, M. Matsushita, K. Fukumori, Development of a new production method for a polypropylene-clay nanocomposite, Polym. Eng. Sci. 44 (2004) 1205–1211. [5] T.L. Zhang, F.J. Zhang, S.S. Dai, Z.F. Li, B.G. Wang, H.P. Quan, Z.Y. Huang, Polyurethane/ organic vermiculite composites with enhanced mechanical properties, J. Appl. Polym. Sci. 133 (2016) 4321913. [6] W.J. Boo, L.Y. Sun, J. Liu, E. Moghbelli, A. Clearfield, H.J. Sue, H. Pham, N.J. Verghese, Effect of nanoplatelet dispersion on mechanical behavior of polymer nanocomposites, Polym. Sci. Pol. Phys. 45 (2007) 1459–1469. [7] P. Li, K.L. White, C.H. Lin, D. Kim, A. Muliana, R. Krishnamoorti, R. Nishimura, H.J. Sue, Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order, ACS Appl. Mater. Interfaces 6 (2014) 10188–10195. [8] L.Y. Sun, W.J. Boo, J. Liu, A. Clearfield, H.J. Sue, N.E. Verghese, H.Q. Pham, J. Bicerano, Effect of nanoplatelets on the rheological behavior of epoxy monomers, Macromol. Mater. Eng. 294 (2009) 103–113. [9] D.Z. Sun, C.C. Chu, H.J. Sue, Simple approach for preparation of epoxy hybrid nanocomposites based on carbon nanotubes and a model clay, Chem. Mater. 22 (2010) 3773–3778. [10] D.Z. Sun, W.N. Everett, C.C. Chu, H.J. Sue, Single-walled carbon-nanotube dispersion with electrostatically tethered nanoplatelets, Small 5 (2009) 2692–2697. [11] H.J. Sue, K.T. Gam, N. Bestaoui, N. Spurr, A. Clearfield, Epoxy nanocomposites based on the synthetic alpha-zirconium phosphate layer structure, Chem. Mater. 16 (2004) 242–249. [12] J. Alongi, A. Frache, Flame retardancy properties of alpha-zirconium phosphate based composites, Polym. Degrad. Stab. 95 (2010) 1928–1933. [13] D. Liu, G.P. Cai, J. Wang, X.F. Tan, H.D. Lu, S.Y. Zhang, Q.Q. Dai, Thermal and flammability performance of polypropylene composites containing melamine and melamine phosphate-modified α-type zirconium phosphates, J. Appl. Polym. Sci. 131 (2014) 4025410. [14] M. George, G.E. Kochimoolayil, J.N. Haridas, Mechanical and thermal properties of modified kaolin clay/unsaturated polyester nanocomposites, J. Appl. Polym. Sci. 133 (2016) 4324513. [15] H.D. Lu, C.A. Wilkie, The influence of alpha-zirconium phosphate on fire performance of EVA and PS composites, Polym. Adv. Technol. 22 (2011) 1123–1130.
254
L. Chen et al. / Materials and Design 122 (2017) 247–254
[16] W.Y. Xing, P. Zhang, L. Song, X. Wang, Y. Hu, Effects of alpha-zirconium phosphate on thermal degradation and flame retardancy of transparent intumescent fire protective coating, Mater. Res. Bull. 49 (2014) 1–6. [17] X.Q. Liu, D.Y. Wang, X.L. Wang, L. Chen, Y.Z. Wang, Synthesis of organo-modified alpha-zirconium phosphate and its effect on the flame retardancy of IFR poly(lactic acid) systems, Polym. Degrad. Stab. 96 (2011) 771–777. [18] E. Picard, A. Vermogen, J.F. Gerard, E. Espuche, Influence of the compatibilizer polarity and molar mass on the morphology and the gas barrier properties of polyethylene/clay nanocomposites, J. Polym. Sci. Polym. Phys. 46 (2008) 2593–2604. [19] J.W. Rhim, H.M. Park, C.S. Ha, Bio-nanocomposites for food packaging applications, Prog. Polym. Sci. 38 (2013) 1629–1652. [20] B. Ghanbarzadeh, S.A. Oleyaei, H. Almasi, Nanostructured materials utilized in biopolymer-based plastics for food packaging applications, Crit. Rev. Food Sci. 55 (2015) 1699–1723. [21] A. Usuki, N. Hasegawa, H. Kadoura, T. Okamoto, Three-dimensional observation of structure and morphology in nylon-6/clay nanocomposites, Nano Lett. 1 (2001) 271–272. [22] Q.H. Zeng, A.B. Yu, G.Q. Lu, D.R. Paul, Clay-based polymer nanocomposites: research and commercial development, J. Nanosci. Nanotechnol. 5 (2005) 1574–1592. [23] M. Fasihi, M.R. Abolghasemi, Oxygen barrier and mechanical properties of masterbatch-based PA6/nanoclay composite films, J. Appl. Polym. Sci. 1251 (2012) E2–E8. [24] Y. Zare, H. Garmabi, Thickness, modulus and strength of interphase in clay/polymer nanocomposites, Appl. Clay Sci. 105 (2015) 66–70. [25] A. Karatrantos, N. Clarke, R.J. Composto, K.I. Winey, Entanglements in polymer nanocomposites containing spherical nanoparticles, Soft Matter 12 (2016) 2567–2574. [26] E. Haque, C.D. Armeniades, Montmorillonite polymer concrete: zero-shrinkage and expanding polymer concrete with enhanced strength, Polym. Eng. Sci. 26 (1986) 1524–1530. [27] N. Salahuddin, M.M. Shehata, Reduction of polymerization shrinkage in methyl methacrylate-montmorillonite composites, Mater. Lett. 52 (2002) 289–294. [28] S.S. Hwang, S.P. Liu, P.P. Hsu, J.M. Yeh, J.P. Yang, K.C. Chang, S.N. Chu, Effect of organoclay and preparation methods on the mechanical/thermal properties of microcellular injection molded polyamide 6-clay nanocomposites, Int. Commun. Heat Mass 38 (2011) 1219–1225. [29] S. Pavlidou, C.D. Papaspyrides, A review on polymer-layered silicate nanocomposites, Prog. Polym. Sci. 33 (2008) 1119–1198. [30] M. Alexandre, P. Dubois, Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials, Mater. Sci. Eng. R 28 (2000) 1–63. [31] M. Kotal, A.K. Bhowmick, Polymer nanocomposites from modified clays: recent advances and challenges, Prog. Polym. Sci. 51 (2015) 127–187. [32] A. Usuki, Y. Kojima, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito, Synthesis of nylon 6-clay hybrid, J. Mater. Res. 8 (1993) 1179–1184.
