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K resin blends
Materials Science and Engineering A 444 (2007) 84–91
Mechanical behavior and fracture toughness evaluation of K resin grafted with maleic anhydride compatibilized polycarbonate/K resin blends Bo Jing, Wenli Dai ∗ , Shubai Chen, Tao Hu, Pengsheng Liu ∗ Institute of Polymer Science and Engineering, College of Chemistry, Xiangtan University, Xiangtan 411105, Hunan Province, China Received 14 July 2006; accepted 13 August 2006
Abstract The mechanical behavior and fracture toughness evaluation of polycarbonate (PC)/K resin (K) blends, with and without maleic anhydride grafted K resin (K-g-MAH) incorporated, have been studied. The effect of K-g-MAH on the mechanical performance of the PC/K blends was investigated. The results showed that both the tensile strength, elongation at break and impact strength of PC/K blends were improved considerably with incorporating K-g-MAH. This resulted from the melioration of compatibility between the PC and K resin phases. The essential work of fracture (EWF) method was employed to determine the fracture toughness of PC/K blends with and without K-g-MAH incorporated. The effect of composition on the EWF parameters of the blends was particularly investigated. The results showed that a significant improvement in we of PC/K blends appeared when the K-g-MAH was incorporated, but it hardly influenced the plastic deformation during the fracture process. © 2006 Published by Elsevier B.V. Keywords: Polycarbonate; K resin; Blends; Mechanical behavior; Fracture toughness; Essential work of fracture (EWF)
1. Introduction Polycarbonate (PC) has found many uses because it combines a high level of heat resistance, flame resistance, transparency and dimensional stability with good insulating properties. However, it is sensitive to notch, poor processability and suffers from a tendency to craze and crack when in contact with organic solvents and hot water. Its application is limited by these disadvantages. Polymer blending is an efficient way to improve some deficient properties of these two polymers. The major problem is the lack of miscibility, leading to the dispersion of large minor phase domains in the matrix of the blends. This results in poor mechanical strength and toughness [1,2]. Effective compatibilization is needed to improve the interfacial adhesion between the phase components. This can be achieved by adding functionalized polymers and block or graft polymers. The rubber-toughened polycarbonate has received considerable attention for many years. PC has been blended with various rubbers like polyolefins [3–6], styrenic copolymers such as methacrylate–butadiene–styrene (MBS), styrene maleic
∗
Corresponding authors. Tel.: +86 732 8292207; fax: +86 732 8292477. E-mail addresses: [email protected] (W. Dai), [email protected] (P. Liu).
0921-5093/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.msea.2006.08.036
anhydride (SMA) copolymer [7–9], core-shell rubbers [10–15], thermoplastic polyurethane and copolyether ester elastomer [16–18]. Rubber modification of PC is known to cause dramatic reductions in both strength and stiffness based on the additivity law. K resin is a styrene–butadiene copolymer with high content styrene and much higher modulus than rubber elastomers. Until recently, very little quantitative information was available on K resin blends [19]. In the present paper, PC was blended with K resin in different weight compositions. maleic anhydride grafted K resin (K-g-MAH) was used to develop sufficient interfacial adhesion between PC and K resin. The impact, static tensile and dynamic mechanical properties as well as fracture toughness of the blends were studied.
2. Experimental 2.1. Materials The polycarbonate (Lexan HF1111) serving as matrix for the blends was a granular material produced by GE Plastic Co. (USA). The K Resin® (KR03) was supplied by Phillips Co. (Korea). K-g-MAH was produced in our laboratory, the details of procedures described in the literature [20].
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2.2. Sample preparation PC and K resin were pre-dried before blending at 110 and 50 ◦ C respectively in a vacuum oven for 8 h. The dried PC and K-g-MAH pellets were mixed with K resin at preselected mass ratios. The extrusion of the mixtures was performed on a SJSH30 twin-screw extruder made by Nanjing Xiangsu machine factory (China), with length to diameter ratio of 25. The temperature profile was in the range of 200–235 ◦ C. The materials were pelletized after extrusion, after drying to remove the attached moisture during extrusion and palletizing, the pellets were injected into both dumb-bell shaped and rectangular samples of 4 mm thickness on a injection molding machine. The temperature profile was 230, 240, 250 and 260 ◦ C from the feeding zone to the nozzle, and both the injection and holding pressures were 50.0 MPa. Then, the part rectangle samples were compressionmolded into sheets of about 0.7 mm thickness at 260 ◦ C and 10 MPa. 2.3. Mechanical characterization Tensile tests were conducted according to ISO 527, using the injected dumb-bell shaped specimens on an Instron universal testing machine equipped with a 500 N load cell with a crosshead speed of 50 mm/min, at room temperature. Four specimens of each composition were tested and the average value reported. Charpy impact specimens with dimensions of 63 mm × 8 mm × 4 mm were cut from the rectangular injection molded bars. They were tested using a XJJ-50 plastic impact machine. The tests were carried out at ambient temperature and 55% relative humidity. At least five specimens were tested and the average values reported. The fracture surfaces of the impact specimens were examined in a scanning electron microscope (JEOL JSM6360). The dynamic mechanical analyses (DMA) tests were made using a thermal dynamical–mechanical analyzer (Perkin Elmer, model DMTA-V). The measurements were carried out in a bending mode, at the heating rate of 3 ◦ C/min from 20 to 160 ◦ C at fixed frequencies of 1 Hz. The double edge notched tension (DENT) specimens (length × width = 100 mm × 35 mm) seen in Fig. 1 were cut from the compression-molded sheets. The sharp pre-cracks on both sides of the specimens were made perpendicularly to the tensile direction with a fresh razor blade. The ligament lengths and the thickness were measured before the test using a microscope and a vernier caliper, respectively. The DENT specimens were loaded on an Instron universal testing machine, the
Fig. 1. Geometry of DENT specimen, indicating the different energy dissipation zone involved.
