Mechanical Properties and Nonisothermal Crystallization of Polyamide 6/Carbon Fiber Composites Toughened by Maleated Elastomers
Yi Li,1 Jinting Xu,2 Zhiyong Wei,2,3 Yuqiang Xu,2 Ping Song,2 Guangyi Chen,2 Lin Sang,2 Ying Chang,2 Jicai Liang1,2 1 Key Laboratory of Automotive Materials, Ministry of Education, and College of Materials Science and Engineering, Jilin University, Chang Chun 130025, China 2
State Key Laboratory of Structural Analysis for Industrial Equipment, School of Automotive Engineering, Dalian University of Technology, Dalian 116024, China 3
Department of Polymer Science and Materials, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
Polyamide 6/carbon fiber (PA6/CF) composites toughened with maleated elastomers were prepared by melt blending using twin-screw extruder followed by injection molding. Three kinds of maleated elastomers, maleic anhydride (MAH)-grafted ethylene-vinyl acetate copolymer (EVA-g-MAH), MAH-grafted ethylene-propylene-diene terpolymer (EPDM-g-MAH), and MAHgrafted hydrogenated styrene-butadiene-styrene (SEBS-g-MAH), were used to toughen the PA6/CF composites. The mechanical properties, morphology, nonisothermal crystallization, and subsequent melting behavior of PA6 hybrid composites were investigated. Mechanical tests indicated that incorporation of elastomers improved the impact properties of CFreinforced PA composites accompanied with loss of tensile strength and modulus. It was observed from scanning electron microscope photographs that modification with maleated elastomers improved the interfacial adhesion between the CFs and PA6 matrix. Nonisothermal crystallization behavior showed that three kinds of elastomers had negative effect on crystallization and retarded crystallization of PA6. Kissinger’s analysis illustrated that addition of CF slightly increased the crystallization activation energy of PA6, whereas incorporation of elastomers reversed it compared with pure PA6. Furthermore, a slight decrease in crystallinity and melting peak of the composites after incorporation of elastomers was observed compared with pure PA6. Polarizing optical microscope results showed that the transcrystallinity phenomenon seemed to be also affected when the matrix was added by the
Correspondence to: Zhiyong Wei; e-mail:
[email protected] or Jicai Liang; e-mail:
[email protected] DOI 10.1002/pc.22881 Published online in Wiley Online Library (wileyonlinelibrary.com). C 2014 Society of Plastics Engineers V
elastomers. POLYM. COMPOS., 35:2170–2179, 2014.
C 2014 V
Society of Plastics Engineers
INTRODUCTION Over the last two decades, the automobile industry has been seeking a variety of technological developments and design strategies to increase automobile performance and decrease fuel consumption [1]. Among these, the reduction of vehicle weight has been accepted to be a very effective method. One practical solution in the vehicle weight reduction strategy is the use of lightweight materials, namely fiber-reinforced polymeric-based composites [2]. The advantages of fiber-reinforced thermoplastic composites include being lightweight and well adapted to mass production methods as well as having low manufacturing costs and superior mechanical properties. The other important advantage is good molding characteristics, allowing the designers to design the products they desire in terms of shape and structure. Compared to the glass fibers, carbon fibers (CFs) can offer higher strength and modulus, lower density, and excellent thermal and electrical conductivity, which make them attractive for many applications especially in the automotive industry [3, 4]. Now, the automotive industry is looking to use stiff and lightweight CF composite frames for electrical cars to replace the metals to the maximum extent; thus, CFs in the production of polymer composites for hightechnology applications are increasing rapidly [5–15]. In our pervious research [16], CF-reinforced polyamide 6 (PA6) composites were prepared by melt blending and injection molding. It was observed that the tensile POLYMER COMPOSITES—2014
TABLE 1.
Composition of PA6/CF composites with different tougheners.
