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polycarbonate blends
Materials Research Bulletin 39 (2004) 1791–1801
Structural-mechanical relationship of epoxy compatibilized polyamide 6/polycarbonate blends S.C. Tjong*, Y.Z. Meng Department of Physics and Materials Science, City University of Hong Kong Tat Chee Avenue, Kowloon, Hong Kong Accepted 16 December 2003
Abstract Polyamide 6 (PA6)/polycarbonate (PC) blends compatibilized with solid epoxy resin (bisphenol type-A) were prepared by extrusion followed by injection molding. The effects of epoxy resin on the microstructure, tensile, impact and compatibility of the PA6/PC blends were investigated. The results showed that both the tensile modulus and elongation at break of PA6/PC blends were inferior as compared to their parent polymers. This resulted from incompatibility between the PA6 and PC phases. SEM observation revealed that the introduction of 0.5 part per hundred (phr) epoxy resin into the PA6/PC75/25 blend yields a finer dispersion of PC phase in PA6 matrix. The boundaries between the PC domains and PA6 matrix became obscure with the incorporation of 1 phr epoxy resin. Such an improvement in compatibility was suggested to be resulted from the formation of in situ epoxy bridged PA6-PC block copolymer in the blend during compounding. Consequently, the tensile modulus, yield strength and impact strength of the PA6/PC 75/25 blend improved considerably with increasing epoxy content. # 2004 Elsevier Ltd. All rights reserved. Keywords: A. Polymers; C. Electron microscopy; D. Mechanical properties; D. Fracture; D. Microstructure
1. Introduction Polyamide 6 (PA6) is a semicrystalline thermoplastic used in a wide range of engineering applications because of its attractive combination of good processability, mechanical property and chemical resistance. However, it has high moisture absorption and low resistance to crack propagation in the presence of a notch. Polycarbonate (PC) is an amorphous polymer that exhibits several distinct properties such as transparency, dimensional stability, flame resistance, high heat distortion temperature, high unnotched impact strength and moisture insensitivity. PC also exhibits several *
Corresponding author. Tel.: þ852 2788 7831; fax: þ852 2788 7830. E-mail address: [email protected] (S.C. Tjong). 0025-5408/$ – see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2003.12.020
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shortcomings like poor solvent resistance, poor processability and notch sensitivity. 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]. 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. In the latter case, the segments of these copolymers can be chemically identical with those in the respective phases or adhered to one of the phases [2]. Some attempts have been reported to improve the compatibility of PA6/PC blends [3–5]. Gatttiglia et al. [3,4] reported that PA6-rich blends with a relatively more extensive interactions and better mechanical properties can be achieved by employing suitable processing conditions such as high temperatures and longer mixing times. Under these conditions, PC tends to react chemically with PA6, forming PA6-PC copolymer that act as an interfacial or compatibilizing agent. The disadvantage of this method is that long processing time is needed (45 min) to achieve good compatibilizing effect. Montaudo et al. [5] have synthesized several ABA and AB block copolymers of the type PC-PA6-PC and PC-PA6 through the reaction of monoamino- or diamino-terminated PA6 with PC in diphenylsulphone at 130 8C. They used such copolymers to compatibilize PA6/PC 75/25 blend. They reported that the size of PC dispersed particles decreases from ABA to AB compatibilized blends. However, the mechanical properties of compatibilized blends show little or no improvement with respect to uncompatibilized blend [5]. Horiuchi et al. have used a small amount of poly(styreneethylene butylene-styrene) (SEBS) and maleated SEBS (SEBS-g-MA) triblock copolymer to improve the mechanical performance of PA6/PC blends. The triblock copolymer acts as an impact modifier and compatibilizer for the PA6/PC blends [6]. Recently, low cost solid epoxy resin (bisphenol type-A) has been used by several workers to compatibilize the polyblends, e.g. PA6/polybutylene terephthalate (PBT), PC/poly(acrylonitrile-butadiene-styrene), PC/PBT/LCP, PP/PBT [7–10]. Solid epoxy resin is attractive in above-mentioned polyblends because the epoxide endgroups can react with endgroups of PA6, PBT or PC, forming in situ block copolymer that acts a compatibilizer [7,8,10]. This paper aims to study the compatibilizing effect of solid epoxy resin on the microstructural, mechanical and thermal properties of PA6/PC blends.