crosshead speed was set as 15 mm/min. The load–displacement curves were recorded and the absorbed energy until failure was calculated by computer integration of the loading curves. 3. Results and discussion 3.1. Tensile behavior The tensile properties of uncompatibilized and K-g-MAH compatibilized PC/K blends are summarized in Table 1. It can be seen that the tensile strength of PC/K blends continuously decrease with the incorporation of K resin in the blend. It is well known that, if the strength of one phase in the blend is lower than the other, the blend will show lower strength than the component with high strength based on the additivity law. The composition dependence of Young’s modulus shows similar features as that of the tensile strength for the PC/K blends. This results from incompatibility between the PC and K resin phases of the blends. However, compares to uncompatibilized PC/K 80/20 blend, the beneficial effect of the addition of K-g-MAH
Table 1 The tensile properties of uncompatibilized and compatibilized PC/K blends PC/K blends
Tensile strength (MPa)
Young’s modulus (MPa)
Strain at break (%)
PC/K/K-g-MAH blends
Tensile strength (MPa)
Young’s modulus (MPa)
Strain at break (%)
100/0 90/10 80/20 70/30
61.9 55.1 49.9 45.0
674.9 646.6 597.9 565.5
106.7 63.5 32.4 71.3
80/20/0 80/15/5 80/10/10 80/5/15
49.9 54.6 53.9 51.0
597.9 632.0 624.9 605.6
32.38 124.7 127.2 110.2
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Table 2 Notched Charpy impact results for PC/K blends and K-g-MAH compatibilized PC/K blends PC/K blends
Impact strength (kJ/M2 )
PC/K/K-g-MAH blends
Impact strength (kJ/M2 )
100/0 90/10 80/20 70/30
141.0 100.1 67.2 39.1
80/20/0 80/15/5 80/10/10 80/5/15
67.2 129.8 113.3 109.7
on the tensile strength, Young’s modulus and strain at break is evident. 3.2. Impact characteristics The notched impact strength of PC/K blends and K-g-MAH compatibilized PC/K blends are listed in Table 2. Apparently, pure PC exhibits high impact strength of 141.0 kJ/m2 . Incorporation of K resin into PC leads to a rapid decrease in the impact strength because both strength and stiffness of K resin are lower than those of PC. However, the addition of K-g-MAH can evidently improve the impact toughness of PC/K blends. A maximum impact toughness of 129.8 kJ/m2 is achieved by blending 5 wt.% K-g-MAH instead of K resin in PC/K 80/20 blend. The addition of K-g-MAH might result in a reduction of the surface tension and an enhancement of the adhesion between PC phase and K resin phase. Thus, the internal stress of the material transmit through the two phase more easily and the impact toughness of the compatibilized PC/K blends is improved. SEM examination of the fracture surfaces of impact specimens provides valuable information on the deformation mechanisms. Fig. 2a shows the impact fracture surface of the slow crack growth zone adjacent to the notch for PC. It is apparent that the surface is very flat and lubricous indicating that this sample experiences little plastic deformation. Fig. 2b showed typical brittle fracture surfaces where many K resin particles are debonding of the PC matrix suggesting poor interfacial adhesion between both phases. In contrast, rougher surface appearance and the clear trace of plastic deformation can be observed in the fractograph of the PC/K/K-g-MAH blend (Fig. 2c). Hence, the impact toughness of the PC/K/K-g-MAH blend is higher than that of the PC/K blend (Table 2). It is generally known that the mechanical properties of polymer blends depend on the morphology and interfacial adhesion between the matrix and disperse phase. An optimum particle size and good interfacial bonding are required for effective toughening [21]. It is well known that the interaction between PC and K resin is limited because PC has a polar group but K resin is a non-polar polymer. It is considered that incorporation of K-g-MAH into PC/K blends can improve the compatibility and enhance the interfacial adhesion between PC matrix and K resin. Hence, it is efficient to improve the toughness of the compatibilized PC/K blends. 3.3. Dynamic mechanical behavior Fig. 3 shows the plots of tan δ and storage modulus versus temperature for the PC/K 80/20, PC/K/K-g-MAH 80/15/5
Fig. 2. SEM fractographs of: (a) PC, (b) PC/K 80/20 blend and (c) PC/K/K-gMAH 80/15/5 blend.
blends. The glass transition temperatures (Tg ) of PC and K resin phases of the PC/K blends are located at 138.3 and 91.8 ◦ C, respectively, indicating that these two blend components are immiscible or incompatible. In order to improve the compatibility between the PC and K resin phases, K-g-MAH is added to the PC/K blend. Fig. 3a reveals that the addition of the Kg-MAH to the PC/K blend has resulted in the shift of Tg of these two components towards each other. This implies that the compatibility between the PC and K resin improves with adding K-g-MAH. Fig. 3b indicates that the addition of K-g-MAH into the PC/K blend leads to a significant increment in the storage modulus.
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Table 3 Fracture parameters for the PC/K blends with varied content of K resin PC/K (mass ratio)
we (kJ/m2 )
βwp (MJ/m3 )
R2
100/0 90/10 80/20 70/30
22.54 19.71 20.91 20.94
22.71 23.25 19.92 18.24
0.95 0.99 0.98 0.97
wf , is given by: wf =
Wf = we + βwp l lt
(3)
According to Eq. (3), plotting wf against ligament yield a straight line whose intercept with the wf -axis gives we and whose slope is βwp .
Fig. 3. tan δ and storage modulus vs. temperature plots for PC/K 80/20, PC/PC/K-g-MAH 80/15/5 blends.