Sample code
PA6 (mass%)
CF (mass%)
EVA-g-MAH (mass%)
EPDM-g-MAH (mass%)
SEBS-g-MAH (mass%)
PA6 PA/EVA/0 PA/EPDM/0 PA/SEBS/0 PA/10 PA/EVA/10 PA/EPDM/10 PA/SEBS/10 PA/20 PA/EVA/20 PA/EPDM/20 PA/SEBS/20
100 80 80 80 90 72 72 72 80 64 64 64
– – – – 10 10 10 10 20 20 20 20
– 20 – – – – – – – – – –
– – 20 – – – – – – – – –
– – – 20 – 18 18 18 – 16 16 16
strength and the modulus of the composites are enhanced by the addition of CFs. However, the impact strength and elongation at break were deteriorated owing to lower resistance of PA6 matrix to crack propagation, which led it may be broken easily at low stress once a crack initiates. Consequently, an achievement in high impact property by toughened composites using suitable elastomers is necessary and very important. The impact modifiers commonly used in PA6 include ethylene propylene rubber, ethylene-propylene-diene monomer (EPDM), polyethylene-octene (POE), and styrene-ethylene butylene-styrene (SEBS) elastomers [17–23]. The cavitation of elastomer particles and associated matrix shear yielding are the main toughening mechanism for PA-based composites. As the compatibility between PA and polyolefin elastomers is relatively low, maleic anhydride (MAH) is grafted to SEBS copolymer before blending with PA. The MAH functional group of SEBS-g-MAH can react with the amine and amide groups of PA, resulting in a finer dispersion of elastomers. The rubber toughening of polyamides is achieved at the expense of their stiffness and strength characteristics. The later deficiencies in rubbertoughened polyamides can be restored by adding short glass or CF reinforcements, leading to the formation of ternary or hybrid composites [24–30]. Both physical and mechanical properties of a semicrystalline polymer are strongly dependent on crystallization behavior and morphology formed during polymer processing; therefore, studies on the crystallization and melting behavior are of great importance in understanding the interrelationship of processing–structure properties. The effect of fibers on crystallization of semicrystalline thermoplastics is a major concern in polymer science because of the technical importance of fiber-reinforced composites [31–35]. In this article, PA6/CF composites toughened with maleated elastomers were prepared by melt blending using twin-screw extruder via continuous fiber feed followed by injection molding. Three kinds of maleated elastomers, MAH-grafted ethylene-vinyl acetate copolymer (EVA-g-MAH), MAH-grafted ethylene-propylenediene tripolymer (EPDM-g-MAH), and MAH-grafted DOI 10.1002/pc
hydrogenated styrene-butadiene-styrene (SEBS-g-MAH), were selected as the tougheners and compatibilizers to enhance the interfacial adhesion between PA6 matrix and CFs and toughen PA6/CF composites. The effect of maleated elastomers on the mechanical properties, morphology, crystallization, and subsequent melting behavior of PA6 hybrid composites was investigated by universal tester, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). EXPERIMENTAL Materials PA6 with melt flow index (MFI) of 2.4–3.6 g 10 min21 and technical specification of standard Q/SH3185021-2005 was supplied in pellet form by Yueyang Baling Jiayun Petrochemical. EVA-g-MAH (KT26, MFI 5 12–16 g 10 min21, the MAH grafting ratio 5 1.0 mass%), EPDM-g-MAH (KT915, MFI 5 0.2– 0.8 g 10 min21, the MAH grafting ratio 5 1.0 mass%), and SEBS-g-MA (KT25, MFI 5 0.8–1.0 g 10 min21, the MAH grafting ratio 5 1.0 mass%) were supplied by Shenyang Ketong Plastic. The continuous CF used in this experiment was T300-12K supplied by Dalian Xingke Carbon Fiber. The characteristics of the CF are as follows: the diameter 7 lm, the tensile strength > 3.3 GPa, and the tensile modulus 230–260 GPa. Preparation of PA/CF Composites The composition of PA/CF composites modified by different elastomers is indicated in Table 1. All the materials were dried in an oven before blending. PA6/elastomer blend at a fixed composition (80:20 in mass ratio) was first melt-mixed together in a twin-screw extruder (SHJ20-X40, Nanjing Giant Machinery). Then, the obtained PA6/elastomer blend was fed from the hopper and the continuous CF was fed from the subfeeding port; the CF was sheared to short CFs and dispersed in matrix POLYMER COMPOSITES—2014 2171
FIG. 1. Tensile strength (a) and impact strength (b) of PA6/CF composites with different tougheners.