[33] W.J. Boo, L. Sun, G.L. Warren, E. Moghbelli, H. Pham, A. Clearfield, H.J. Sue, Effect of nanoplatelet aspect ratio on mechanical properties of epoxy nanocomposites, Polymer 48 (2007) 1075–1082. [34] C. Liu, Y. Yang, Effects of alpha-zirconium phosphate aspect ratio on the properties of polyvinyl alcohol nanocomposites, Polym. Test. 28 (2009) 801–807. [35] A. Clearfield, S.D. Smith, Crystal structure of zirconium phosphate and mechanism of its ion exchange behavior, J. Colloid Interface Sci. 28 (1968) 325–330. [36] J. Clearfield, A. Stynes, The preparation of crystalline zirconium phosphate and some observations on its ion exchange behavior, J. Inorg. Nucl. Chem. 26 (1964) 117–129. [37] M. Pica, R. Vivani, A. Donnadio, E. Troni, S. Fop, M. Casciola, Small is beautiful: the unusual transformation of nanocrystalline layered α-zirconium phosphate into a new 3D structure, Inorg. Chem. 54 (2015) 9146–9153. [38] L.Y. Sun, W.J. Boo, H.J. Sue, A. Clearfield, Preparation of alpha-zirconium phosphate nanoplatelets with wide variations in aspect ratios, New J. Chem. 31 (2007) 39–43. [39] W.J. Boo, L.Y. Sun, J. Liu, A. Clearfield, H.J. Sue, Effective intercalation and exfoliation of nanoplatelets in epoxy via creation of porous pathways, J. Phys. Chem. C 111 (2007) 10377–10381. [40] H.J. Sue, K.T. Gam, N. Bestaoui, N. Spurr, A. Clearfield, Epoxy nanocomposites based on the synthetic α-zirconium phosphate layer structure, Chem. Mater. 16 (2004) 242–249. [41] H. Sue, K.T. Gam, N. Bestaoui, A. Clearfield, M. Miyamoto, N. Miyatake, Fracture behavior of alpha-zirconium phosphate-based epoxy nanocomposites, Acta Mater. 52 (2004) 2239–2250. [42] W.J. Boo, J. Liu, H. Sue, Fracture behaviour of nanoplatelet reinforced polymer nanocomposites, J. Mater. Sci. Tech.-Lond. 22 (2006) 829–834. [43] W.J. Boo, L.Y. Sun, J. Liu, A. Clearfield, H.J. Sue, M.J. Mullins, H. Pham, Morphology and mechanical behavior of exfoliated epoxy/alpha-zirconium phosphate nanocomposites, Compos. Sci. Technol. 67 (2007) 262–269. [44] R.K. Shah, D.R. Paul, Nylon 6 nanocomposites prepared by a melt mixing masterbatch process, Polymer 45 (2004) 2991–3000. [45] A. Frache, O. Monticelli, S. Ceccia, A. Brucellaria, A. Casale, Preparation of nanocomposites based on PP and PA6 by direct injection molding, Polym. Eng. Sci. 48 (2008) 2373–2381. [46] F. Osman, H. Kalo, M.S. Hassan, T.W. Hong, F. Azmi, Pre-dispersing of montmorillonite nanofiller: impact on morphology and performance of melt compounded ethyl vinyl acetate nanocomposites, J. Appl. Polym. Sci. 133 (2016) 43204. [47] H. Günzler, H. Gremlich, IR Spectroscopy : An Introduction, Wiley-VCH, Weinheim, Germany, 2002 (Chapter 6). [48] F. Hussain, M. Hojjati, M. Okamoto, R.E. Gorga, Review article: polymer-matrix nanocomposites, processing, manufacturing, and application: an overview, J. Compos. Mater. 40 (2006) 1511–1575.
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Exfoliation of layered zirconium phosphate nanoplatelets by melt compounding Lei Chen a,b, Dazhi Sun a,⁎, Jin Li b, Guangdao Zhu c a Shenzhen Key Laboratory of Nanoimprint Technology, Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, People's Republic of China b Department of Materials Science, Fudan University, Shanghai 200433, People's Republic of China c Huaian Nylon Chemical Fibre Co., Ltd., Huaian, Jiangshu 223400, People's Republic of China
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• ZrP nanoplatelets with various sizes were successfully exfoliated by the presented melt compounding method. • This fabrication method could be used to prepare polymer nanocomposites with exfoliated ZrP nanoplatelets in a large scale. • The improvement of modulus of elasticity of ZrP/POE-g-MA was attributed to the well-exfoliated nanoplatelets. • The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by diglycolamine.
a r t i c l e
i n f o
Article history: Received 10 January 2017 Received in revised form 6 March 2017 Accepted 7 March 2017 Available online 07 March 2017 Keywords: Zirconium phosphate nanoplatelets Exfoliation Melt compounding method Polymer nanocomposite Maleic anhydride grafted polymer
a b s t r a c t A melt compounding method to achieve the exfoliation of layered zirconium phosphate (ZrP) nanoplatelets was presented in this work. ZrP nanoplatelets were first intercalated by diglycolamine (DGA) to increase the interlayer distance and functionality. In the next melt compounding process, the cyclic anhydrides of maleic anhydride grafted polyolefin elastomers (POE-g-MA) reacted with the hydroxyls in DGA-ZrP. Subsequently, the long polyolefin chains of POE-g-MA intercalated into the interlayer of ZrP smoothly and exfoliated the nanoplatelets successfully. ZrP nanoplatelets with various sizes were fully exfoliated in POE-g-MA matrices. The modulus of elasticity of POE-g-MA was improved by the incorporation of ZrP nanoplatelets and further increased if the nanoplatelets are exfoliated. The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by DGA and then exfoliated, especially for the smaller nanoplatelets. Our work provides a general method to prepare polymer nanocomposites containing exfoliated ZrP nanoplatelets in a large scale. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction
⁎ Corresponding author. E-mail address: [email protected] (D. Sun).
http://dx.doi.org/10.1016/j.matdes.2017.03.026 0264-1275/© 2017 Elsevier Ltd. All rights reserved.