3.4. Fracture toughness 3.4.1. Essential work of fracture (EWF) method In recent years, the essential work of fracture method originated with Broberg [22] and then developed by Cotterell [23–25], Karger-Kocsis [26–29] and Mai [30–34]. It is a method of quantifying the relative contributing effects in fracture. In this analysis, the total work of fracture (Wf ), or the energy absorbed in the fracture of a test specimen, can be divided into two basic components (Fig. 1), i.e. (a) the essential work of fracture (We ) performed in the inner fracture process zone (IFPZ); (b) the nonessential work of fracture (Wp ) that occurs in the outer plastic deformation zone (OPDZ). The total fracture work (Wf ) can be expressed by: Wf = We + Wp
(1)
When both the IFPZ and the OPDZ are contained in the ligament, then We is surface related and proportional to ligament length, l, the Wp is volume related and proportional to the square of the ligament length, l2 . Hence it can be written as We = we lt,
Wp = βwp l2 t
(2)
where we and βwp are the specific essential work of fracture and specific non-essential work of fracture, respectively. The parameter β is a geometry-dependent plastic zone shape factor and t is the specimen thickness. The specific total fracture work,
3.4.2. Variations of EWF parameters The load–displacement curves of DENT specimens for PC/K resin and PC/K/K-g-MAH blends during EWF tests as a function of ligament length are shown in Figs. 4 and 5, respectively. For all the blends, similar trends were observed. The load increased tardily with slight increase of the displacement before the definite upper point in the initial stage. After the peak, a slowly drop in load occurred with further increase of displacement and finally a rapid load drop at the end stage of the curves indicated the fracture of the specimens. Though the crack propagation displacements were not too big, the curves showed that the ligament yielded and the crack propagated in a stable manner. This is one of the necessary conditions which guaranteed the validity of EWF testing. On the other hand, the curves for each group of specimens at the same composition showed excellent reproducibility. The maximum load and the displacement to failure increased regularly with increasing ligament length. This is another crucial criterion for the application of EWF method, which ensures that the cracks propagated under similar stress conditions, being unchanged with the ligament length [35]. With a general comparison of the curves at the same ligament length, it was found that the maximum load decreased with increasing content of K resin, which indicated the decrease of strength as K resin particles were added into the polymer. However, the load peaks of PC/K/K-g-MAH blends with different K-g-MAH content were slightly higher than that of PC/K resin, indicating that incorporation of K-g-MAH improved the strength of the blends. The plot of wf versus l of PC/K and PC/K/K-g-MAH blends are shown in Fig. 6. It is notable that the wf –l diagrams gave very good linear relationships for all the materials studied in this work, as proved by the linear regression coefficient (R2 ) being in most cases higher than 0.95. The values of we and βwp obtained from the interception and slope of the straight lines extrapolated to zero ligament length, together with the regression coefficient, are listed in Tables 3 and 4. From the values listed in Table 3, it is clear that the we values for PC with different K resin content were lower than that of the pure PC, indicating that the crack resistance of the blends reduced. This may be caused by the incompatibility between
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Fig. 4. Load–displacement curves for PC/K blends at different mass ratio: (a) 100/0, (b) 90/10, (c) 80/20, (d) 70/30.
Fig. 5. Load–displacement curves for PC/K/K-g-MAH blends at different mass ratio: (a), 80/20/0; (b), 80/15/5; (c), 80/10/10; (d), 80/5/15.
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30.06 kJ/m2 . This is higher than that of PC/K resin (80/20) and even higher than that of pure PC, indicating that incorporation of K-g-MAH had remarkably positive effect on the fracture toughness, which may be caused by the reinforced adhesion between the PC matrix and the K resin particles, as K-g-MAH is finely dispersed on the interface. After that, the we values decreased with further increasing amount of K-g-MAH, revealing that an optimum content range for K-g-MAH existed, beyond which the excessive K-g-MAH would impair the toughening effect because it was not so finely dispersed. However, it was found that the βwp values of the PC/K/K-g-MAH blends changed little with increasing amount of K-g-MAH, indicating the effect of the incorporated of K-g-MAH on plastic energy was very small. 3.4.3. Constituting terms of essential and non-essential work In order to find out the energy distribution during the fracture process, a method of partition, between the specific work of fracture for yielding and for necking and subsequent fracture was employed, making the peak of the load–displacement curves as the cut-off point. As the composed terms were under plane stress, Eq. (3) can be rewritten as
Fig. 6. Specific work of fracture against ligament length for: (1) PC/K blends at different mass ratios: (a) 100/0; (b) 90/10; (c) 80/20; (d) 70/30; (2) PC/K/K-gMAH blends at different mass ratios: (a) 80/20/0; (b) 80/20/5; (c) 80/20/3; (d) 80/20/7.