owing to the shear force during extruding. The temperature profile of the extruder was maintained at 230, 240, 250, 250, 250, and 240 C from hopper to die, respectively. The resultant composite ribbons were cooled in cold water and granulated to pellets. The extruded pellets were dried at 110 C for at least 9 h under vacuum before injection molding. Samples used for mechanical tests were prepared by injection molding using a XTK1200 injection molding machine (Xiatian General Machinery, Ningbo, China). The temperature profile was 210, 220, and 240 C at three injection regions and 230 C in the nozzle. Characterization Tensile tests of PA6/CF composites were performed on Instron 1211 with a cross-head speed of 2 mm min21. The dumbbell samples were fabricated according to GB/T 1040:2–2006. Seven specimens were tested at room temperature and the average results were reported. The notched charpy impact tests of the samples were carried out with XQZ-II impact testing machine (JJ-TEST Chengde, Hebei, China). The samples of 50 mm 3 6 mm 3 4 mm in size were tested at room temperature according to GB/T 1843–2008. An average value on five tests was taken for each material. Surface morphologies of the composites were observed by a Zeiss FE-SEM S-4800N SEM. Impact fracture surfaces were coated with a thin layer of gold before analysis. The nonisothermal crystallization and melting process of the composites were performed on a METTLER DSC 1 thermal analyzer as follows: the samples were heated from 25 to 260 C at a rate of 40 C min21 and kept for 5 min to eliminate the heat history; then they were cooled to 100 C at a specified cooling rate of 5, 10, 15, and 20 C min21; after keeping at 100 C for 5 min, the samples were heated to 260 C at a heating rate of 10 C min21. Both the exothermic and endothermic curves were recorded under N2 atmosphere. 2172 POLYMER COMPOSITES—2014
Spherulite morphologies were performed with a LeicaDM4500P polarizing optical microscope (POM) equipped with a digital camera. The samples were placed between two cover glasses, melted, and pressed at 250 C for 5 min on a Linkam THMS600 hot stage. Then they were quickly cooled to 207 C for isothermal crystallization. The spherulite morphologies were recorded at 8 min. RESULTS AND DISCUSSION Mechanical Properties As reported in our previous article [16], the tensile strength and the modulus of short CF-reinforced PA6 composites increased by increasing CF loading level. However, the elongation at break and the impact strength dramatically decreased. In this work, three types of maleated elastomers, EVA-g-MAH, EPDM-g-MAH, and SEBS-g-MAH, were selected as the tougheners and compatibilizers to enhance the interfacial adhesion between PA6 matrix and CFs and toughen PA6/CF composites. TABLE 2. Mechanical property of PA6/CF composites with different tougheners.
Sample PA6 PA/EVA/0 PA/EPDM/0 PA/SEBS/0 PA/10 PA/EVA/10 PA/EPDM/10 PA/SEBS/10 PA/20 PA/EVA/20 PA/EPDM/20 PA/SEBS/20
Tensile strength (MPa)
Strain at break (%)
Tensile modulus (GPa)
Impact strength (J cm22)
73.4 6 3.1 59.2 6 3.3 49.1 6 2.9 49.1 6 1.9 96.9 6 3.7 76.5 6 4.3 83.3 6 3.9 85.6 6 2.1 110.3 6 5.4 83.9 6 0.9 82.8 6 3.9 87.6 6 2.3
86.8 6 10.5 412.6 6 46.6 473.1 6 57.0 471.4 6 64.1 5.5 6 0.6 6.8 6 0.6 7.1 6 0.4 6.7 6 0.3 6.1 6 1.2 6.0 6 0.3 6.4 6 0.4 7.0 6 0.4
1.84 6 0.09 0.88 6 0.04 0.80 6 0.03 0.83 6 0.17 2.62 6 0.08 2.31 6 0.84 2.63 6 0.14 2.46 6 0.05 3.02 6 0.05 2.71 6 0.61 2.68 6 0.24 2.71 6 0.09
5.94 6 0.52 14.50 6 1.49 55.69 6 1.99 72.03 6 1.46 4.33 6 0.24 7.97 6 0.73 11.49 6 0.40 8.63 6 0.60 4.96 6 0.42 6.83 6 0.76 8.86 6 0.23 7.85 6 0.48
DOI 10.1002/pc
FIG. 2. SEM micrographs of PA6/CF composites with different tougheners after impact test: (a) PA/20, (b) PA/EVA/20, (c) PA/EPDM/20, and (d) PA/SEBS/20.