Adding synthetic or natural nanoscale inorganic compounds into polymeric materials is a well-known technique to improve various properties of the organic matrices, such as mechanical strength [1–11], flame retardancy [12–18], barrier properties [18–24],
248
L. Chen et al. / Materials and Design 122 (2017) 247–254
dimensional stability [25–28], and so on. Such prepared polymer nanocomposites can be distinguished into three types, depending on the dimension of the incorporated nanoparticles, i.e. 0-dimensional (0D) spherical/quasi-spherical nanoparticles, 1-dimensional (1D) nanorods/ nanotubes/nanowires and 2-dimensional (2D) nanoplatelets/nanosheets [29,30]. Among all the potential nanocomposite additives, clay and layered silicates have been widely investigated probably because they are easily available and their intercalation chemistry has been studied for a long time [29–32]. Clays have several advantages, such as high ion exchange capacity, high aspect ratio and inexpensiveness, thereby resulting in high potential for large-scale commercial uses. But the main drawback of clays is that they are produced via purification and modification of the mined clay. It is extremely difficult to achieve 100% purity, narrow particle size distribution and controlled aspect ratio for clays, which affect the mechanical properties of polymer nanocomposites directly [11,33,34]. Compared with clay, synthetic zirconium phosphate (Zr(HPO4)2·H2O, ZrP) nanoplatelets have a much higher ion exchange capacity (6 times higher than clay), and their size and aspect ratio can be controlled by varying reaction time and reactant concentrations [35–38]. Furthermore, the size distribution of ZrP nanoplatelets has been found to be quite narrow, thus suitable for fundamental study of nanofiller effect on the properties of the host polymers. Moreover, ZrP nanoplatelets have also been found to improve the flame retardancy of the polymer matrices mainly through catalytic carbonization effect, rather than physical effects, by forming a highperformance carbonaceous char on the sample surface [13]. In preparing polymer nanocomposites containing layered nanoplatelets, intercalation and exfoliation have always been the two most critical steps. In general, inorganic nanoplatelets cannot be easily dispersed in most polymers due to their preferred face-to-face stacking in agglomerated tactoids. Dispersion of the tactoids into discrete monolayers is further hindered by the intrinsic incompatibility of hydrophilic layered inorganic compounds and hydrophobic engineering plastics. Effective intercalation has been shown to be essential for the preparation of fully exfoliated polymer nanocomposites with greatly improved modulus and barrier properties [39–43]. In the past two decades, the most traditional and popular approach is to intercalate the nanoplatelets by organic amines to produce polymer–compatible nanoplatelets. There are three methods to prepare polymer nanocomposites, i.e. intercalation of a suitable monomer followed by polymerization, polymer intercalation from solution, and direct polymer melt compounding [3]. Among them, direct polymer melt compounding is the most attractive because of its low cost, high productivity and compatibility with current polymer processing techniques. It uses widespread and conventional equipments in the plastic industry with high producing rates. Up till now, a few exfoliated nanocomposites with clay were successfully prepared by melt compounding method, such as PP/clay [4], PA6/clay [44,45], and EVA/clay [46] composites. The intercalated-exfoliated type of PA6/ZrP nanocomposites have also been prepared whereas PET/ZrP, PP/ZrP and EVA/ZrP compounds appear to be micro-composites [12]. To the best of our knowledge, no
exfoliated nanocomposites with ZrP nanoplatelets have been successfully prepared by melt compounding method. Hence, the objective of this study is to develop a viable melt compounding method for achieving full exfoliation of layered zirconium phosphate nanoplatelets. This was done using a two-step process: in the first, ZrP nanoplatelets were intercalated by diglycolamine. Secondly, the intercalated ZrP nanoplatelets were mixed with maleic anhydride grafted polymer (polymer-g-MA) matrices using a mixer rheometer. To demonstrate the validity of this method, ZrP nanoplatelets with different sizes were prepared. The usefulness of polymer-g-MA to exfoliate layered ZrP nanoplatelets was monitored using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscope. To study the effect of ZrP nanoplatelets on the mechanical property of polymer-g-MA matrices, the tensile properties of the ZrP/polymer-gMA nanocomposites were also tested and discussed. 2. Experimental section 2.1. Materials Zirconyl chloride (ZrOCl2·8H2O, 98%, Aladdin Industrial Co., Ltd), phosphoric acid (85%, Tianjin Yongda Chemical Reagent Co., Ltd), and diglycolamine (DGA, Aladdin Industrial Co., Ltd) were used as received. Maleic anhydride grafted polyolefin elastomer (POE-g-MA, 1801B, Guangzhou Haosu Chemical Co., Ltd) was chosen as the polymer-gMA to exfoliate ZrP nanoplatelets. The chemical structure of POE-gMA was shown in Fig. 1. Table 1 The abbreviations of all the samples in this work. The abbreviation of sample
The description of sample
ZrP Refl3MZrP
Zirconium phosphate nanoplatelets ZrP synthesized by refluxing method in the condition of 3.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 3.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 6.0 mol/L H3PO4 ZrP synthesized by hydrothermal method in the condition of 9.0 mol/L H3PO4 Zirconium phosphate intercalated by diglycolamine (DGA) Refl3MZrP intercalated by diglycolamine 3MZrP intercalated by diglycolamine 6MZrP intercalated by diglycolamine 9MZrP intercalated by diglycolamine Maleic anhydride grafted polyolefin elastomer The compounds of ZrP with POE-g-MA The compounds of Refl3MZrP with POE-g-MA
3MZrP 6MZrP 9MZrP DGA-ZrP DGA-Refl3MZrP DGA-3MZrP DGA-6MZrP DGA-9MZrP POE-g-MA ZrP/POE-g-MA Refl3MZrP/POE-g-MA or R3M/MA DGA-Refl3MZrP/POE-g-MA or DGA-R3M/MA 3MZrP/POE-g-MA or 3M/MA DGA-3MZrP/POE-g-MA or DGA-3M/MA 6MZrP/POE-g-MA or 6M/MA DGA-6MZrP/POE-g-MA or DGA-6M/MA 9MZrP/POE-g-MA or 9M/MA DGA-9MZrP/POE-g-MA or DGA-9M/MA POE-g-MA-1 POE-g-MA-2 POE-g-MA-3
Fig. 1. The chemical structure of POE-g-MA: a) the details of the structure of POE-g-MA, b) the simplified version of POE-g-MA.