the PC and K resin phase. The decreases of we values for PC/K resin (90/10) blends was evident. However, an increase instead of gradual reduction of the we values was observed with the further increase of K resin content, which may be related to the overlapping of the stress fields caused by more points of stress concentration, reducing the negative effect of the defects on we [36]. On the other hand, the βwp values for PC/K blends could also be seen from Table 3, it fluctuated appreciably with increasing K resin content which revealed that incorporation of K resin slightly influenced the plastic deformation during the fracture process. The variation of we for PC/K/K-g-MAH blends is listed in Table 4. A significant improvement in we appeared when the K-g-MAH was incorporated, such as in the PC/K/K-g-MAH blends at the mass ratio of 80/15/5, reaching a peak value of Table 4 Fracture parameters for the PC/K/K-g-MAH blends with varied content of K-gMAH PC/K/K-g-MAH (mass ratio)
we (kJ/m2 )
βwp (MJ/m3 )
R2
80/20/0 80/15/5 80/10/10 80/5/15
20.91 30.06 24.56 26.21
19.92 18.65 19.63 19.44
0.98 0.98 0.95 0.97
wf = wy + wn
(4)
wy = we,y + β wp,y l
(5)
wn = we,n + β wp,n l
(6)
where we,y and we,n , were the yielding and the necking and subsequent fracture related parts of the specific essential work of fracture, respectively; β wp,y and β wp,n were the yielding and the necking and subsequent fracture component of the nonspecific essential work of fracture, respectively. The results for splitting the essential and non-essential work of fracture as yielding and necking terms are given in Tables 5 and 6, which were obtained by plotting wy and wn versus l as shown in Figs. 7 and 8. The regression coefficient (R2 ) of PC/K resin kept above 0.94 and that of PC/K/K-g-MAH mostly above 0.92, which indicated that the partition method was also well applicable for these blends systems. From the results listed in Tables 5 and 6, it was clear that for all materials, the specific essential work of fracture for necking and subsequent fracture was all less than the corresponding term for yielding. The same result was found for the specific plastic work of fracture for yielding and the corresponding term for necking and subsequent fracture. These results indicated that both we and β wp,y in the whole fracture process for PC and the blends were mostly determined by the specific work of fracture for yielding. As shown in Table 5, the variation of we,y of the PC/K blends as K resin content increased was similar to that of we , and the characteristic decrease followed by the increase was even more evident. In spite of the small values, a remarkable decrease of we,n with increasing content of K resin was found for the PC/K blends and the we,y value was half that of pure PC when the K resin concentration exceeded 30 wt.%. Hence, the effect of K resin content on the crack resistance in the both yielding
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Table 5 Constituting terms of essential work of fracture for the PC/K blends with varied content of K resin PC/K (mass ratio)
we,y (kJ/m2 )
β wp,y (MJ/m3 )
R2 (for wy –l)
we,n (kJ/m2 )
β wp,n (MJ/m3 )
R2 (for wn –l)
100/0 90/10 80/20 70/30
18.65 17.32 19.06 19.08
18.37 19.57 15.56 15.28
0.97 0.98 0.96 0.97
3.85 2.40 1.84 1.90
4.34 3.68 4.36 2.96
0.95 0.99 0.94 0.98
Table 6 Constituting terms of essential work of fracture for the PC/K/K-g-MAH blends with varied of K-g-MAH PC/K/K-MAH (mass ratio)
we,y (kJ/m2 )
β wp,y (MJ/m3 )
R2 (for wy –l)
we,n (kJ/m2 )
β wp,n (MJ/m3 )
R2 (for wn –l)
80/20/0 80/15/5 80/10/10 80/5/15
19.07 28.39 23.51 23.37
15.56 13.47 16.11 16.16
0.96 0.94 0.98 0.98
1.83 1.67 1.06 2.83
4.36 5.13 3.49 3.27
0.94 0.98 0.97 0.92
stage and necking and subsequent fracture stage could not be neglected, but the effect of K resin content on the fracture toughness was mainly achieved through its influence on we,y . For the sake of blends with high fracture toughness, sufficient attention should be paid to the value of we,y . On the other hand, the influence of K resin content on β wp,y and β wp,n for the PC/K blends was similar to that on βwp , in other words, both of them
increased firstly and then decreased gradually with increasing K resin content. The result indicated that the variation of plastic energy absorbed in the stage of yielding and necking coincided with that in the whole fracture process. The we,y values of the PC/K/K-g-MAH blends with different K-g-MAH content were all higher than that of PC/K blends, as can be seen from Table 6. This indicated that incorporation of K-g-MAH effectively improved the crack resistance in the
Fig. 7. Yielding and necking specific work of fracture against ligament length for PC/K blends: (a) pure PC; (b) PC/K (90/10); (c) PC/K (80/20); (d) PC/K (70/30).
Fig. 8. Yielding and necking specific work of fracture against ligament length for PC/K/K-g-MAH blends: (a) PC/K/K-g-MAH (80/20/0); (b) PC/K/K-g-MAH (80/15/5); (c) PC/K/K-g-MAH (80/10/10); (d) PC/K/K-g-MAH (80/5/15).
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yielding stage. Comparing with the variation of we,y , the we,n values is very small. It decreased with a small amount of Kg-MAH, and then increased with further increase in K-g-MAH content, revealing that only an optimum content of K-g-MAH could improve the crack resistance in the stage of necking and subsequent fracture. Similar to the PC/K blends, the effect of K-g-MAH content on the fracture toughness for the PC/K/K-gMAH blends was mainly achieved through its influence on we,y . The influence of K-g-MAH content on β wp,y and β wp,n for the PC/K/K-g-MAH blends was also shown in Table 6. Comparing to the variation of we,y , the we,n values, the β wp,y and β wp,n values did not show significant effect on the content of K-gMAH. 4. Conclusions This work attempts to develop PC/K blends modified with Kg-MAH with good tensile properties, improved impact strength and fracture toughness. The results show that maximum impact strength can be achieved by blending 5 wt.% K-g-MAH into PC/K 80/15 blend. Static tensile and DMA measurements show that the addition of K-g-MAH increases the stiffness of PC/K blends. The result of SEM fractographs implies that Kg-MAH improves the interfacial bonding between PC and K resin. Finally, the essential work of fracture method reveals that a strong effect of composition on the EWF parameters of the blends, a significant improvement in we of PC/K blends appeared with K-g-MAH incorporated. References [1] S.C. Tjong, Y.Z. Meng, Mater. Res. Bull. 39 (2004) 1791. [2] E. Gattiglia, A. Turturro, E. Pedemonte, J. Appl. Polym. Sci. 41 (1990) 1411.