2. Experimental 2.1. Materials Polyamide 6 (Durethan B30S) and PC (Makrolon 2605) used in this study were supplied by Bayer (China) Ltd. Solid-state epoxy resin (NPES-909) with an epoxide equivalent weight of 2389 g/equiv. was kindly supplied by Nan Ya Plastics of Taiwan. 2.2. Blending The PC, PA6 pellets were dried in an oven at 100 8C over 24 h prior to compounding. Uncompatibilized PA6/PC blends were melt blended in a twin-screw Brabender Plasticorder with a temperature profile of 260, 260, 260, and 230 8C at 30 rpm. The extrudates were subsequently pelletized. The epoxy was added to a selected PA6/PC 75/25 (wt.%) blend. The epoxy contents added
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were 0.5 and 1.0 phr (based on the weight of PA6/PC 75/25 blend). The compatibilized PA6/PC/Epoxy (E) blends were also extruded in Brabender with a temperature profile of 290, 290, 290, and 250 8C at 20 rpm. The extrudates were also pelletized. Dog-bone shaped tensile bars (ASTM D-638) were injection molded from these pellets. The barrel zone temperatures of the injection molder were set at 265, 265 and 255 8C. 2.3. Mechanical measurements The tensile behavior of the blends was determined using an Instron tensile tester (model 4206) at room temperature under a cross-head speed of 5 mm/min. The gauge length of specimens was 57 mm. At least five specimens of each composition were tested and the average values reported. Izod impact specimens with dimensions of 63 mm 13 mm 3.2 mm were cut from the midsection of tensile bars. They were tested using a Ceast impact pendulum tester. At least seven specimens were tested and the average values reported. 2.4. Morphological observations The morphologies of the fractured surfaces of the blends were observed in a scanning electron microscope (SEM; Jeol JSM 820). The blend specimens were cryo-fractured in liquid nitrogen. They were then coated with a thin layer of gold prior to SEM observations. 2.5. Dynamic mechanical analysis Dynamic mechanical analysis (DMA) of the injection molded specimens were conducted using a TA DMA instrument (model 2910) at a fixed frequency of 1 Hz and an oscillation amplitude of 10 mm. The temperature studied ranged from 0 to 200 8C with a heating rate of 5 8C/min. 2.6. Torque measurements Torque values for the PA/PC 75/25 and PA6/PC/E 75/25/1.0 blends prepared by one-step compounding were determined using a Brabender Plasticorder batch mixer at 260 and 290 8C, respectively, under 35 rpm for 15 min. The mixer volume was 50 cm3. Material with 35 g was loaded into the batch during the test. For the purposes of comparison, torque measurements for the PA6/PC/E 75/25/1 blend specimens prepared by successive (two-step) blending of PA/epoxy (PA pre-treated with epoxy resin under the same conditions for PA/PC/epoxy one-step blending) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with PA6 were also carried at 260 8C.
3. Results and discussion 3.1. Mechanical behavior of uncompatibilized PA6/PC blends The tensile properties of uncompatibilized PA6/PC blends are summarized in Table 1. It can be seen that the yield strength of PA6/PC 90/10 blend is slightly higher than that of PA6. This is attributed to a
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Table 1 Static mechanical properties of uncompatibilized PA6/PC blends Specimen
Tensile modulus (MPa)
PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC
1240 1130 1230 1200 1160 1180 1508
100/0 90/10 75/25 50/50 25/75 10/90 0/100
38 35 31 34 30 33 61
Yield strength (MPa) 60.41 62.85 51.59 42.12 41.34 56.24 64.07
Strength at break (MPa)
2.5 2.1 1.8 1.6 0.9 2.1 2.4
56.87 57.88 50.49 55.23 41.46 56.25 64.39
2.2 1.8 2.1 1.9 1.5 1.6 1.9
Strain at break (%) 244.5 133.3 5.10 4.80 4.67 71.68 134.7
9.4 5.6 0.5 0.6 0.4 4.4 6.5
possible chemical interchain interaction occurs at this blend composition [1]. The stiffness, yield strength and strain at break of other PA6/PC blends are lower than their parent homopolymers. This results from incompatibility between the PA6 and PC phases of the blends. Fig. 1 shows the variation of Izod impact strength with PC content. Similarly, the PA6/PC 90/10 blend. It is apparent that the PA6/PC 90/10 blend exhibits much higher impact strength compares to PA6. Other PA6/PC blends exhibit low impact strength and fail in a brittle mode as expected. 3.2. Compatibility Fig. 2 shows the plots of tan d versus temperature for the PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends. The glass transition temperatures (Tgs) of PA6 and PC phases of the PA6/ PC/Epoxy blends are located at 58.95 and 129.5 8C, respectively, indicating that these two blend components are immiscible or incompatible. 900
Izod impact strength, J/m
800 700
rule of the mixture
600 500 400 300 200 100 0 0
20
40
60
80
100
PC content, mol% Fig. 1. Variation of Izod impact strength with PC content for PA6/PC blends.
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0.30
PA/PC 75/25 PA/PC/E 75/25/0.5 PA/PC/E 75/25/1.0
0.25
Tan Delta
0.20
0.15
0.10
0.05
0.00 0
50
100
150 o
Temperature, C Fig. 2. tan d vs. temperature plots for PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends.