POE-g-MA-4
The compounds of DGA-Refl3MZrP with POE-g-MA The compounds of 3MZrP with POE-g-MA The compounds of DGA-3MZrP with POE-g-MA The compounds of 6MZrP with POE-g-MA The compounds of DGA-6MZrP with POE-g-MA The compounds of 9MZrP with POE-g-MA The compounds of DGA-9MZrP with POE-g-MA POE-g-MA prepared in the same melt compounding conditions with the samples of Refl3MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 3MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 6MZrP series POE-g-MA prepared in the same melt compounding conditions with the samples of 9MZrP series
L. Chen et al. / Materials and Design 122 (2017) 247–254 Table 2 Melt compounding processing conditions used in this study. Sample
Melt compounding processing conditions
Refl3MZrP series 3MZrP series
Mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 10 min Mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 15 min The 1st stage, mixing temp.: 185 °C, rotor speed: 50 rpm and mixing time: 15 min; The 2nd stage, mixing temp.: 190 °C, rotor speed: 50 rpm and mixing time: 4 min The 1st stage, mixing temp.: 190 °C, rotor speed: 50 rpm and mixing time: 12 min; The 2nd stage, mixing temp.: 195 °C, rotor speed: 50 rpm and mixing time: 7 min
6MZrP series
9MZrP series
2.2. Preparation of ZrP Zirconium phosphate nanoplatelets with different sizes were prepared by the refluxing and hydrothermal methods [38]. In a typical refluxing method, a sample of 500.0 g ZrOCl2·8H2O was refluxed with 5 L 3.0 M (3.0 mol/L) H3PO4 in a 10 L double layer glass jacketed pilot plant reactor at 100 °C for 24 h. After the reaction, the product was washed by deionized water and collected by centrifugation five times. Then, the ZrP nanoplatelets were dried at 70 °C for 24 h. The dried ZrP nanoplatelets were ground into fine powders in an agate mortar. The final products were identified as Refl3MZrP. In the hydrothermal method, a sample of 20.0 g ZrOCl2·8H2O was mixed with 100.0 mL 3.0/6.0/ 9.0 M H3PO4 and sealed into a Teflon-lined pressure vessel and heated at 200 °C for 24 h. After the reaction, the products were treated by the same procedure as described in refluxing method. The final products were identified as 3MZrP, 6MZrP and 9MZrP, respectively.
249
2.3. Exfoliation of ZrP Firstly, four pristine ZrP samples were completely intercalated by DGA under the action of 45 kHz ultrasonic for 8 h in solution. After the reaction, the intercalated ZrP samples were washed by ethyl alcohol and collected by centrifugation five times. Then, the intercalated ZrP samples were dried at 70 °C for 24 h and ground into fine powders in an agate mortar. The intercalated ZrP samples were identified as DGARefl3MZrP, DGA-3MZrP, DGA-6MZrP and DGA-9MZrP, respectively. Finally, the intercalated ZrP samples were mixed with POE-g-MA matrices in a Harpro mixer rheometer (RM-200C, Harbin Harpro Electric Technology Co., Ltd). The mass ratio of ZrP nanoplatelets and POE-gMA matrices was 1/19. Because ZrP nanoplatelets would increase the weight by 50% if they were completely intercalated by DGA, DGA-ZrP/ POE-g-MA (1.5/19), ZrP/POE-g-MA (1/19) and pure POE-g-MA were prepared for the melt compounding experiments. Four series of samples, i.e. Refl3MZrP series, 3MZrP series, 6MZrP series and 9MZrP series, were prepared in this study. Refl3MZrP series contain three samples, i.e. Refl3MZrP/POE-g-MA compounds (R3M/MA, 1.5 g/28.5 g), DGARefl3MZrP/POE-g-MA compounds (DGA-R3M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-g-MA-1, 30 g). 3MZrP series also contain three samples, i.e. 3MZrP/POE-g-MA compounds (3 M/MA, 1.5 g/28.5 g), DGA-3MZrP/POE-g-MA compounds (DGA-3 M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-g-MA-2, 30 g). Similarly, 6MZrP series contain three samples: 6MZrP/POE-g-MA compounds (6 M/MA, 1.5 g/28.5 g), DGA-6MZrP/POE-g-MA compounds (DGA-6 M/MA, 2.25 g/28.5 g) and pure POE-g-MA matrices (POE-gMA-3, 30 g). In the same way, 9MZrP series contain three samples: 9MZrP/POE-g-MA compounds (9 M/MA, 1.5 g/28.5 g), DGA-9MZrP/ POE-g-MA compounds (DGA-9 M/MA, 2.25 g/28.5 g) and pure POE-gMA matrices (POE-g-MA-4, 30 g). The descriptions of abbreviations of
Fig. 2. SEM images of ZrP nanoplatelets with different size: a) Refl3MZrP; b) 3MZrP; c) 6MZrP; d) 9MZrP.
250
L. Chen et al. / Materials and Design 122 (2017) 247–254
Fig. 3. The comparison of XRD patterns of ZrP nanoplatelets and corresponding ZrP/POE-g-MA compounds.
all the samples were summarized in Table 1. The melt compounding processing conditions were shown in Table 2. 2.4. Characterizations X-ray diffraction (XRD) measurements were made directly from ZrP powders, DGA-ZrP powders, ZrP/POE-g-MA bulk, DGA-ZrP/POE-g-MA bulk and pure POE-g-MA bulk. All XRD patterns were obtained for 2θ in the range from 2 to 70°, with a step interval of 0.02° in a X-ray diffractometer (XRD Smartlab, Rigaku Co., Ltd) using the Cu-Kα radiation source at λ = 0.15418 nm. The morphology of these samples was imaged using a scanning electron microscope (SEM VEGA 3 LMH, Tescan Co., Ltd). The infrared spectra of ZrP/POE-g-MA bulk, DGA-ZrP/POE-gMA bulk and pure POE-g-MA bulk were detected by a Fourier transform infrared spectroscopy (FTIR Spectrum TWO, PerkinElmer Co., Ltd). To prepare samples for mechanical testing, all the melt-mixed compounds were dried at 70 °C for 24 h firstly. Then they were granulated by a plastic crusher (MTLS 160, Mitex automatic machine Co., Ltd). All tensile testing specimens (ASTM D638 Type V) were injection molded by Haake Minijet II microinjection molding machine under the same injection molding processing conditions. The injection molding processing conditions were 185 °C of melt temperature, 55 °C of mold temperature, 490 bar of injection pressure, 3 s of injection time, 490 bar of packing pressure and 15 s of packing time. All specimens were kept in a sealed desiccator under vacuum for 24 h before mechanical property measurements were performed. Tensile testing was performed on an Instron Legend 2367 testing system with 1 kN load cell at a crosshead speed of 20 mm/min for modulus of elasticity. To improve accuracy, an Instron strain gauge extensometer (10 mm gauge) was used. The data values were reported with an average from five measurements.