The incorporation of 20 wt% elastomers to PA6 matrix led to a sharp increase in both the elongation at break and the impact strength of PA6/elastomers blend, although the tensile strength and Young’s modulus slightly decreased by addition of the elastomers. The mechanical properties of all specimens investigated are shown in Fig. 1 and summarized in Table 2. The tensile strength of toughened PA6/CF composites lowered slightly compared with the PA6/CF composites. It is interesting to point out that the impact strength of PA/ EPDM-g-MAH and PA/SEBS-g-MAH is improved by 8.4 and 11 times higher than that of pure PA6, respectively; however, it is only 1.5 times for PA/EVA-g-MAH. Similar results were reported for toughening of nylon1010 by three types of maleated elastomers [36]. Thus, it is attributed to a strong interaction between the amide group of PA6 and MAH functional group of SEBS, forming an imide linkage [22], but it also depended on elastomer type [36]. However, addition of CFs to the PA6/elastomers blend caused a dramatic decrease in the impact strength but was still higher than that of pure PA6. Addition of a rigid filler or fiber restricts the chain mobility of polymer molecules because molecules cannot move freely. This may lead to the formation of microcracks in the composites [13]. Furthermore, increase of stress concentration at the ends of fibers is another reason for crack formation in the matrix. It is known that, when the extent DOI 10.1002/pc
of cracking on the specimen reaches to a critical level especially in surrounding fibers, matrix cannot resist to applied load and then cracks can initiate in those regions [8, 37]. For the same composition species modified by different elastomers, the improvement of impact strength ranked as: EPDM-g-MAH > SEBS-g-MAH > EVA-gMAH. A strong interfacial adhesion between the matrix and the fibers will reduce polymer mobility and prevent fibers pull-outs from the matrix [38]. Hence, the toughened composite will require more energy to failure owing to good interaction between CF and both matrix systems. The morphological observations by SEM evaluated the interfacial adhesion in the composites with grafted matrices and correlated to the mechanical measurements. Surface Morphology The effects of different maleated elastomers on impact fracture surface morphology of PA6/CF composites are shown in Fig. 2a–d. From Fig. 2a, the untoughened PA/ CF composite exhibited relatively smooth fracture surfaces and poor adhesion at the interface. This poor adhesion is deduced not only from the great length of the fibers that come out of the fracture surfaces of the samples but also from the high amount of empty hollows on the surfaces owing to the fibers that have been pulled out of the POLYMER COMPOSITES—2014 2173
FIG. 3. Nonisothermal crystallization curves of PA6/CF composites at various cooling rates: (a) PA/20, (b) PA/EVA/20, (c) PA/EPDM/20, and (d) PA/SEBS/20.