The degree of miscibility (D) of a polymer blend can be defined as the ratio of the difference in Tgs of the components in the blend to the difference in Tgs of the pure polymers. Mathematically, it can be expressed as, B B Tg1 Tg2 P TP Tg1 g2
;
0
1.0
0.8
D value
D¼
0.6
PA6/PC blends without epoxy
0.4 0
20
40
60
PC content, mol% Fig. 3. Variation of D value with PC content.
80
100
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Table 2 Glass transition temperature, D value of PA6, PC and their blends Specimen
TgPC (8C)
TgPA (8C)
D ¼ (TgB1 TgB2 )/(TgP1 TgP2 )
PA6 PC PA6/PC 75/25 PA6/PC/E 25/25/0.5 PA6/PC/E 25/25/1.0
– 148.9 129.5 121.1 104.4
50.25 – 58.95 63.82 64.66
– – 0.715 0.581 0.403
B P where Tg1 and Tg1 are the Tgs of the component 1 of a blend, and pure polymer, respectively. For the PA6/PC blends, the D values are close to unity, indicating the immiscibility between the PA6 and PC (Fig. 3). The D values of the PA6, PC and PA6/PC 75/25 samples are listed in Table 2.
Fig. 4. SEM micrographs showing the morphology of (a) PA6/PC 75/25, (b) PA6/PC/E 75/25/0.5 and (c) PA6/PC/E 75/25/1.0 blends.
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In order to improve the compatibility between the PA6 and PC phases, 0.5 and 1.0 phr epoxy resin are added to the PA6/PC 75/25 blend. Fig. 2 reveals that the addition of 0.5 phr epoxy to the PA6/PC blend has resulted in the shift of Tgs of these two components towards each other. The Tgs and D values of the PA6/PC/Epoxy blends are also listed in Table 2. This Table reveals that the D value of the PA6/ PC/E 25/25/0.5 blend is reduced from 0.715 to 0.581 with the incorporation of a very small amount of epoxy resin. Addition of 1.0 phr epoxy resin into the blend results in a further reduction of D value. This implies that the compatibility between the PA6 and PC improves with increasing epoxy content. The epoxy additions can also lead to substantial microstructural changes in the PA6/PC blends. Fig. 4(a) is the SEM micrograph showing the cryo-fractured surface of uncompatibilized PA6/PC 75/25 blend. Apparently, PC disperses into large domains of 2.5 mm within the PA6 matrix. This is a typical morphology of incompatible blend. The addition of 0.5 phr epoxy resin gives rise to a finer dispersion of PC in PA6 matrix. The size of PC domains is reduced to 1 mm (Fig. 4(b)). As the epoxy resin content is increased to 1.0 phr, the PC domains and PA6 boundaries become more obscure, indicating a dramatic improvement in compatibility between the PA6 and PC (Fig. 4(c)). On the basis of these results, it is evident that the epoxy resin can react with the end groups of both PA6 and PC simultaneously, i.e., –COOH, –NH2 or –OH, thereby facilitating the formation of the in situ PA6-PC block copolymer during compounding. The possible reactions among them are depicted in Fig. 5. Such in situ copolymer appears to improve the compatibility between PA6 and PC considerably. Fig. 6 shows the plots of the torque versus mixing time for the PA6/PC 75/25 and PA6/PC/E 75/25/1.0 blends. The torque value is considered to be associated with the viscosity of the blends during compounding. For mixing time of 6 min and above, the torque value of the PA6/PC/E 75/25/1 blend is considerably higher than that of the uncompatibilized PA6/PC 75/25 blend. An increment in the viscosity implies that the epoxy acts effectively as a compatibilizing agent, leading to an increase in the molecular weight of the blends as depicted in Fig. 5. To ensure the in situ formation of epoxy bridge PA6/PC block copolymer during reactive compounding, torque measurements for the PA6/PC/E 75/25/1.0 blend specimens prepared by successive (two-step) blending of PA/epoxy (PA pre-treated with epoxy resin under the same conditions for PA/PC/epoxy one-step blending) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with
Fig. 5. Reaction scheme for epoxy with PA6 and PC.
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1.2
PA6/PC/E 75/25/1 PA6/PC 75/25 PA6/PC/E 75/25/1.0
Torque, Nm
1.0
0.8
0.6
0
2
4
6
8
10
12
14
16
Time, min Fig. 6. Torque vs. mixing time curves for the PA6/PC 75/25 (~) and PA6/PC/E 75/25/1.0 (*) blends at 260 8C. The curve for PA6/PC/E 75/25/1.0 blend at 290 8C is also shown for the purpose of comparison (!).
PA6 were carried out. Fig. 7 shows the plots of the torque versus mixing time for the PA6/PC/E 75/25/ 1.0 blend specimens prepared by successive blending techniques. It can be seen that the torque of PA6/ PC/E 75/25/1.0 blend prepared by mixing (PA6/epoxy) with PC increases gradually from the beginning up to 8 min. However, the torque level of PA6/PC/E 75/25/1.0 blend prepared by mixing (PC/epoxy)
Fig. 7. Torque vs. mixing time for the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of (a) PA/epoxy (PA pre-treated with epoxy resin) with PC and (b) PC/epoxy (PC pre-treated with epoxy resin) with PA6 at 260 8C.
