Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber

Transcription

1 Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang* Research Institute of Polymer Materials, Shanghai Jiao Tong University, Shanghai , China Received: 9 July 2002 Accepted: November 2002 ABSTRACT Vulcanizates of blends of ethylene-propylene-diene rubber (EPDM) and polyamide (PA) copolymer were prepared by reactive compatibilization. A reactive route was employed to compatibilize these blends by the addition of maleic anhydride EPDM (MAH-g- EPDM). In this paper, the influence of compatibilizers, crosslinking agents, and blend composition on the mechanical properties of the blends were investigated. The morphologies of the blends were determined by scanning electron microscopy. It was found that the addition of MAH-g-EPDM reduced the particle size of the dispersed phase remarkably. The stability of the blend was measured by thermal ageing at high temperature in the presence of compatibilizer. Both dynamic mechanical thermal analysis and differential scanning calorimetry experiments were carried out to investigate the effect of MAH-g-EPDM addition on the T g s of the blend components. The addition of PA copolymer caused significant improvement in the tensile properties of these blends.. INTRODUCTION PAs have been used for numerous engineering applications, since they became available as moulding and extrusion materials. Some of their favourable properties are high strength and modulus, good chemical and abrasion resistance, high melting point, low coefficient of friction and toughness. Since the 960s numerous efforts have resulted in hundreds of patents describing toughened PA compositions with improved ductility. Usually, the toughened PAs are obtained by melt blending PA with acid- and anhydride-containing elastomers. Nowadays, most producers have a rubber-toughened grade in their product range. Until now, most of the research effort when studying PA/rubber blends was directed towards improving the impact properties of PA. In fact, blends of rubber/pa blends can be sorted into three groups according to their composition or processing technology. First, the toughness of PA is improved by properly blending these glassy polymers with small amounts of suitable rubbery polymers. Important reviews have described extensively the *Corresponding author: address: yxzhang@sjtu.edu.cn. Fax: +86-(02) technology of the rubber toughening of brittle plastics,2. Second, PA and a rubber are melt-mixed in presence of rubber crosslinking agents to prepare a thermoplastic vulcanizate (TPV). Using a suitable compatibilizer and crosslinking the rubber phase during melt-mixing, it is possible to disperse up to 60 wt% rubber in the PA matrix and to improve the mechanical properties markedly 3-7. These TPVs combine good elastic properties with thermoplastic processability. The original investigations of dynamic vulcanization of TPVs were performed on polypropylene and various rubber compositions, and were initiated by Fisher 8 and Coran et al 9. Third, reinforcing rubber by melt mixing with PA is a new research subject in this field. Only a few studies have been reported on PA reinforced EPDM 0-2. EPDM is well known for its excellent heat resistance, attributed to its saturated backbone structure and nonpolarity. But the poor mechanical properties of EPDM vulcanizates, especially those cured by sulfur, are obstacles in the way of EPDM expanding its application. It is difficult to reinforce EPDM with high melting point PAs such as PA 6 or PA 66 because of differences in processing temperature. However, the PA terpolymer has a low melting temperature, and a T g of C. These characteristics are suitable Polymers & Polymer Composites, Vol., No. 3,