3. Results and discussion ZrP nanoplatelets were first prepared via the refluxing and hydrothermal methods. It is anticipated that the crystallinity and the size of ZrP nanoplatelets will increase with increasing the concentration of phosphoric acid. Furthermore, compared with the refluxing method, the hydrothermal method can produce ZrP nanoplatelets with larger size in the same concentration of phosphoric acid [38]. This is validated by the SEM images of Refl3MZrP, 3MZrP, 6MZrP and 9MZrP shown in Fig. 2. The SEM images show that the length dimensions of the prepared
Fig. 4. The FTIR spectra of ZrP nanoplatelets and ZrP/POE-g-MA compounds.
L. Chen et al. / Materials and Design 122 (2017) 247–254
251
Scheme 1. The esterification of POE-g-MA with DGA-ZrP.
ZrP nanoplatelets are 50–100 nm of Refl3MZrP, 250–500 nm of 3MZrP, 350–800 nm of 6MZrP and 500–1200 nm of 9MZrP, respectively. ZrP nanoplatelets with size variations are ideal for studying the size effect on the exfoliation and mechanical properties of nanoplatelets in polymer matrices. The XRD patterns of ZrP powders, DGA-ZrP powders, ZrP/POE-g-MA bulk, DGA-ZrP/POE-g-MA bulk and pure POE-g-MA bulk are presented in Fig. 3. For instance, Fig. 3a shows the XRD patterns of Refl3MZrP series. The first peak (2θ = 11.56°) in the XRD pattern of Refl3MZrP nanoplatelets is the crystal face of ⟨002〉, which corresponds to the 7.7 Å interlayer distance. And the other peaks at 2θ of 19.78°, 25.02° and 34.08° reveal the crystal faces of ⟨110〉, ⟨112〉 and ⟨215〉, respectively. The relatively broad peaks in the XRD pattern indicate that the crystallinity of Refl3MZrP nanoplatelets is relatively low. Furthermore, the peaks in the XRD patterns of ZrP nanoplatelets become narrower with the increase of the concentration of phosphoric acid during the synthesis, which indicate the improving crystallinity of ZrP nanoplatelets. This results is consistent with Sun L. Y. et al.'s work [38]. The first peaks of the XRD patterns of 3MZrP, 6MZrP and 9MZrP nanoplatelets appear at 2θ of 11.6°, 11.68° and 11.7°,respectively, corresponding to the same interlayer distance (d002 = 7.6 Å) of these ZrP nanoplatelets with different size. However, the interlayer distances of DGA-3MZrP, DGA-6MZrP and DGA-9MZrP nanoplatelets have some difference, which can be shown by the positions of the first peaks of these three corresponding XRD patterns. After the intercalation of DGA, the first peaks of DGA-3MZrP, DGA-6MZrP and DGA-9MZrP nanoplatelets shift from 7.6 Å to 17.3 Å (2θ = 5.12°), 18.4 Å (2θ = 4.8°) and 20.5 Å (2θ = 4.32°), respectively. Compared with Refl3MZrP, Refl3MZrP/POE-g-MA and POE-g-MA-1, the XRD pattern of Refl3MZrP/POE-g-MA contains the peaks from the XRD patterns of both pristine Refl3MZrP nanoplatelets and pure POEg-MA, which indicates that POE-g-MA has no effect on the crystal structure of Refl3MZrP nanoplatelets and that POE-g-MA cannot exfoliate pristine Refl3MZrP nanoplatelets in melt compounding process directly. The first peak at 2θ of 4.46° in the XRD pattern of DGA-Refl3MZrP nanoplatelets corresponds to the intercalated interlayer distance of 19.8 Å. The increment of interlayer distance of Refl3MZrP nanoplatelets is 12.1 Å which is larger than the length of DGA with approximate 8.5 Å. Therefore, no peak at 2θ of 11.56° indicates that Refl3MZrP nanoplatelets were fully intercalated by DGA. The peaks in the XRD pattern of DGA-Refl3MZrP/POE-g-MA appear at the same angles with the XRD pattern of POE-g-MA, which are totally different with the XRD pattern of DGA-Refl3MZrP nanoplatelets, indicating that the Refl3MZrP
nanoplatelets can be successfully exfoliated by POE-g-MA in melt compounding process if they were intercalated by DGA first. Similarly, Fig. 3b–3d present the XRD patterns of 3MZrP series, 6MZrP series and 9MZrP series, respectively, which shows the same exfoliation results with Refl3MZrP series. It is also noted that POE-g-MA can completely exfoliate ZrP nanoplatelets to monolayers if the nanoplatelets were intercalated by DGA first regardless of the size of ZrP nanoplatelets. In the intercalating process, DGA molecules insert into the interlayer of ZrP nanoplatelets by the acid-base reaction between amine groups and hydroxyl groups on ZrP nanoplatelets, which lowers the surface energy of the inorganic nanoplatelets and improves the wetting with the polymer matrices. Furthermore, the interlayer distance of ZrP nanoplatelets increases from 7.6 Å to around 19 Å. Subsequently, with an aid of shearing force during the melt mixing, the maleic anhydride groups of POE-g-MA react with diglycolamine of DGA-ZrP in a high temperature condition. The acylation of maleic anhydride groups with diglycolamine has two forms, esterification and amidation. In order to understand the reaction mechanism further, the infrared spectra of 6MZrP nanoplatelets, DGA-6MZrP nanoplatelets, pure POE-g-MA, 6MZrP/POE-g-MA compounds and DGA-6MZrP/POE-g-MA compounds were detected by FTIR, as shown in Fig. 4. It was found that two bands at 1857 cm− 1 and 1781 cm− 1 have appeared in the infrared spectra of both pure POE-g-MA and the 6MZrP/POE-g-MA compounds, but they did not appear in the infrared spectrum of DGA-6MZrP/POE-g-MA compounds. The bands at 1857 cm−1 and 1781 cm−1 corresponded to the antisymmetric and symmetric stretch of C_O of cyclic anhydride, respectively [47]. This result indicated that POE-g-MA reacted with DGA-ZrP nanoplatelets in the melt compounding process and cyclic anhydride groups of POE-g-MA have reacted completely. The C\\O bond of cyclic anhydride was broken and reacted with the hydroxyl of DGA by the reaction of esterification, which was proved by the band at 1771 cm− 1 which has appeared in the infrared spectra of DGA6MZrP/POE-g-MA compounds. The band at 1771 cm−1 corresponded to the stretch of C_O of ester. Furthermore, there was no peak at the bands from 1680 cm−1 to 1630 cm− 1, which corresponded to the stretch of C_O of amide. The above phenomena indicate that in the melt compounding process, the acylation of maleic anhydride groups of POE-g-MA with diglycolamine of DGA-ZrP happened in the form of esterification only. The details of the chemical reaction are shown in Scheme 1. Because of the increasing interlayer distance of ZrP nanoplatelets, the cyclic anhydrides of POE-g-MA react with the hydroxyls of DGA-ZrP in the melt compounding process. Subsequently, the long polyolefin chains of POE-g-MA intercalate into the interlayer
Fig. 5. The scheme of the exfoliation of ZrP by POE-g-MA.