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with PA6 increase sharply with time. Its values are considerably larger than those prepared by mixing (PA6/epoxy) with PC. This can be explained in terms of the reactivity of epoxy group with amine (– NH2) is substantially greater than with hydroxyl or phenolic OH [11]. For the PA6/PC/E 75/25/1.0 blend prepared from the mixing of (PA6/epoxy) with PC, the epoxy resin reacts readily with –NH2 of
Fig. 8. SEM micrographs showing the morphology of the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of (a) PA/epoxy (PA pre-treated with epoxy resin) with PC and (b) PC/epoxy (PC pre-treated with epoxy resin) with PA6.
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Table 3 Static tensile and impact properties of uncompatibilized and epoxy compatibilized PA6/PC blends Specimen
Tensile modulus (MPa)
Yield strength (MPa)
Strength at break (MPa)
Strain at break (%)
Impact Energy (J/m)
PA6/PC 75/25 PA6/PC/E 75/25/0.5 PA6/PC/E 75/25/1.0
1230 31 1370 36 1430 44
51.59 2.4 56.85 1.2 59.27 1.9
50.49 2.1 55.25 1.4 57.01 1.1
5.10 0.5 5.53 0.3 10.77 0.7
43.3 0.8 67.0 0.8 74.8 0.9
PA, at both terminal positions during compounding. Accordingly, the epoxy resin with two-expoxide terminal groups would have been consumed to a large extent with amine, leaving to small fraction of terminal groups has the chance to react with PC during successive blending. Thus, the torque values increase slowly with time. The block copolymer segments formed are likely to compatible with PC domains and to acts a compatibilizer for PA/PC. In contrast, only a fraction of epoxide terminal groups is consumed by reacting with –OH hydroxyl group of PC for the PA6/PC/E 75/25/1 blend prepared by mixing (PC/epoxy) with PA6. The remained epoxide terminal groups then react readily with –NH2 of PA, leading to a sharp increase in the torque level with time. Such increasing torque during reactive mixing is indicative of the formation of graft copolymers. Fig. 8(a)–(b) show the SEM micrographs of the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of PA/epoxy (PA pre-treated with epoxy resin) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with PA6, respectively. It is apparent that the boundaries between PC domains and PA6 matrix are obscured by the epoxy bridge PA6/PC block copolymer formed during successive compounding. The morphology of the PA6/PC/E 75/25/1.0 blend prepared by two-step mixing is similar to that fabricated by one-step blending (Fig. 4(c)). 16000 14000
Storage modulus, MPa
12000
PA/PC/E 75/25/0.5 PA/PC 75/25 PA/PC/E 75/25/1.0
10000 8000 6000 4000 2000 0 0
50
100
150
200
o
Temperature, C Fig. 9. Storage modulus vs. temperature plots for the PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends.
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3.3. Mechanical properties of compatibilized blends The tensile and impact properties of epoxy compatibilized blends are listed in Table 3. Compares to uncompatibilized PA6/PC 75/25 blend, the beneficial effect of the epoxy addition on the tensile modulus, yield strength and strain at break is evident. Moreover, the impact energy of compatibilized blends also improves considerably with increasing epoxy content. Addition of 1 phr epoxy to the PA6/ PC 75/25 blend also leads to a significant increment in the storage modulus from 0 to 50 8C (Fig. 9).
4. Conclusions This work aims to study the compatibilizing effect of solid epoxy resin of bisphenol-type A on the microstructural, tensile, impact and thermal properties of PA6/PC 75/25 blend. The results show that the solid epoxy resin is beneficial in enhancing the compatibility between PA6 and PC phases of the PA6/PC 75/25 blend on the basis of the SEM examinations and DMA results. Enhancement in the compatibility is suggested to be associated with the formation of in situ epoxy bridged PA6-PC block copolymer in the blend during compounding. Consequently, the tensile modulus, yield strength and impact strength of the PA6/PC 75/25 blend improves considerably with increasing epoxy content.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
E. Gattiglia, A. Turturro, E. Pedemonte, J. Appl. Polym. Sci. 41 (1990) 1411–1423. D.R. Paul, C.B. Bucknall, Polymer Blends, vol. 1, Wiley, New York, 2000. E. Gattiglia, A. Turturro, F.P. Lamantia, A. Valenza, Polym. Bull. 21 (1989) 47–52. E. Gattiglia, A. Turturro, F.P. Lamantia, A. Valenza, J. Appl. Polym. Sci. 46 (1992) 1887–1897. G. Montaudo, C. Puglisi, F. Samperi, F.P. Lamantia, J. Polym. Sci. Part A: Polym. Chem. 34 (1996) 1283–1290. S. Horiuchi, N. Matchariyakul, K. Yase, T. Kitano, H.K. Choi, Y.M. Lee, Polymer 38 (1997) 59–78. C.C. Huang, F.C. Chang, Polymer 38 (1997) 4287–4293. S.C. Tjong, Y.Z. Meng, J. Appl. Polym. Sci. 74 (1999) 1827–1835. S.C. Tjong, Y.Z. Meng, Eur. Polym. J. 36 (2000) 123–129. R.M. Holsti-Mettinen, M.T. Heino, J.V. Seppala, J. Appl. Polym. Sci. 57 (1995) 573–586. C.C. Huang, F.C. Chang, Polymer 38 (1997) 2135–2141.