2 Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang for PA copolymer blending with EPDM. Maleated elastomers have been widely used in rubber toughening PA research. In this work, several maleated elastomers and CPE were used as compatibilizers. All of them contain functionalities that can form graft copolymers in-situ during melt mixing with PA. The pioneering work of EPDM reinforced by PA and carbon black had been reported by Luo 0. But to our knowledge EPDM reinforced totally by PA has not been researched in detail. The purpose of the present study is to find out a suitable method that can reinforce EPDM by PA. The experimental results indicate that the vulcanized EPDM/PA blends, when made with a suitable compatibilizer, display attractive mechanical properties and heat resistance. 2. EXPERIMENTAL 2. Materials EPDM, EP4045 was produced by the Jilin Petroleum Chemical Co., Ltd., China, having a diene component 5-ethylidene-2-norbornene (ENB) as third monomer. The propylene content was 35.9 mol%, and Mooney viscosity, ML(+4) at 00 C, 42. Copolymer of PA 00/66/6 (70 wt% PA 00, 20 wt% PA 66, 0 wt% PA 6) with melting point 50 C was produced by Shanghai Celluloid Factory. Maleic anhydride grafted ethylene-propylene rubber (MAH-G-EPR Exxelor VA 80, grafting degree 0.7%) was produced by Exxon Co., Ltd., USA. Maleic anhydride grafted EPDM (MAH- G-EPDM, CMG9802, grafting degree 0.8%) was produced by Sunrise Chemical Cooperation, China. Chlorinated polyethylene (CPE) with a chlorine content of 36% was a product of the Jiangsu Dongtai Chemical Factory, China. Carboxylated nitrile rubber (XNBR, Krynac X7.50) was produced by Bayer Co. Ltd., Germany. Carbon black HAF N330 was provided by Cabot Shanghai Co., Ltd., China. Zinc oxide (ZnO), stearic acid (SA), tetramethylthiuram disulfide (TMTD), N, N -m-phenylene bismaleimide (HVA-2), dicumyl peroxide (DCP), and dibenzothiazyl disulfide (MBTS) and sulfur were used as received. 2.2 Blend Preparation Prior to all the melt processing steps, PA was dried in a vacuum oven at 80 C for at least 2 h. The blends of EPDM/PA/MAH-g-EPDM were prepared at 80 C and 60 rpm in the mixing chamber of a Haake Rheometer RC90. One minute after melting the MAHg-EPDM/PA blends in the chamber, EPDM was added. 4 minutes later, the batch was dumped. The batch was passed once through a cold roll mill to give a sheet about 2 mm in thickness. After cooling to room temperature, the batch was reloaded on the cold mill and all the crosslinking agents were incorporated into it to give a blend. In these experiments, both EPDM and compatibilizers were used as rubber components and so their total content was 00 phr. 2.3 Measurements 2.3. Cure Characteristics Cure characteristics were measured over a 5 min period at 60 C, 70 C, 80 C respectively using a moving-die rheometer (UCAN 2030 from Taiwan) according to ASTM standard D Mechanical Testing The mechanical properties of vulcanized EPDM/ MAH-g-EPDM/PA blends were measured according to ASTM standard D42 using an Instron 4465 tensile tester. Shore A hardness was determined using a Shore A durometer according to ASTM standard D Scanning Electron Microscopy The blend samples were cryogenically fractured in liquid nitrogen into two pieces or broken in tension into two pieces at room temperature on the tensile tester. To dissolve the dispersed phase, the fracture surfaces were etched in formic acid for 24 h. After coating with gold, fractured surface of the samples were observed using a Hitachi S-250 scanning electron microscope. Micrographs were obtained at magnifications of around Differential Scanning Clorimetry A Perkin-Elmer DSC Pyris was used to study the thermal behavior. The glass transition temperature, Tg, was obtained by heating a sample over a temperature range from - 60 C to 00 C at 20 C/min Dynamic Mechanical Properties Dynamic mechanical properties of the vulcanized blends were determined on a Rheometric Scientific instrument DMTA IV. The samples were all tested under a multiwave dynamic tension mode at a frequency of 0Hz. The temperature range of the measurements was from 00 to 00 C at a heating rate of 3 C/min. The specimen dimensions were 2 x 4 x mm. 80 Polymers & Polymer Composites, Vol., No. 3, 2003