matrix. Figure 2b–d shows the morphology of the PA6/ CF composites with EVA-g-MAH, EPDM-g-MAH, and SEBS-g-MAH, respectively. In both cases, a considerable improvement of the adhesion at the interface is observed, and there are hardly any voids in the fracture surface, which indicates that the fibers are so well trapped by the polymer matrix that fiber pull-out during impact tests considerably decreases [38]. It can also be seen that there is good contact between the fibers and the polymer matrices owing to the better bonding promoted by the maleic groups and to the fibers protruding from the polymer matrix covered with a polymer layer. An improvement in terms of fiber/matrix adhesion was observed when the maleated elastomers were added to the blend by a general reduction of pulled-out fiber length [38]. Nonisothermal Crystallization Behavior From a technological point of view, the resulting physical and mechanical properties of a semicrystalline poly2174 POLYMER COMPOSITES—2014
mer are strongly dependent on the extent of polymer crystallization and morphology developed during processing. It is of great practical importance to understand the crystallization of polymers under nonisothermal conditions. Figure 3 shows the nonisothermal crystallization of PA6/CF composites toughened by three types of maleated elastomers with cooling rates from 5 to 20 C min21. Apparently, for all the samples, the crystallization exotherms shifted to lower temperature with increasing cooling rate. The detailed crystallization parameters (Ton: onset crystallization temperature, Tp: crystallization peak temperature, t1/2: crystallization half time, and DHc: crystallization enthalpy) are listed in Table 3. As expected, the increasing cooling rate resulted in the decrease of Ton, Tp, t1/2, and DHc. This is because the polymer melt was supercooled at a higher cooling rate and the activation of nucleation became more difficult. Of particular note that the Ton and Tp of PA6/CF composites were higher than those of pure PA6 at the same cooling rate. It was attributed to the effective nucleating effect of CFs [39]. DOI 10.1002/pc
TABLE 3. Nonisothermal crystallization and melting parameters of PA6/toughener/CF composites. Samples PA6
PA/20
PA/EVA/20
PA/EPDM/20
PA/SEBS/20
U ( C min21)
Ton ( C)
Tp ( C)
t1/2 (s)
DHc (J g21)
Xc (%)
Tm1 ( C)
Tm2 ( C)
DHm (J g21)
5 10 15 20 5 10 15 20 5 10 15 20 5 10 15 20 5 10 15 20
194.1 190.0 187.4 185.6 197.8 193.8 191.2 189.2 193.2 189.1 186.5 184.6 193.5 189.4 186.7 184.6 194.7 190.5 187.7 185.6
191.8 187.0 183.8 181.3 194.9 190.5 187.4 185.0 190.1 185.5 182.4 180.2 190.3 185.4 182.2 179.5 191.9 187.1 184.1 181.3
35.4 24.6 20.4 18.0 49.2 29.4 21.0 18.0 89.2 46.3 38.2 30.4 88.1 48.5 38.6 31.4 83.4 47.4 34.1 28.3
59.6 55.7 54.4 53.5 49.3 45.5 43.2 42.8 33.2 32.3 32.3 32.4 32.5 31.2 31.3 31.3 38.1 36.6 35.9 36.2
24.8 23.2 22.7 22.3 25.7 23.7 22.5 22.3 21.6 21.0 21.0 21.1 21.2 20.3 20.4 20.4 24.8 23.8 23.4 23.6
215.5 213.7 212.5 211.3 – 215.2 213.8 212.8 – 212.6 210.7 209.3 – 212.7 211.8 210.8 215.1 212.9 211.5 210.5
220.0 220.0 220.0 220.0 217.1 219.3 219.6 219.6 217.4 218.2 218.2 218.2 217.7 218.6 218.6 218.6 218.7 218.3 218.3 218.3
63.9 60.1 57.5 55.4 47.3 44.6 41.8 37.0 41.9 40.0 36.7 38.0 40.5 39.1 36.9 36.5 45.9 43.7 41.4 40.1
Furthermore, the corresponding crystallization peak temperatures (Tp) at different cooling rates obtained from the cooling curves are shown in Fig. 4. It can be recognized that, at the same cooling rates, Tp of PA/20 was greatly increased compared with that of pure PA6. In addition, the incorporation of grafted elastomers with the maleic groups slowed the crystallization process. Particularly, Tp of PA/SEBS/20 was equal to that of PA6; however, Tps of PA/EVA/20 and PA/EPDM/20 were even lower than that of PA6. The results indicated that all the three kinds of elastomers had negative effect on crystallization and retarded crystallization of PA6 [40, 41]. It can also be attributed to a strong interaction between the amide group of PA6 and MAH functional group of maleated elastomers, forming an imide linkage [22]. In this studied system, the functional maleated elastomers
are ineffective in promoting the crystallization of PA6, as evidenced by a shift to a lower value of Tps. Also, a similar effect of SEBS-g-MAH and POE-g-MAH elastomers on PP/wood fiber composites was reported [42]. The degree of crystallinity (Xc) of PA6 phase can be determined from the following equation: Xc ð%Þ5
DHc 3100; o uDHm
(1)