Structural-mechanical relationship of epoxy compatibilized polyamide 6/polycarbonate blends S.C. Tjong*, Y.Z. Meng Department of Physics and Materials Science, City University of Hong Kong Tat Chee Avenue, Kowloon, Hong Kong Accepted 16 December 2003
Abstract Polyamide 6 (PA6)/polycarbonate (PC) blends compatibilized with solid epoxy resin (bisphenol type-A) were prepared by extrusion followed by injection molding. The effects of epoxy resin on the microstructure, tensile, impact and compatibility of the PA6/PC blends were investigated. The results showed that both the tensile modulus and elongation at break of PA6/PC blends were inferior as compared to their parent polymers. This resulted from incompatibility between the PA6 and PC phases. SEM observation revealed that the introduction of 0.5 part per hundred (phr) epoxy resin into the PA6/PC75/25 blend yields a finer dispersion of PC phase in PA6 matrix. The boundaries between the PC domains and PA6 matrix became obscure with the incorporation of 1 phr epoxy resin. Such an improvement in compatibility was suggested to be resulted from the formation of in situ epoxy bridged PA6-PC block copolymer in the blend during compounding. Consequently, the tensile modulus, yield strength and impact strength of the PA6/PC 75/25 blend improved considerably with increasing epoxy content. # 2004 Elsevier Ltd. All rights reserved. Keywords: A. Polymers; C. Electron microscopy; D. Mechanical properties; D. Fracture; D. Microstructure
1. Introduction Polyamide 6 (PA6) is a semicrystalline thermoplastic used in a wide range of engineering applications because of its attractive combination of good processability, mechanical property and chemical resistance. However, it has high moisture absorption and low resistance to crack propagation in the presence of a notch. Polycarbonate (PC) is an amorphous polymer that exhibits several distinct properties such as transparency, dimensional stability, flame resistance, high heat distortion temperature, high unnotched impact strength and moisture insensitivity. PC also exhibits several *
Corresponding author. Tel.: þ852 2788 7831; fax: þ852 2788 7830. E-mail address: [email protected] (S.C. Tjong). 0025-5408/$ – see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2003.12.020
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shortcomings like poor solvent resistance, poor processability and notch sensitivity. 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]. 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. In the latter case, the segments of these copolymers can be chemically identical with those in the respective phases or adhered to one of the phases [2]. Some attempts have been reported to improve the compatibility of PA6/PC blends [3–5]. Gatttiglia et al. [3,4] reported that PA6-rich blends with a relatively more extensive interactions and better mechanical properties can be achieved by employing suitable processing conditions such as high temperatures and longer mixing times. Under these conditions, PC tends to react chemically with PA6, forming PA6-PC copolymer that act as an interfacial or compatibilizing agent. The disadvantage of this method is that long processing time is needed (45 min) to achieve good compatibilizing effect. Montaudo et al. [5] have synthesized several ABA and AB block copolymers of the type PC-PA6-PC and PC-PA6 through the reaction of monoamino- or diamino-terminated PA6 with PC in diphenylsulphone at 130 8C. They used such copolymers to compatibilize PA6/PC 75/25 blend. They reported that the size of PC dispersed particles decreases from ABA to AB compatibilized blends. However, the mechanical properties of compatibilized blends show little or no improvement with respect to uncompatibilized blend [5]. Horiuchi et al. have used a small amount of poly(styreneethylene butylene-styrene) (SEBS) and maleated SEBS (SEBS-g-MA) triblock copolymer to improve the mechanical performance of PA6/PC blends. The triblock copolymer acts as an impact modifier and compatibilizer for the PA6/PC blends [6]. Recently, low cost solid epoxy resin (bisphenol type-A) has been used by several workers to compatibilize the polyblends, e.g. PA6/polybutylene terephthalate (PBT), PC/poly(acrylonitrile-butadiene-styrene), PC/PBT/LCP, PP/PBT [7–10]. Solid epoxy resin is attractive in above-mentioned polyblends because the epoxide endgroups can react with endgroups of PA6, PBT or PC, forming in situ block copolymer that acts a compatibilizer [7,8,10]. This paper aims to study the compatibilizing effect of solid epoxy resin on the microstructural, mechanical and thermal properties of PA6/PC blends.