3 Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber 3. RESULTS AND DISCUSSION 3. Cure Characteristics EPDM can be cured either by sulfur or a peroxide cross-linking system. To determine the optimum rheometer cure times or T 90 values at given temperature. EPDM was cured by sulfur and DCP at 60 C, 70 C and 80 C, respectively. Figure shows the experimental results from the two curing systems. The T 90 was of EPDM cured by sulfur at 60 C, 70 C and 80 C were 0, 7.5, 4.4 min respectively. The T 90 cured by of EPDM cured by DCP at 60 0 C, 70 0 C and 80 C were 7.5, 4.0,.2 min respectively. The test samples of EPDM/PA blends were cured by the sulfur cure system at 60 C for 2min and by the DCP cure system at 60 C for 0 min. Figure Cure characteristics for sulfur and peroxide crosslinking system. Formulation: EPDM 86, MAH-g-EPDM 4, PA 40, a) S 2, TMTD, DM 0.5, SA 2, ZnO 5 b) S, DCP 4, HVA-2, SA, ZnO 5 (a) (b) Polymers & Polymer Composites, Vol., No. 3,

4 Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang 3.2 Effects of Compatibilizers and Crosslinking Agents It is well known that EPDM and PA are immiscible. To achieve a fine dispersion of the PA in the EPDM matrix, it is necessary to compatibilize the blend by adding a compatibilizer. To search for suitable compatibilizers, a series of compositions was investigated. Several compatibilizers, such as MAHg-EPR, MAH-g-EPDM, CPE, MAH-g-POE and XNBR rubber were used as compatibilizers in EPDM/PA blends. The effects of the compatibilizer on the mechanical properties of EPDM/PA vulcanizates are shown in Table. The vulcanized EPDM/PA blends compatibilized by MAH-g-EPR, MAH-g-EPDM and CPE all show improved mechanical properties compared with the vulcanized EPDM/PA blends without compatibilizer when EPDM was cured by sulfur. But MAH-g-EPDM and CPE led to the best mechanical properties. In this paper, we reported mainly the study on EPDM/ MAH-g-EPDM/PA blends. The mechanical properties of the EPDM/PA blends with the above mentioned compatibilizers and cured by DCP were also measured. The results are shown in Table 2. The blends compatibilized by MAH-g-EPR, MAH-g-EPDM, MAH-g-POE and XNBR rubber show improved mechanical properties. However, the blends cured by DCP are compared with the uncompatibilized samples cured by sulfur and the results are shown in Table. The tensile strength increases only about 50%. When the blends were cured with DCP, the blends had a relatively high elongation at break (about 450%). When they were cured by sulfur vulcanizing agents, the blends had a relatively high tensile strength (about 4 MPa). The results also indicate that there is a matching relationship between compatibilizer and crosslinking agents. 3.3 Effect of MAH-g-EPDM Content on the Mechanical Properties of the Vulcanized EPDM/ MAH-g-EPDM /PA Blends The effect of the amount of MAH-g-EPDM as a compatibilizer on the mechanical properties of the vulcanized EPDM/MAH-g-EPDM/PA blends is shown in Figure 2. The tensile strength and elongation at break increased with increasing MAH-g-EPDM content up to 20 phr, followed by a decrease at higher MAH-g-EPDM contents. The results indicate that tensile set at break and hardness increased with MAH-g-EPDM content in the range of 0 to 60 phr in the EPDM/PA blends. In this blend system, the compatibilization is considered to occur through chemical bonds between MAH-g- Table Effects of compatibilizers on mechanical properties of the vulcanized EPDM/PA blends Compatibilizer MAH-g-EPR MAH-g-EPDM CPE XNBR - Tensile strength (MPa) Elongation at break (%) Tensile set at break (%) Shore A hardness Formulation: EPDM 86, compatibilizer 4, PA 40, S 2, TMTD, MBTS 0.5, SA 2, ZnO 5 phr Table 2 Effect of compatibilizers on mechanical properties of the vulcanized EPDM/PA blends Compatibilizer MAH-g-EPR MAH-g-EPDM CPE MAH-g-POE XNBR Tensile strength (MPa) Elongation at break (%) Tensile set at break (%) Shore A hardness Formulation: EPDM 86, compatibilizer 4, PA 40, S, DCP 4, HVA-2, SA, ZnO 5 phr 82 Polymers & Polymer Composites, Vol., No. 3, 2003