252
L. Chen et al. / Materials and Design 122 (2017) 247–254
Fig. 6. The SEM images of ZrP/POE-g-MA compounds: a) 9MZrP/POE-g-MA, b) DGA-9MZrP/POE-g-MA.
of ZrP nanoplatelets smoothly and finally exfoliate ZrP nanoplatelets, as shown in Fig. 5. Fig. 6 shows the selected SEM images of 9MZrP/POE-g-MA compounds and DGA-9MZrP/POE-g-MA compounds, respectively. ZrP nanoplatelets could be seen easily in the SEM image of 9MZrP/POE-g-
MA compounds. In the case of ZrP/POE-g-MA compounds, the POE-gMA matrices were unable to intercalate into the interlayer of ZrP nanoplatelets, a phase-separated composite was obtained, and the properties would be in the same range as those for traditional microcomposites [22,29,48]. In contrast to 9MZrP/POE-g-MA
Fig. 7. The tensile testing results of ZrP/POE-g-MA systems: a) the modulus of elasticity of ZrP/POE-g-MA systems, b) the tensile behavior of Refl3MZrP/POE-g-MA compounds, c) the tensile behavior of 6MZrP/POE-g-MA compounds.
L. Chen et al. / Materials and Design 122 (2017) 247–254
compounds, ZrP nanoplatelets were invisible in DGA-9MZrP/POE-g-MA compounds. Only some ZrP monolayers wrapped by POE-g-MA could be identified in the edge, which proves the successful exfoliation of ZrP nanoplatelets in the case of DGA-ZrP/POE-g-MA compounds. Fig. 7a shows the average of modulus of elasticity of ZrP/POE-MA systems. The corresponding black lines denote the error bars of the average of modulus elasticity of all materials. Due to different melt compounding processing conditions of these 4 groups of experiments, the modulus of elasticity of each pure POE-g-MA sample was different from any other pure POE-g-MA sample's modulus of elasticity as well, as presented in Fig. 7a. The testing results indicate that the modulus of elasticity of POE-g-MA matrices increased due to the filling of pristine ZrP nanoplatelets in the case of Refl3MZrP, 3MZrP and 6MZrP. In particular, the modulus of elasticity of POE-g-MA matrices with 3MZrP further improved if the nanoplatelets were exfoliated. Among all the prepared ZrP samples, 9MZrP nanoplatelets with the largest size are different from others. The modulus of elasticity of POE-g-MA matrices decreased with the filling of pristine 9MZrP nanoplatelets but increased significantly if 9MZrP nanoplatelets were first intercalated by DGA. When the pristine inorganic ZrP nanoplatelets fill into organic POE-g-MA matrices, the nanoplatelets will stack into agglomerated tactoids. Due to the agglomeration of nanoplatelets, the stress defects will be formed in ZrP/POE-g-MA compounds, which have negative effects on the mechanical property of polymer compounds. The stress defects are related to the size and volume of the agglomerated tactoids, and the concentration of the pristine ZrP nanoplatelets accounts for the same mass ratio of 5 wt% in each group of our experiments, therefore the size of the agglomerated tactoids is the main reason for the observed stress defects. With the increase of the size of nanoplatelets, the stress defects increase and reduce the mechanical property of polymer compounds as in the case of 9MZrP with the largest size in this study. The observed modulus of elasticity of POE-g-MA decreased with addition of the pristine 9MZrP nanoplatelets. However, after intercalated by DGA, DGA-9MZrP nanoplatelets became compatible with POE-g-MA matrices and were completely exfoliated and dispersed well during the melt compounding process, resulting in an obvious improvement of the modulus of elasticity of the polymer matrices. The tensile stress-strain curves of Refl3MZrP/POE-g-MA compounds and 6MZrP/POE-g-MA compounds are shown in Fig. 7b and c, respectively. By comparison with the curves of POE-g-MA and ZrP/POE-gMA compounds, it was found that the filled nanoplatelets made the polymer matrices brittle, while the yield strength increased and the elongation at break decreased at the same time. By comparison with the curves of ZrP/POE-g-MA and DGA-ZrP/POE-g-MA compounds, it was found that the elongation at break of DGA-ZrP/POE-g-MA compounds all increased due to the intercalation of ZrP nanoplatelets by DGA. Normally, the filled nanoplatelets could increase the strength but decrease the ductility of polymer compounds. However, in the case of Refl3MZrP nanoplatelets with the smallest size, the strength and ductility of DGA-Refl3MZrP/POE-g-MA compounds were larger than the pure POE-g-MA, which is mainly due to the fact that the DGA-Refl3MZrP nanoplatelets are completely exfoliated and associated with POE-gMA by the strong covalent bonding. Furthermore, the small size of the Refl3MZrP nanoplatelets of less than 100 nm would results in smaller stress defects in the polymer matrices as compared to other larger nanoplatelets, which is also attributed to the improved mechanical performance. 4. Conclusions Layered zirconium phosphate nanoplatelets were completely exfoliated by melt compounding methods in two steps. Firstly, ZrP nanoplatelets were intercalated by DGA. Then, due to the esterification reaction between the cyclic anhydrides of POE-g-MA and hydroxyls of DGA-ZrP nanoplatelets, DGA-ZrP nanoplatelets were completely exfoliated by POE-g-MA in the melt compounding process, regardless of the