2. Experimental 2.1. Materials Polyamide 6 (Durethan B30S) and PC (Makrolon 2605) used in this study were supplied by Bayer (China) Ltd. Solid-state epoxy resin (NPES-909) with an epoxide equivalent weight of 2389 g/equiv. was kindly supplied by Nan Ya Plastics of Taiwan. 2.2. Blending The PC, PA6 pellets were dried in an oven at 100 8C over 24 h prior to compounding. Uncompatibilized PA6/PC blends were melt blended in a twin-screw Brabender Plasticorder with a temperature profile of 260, 260, 260, and 230 8C at 30 rpm. The extrudates were subsequently pelletized. The epoxy was added to a selected PA6/PC 75/25 (wt.%) blend. The epoxy contents added
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were 0.5 and 1.0 phr (based on the weight of PA6/PC 75/25 blend). The compatibilized PA6/PC/Epoxy (E) blends were also extruded in Brabender with a temperature profile of 290, 290, 290, and 250 8C at 20 rpm. The extrudates were also pelletized. Dog-bone shaped tensile bars (ASTM D-638) were injection molded from these pellets. The barrel zone temperatures of the injection molder were set at 265, 265 and 255 8C. 2.3. Mechanical measurements The tensile behavior of the blends was determined using an Instron tensile tester (model 4206) at room temperature under a cross-head speed of 5 mm/min. The gauge length of specimens was 57 mm. At least five specimens of each composition were tested and the average values reported. Izod impact specimens with dimensions of 63 mm 13 mm 3.2 mm were cut from the midsection of tensile bars. They were tested using a Ceast impact pendulum tester. At least seven specimens were tested and the average values reported. 2.4. Morphological observations The morphologies of the fractured surfaces of the blends were observed in a scanning electron microscope (SEM; Jeol JSM 820). The blend specimens were cryo-fractured in liquid nitrogen. They were then coated with a thin layer of gold prior to SEM observations. 2.5. Dynamic mechanical analysis Dynamic mechanical analysis (DMA) of the injection molded specimens were conducted using a TA DMA instrument (model 2910) at a fixed frequency of 1 Hz and an oscillation amplitude of 10 mm. The temperature studied ranged from 0 to 200 8C with a heating rate of 5 8C/min. 2.6. Torque measurements Torque values for the PA/PC 75/25 and PA6/PC/E 75/25/1.0 blends prepared by one-step compounding were determined using a Brabender Plasticorder batch mixer at 260 and 290 8C, respectively, under 35 rpm for 15 min. The mixer volume was 50 cm3. Material with 35 g was loaded into the batch during the test. For the purposes of comparison, torque measurements for the PA6/PC/E 75/25/1 blend specimens prepared by successive (two-step) blending of PA/epoxy (PA pre-treated with epoxy resin under the same conditions for PA/PC/epoxy one-step blending) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with PA6 were also carried at 260 8C.
3. Results and discussion 3.1. Mechanical behavior of uncompatibilized PA6/PC blends The tensile properties of uncompatibilized PA6/PC blends are summarized in Table 1. It can be seen that the yield strength of PA6/PC 90/10 blend is slightly higher than that of PA6. This is attributed to a
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Table 1 Static mechanical properties of uncompatibilized PA6/PC blends Specimen
Tensile modulus (MPa)
PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC PA6/PC
1240 1130 1230 1200 1160 1180 1508
100/0 90/10 75/25 50/50 25/75 10/90 0/100
38 35 31 34 30 33 61
Yield strength (MPa) 60.41 62.85 51.59 42.12 41.34 56.24 64.07
Strength at break (MPa)
2.5 2.1 1.8 1.6 0.9 2.1 2.4
56.87 57.88 50.49 55.23 41.46 56.25 64.39
2.2 1.8 2.1 1.9 1.5 1.6 1.9
Strain at break (%) 244.5 133.3 5.10 4.80 4.67 71.68 134.7
9.4 5.6 0.5 0.6 0.4 4.4 6.5
possible chemical interchain interaction occurs at this blend composition [1]. The stiffness, yield strength and strain at break of other PA6/PC blends are lower than their parent homopolymers. This results from incompatibility between the PA6 and PC phases of the blends. Fig. 1 shows the variation of Izod impact strength with PC content. Similarly, the PA6/PC 90/10 blend. It is apparent that the PA6/PC 90/10 blend exhibits much higher impact strength compares to PA6. Other PA6/PC blends exhibit low impact strength and fail in a brittle mode as expected. 3.2. Compatibility Fig. 2 shows the plots of tan d versus temperature for the PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends. The glass transition temperatures (Tgs) of PA6 and PC phases of the PA6/ PC/Epoxy blends are located at 58.95 and 129.5 8C, respectively, indicating that these two blend components are immiscible or incompatible. 900
Izod impact strength, J/m
800 700
rule of the mixture
600 500 400 300 200 100 0 0
20
40
60
80
100
PC content, mol% Fig. 1. Variation of Izod impact strength with PC content for PA6/PC blends.