5 Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber Figure 2 Effect of MAH-g-EPDM content on mechanical properties of vulcanized EPDM/PA blends. Formulation: rubber 00, PA 40, EPDM/MAH-EPDM=00/0, 95/5, 90/0, 86/4, 80/20, 70/30, 40/60, 50/50; S 2, TMTD, SA 2, DM 0.5, ZnO 5 (a) (b) EPDM and PA molecules. It is proposed that a grafting copolymer EPDM-g-MAH-PA may form during the melt mixing process of MAH-g-EPDM and PA and it enhances the interfacial inter-actions of EPDM and PA. The proposed reaction pattern can be represented schematically as follows 3 : Polymers & Polymer Composites, Vol., No. 3,

6 Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang 3.4 Effect of PA Content It is well known that rubber is normally reinforced by carbon black. In this paper, PA was used as a reinforcing agent for EPDM. The effect of PA content on the mechanical properties of the vulcanized EPDM/ MAH-g-EPDM/PA blends is shown in Figure 3. The tensile strength and elongation at break increased with increasing the PA content from 0 to 60 phr. The tensile set at break and the hardness increase steadily with increasing PA content at the range of 0 to 60 phr. Typical stress-strain curves for the vulcanized EPDM/ MAH-g-EPDM/PA blends with different PA contents are shown in Figure 4. The stress-strain curves of the vulcanizates exhibit the characteristic of rubber tension curves in the whole range of PA content. No tensile yield appears in the curves in the range of PA Figure 3 Effect of PA content on mechanical properties of vulcanized EPDM/PA blends. Formulation: EPDM 86, MAHg-EPDM 4; PA as shown; S 2, SA 2, TMTD, MBTS 0.5, ZnO 5 (a) (b) 84 Polymers & Polymer Composites, Vol., No. 3, 2003

7 Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber content from 0 to 60 phr, which implies that the rubber is the continuous phase. 3.5 Ageing Resistance of EPDM/MAH-g- EPDM/PA Blends Table 3 shows the ageing resistance of the vulcanized EPDM/MAH-g-EPDM/PA blends and the EPDM vulcanizate reinforced by carbon black. The EPDM/ MAH-g-EPDM/PA vulcanizates keep a relatively high tensile strength and elongation at break after ageing at 35 C for 68 h, indicating that the EPDM/MAH-g- EPDM/PA blends has good ageing resistance. 3.6 Differential Scanning Calorimetry DSC experiments were carried out to investigate the effect of MAH-g-EPDM on the T g s of EPDM and PA. The results are shown in Table 4. Figure 4 Stress-strain curve of vulcanized EPDM/PA blends with different PA content. Formulation: EPDM 86, MAHg-EPDM 4; PA 0, 20, 30, 40, 50, 60; S 2, SA 2, TMTD, MBTS 0.5, ZnO 5 Table 3 Ageing resistance of EPDM/CPE/PA blends (ageing at 350C) S ample No. Time (day) Tensile strength (MPa) Elongation at (%) break Tensile set at break (%) Shore A hardness Formulation:. EPDM 00 carbon black 40;S 2, SA 2, TMTD, MBTS 0.5, ZnO 5 2. EPDM 86, MAH-g-EPDM 4, PA 40; S 2, SA 2, TMTD, MBTS 0.5, ZnO 5 phr Polymers & Polymer Composites, Vol., No. 3,