where DHc is the apparent enthalpy of crystallization, u o is the weight fraction of PA6, and DHm is the extrapolated value of enthalpy determined from the melting of 100% crystalline PA6. Because PA6 exhibits different polymorphic forms, an average value of 240 J g21 is choo [43]. sen for DHm The calculated results in Table 3 showed that the addition of elastomers into the PA6 matrix led to a decrease of Xc, which was consistent with the previous discussion that the retarding effect of elastomers on PA6 crystallization, especially the EVA-g-MAH and EPDM-g-MAH. This arises from strong chemical interactions between the terminal amine group of PA6 and MAH group of elastomers as discussed previously. A similar result was also reported [44] for the PA6/PP/SEBS-g-MA/clay composites. They attributed the reduced crystallinity to the presence of the SEBS-g-PA6 copolymer formed at the PA6/ PP interface, thereby inhibiting crystal formation. Nonisothermal Crystallization Activation Energy
FIG. 4. Crystallization peak temperature (Tp) of PA6/CF composites at various cooling rates.
DOI 10.1002/pc
The Kissinger’s method has been widely applied to evaluate the overall effective activation energy by considering the variation of the crystallization peak temperature with the cooling rate [45]. POLYMER COMPOSITES—2014 2175
d ln TU2 DE p 52 ; R d T1p
(2)
where U is the cooling rate, Tp is the crystallization peak temperature, R is the gas constant, and DE is the activation energy of nonisothermal crystallization. The activation energy of nonisothermal crystallization (DE) is calculated from the slope of ln U/Tp2 versus 1/Tp (correlation coefficient > 0.99). As shown in Fig. 5, the DE values of PA6, PA/20, PA/EVA/20, PA/ EPDM/20, and PA/SEBS/20 during nonisothermal crystallization were determined to be 2240, 2258, 2252, 2233, and 2240 kJ mol21, respectively. It should be noted that the obtained activation energy (DE) is indicative of the diffusion process to the crystal growth, not reflected by the nucleation effect. The results indicated that addition of CF slightly increased the crystallization activation energy of PA6, which probably result from the confinement effect of CF on the transfer of PA6 chains. In the case of incorporation of elastomers into
FIG. 5. Plots of ln (U/Tp2) versus 1/Tp to determine the activation energy of nonisothermal crystallization of PA6/CF composites.
PA6 matrix, a little decrease in DE was observed and attributed to their plasticizing effect on the motion of PA6 segments.
FIG. 6. Melting curves of PA6/toughener/CF composites after nonisothermal crystallization at various cooling rates: (a) PA/20, (b) PA/EVA/20, (c) PA/EPDM/20, and (d) PA/SEBS/20.
2176 POLYMER COMPOSITES—2014
DOI 10.1002/pc
FIG. 7. POM photographs of PA6/CF composites with different tougheners: (a) PA/20, (b) PA/EVA/20, (c) PA/EPDM/20, and (d) PA/SEBS/20. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Subsequent Melting Behavior After nonisothermal crystallization, subsequent melting behavior of PA6/CF composites subject to various cooling rates is shown in Fig. 6. PA6 exhibits different polymorphic forms, and the melting points of the two main crystal forms, i.e., g-form and a-form, are 215 and 225 C, respectively. It can be observed that, in the main melting region between 200 and 230 C of PA6, there are two melting peaks, Tm1 (ca. 215 C) and Tm2 (ca. 220 C), corresponding to the melting events of g-form and a-form crystals, respectively [46]. In all samples the peak positions of Tm1 shifted to lower temperatures, whereas the position of main peak (Tm2) did not change with the increasing cooling rate. Therefore, we considered that the existence of either mixed crystal structure of PA-6 (i.e., a and g form) or a combined process of melting and recrystallization during the heating cycle resulted in the multiple melting behavior [47]. The melting parameters of all samples are also listed in Table 3. In the case of the crystalline melting temperature (Tm), no significant change was observed by incorporation of CF, which may be due to not much change of the crystal size of PA6. Similar DOI 10.1002/pc
results were reported for PA-6/SMA-encapsulated SWNT composites [47]. For the PA6/CF composites toughened by elastomers, a slight decrease was detected compared with pure PA6. The difference in melting point parameters may be attributed to the spherulites with different size and perfection or different crystal layer thickness formed at various cooling rates.