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0.30
PA/PC 75/25 PA/PC/E 75/25/0.5 PA/PC/E 75/25/1.0
0.25
Tan Delta
0.20
0.15
0.10
0.05
0.00 0
50
100
150 o
Temperature, C Fig. 2. tan d vs. temperature plots for PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends.
The degree of miscibility (D) of a polymer blend can be defined as the ratio of the difference in Tgs of the components in the blend to the difference in Tgs of the pure polymers. Mathematically, it can be expressed as, B B Tg1 Tg2 P TP Tg1 g2
;
0
1.0
0.8
D value
D¼
0.6
PA6/PC blends without epoxy
0.4 0
20
40
60
PC content, mol% Fig. 3. Variation of D value with PC content.
80
100
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Table 2 Glass transition temperature, D value of PA6, PC and their blends Specimen
TgPC (8C)
TgPA (8C)
D ¼ (TgB1 TgB2 )/(TgP1 TgP2 )
PA6 PC PA6/PC 75/25 PA6/PC/E 25/25/0.5 PA6/PC/E 25/25/1.0
– 148.9 129.5 121.1 104.4
50.25 – 58.95 63.82 64.66
– – 0.715 0.581 0.403
B P where Tg1 and Tg1 are the Tgs of the component 1 of a blend, and pure polymer, respectively. For the PA6/PC blends, the D values are close to unity, indicating the immiscibility between the PA6 and PC (Fig. 3). The D values of the PA6, PC and PA6/PC 75/25 samples are listed in Table 2.
Fig. 4. SEM micrographs showing the morphology of (a) PA6/PC 75/25, (b) PA6/PC/E 75/25/0.5 and (c) PA6/PC/E 75/25/1.0 blends.
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In order to improve the compatibility between the PA6 and PC phases, 0.5 and 1.0 phr epoxy resin are added to the PA6/PC 75/25 blend. Fig. 2 reveals that the addition of 0.5 phr epoxy to the PA6/PC blend has resulted in the shift of Tgs of these two components towards each other. The Tgs and D values of the PA6/PC/Epoxy blends are also listed in Table 2. This Table reveals that the D value of the PA6/ PC/E 25/25/0.5 blend is reduced from 0.715 to 0.581 with the incorporation of a very small amount of epoxy resin. Addition of 1.0 phr epoxy resin into the blend results in a further reduction of D value. This implies that the compatibility between the PA6 and PC improves with increasing epoxy content. The epoxy additions can also lead to substantial microstructural changes in the PA6/PC blends. Fig. 4(a) is the SEM micrograph showing the cryo-fractured surface of uncompatibilized PA6/PC 75/25 blend. Apparently, PC disperses into large domains of 2.5 mm within the PA6 matrix. This is a typical morphology of incompatible blend. The addition of 0.5 phr epoxy resin gives rise to a finer dispersion of PC in PA6 matrix. The size of PC domains is reduced to 1 mm (Fig. 4(b)). As the epoxy resin content is increased to 1.0 phr, the PC domains and PA6 boundaries become more obscure, indicating a dramatic improvement in compatibility between the PA6 and PC (Fig. 4(c)). On the basis of these results, it is evident that the epoxy resin can react with the end groups of both PA6 and PC simultaneously, i.e., –COOH, –NH2 or –OH, thereby facilitating the formation of the in situ PA6-PC block copolymer during compounding. The possible reactions among them are depicted in Fig. 5. Such in situ copolymer appears to improve the compatibility between PA6 and PC considerably. Fig. 6 shows the plots of the torque versus mixing time for the PA6/PC 75/25 and PA6/PC/E 75/25/1.0 blends. The torque value is considered to be associated with the viscosity of the blends during compounding. For mixing time of 6 min and above, the torque value of the PA6/PC/E 75/25/1 blend is considerably higher than that of the uncompatibilized PA6/PC 75/25 blend. An increment in the viscosity implies that the epoxy acts effectively as a compatibilizing agent, leading to an increase in the molecular weight of the blends as depicted in Fig. 5. To ensure the in situ formation of epoxy bridge PA6/PC block copolymer during reactive compounding, torque measurements for the PA6/PC/E 75/25/1.0 blend specimens prepared by successive (two-step) blending of PA/epoxy (PA pre-treated with epoxy resin under the same conditions for PA/PC/epoxy one-step blending) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with
Fig. 5. Reaction scheme for epoxy with PA6 and PC.
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PA6/PC/E 75/25/1 PA6/PC 75/25 PA6/PC/E 75/25/1.0
Torque, Nm
1.0
0.8
0.6
0
2
4
6
8
10
12
14
16
Time, min Fig. 6. Torque vs. mixing time curves for the PA6/PC 75/25 (~) and PA6/PC/E 75/25/1.0 (*) blends at 260 8C. The curve for PA6/PC/E 75/25/1.0 blend at 290 8C is also shown for the purpose of comparison (!).