8 Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang Table 4 Effect of addition of MAH-g-EPDM in the blend system on the Tgs of EPDM and PA Sample TgEPDM T gpa DSC DMTA DSC DMTA Pure EPDM - 50 C - 36 C Pure PA 20 C 34 C EPDM/PA 00/40-50 C - 36 C 25 C 4 C EPDM/MAH-g-EPDM/PA blends (86/4/40) - 50 C - 34 C 2 C 3 C The blends are a two-phase system and the T g s of pure EPDM and pure PA are 50 C and 20 C respectively. The T g of EPDM in the simple blends of EPDM/PA did not change compared with that of pure EPDM. But the T g of PA in the simple blends of EPDM/PA was 5 C higher than that of the pure PA. The reason for the increasing in the T g of PA is not known. In Table 4, the T g of PA in the blends fell by 8 C when 4 phr MAH-g-EPDM was added to the EPDM/PA blends. The decrease in Tg suggests that the segmental motion of the PA chains occurs at lower temperature in the ternary blend than in EPDM/PA blend. It is reported that the segmental motion in the chains of a polymer when attached to a more mobile component is enhanced compared to that in the homopolyer 4. This can be caused by the chemical reaction between PA and MAH-g-EPDM. Another interesting observation is that the addition of MAH-g-EPDM did not affect the T g of EPDM at all. 3.7 DMTA The glass transition temperature T g s (α transition) determined by DMTA for EPDM (cured with sulfur) and PA were 36 C, 34 C respectively Figure 5. At low temperature a β peak (-67 C) with a small intensity could be observed in the tanδ-temperature curve of PA, probably due to the relatively fast cooling of the test specimen. This results in the preservation of weak hydrogen bonds between the carbon amide groups. The similar β peak of PA could also be observed in the relaxation behavior of other kinds of polyamide such as PA 6 or PA The temperature dependence of the storage modulus for EPDM and PA is shown in Figure 6. As expected, PA has a relatively high modulus compared with EPDM in a given temperature range. Figure 5 Tanδ as a function of temperature for EPDM, PA, and EPDM/MAH-g-EPDM/PA vulcanizates 86 Polymers & Polymer Composites, Vol., No. 3, 2003

9 Polyamide Reinforced EPDM Compatibilized with Maleic Anhydride Grafted Ethylene-Propylene-Diene Rubber Figure 6 Storage modulus as a function of temperature for EPDM, PA and EPDM/MAH-g-EPDM/PA vulcanizates The tanδ of blends of uncompatibilized and compatibilized EPDM/PA vulcanizates are shown in Figure 5. In 00/40 EPDM/PA blends, the Tgs of EPDM and PA were -36 C and 4 C respectively. In 86/4/40 EPDM/MAH-g-EPDM blends, the Tgs of EPDM and PA were -34 C and 3 C respectively. The Tg of PA in the blends decreased by 0 C after 4 phr MAH-g-EPDM was added to the blends. This indicates that the segmental motion of the PA chains occurs at a lower temperature in the ternary blend than in the EPDM/PA blends. The Tg of EPDM in the blends remained unchanged, regardless of whether the blends were compatibilized or not. These results are consistent with those obtained by DSC. The storage modulus of the EPDM/MAH-g-EPDM/PA vulcanizates with different PA contents are shown in Figure 6. The tendency towards a high modulus on increasing the PA content is reasonable. Thus the modulus of the blends can easily be controlled by adjusting the PA content in the EPDM/MAH-g-EPDM/ PA blends. Figure 7 SEM micrographs of EPDM/PA and EPDM/ MAH-g-EPDM/PA blends (tension fracture surface). (a) EPDM/PA 00/40, (b) EPDM/MAH-g-EPDM/PA 86/4/40 (a) (b) 3.8 Morphologies of the Vulcanized Blends To determine the effect of the addition of MAH-g- EPDM on the morphologies of the vulcanized EPDM/ PA blends, a series of samples was observed in SEM. The tensile fracture surfaces of the EPDM/PA (00/ 40) and EPDM/MAH-g-EPDM/PA (86/4/40) blends are shown in Figure 7. The dispersed PA phase was pulled out from the rubber matrix under stress and the fracture surface was smooth on the EPDM/PA micrograph. The dispersed PA particles did not distribute uniformly. Compared with the EPDM/PA micrograph, the tensile fracture surface of the EPDM/ MAH-g-EPDM/PA blend was rough and coarse. Polymers & Polymer Composites, Vol., No. 3,