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Mechanical behavior and fracture toughness evaluation of K resin grafted with maleic anhydride compatibilized polycarbonate/K resin blends Bo Jing, Wenli Dai ∗ , Shubai Chen, Tao Hu, Pengsheng Liu ∗ Institute of Polymer Science and Engineering, College of Chemistry, Xiangtan University, Xiangtan 411105, Hunan Province, China Received 14 July 2006; accepted 13 August 2006
Abstract The mechanical behavior and fracture toughness evaluation of polycarbonate (PC)/K resin (K) blends, with and without maleic anhydride grafted K resin (K-g-MAH) incorporated, have been studied. The effect of K-g-MAH on the mechanical performance of the PC/K blends was investigated. The results showed that both the tensile strength, elongation at break and impact strength of PC/K blends were improved considerably with incorporating K-g-MAH. This resulted from the melioration of compatibility between the PC and K resin phases. The essential work of fracture (EWF) method was employed to determine the fracture toughness of PC/K blends with and without K-g-MAH incorporated. The effect of composition on the EWF parameters of the blends was particularly investigated. The results showed that a significant improvement in we of PC/K blends appeared when the K-g-MAH was incorporated, but it hardly influenced the plastic deformation during the fracture process. © 2006 Published by Elsevier B.V. Keywords: Polycarbonate; K resin; Blends; Mechanical behavior; Fracture toughness; Essential work of fracture (EWF)
1. Introduction Polycarbonate (PC) has found many uses because it combines a high level of heat resistance, flame resistance, transparency and dimensional stability with good insulating properties. However, it is sensitive to notch, poor processability and suffers from a tendency to craze and crack when in contact with organic solvents and hot water. Its application is limited by these disadvantages. Polymer blending is an efficient way to improve some deficient properties of these two polymers. The major problem is the lack of miscibility, leading to the dispersion of large minor phase domains in the matrix of the blends. This results in poor mechanical strength and toughness [1,2]. Effective compatibilization is needed to improve the interfacial adhesion between the phase components. This can be achieved by adding functionalized polymers and block or graft polymers. The rubber-toughened polycarbonate has received considerable attention for many years. PC has been blended with various rubbers like polyolefins [3–6], styrenic copolymers such as methacrylate–butadiene–styrene (MBS), styrene maleic
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0921-5093/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.msea.2006.08.036
anhydride (SMA) copolymer [7–9], core-shell rubbers [10–15], thermoplastic polyurethane and copolyether ester elastomer [16–18]. Rubber modification of PC is known to cause dramatic reductions in both strength and stiffness based on the additivity law. K resin is a styrene–butadiene copolymer with high content styrene and much higher modulus than rubber elastomers. Until recently, very little quantitative information was available on K resin blends [19]. In the present paper, PC was blended with K resin in different weight compositions. maleic anhydride grafted K resin (K-g-MAH) was used to develop sufficient interfacial adhesion between PC and K resin. The impact, static tensile and dynamic mechanical properties as well as fracture toughness of the blends were studied.
2. Experimental 2.1. Materials The polycarbonate (Lexan HF1111) serving as matrix for the blends was a granular material produced by GE Plastic Co. (USA). The K Resin® (KR03) was supplied by Phillips Co. (Korea). K-g-MAH was produced in our laboratory, the details of procedures described in the literature [20].
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2.2. Sample preparation PC and K resin were pre-dried before blending at 110 and 50 ◦ C respectively in a vacuum oven for 8 h. The dried PC and K-g-MAH pellets were mixed with K resin at preselected mass ratios. The extrusion of the mixtures was performed on a SJSH30 twin-screw extruder made by Nanjing Xiangsu machine factory (China), with length to diameter ratio of 25. The temperature profile was in the range of 200–235 ◦ C. The materials were pelletized after extrusion, after drying to remove the attached moisture during extrusion and palletizing, the pellets were injected into both dumb-bell shaped and rectangular samples of 4 mm thickness on a injection molding machine. The temperature profile was 230, 240, 250 and 260 ◦ C from the feeding zone to the nozzle, and both the injection and holding pressures were 50.0 MPa. Then, the part rectangle samples were compressionmolded into sheets of about 0.7 mm thickness at 260 ◦ C and 10 MPa. 2.3. Mechanical characterization Tensile tests were conducted according to ISO 527, using the injected dumb-bell shaped specimens on an Instron universal testing machine equipped with a 500 N load cell with a crosshead speed of 50 mm/min, at room temperature. Four specimens of each composition were tested and the average value reported. Charpy impact specimens with dimensions of 63 mm × 8 mm × 4 mm were cut from the rectangular injection molded bars. They were tested using a XJJ-50 plastic impact machine. The tests were carried out at ambient temperature and 55% relative humidity. At least five specimens were tested and the average values reported. The fracture surfaces of the impact specimens were examined in a scanning electron microscope (JEOL JSM6360). The dynamic mechanical analyses (DMA) tests were made using a thermal dynamical–mechanical analyzer (Perkin Elmer, model DMTA-V). The measurements were carried out in a bending mode, at the heating rate of 3 ◦ C/min from 20 to 160 ◦ C at fixed frequencies of 1 Hz. The double edge notched tension (DENT) specimens (length × width = 100 mm × 35 mm) seen in Fig. 1 were cut from the compression-molded sheets. The sharp pre-cracks on both sides of the specimens were made perpendicularly to the tensile direction with a fresh razor blade. The ligament lengths and the thickness were measured before the test using a microscope and a vernier caliper, respectively. The DENT specimens were loaded on an Instron universal testing machine, the
Fig. 1. Geometry of DENT specimen, indicating the different energy dissipation zone involved.