253
size of the nanoplatelets. The modulus of elasticity of POE-g-MA matrices increased due to the filling of ZrP nanoplatelets of various sizes and improved further if the nanoplatelets were exfoliated. Furthermore, the ductility of ZrP/POE-g-MA compounds will become better if ZrP nanoplatelets were first intercalated by DGA especially for the Refl3MZrP nanoplatelets with the smallest size. Maleic anhydride grafted polymers are a class of compatilizers used in polymer processing, therefore, by utilizing our melt compounding method, layered zirconium phosphate nanoplatelets can be exfoliated and dispersed well in different polymer matrices, which is very suitable for the industrial applications. Moreover, this melt compounding method is also of great potential in producing masterbatches of high-concentration nanoplatelets for further polymer nanocomposite processing. Author contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding sources This work was supported by the start-up fundings from Southern University of Science and Technology (SUSTech) and “The Recruitment Program of Global Youth Experts of China”, the Foundation of Shenzhen Science and Technology Innovation Committee (Grant no.: ZDSYS20140509142721431, JCYJ20160315164631204, and KQTD20140630110339343), and National Natural Science Foundation of China (NSFC Grant no.: 21306077). Acknowledgment We are grateful to Ms. Sixia Hu, the engineer of the Materials Characterization Center in SUSTech, for her support in XRD measurements and Mr. Huaisong Yong for valuable discussions. References [1] Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito, Mechanical properties of nylon 6-clay hybrid, J. Mater. Res. 8 (1993) 1185–1189. [2] R.A. Damiani, J.F. Junior, J.R. Silvano, Influence of the injection molding process on the mechanical properties of (PA6/GF/MMT) nanocomposite, Polym. Compos. 36 (2) (2015) 237–244. [3] H. Wang, C.C. Zeng, M. Elkovitch, L.J. Lee, K.W. Koelling, Processing and properties of polymeric nano-composites, Polym. Eng. Sci. 41 (2001) 2036–2046. [4] M. Kato, M. Matsushita, K. Fukumori, Development of a new production method for a polypropylene-clay nanocomposite, Polym. Eng. Sci. 44 (2004) 1205–1211. [5] T.L. Zhang, F.J. Zhang, S.S. Dai, Z.F. Li, B.G. Wang, H.P. Quan, Z.Y. Huang, Polyurethane/ organic vermiculite composites with enhanced mechanical properties, J. Appl. Polym. Sci. 133 (2016) 4321913. [6] W.J. Boo, L.Y. Sun, J. Liu, E. Moghbelli, A. Clearfield, H.J. Sue, H. Pham, N.J. Verghese, Effect of nanoplatelet dispersion on mechanical behavior of polymer nanocomposites, Polym. Sci. Pol. Phys. 45 (2007) 1459–1469. [7] P. Li, K.L. White, C.H. Lin, D. Kim, A. Muliana, R. Krishnamoorti, R. Nishimura, H.J. Sue, Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order, ACS Appl. Mater. Interfaces 6 (2014) 10188–10195. [8] L.Y. Sun, W.J. Boo, J. Liu, A. Clearfield, H.J. Sue, N.E. Verghese, H.Q. Pham, J. Bicerano, Effect of nanoplatelets on the rheological behavior of epoxy monomers, Macromol. Mater. Eng. 294 (2009) 103–113. [9] D.Z. Sun, C.C. Chu, H.J. Sue, Simple approach for preparation of epoxy hybrid nanocomposites based on carbon nanotubes and a model clay, Chem. Mater. 22 (2010) 3773–3778. [10] D.Z. Sun, W.N. Everett, C.C. Chu, H.J. Sue, Single-walled carbon-nanotube dispersion with electrostatically tethered nanoplatelets, Small 5 (2009) 2692–2697. [11] H.J. Sue, K.T. Gam, N. Bestaoui, N. Spurr, A. Clearfield, Epoxy nanocomposites based on the synthetic alpha-zirconium phosphate layer structure, Chem. Mater. 16 (2004) 242–249. [12] J. Alongi, A. Frache, Flame retardancy properties of alpha-zirconium phosphate based composites, Polym. Degrad. Stab. 95 (2010) 1928–1933. [13] D. Liu, G.P. Cai, J. Wang, X.F. Tan, H.D. Lu, S.Y. Zhang, Q.Q. Dai, Thermal and flammability performance of polypropylene composites containing melamine and melamine phosphate-modified α-type zirconium phosphates, J. Appl. Polym. Sci. 131 (2014) 4025410. [14] M. George, G.E. Kochimoolayil, J.N. Haridas, Mechanical and thermal properties of modified kaolin clay/unsaturated polyester nanocomposites, J. Appl. Polym. Sci. 133 (2016) 4324513. [15] H.D. Lu, C.A. Wilkie, The influence of alpha-zirconium phosphate on fire performance of EVA and PS composites, Polym. Adv. Technol. 22 (2011) 1123–1130.