10 Xin Liu, Hua Huang, Yong Zhang, Yinxi Zhang The brittle failure surfaces of EPDM/PA (00/40) and EPDM/MAH-g-EPDM/PA (86/4/40) blends are shown in Figure 8. The holes formed by etching the dispersed PA phase from the EPDM matrix were not uniform and their size was in the range of 5 to 50 µm on the EPDM/PA micrograph. Compared with the EPDM/PA micrograph, the holes in the EPDM/ MAH-g-EPDM/PA micrograph were more uniform and in the range of to 5 µm. This proves that the addition of MAH-g-EPDM makes the dispersed phase smaller and better distributed and thus improves the mechanical properties of compatibilized vulcanizates. Figure 8 SEM micrographs of EPDM/PA and EPDM/ CPE/PA blends. (Brittle failure surface) (a) EPDM/PA 00/40, (b) EPDM/MAH-g-EPDM/PA 86/4/40 (a) CONCLUSIONS In situ compatibilized EPDM/MAH-g-EPDM/PA vulcanizates with excellent mechanical properties were prepared. Compared with other compatibilizers, both MAH-g-EPDM and CPE showed better performance in compatibilizing the EPDM/PA blends. The vulcanized EPDM/MAH-g-EPDM/PA blend using sulfur as curative had a higher tensile strength than those cured by DCP. But the vulcanized EPDM/ MAH-g-EPDM/PA cured by DCP gave a higher elongation at break than the vulcanized blends cured by sulfur. Both tensile strength and elongation at break increased with increasing MAH-g-EPDM content and reached a maximum in the range of MAH-g-EPDM content from 20 to 25 phr. The tensile strength and elongation at break increased steadily with increasing PA content in the range from 0 to 60 phr. The stress-strain curves of the vulcanized EPDM/MAH-g-EPDM/PA blends exhibited the characteristics of rubber extension in the given PA content range. Both DSC and DMTA experiments indicate that the addition of MAH-g-EPDM did not affect the Tg of EPDM but decreased the Tg of PA. Scanning electron microscopy results indicate that the addition of MAH-g-EPDM can decrease the particle size of the PA phase that exists at an average size of 3 µm in the vulcanized EPDM/MAH-g-EPDM/PA blends. These blends showed good thermal ageing resistance. REFERENCES. Paul, D.R. and Newman, S., Polymer Blends, Vol.2. Academic Press, New York Bucknall, C.B., Toughened Plastics, Applied Science, London, Oderkerk, J. and Groeninckx G., Polymer, 43, (2002) Okada, O., Keskkula, H. and Paul, D.R., Polymer, 40, (999) 2699 (b) 5. Hua, H., Junling, Y., Xin, L. and Yinxi, Z., European Polymer Journal, 38(2002) Xin, L. and Yinxi, Z., China Synth. Rubber Ind., 25(2), (2002) 7 7. Xin, L., Zhiyun, X., Yong, Z. and YinXi, Z. Polymer Testing, 22(), (2003) 9 8. Fischer, W.K., US Pat. 3,806, Coran, A.Y. and Patel, R., Rubber Chem Technol, 53 (), (980) 4 0. Dongshan, L. and Zhen Cai, L., China Synth Rubber Ind, 4(), (99) 46. Xiangfu, Z., Yinxi, Z., China Rubber Ind, 4(), (994) Ma, J., Y.X.Feng. Polymer, 43 (2002) Tessier, M. and Maréchal, E., J. Pol. Sci., Pol. Chem., A26, (988) Eastmond, G.C., Smith E.G., Polymer, 8, (977) Tomova, D., Kressler, J., Radusch, H.J., Polymer, 4, (2000) Polymers & Polymer Composites, Vol., No. 3, 2003