Spherulitic Morphology To supplement the DSC observations of crystallization of PA6 in the presence of both CFs and elastomers, POM was used to observe the spherulitic morphology (Fig. 7a– d). POM images showed that the fibers can act as restriction sites for PA6 segments, hindering them from forming highly ordered spherulites. It is interesting that the phenomenon of transcrystallization on the CF surface can be easily observed. However, when the matrix was added by the elastomers, the transcrystallinity phenomenon seemed to be hindered. Particularly, it was observed that the PA6 average size and number of the spherulites decreased by the incorporation of EVA-g-MAH and EPDM-g-MAH POLYMER COMPOSITES—2014 2177
elastomers compared with PA/CF, whereas the addition of SEBS-g-MAH did not significantly affect the crystal size and spherulitic numbers of PA6 matrix. Thus, a change in the average size and number of the spherulites is induced by the incorporation of the elastomers, and this structural change is very important for interpreting the function of the elastomers as an impact modifier in the PA6 matrix.
CONCLUSIONS A series of the reinforced and toughened PA6 composites with different content of CFs were prepared by twinscrew extruder. Three kinds of elastomers, EVA-g-MAH, EPDM-g-MAH, and SEBS-g-MAH elastomers, were evaluated for toughening PA/CF composites. Meanwhile, mechanical property, surface morphology, thermal behavior, and spherulitic morphology of composites were studied. SEM observations indicated that the addition of elastomers enhanced the dispersion and the interface adhesion of CF in PA/CF composites and further improved the impact strength. The toughened efficiency for PA/CF composites ranked as EPDM-g-MAH > SEBSg-MAH > EVA-g-MAH. The DSC results indicated that all the three kinds of elastomers had negative effect on crystallization and retarded crystallization of PA6. Furthermore, a slight decrease in crystallinity and melting point was detected compared with pure PA6 when incorporated with elastomers. POM results showed that the transcrystallinity phenomenon seemed to be affected when the matrix was added by the elastomers. REFERENCES 1. C.D. Warren, SAMPE J., 37, 26 (2001). 2. F. Rezaei, R. Yunus, N.A. Ibrahim, and E.S. Mahdi, Polym. Plast. Technol. Eng., 47, 351 (2008). 3. H.S. Park and X.P. Dang, Int. J. Automot. Technol., 12, 83 (2011). 4. E. Frank, F. Hermanutz, and M.R. Buchmeiser, Macromol. Mater. Eng., 297, 493 (2012). 5. D.A. Baker and T.G. Rials, J. Appl. Polym. Sci., 130, 713 (2013). 6. S. Molnar, S. Rosenberger, J. Gulyas, and B. Pukanszky, J. Macromol. Sci. Part B: Phys., 38, 721 (1999). 7. C. Zhang, X.S. Yi, S. Asai, and M. Sumita, J. Mater. Sci., 35, 673 (2000). 8. S.Y. Fu, B. Lauke, E. M€ader, C.Y. Yue, and X. Hu, Composites: Part A, 31, 1117 (2000). 9. S. Fu, B. Lauke, E. M€ader, C. Yue, X. Hu, and Y. Mai, J. Mater. Sci., 36, 1243 (2001). 10. E.C. Botelho, L. Figiel, M.C. Rezende, and B. Lauke, Compos. Sci. Technol., 63, 1843 (2003). 11. A. Hassan, P.R. Hornsby, and M.J. Folkes, Polym. Test., 22, 185 (2003). 2178 POLYMER COMPOSITES—2014
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