254
L. Chen et al. / Materials and Design 122 (2017) 247–254
[16] W.Y. Xing, P. Zhang, L. Song, X. Wang, Y. Hu, Effects of alpha-zirconium phosphate on thermal degradation and flame retardancy of transparent intumescent fire protective coating, Mater. Res. Bull. 49 (2014) 1–6. [17] X.Q. Liu, D.Y. Wang, X.L. Wang, L. Chen, Y.Z. Wang, Synthesis of organo-modified alpha-zirconium phosphate and its effect on the flame retardancy of IFR poly(lactic acid) systems, Polym. Degrad. Stab. 96 (2011) 771–777. [18] E. Picard, A. Vermogen, J.F. Gerard, E. Espuche, Influence of the compatibilizer polarity and molar mass on the morphology and the gas barrier properties of polyethylene/clay nanocomposites, J. Polym. Sci. Polym. Phys. 46 (2008) 2593–2604. [19] J.W. Rhim, H.M. Park, C.S. Ha, Bio-nanocomposites for food packaging applications, Prog. Polym. Sci. 38 (2013) 1629–1652. [20] B. Ghanbarzadeh, S.A. Oleyaei, H. Almasi, Nanostructured materials utilized in biopolymer-based plastics for food packaging applications, Crit. Rev. Food Sci. 55 (2015) 1699–1723. [21] A. Usuki, N. Hasegawa, H. Kadoura, T. Okamoto, Three-dimensional observation of structure and morphology in nylon-6/clay nanocomposites, Nano Lett. 1 (2001) 271–272. [22] Q.H. Zeng, A.B. Yu, G.Q. Lu, D.R. Paul, Clay-based polymer nanocomposites: research and commercial development, J. Nanosci. Nanotechnol. 5 (2005) 1574–1592. [23] M. Fasihi, M.R. Abolghasemi, Oxygen barrier and mechanical properties of masterbatch-based PA6/nanoclay composite films, J. Appl. Polym. Sci. 1251 (2012) E2–E8. [24] Y. Zare, H. Garmabi, Thickness, modulus and strength of interphase in clay/polymer nanocomposites, Appl. Clay Sci. 105 (2015) 66–70. [25] A. Karatrantos, N. Clarke, R.J. Composto, K.I. Winey, Entanglements in polymer nanocomposites containing spherical nanoparticles, Soft Matter 12 (2016) 2567–2574. [26] E. Haque, C.D. Armeniades, Montmorillonite polymer concrete: zero-shrinkage and expanding polymer concrete with enhanced strength, Polym. Eng. Sci. 26 (1986) 1524–1530. [27] N. Salahuddin, M.M. Shehata, Reduction of polymerization shrinkage in methyl methacrylate-montmorillonite composites, Mater. Lett. 52 (2002) 289–294. [28] S.S. Hwang, S.P. Liu, P.P. Hsu, J.M. Yeh, J.P. Yang, K.C. Chang, S.N. Chu, Effect of organoclay and preparation methods on the mechanical/thermal properties of microcellular injection molded polyamide 6-clay nanocomposites, Int. Commun. Heat Mass 38 (2011) 1219–1225. [29] S. Pavlidou, C.D. Papaspyrides, A review on polymer-layered silicate nanocomposites, Prog. Polym. Sci. 33 (2008) 1119–1198. [30] M. Alexandre, P. Dubois, Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials, Mater. Sci. Eng. R 28 (2000) 1–63. [31] M. Kotal, A.K. Bhowmick, Polymer nanocomposites from modified clays: recent advances and challenges, Prog. Polym. Sci. 51 (2015) 127–187. [32] A. Usuki, Y. Kojima, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito, Synthesis of nylon 6-clay hybrid, J. Mater. Res. 8 (1993) 1179–1184.
[33] W.J. Boo, L. Sun, G.L. Warren, E. Moghbelli, H. Pham, A. Clearfield, H.J. Sue, Effect of nanoplatelet aspect ratio on mechanical properties of epoxy nanocomposites, Polymer 48 (2007) 1075–1082. [34] C. Liu, Y. Yang, Effects of alpha-zirconium phosphate aspect ratio on the properties of polyvinyl alcohol nanocomposites, Polym. Test. 28 (2009) 801–807. [35] A. Clearfield, S.D. Smith, Crystal structure of zirconium phosphate and mechanism of its ion exchange behavior, J. Colloid Interface Sci. 28 (1968) 325–330. [36] J. Clearfield, A. Stynes, The preparation of crystalline zirconium phosphate and some observations on its ion exchange behavior, J. Inorg. Nucl. Chem. 26 (1964) 117–129. [37] M. Pica, R. Vivani, A. Donnadio, E. Troni, S. Fop, M. Casciola, Small is beautiful: the unusual transformation of nanocrystalline layered α-zirconium phosphate into a new 3D structure, Inorg. Chem. 54 (2015) 9146–9153. [38] L.Y. Sun, W.J. Boo, H.J. Sue, A. Clearfield, Preparation of alpha-zirconium phosphate nanoplatelets with wide variations in aspect ratios, New J. Chem. 31 (2007) 39–43. [39] W.J. Boo, L.Y. Sun, J. Liu, A. Clearfield, H.J. Sue, Effective intercalation and exfoliation of nanoplatelets in epoxy via creation of porous pathways, J. Phys. Chem. C 111 (2007) 10377–10381. [40] H.J. Sue, K.T. Gam, N. Bestaoui, N. Spurr, A. Clearfield, Epoxy nanocomposites based on the synthetic α-zirconium phosphate layer structure, Chem. Mater. 16 (2004) 242–249. [41] H. Sue, K.T. Gam, N. Bestaoui, A. Clearfield, M. Miyamoto, N. Miyatake, Fracture behavior of alpha-zirconium phosphate-based epoxy nanocomposites, Acta Mater. 52 (2004) 2239–2250. [42] W.J. Boo, J. Liu, H. Sue, Fracture behaviour of nanoplatelet reinforced polymer nanocomposites, J. Mater. Sci. Tech.-Lond. 22 (2006) 829–834. [43] W.J. Boo, L.Y. Sun, J. Liu, A. Clearfield, H.J. Sue, M.J. Mullins, H. Pham, Morphology and mechanical behavior of exfoliated epoxy/alpha-zirconium phosphate nanocomposites, Compos. Sci. Technol. 67 (2007) 262–269. [44] R.K. Shah, D.R. Paul, Nylon 6 nanocomposites prepared by a melt mixing masterbatch process, Polymer 45 (2004) 2991–3000. [45] A. Frache, O. Monticelli, S. Ceccia, A. Brucellaria, A. Casale, Preparation of nanocomposites based on PP and PA6 by direct injection molding, Polym. Eng. Sci. 48 (2008) 2373–2381. [46] F. Osman, H. Kalo, M.S. Hassan, T.W. Hong, F. Azmi, Pre-dispersing of montmorillonite nanofiller: impact on morphology and performance of melt compounded ethyl vinyl acetate nanocomposites, J. Appl. Polym. Sci. 133 (2016) 43204. [47] H. Günzler, H. Gremlich, IR Spectroscopy : An Introduction, Wiley-VCH, Weinheim, Germany, 2002 (Chapter 6). [48] F. Hussain, M. Hojjati, M. Okamoto, R.E. Gorga, Review article: polymer-matrix nanocomposites, processing, manufacturing, and application: an overview, J. Compos. Mater. 40 (2006) 1511–1575.