PA6 were carried out. Fig. 7 shows the plots of the torque versus mixing time for the PA6/PC/E 75/25/ 1.0 blend specimens prepared by successive blending techniques. It can be seen that the torque of PA6/ PC/E 75/25/1.0 blend prepared by mixing (PA6/epoxy) with PC increases gradually from the beginning up to 8 min. However, the torque level of PA6/PC/E 75/25/1.0 blend prepared by mixing (PC/epoxy)
Fig. 7. Torque vs. mixing time for the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of (a) PA/epoxy (PA pre-treated with epoxy resin) with PC and (b) PC/epoxy (PC pre-treated with epoxy resin) with PA6 at 260 8C.
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with PA6 increase sharply with time. Its values are considerably larger than those prepared by mixing (PA6/epoxy) with PC. This can be explained in terms of the reactivity of epoxy group with amine (– NH2) is substantially greater than with hydroxyl or phenolic OH [11]. For the PA6/PC/E 75/25/1.0 blend prepared from the mixing of (PA6/epoxy) with PC, the epoxy resin reacts readily with –NH2 of
Fig. 8. SEM micrographs showing the morphology of the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of (a) PA/epoxy (PA pre-treated with epoxy resin) with PC and (b) PC/epoxy (PC pre-treated with epoxy resin) with PA6.
1800
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Table 3 Static tensile and impact properties of uncompatibilized and epoxy compatibilized PA6/PC blends Specimen
Tensile modulus (MPa)
Yield strength (MPa)
Strength at break (MPa)
Strain at break (%)
Impact Energy (J/m)
PA6/PC 75/25 PA6/PC/E 75/25/0.5 PA6/PC/E 75/25/1.0
1230 31 1370 36 1430 44
51.59 2.4 56.85 1.2 59.27 1.9
50.49 2.1 55.25 1.4 57.01 1.1
5.10 0.5 5.53 0.3 10.77 0.7
43.3 0.8 67.0 0.8 74.8 0.9
PA, at both terminal positions during compounding. Accordingly, the epoxy resin with two-expoxide terminal groups would have been consumed to a large extent with amine, leaving to small fraction of terminal groups has the chance to react with PC during successive blending. Thus, the torque values increase slowly with time. The block copolymer segments formed are likely to compatible with PC domains and to acts a compatibilizer for PA/PC. In contrast, only a fraction of epoxide terminal groups is consumed by reacting with –OH hydroxyl group of PC for the PA6/PC/E 75/25/1 blend prepared by mixing (PC/epoxy) with PA6. The remained epoxide terminal groups then react readily with –NH2 of PA, leading to a sharp increase in the torque level with time. Such increasing torque during reactive mixing is indicative of the formation of graft copolymers. Fig. 8(a)–(b) show the SEM micrographs of the PA6/PC/E 75/25/1.0 blend specimens prepared by successive blending of PA/epoxy (PA pre-treated with epoxy resin) with PC, and PC/epoxy (PC pre-treated with epoxy resin) with PA6, respectively. It is apparent that the boundaries between PC domains and PA6 matrix are obscured by the epoxy bridge PA6/PC block copolymer formed during successive compounding. The morphology of the PA6/PC/E 75/25/1.0 blend prepared by two-step mixing is similar to that fabricated by one-step blending (Fig. 4(c)). 16000 14000
Storage modulus, MPa
12000
PA/PC/E 75/25/0.5 PA/PC 75/25 PA/PC/E 75/25/1.0
10000 8000 6000 4000 2000 0 0
50
100
150
200
o
Temperature, C Fig. 9. Storage modulus vs. temperature plots for the PA6/PC 75/25, PA6/PC/E 75/25/0.5 and PA6/PC/E 75/25/1.0 blends.
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3.3. Mechanical properties of compatibilized blends The tensile and impact properties of epoxy compatibilized blends are listed in Table 3. Compares to uncompatibilized PA6/PC 75/25 blend, the beneficial effect of the epoxy addition on the tensile modulus, yield strength and strain at break is evident. Moreover, the impact energy of compatibilized blends also improves considerably with increasing epoxy content. Addition of 1 phr epoxy to the PA6/ PC 75/25 blend also leads to a significant increment in the storage modulus from 0 to 50 8C (Fig. 9).
4. Conclusions This work aims to study the compatibilizing effect of solid epoxy resin of bisphenol-type A on the microstructural, tensile, impact and thermal properties of PA6/PC 75/25 blend. The results show that the solid epoxy resin is beneficial in enhancing the compatibility between PA6 and PC phases of the PA6/PC 75/25 blend on the basis of the SEM examinations and DMA results. Enhancement in the compatibility is suggested to be associated with the formation of in situ epoxy bridged PA6-PC block copolymer in the blend during compounding. Consequently, the tensile modulus, yield strength and impact strength of the PA6/PC 75/25 blend improves considerably with increasing epoxy content.
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