crosshead speed was set as 15 mm/min. The load–displacement curves were recorded and the absorbed energy until failure was calculated by computer integration of the loading curves. 3. Results and discussion 3.1. Tensile behavior The tensile properties of uncompatibilized and K-g-MAH compatibilized PC/K blends are summarized in Table 1. It can be seen that the tensile strength of PC/K blends continuously decrease with the incorporation of K resin in the blend. It is well known that, if the strength of one phase in the blend is lower than the other, the blend will show lower strength than the component with high strength based on the additivity law. The composition dependence of Young’s modulus shows similar features as that of the tensile strength for the PC/K blends. This results from incompatibility between the PC and K resin phases of the blends. However, compares to uncompatibilized PC/K 80/20 blend, the beneficial effect of the addition of K-g-MAH
Table 1 The tensile properties of uncompatibilized and compatibilized PC/K blends PC/K blends
Tensile strength (MPa)
Young’s modulus (MPa)
Strain at break (%)
PC/K/K-g-MAH blends
Tensile strength (MPa)
Young’s modulus (MPa)
Strain at break (%)
100/0 90/10 80/20 70/30
61.9 55.1 49.9 45.0
674.9 646.6 597.9 565.5
106.7 63.5 32.4 71.3
80/20/0 80/15/5 80/10/10 80/5/15
49.9 54.6 53.9 51.0
597.9 632.0 624.9 605.6
32.38 124.7 127.2 110.2
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Table 2 Notched Charpy impact results for PC/K blends and K-g-MAH compatibilized PC/K blends PC/K blends
Impact strength (kJ/M2 )
PC/K/K-g-MAH blends
Impact strength (kJ/M2 )
100/0 90/10 80/20 70/30
141.0 100.1 67.2 39.1
80/20/0 80/15/5 80/10/10 80/5/15
67.2 129.8 113.3 109.7
on the tensile strength, Young’s modulus and strain at break is evident. 3.2. Impact characteristics The notched impact strength of PC/K blends and K-g-MAH compatibilized PC/K blends are listed in Table 2. Apparently, pure PC exhibits high impact strength of 141.0 kJ/m2 . Incorporation of K resin into PC leads to a rapid decrease in the impact strength because both strength and stiffness of K resin are lower than those of PC. However, the addition of K-g-MAH can evidently improve the impact toughness of PC/K blends. A maximum impact toughness of 129.8 kJ/m2 is achieved by blending 5 wt.% K-g-MAH instead of K resin in PC/K 80/20 blend. The addition of K-g-MAH might result in a reduction of the surface tension and an enhancement of the adhesion between PC phase and K resin phase. Thus, the internal stress of the material transmit through the two phase more easily and the impact toughness of the compatibilized PC/K blends is improved. SEM examination of the fracture surfaces of impact specimens provides valuable information on the deformation mechanisms. Fig. 2a shows the impact fracture surface of the slow crack growth zone adjacent to the notch for PC. It is apparent that the surface is very flat and lubricous indicating that this sample experiences little plastic deformation. Fig. 2b showed typical brittle fracture surfaces where many K resin particles are debonding of the PC matrix suggesting poor interfacial adhesion between both phases. In contrast, rougher surface appearance and the clear trace of plastic deformation can be observed in the fractograph of the PC/K/K-g-MAH blend (Fig. 2c). Hence, the impact toughness of the PC/K/K-g-MAH blend is higher than that of the PC/K blend (Table 2). It is generally known that the mechanical properties of polymer blends depend on the morphology and interfacial adhesion between the matrix and disperse phase. An optimum particle size and good interfacial bonding are required for effective toughening [21]. It is well known that the interaction between PC and K resin is limited because PC has a polar group but K resin is a non-polar polymer. It is considered that incorporation of K-g-MAH into PC/K blends can improve the compatibility and enhance the interfacial adhesion between PC matrix and K resin. Hence, it is efficient to improve the toughness of the compatibilized PC/K blends. 3.3. Dynamic mechanical behavior Fig. 3 shows the plots of tan δ and storage modulus versus temperature for the PC/K 80/20, PC/K/K-g-MAH 80/15/5
Fig. 2. SEM fractographs of: (a) PC, (b) PC/K 80/20 blend and (c) PC/K/K-gMAH 80/15/5 blend.
blends. The glass transition temperatures (Tg ) of PC and K resin phases of the PC/K blends are located at 138.3 and 91.8 ◦ C, respectively, indicating that these two blend components are immiscible or incompatible. In order to improve the compatibility between the PC and K resin phases, K-g-MAH is added to the PC/K blend. Fig. 3a reveals that the addition of the Kg-MAH to the PC/K blend has resulted in the shift of Tg of these two components towards each other. This implies that the compatibility between the PC and K resin improves with adding K-g-MAH. Fig. 3b indicates that the addition of K-g-MAH into the PC/K blend leads to a significant increment in the storage modulus.
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Table 3 Fracture parameters for the PC/K blends with varied content of K resin PC/K (mass ratio)
we (kJ/m2 )
βwp (MJ/m3 )
R2
100/0 90/10 80/20 70/30
22.54 19.71 20.91 20.94
22.71 23.25 19.92 18.24
0.95 0.99 0.98 0.97
wf , is given by: wf =
Wf = we + βwp l lt
(3)
According to Eq. (3), plotting wf against ligament yield a straight line whose intercept with the wf -axis gives we and whose slope is βwp .
Fig. 3. tan δ and storage modulus vs. temperature plots for PC/K 80/20, PC/PC/K-g-MAH 80/15/5 blends.
3.4. Fracture toughness 3.4.1. Essential work of fracture (EWF) method In recent years, the essential work of fracture method originated with Broberg [22] and then developed by Cotterell [23–25], Karger-Kocsis [26–29] and Mai [30–34]. It is a method of quantifying the relative contributing effects in fracture. In this analysis, the total work of fracture (Wf ), or the energy absorbed in the fracture of a test specimen, can be divided into two basic components (Fig. 1), i.e. (a) the essential work of fracture (We ) performed in the inner fracture process zone (IFPZ); (b) the nonessential work of fracture (Wp ) that occurs in the outer plastic deformation zone (OPDZ). The total fracture work (Wf ) can be expressed by: Wf = We + Wp
(1)
When both the IFPZ and the OPDZ are contained in the ligament, then We is surface related and proportional to ligament length, l, the Wp is volume related and proportional to the square of the ligament length, l2 . Hence it can be written as We = we lt,
Wp = βwp l2 t
(2)
where we and βwp are the specific essential work of fracture and specific non-essential work of fracture, respectively. The parameter β is a geometry-dependent plastic zone shape factor and t is the specimen thickness. The specific total fracture work,
3.4.2. Variations of EWF parameters The load–displacement curves of DENT specimens for PC/K resin and PC/K/K-g-MAH blends during EWF tests as a function of ligament length are shown in Figs. 4 and 5, respectively. For all the blends, similar trends were observed. The load increased tardily with slight increase of the displacement before the definite upper point in the initial stage. After the peak, a slowly drop in load occurred with further increase of displacement and finally a rapid load drop at the end stage of the curves indicated the fracture of the specimens. Though the crack propagation displacements were not too big, the curves showed that the ligament yielded and the crack propagated in a stable manner. This is one of the necessary conditions which guaranteed the validity of EWF testing. On the other hand, the curves for each group of specimens at the same composition showed excellent reproducibility. The maximum load and the displacement to failure increased regularly with increasing ligament length. This is another crucial criterion for the application of EWF method, which ensures that the cracks propagated under similar stress conditions, being unchanged with the ligament length [35]. With a general comparison of the curves at the same ligament length, it was found that the maximum load decreased with increasing content of K resin, which indicated the decrease of strength as K resin particles were added into the polymer. However, the load peaks of PC/K/K-g-MAH blends with different K-g-MAH content were slightly higher than that of PC/K resin, indicating that incorporation of K-g-MAH improved the strength of the blends. The plot of wf versus l of PC/K and PC/K/K-g-MAH blends are shown in Fig. 6. It is notable that the wf –l diagrams gave very good linear relationships for all the materials studied in this work, as proved by the linear regression coefficient (R2 ) being in most cases higher than 0.95. The values of we and βwp obtained from the interception and slope of the straight lines extrapolated to zero ligament length, together with the regression coefficient, are listed in Tables 3 and 4. From the values listed in Table 3, it is clear that the we values for PC with different K resin content were lower than that of the pure PC, indicating that the crack resistance of the blends reduced. This may be caused by the incompatibility between
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Fig. 4. Load–displacement curves for PC/K blends at different mass ratio: (a) 100/0, (b) 90/10, (c) 80/20, (d) 70/30.
Fig. 5. Load–displacement curves for PC/K/K-g-MAH blends at different mass ratio: (a), 80/20/0; (b), 80/15/5; (c), 80/10/10; (d), 80/5/15.
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30.06 kJ/m2 . This is higher than that of PC/K resin (80/20) and even higher than that of pure PC, indicating that incorporation of K-g-MAH had remarkably positive effect on the fracture toughness, which may be caused by the reinforced adhesion between the PC matrix and the K resin particles, as K-g-MAH is finely dispersed on the interface. After that, the we values decreased with further increasing amount of K-g-MAH, revealing that an optimum content range for K-g-MAH existed, beyond which the excessive K-g-MAH would impair the toughening effect because it was not so finely dispersed. However, it was found that the βwp values of the PC/K/K-g-MAH blends changed little with increasing amount of K-g-MAH, indicating the effect of the incorporated of K-g-MAH on plastic energy was very small. 3.4.3. Constituting terms of essential and non-essential work In order to find out the energy distribution during the fracture process, a method of partition, between the specific work of fracture for yielding and for necking and subsequent fracture was employed, making the peak of the load–displacement curves as the cut-off point. As the composed terms were under plane stress, Eq. (3) can be rewritten as
Fig. 6. Specific work of fracture against ligament length for: (1) PC/K blends at different mass ratios: (a) 100/0; (b) 90/10; (c) 80/20; (d) 70/30; (2) PC/K/K-gMAH blends at different mass ratios: (a) 80/20/0; (b) 80/20/5; (c) 80/20/3; (d) 80/20/7.
the PC and K resin phase. The decreases of we values for PC/K resin (90/10) blends was evident. However, an increase instead of gradual reduction of the we values was observed with the further increase of K resin content, which may be related to the overlapping of the stress fields caused by more points of stress concentration, reducing the negative effect of the defects on we [36]. On the other hand, the βwp values for PC/K blends could also be seen from Table 3, it fluctuated appreciably with increasing K resin content which revealed that incorporation of K resin slightly influenced the plastic deformation during the fracture process. The variation of we for PC/K/K-g-MAH blends is listed in Table 4. A significant improvement in we appeared when the K-g-MAH was incorporated, such as in the PC/K/K-g-MAH blends at the mass ratio of 80/15/5, reaching a peak value of Table 4 Fracture parameters for the PC/K/K-g-MAH blends with varied content of K-gMAH PC/K/K-g-MAH (mass ratio)
we (kJ/m2 )
βwp (MJ/m3 )
R2
80/20/0 80/15/5 80/10/10 80/5/15
20.91 30.06 24.56 26.21
19.92 18.65 19.63 19.44
0.98 0.98 0.95 0.97
wf = wy + wn
(4)
wy = we,y + β wp,y l
(5)
wn = we,n + β wp,n l
(6)
where we,y and we,n , were the yielding and the necking and subsequent fracture related parts of the specific essential work of fracture, respectively; β wp,y and β wp,n were the yielding and the necking and subsequent fracture component of the nonspecific essential work of fracture, respectively. The results for splitting the essential and non-essential work of fracture as yielding and necking terms are given in Tables 5 and 6, which were obtained by plotting wy and wn versus l as shown in Figs. 7 and 8. The regression coefficient (R2 ) of PC/K resin kept above 0.94 and that of PC/K/K-g-MAH mostly above 0.92, which indicated that the partition method was also well applicable for these blends systems. From the results listed in Tables 5 and 6, it was clear that for all materials, the specific essential work of fracture for necking and subsequent fracture was all less than the corresponding term for yielding. The same result was found for the specific plastic work of fracture for yielding and the corresponding term for necking and subsequent fracture. These results indicated that both we and β wp,y in the whole fracture process for PC and the blends were mostly determined by the specific work of fracture for yielding. As shown in Table 5, the variation of we,y of the PC/K blends as K resin content increased was similar to that of we , and the characteristic decrease followed by the increase was even more evident. In spite of the small values, a remarkable decrease of we,n with increasing content of K resin was found for the PC/K blends and the we,y value was half that of pure PC when the K resin concentration exceeded 30 wt.%. Hence, the effect of K resin content on the crack resistance in the both yielding
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Table 5 Constituting terms of essential work of fracture for the PC/K blends with varied content of K resin PC/K (mass ratio)
we,y (kJ/m2 )
β wp,y (MJ/m3 )
R2 (for wy –l)
we,n (kJ/m2 )
β wp,n (MJ/m3 )
R2 (for wn –l)
100/0 90/10 80/20 70/30
18.65 17.32 19.06 19.08
18.37 19.57 15.56 15.28
0.97 0.98 0.96 0.97
3.85 2.40 1.84 1.90
4.34 3.68 4.36 2.96
0.95 0.99 0.94 0.98
Table 6 Constituting terms of essential work of fracture for the PC/K/K-g-MAH blends with varied of K-g-MAH PC/K/K-MAH (mass ratio)
we,y (kJ/m2 )
β wp,y (MJ/m3 )
R2 (for wy –l)
we,n (kJ/m2 )
β wp,n (MJ/m3 )
R2 (for wn –l)
80/20/0 80/15/5 80/10/10 80/5/15
19.07 28.39 23.51 23.37
15.56 13.47 16.11 16.16
0.96 0.94 0.98 0.98
1.83 1.67 1.06 2.83
4.36 5.13 3.49 3.27
0.94 0.98 0.97 0.92
stage and necking and subsequent fracture stage could not be neglected, but the effect of K resin content on the fracture toughness was mainly achieved through its influence on we,y . For the sake of blends with high fracture toughness, sufficient attention should be paid to the value of we,y . On the other hand, the influence of K resin content on β wp,y and β wp,n for the PC/K blends was similar to that on βwp , in other words, both of them
increased firstly and then decreased gradually with increasing K resin content. The result indicated that the variation of plastic energy absorbed in the stage of yielding and necking coincided with that in the whole fracture process. The we,y values of the PC/K/K-g-MAH blends with different K-g-MAH content were all higher than that of PC/K blends, as can be seen from Table 6. This indicated that incorporation of K-g-MAH effectively improved the crack resistance in the
Fig. 7. Yielding and necking specific work of fracture against ligament length for PC/K blends: (a) pure PC; (b) PC/K (90/10); (c) PC/K (80/20); (d) PC/K (70/30).
Fig. 8. Yielding and necking specific work of fracture against ligament length for PC/K/K-g-MAH blends: (a) PC/K/K-g-MAH (80/20/0); (b) PC/K/K-g-MAH (80/15/5); (c) PC/K/K-g-MAH (80/10/10); (d) PC/K/K-g-MAH (80/5/15).
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yielding stage. Comparing with the variation of we,y , the we,n values is very small. It decreased with a small amount of Kg-MAH, and then increased with further increase in K-g-MAH content, revealing that only an optimum content of K-g-MAH could improve the crack resistance in the stage of necking and subsequent fracture. Similar to the PC/K blends, the effect of K-g-MAH content on the fracture toughness for the PC/K/K-gMAH blends was mainly achieved through its influence on we,y . The influence of K-g-MAH content on β wp,y and β wp,n for the PC/K/K-g-MAH blends was also shown in Table 6. Comparing to the variation of we,y , the we,n values, the β wp,y and β wp,n values did not show significant effect on the content of K-gMAH. 4. Conclusions This work attempts to develop PC/K blends modified with Kg-MAH with good tensile properties, improved impact strength and fracture toughness. The results show that maximum impact strength can be achieved by blending 5 wt.% K-g-MAH into PC/K 80/15 blend. Static tensile and DMA measurements show that the addition of K-g-MAH increases the stiffness of PC/K blends. The result of SEM fractographs implies that Kg-MAH improves the interfacial bonding between PC and K resin. Finally, the essential work of fracture method reveals that a strong effect of composition on the EWF parameters of the blends, a significant improvement in we of PC/K blends appeared with K-g-MAH incorporated. References [1] S.C. Tjong, Y.Z. Meng, Mater. Res. Bull. 39 (2004) 1791. [2] E. Gattiglia, A. Turturro, E. Pedemonte, J. Appl. Polym. Sci. 41 (1990) 1411.
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