Abstract:

    Polyamide thermoplastic elastomers have excellent mechanical properties, heat resistance, chemical solvent resistance. It has been widely used in many fields, such as automobile manufacturing, sports equipment and electronic appliances. Commercial polyamide thermoplastic elastomers are mainly several polyamide block copolymers with high price, which limits their application. In this study, ethylene-vinyl acetate rubber (EVM) with vinyl acetate content over 40% was blended with polyamides to prepare blends and graft copolymer thermoplastic elastomers with excellent comprehensive properties by using dynamic vulcanization and excahange reaction. EVM/ternary polyamide copolymer (tPA) thermoplastic elastomers (TPE) were prepared through a dynamic vulcanization process in the presence of dicumyl peroxide (DCP). For EVM/tPA (70/30) blend, a phase inversion of occurred during dynamic vulcanization, and the continuous EVM phase was crosslinked and changed to the dispersed phase. A high performance EVM/tPA (70/30) thermoplastic elastomer with Shore A hardness of 75, tensile strength of 24 MPa, elongation at break of 361% and set at break of 20% was obtained by adding 5 wt% of EVM-g-MAH and 3.5 phr DCP. It had good heat oil resistance, with the mass change lower than 35% in the swelling test (100 ℃, 24 h). Further, the transesterification crosslinking reaction of EVM with tetraethyloxysilane (TEOS) was investigated. As suggested from the vulcanization reaction kinetics, the crosslinking reaction of EVM with TEOS presented lower reaction rate constant and activation energy than the crosslinking reaction of EVM initiated by DCP, which offers EVM a wider curing window and higher curing temperatures. The ester-amide exchange reaction between polyamide 6 (PA6) and EVM can take place during melt blending, leading to the formation of PA6 grafted EVM copolymer (EVM-g-PA6) and acetamide-terminated PA6. The reaction kinetic parameters were calculated according to a second-order reversible reaction mechanism. The rate constant was dependent on the catalyst concentration, PA6/EVM ratio and shearing action. The yield of EVM-g-PA6 copolymer was 6.8 wt% for PA6/EVM/DBTO (60/40/1) blend at 230 ℃ for 60 min. EVM-g-PA6 copolymer was further synthesized by combining ring-opening polymerization of caprolactam (CL) and the ester-amide exchange reaction, and its composition and structure were quantitatively characterized. When the conversion of CL was about 15% at elevated temperatures, the yield of the copolymer was 26.4 wt% in the CL/EVM (60/40) mixture. The copolymer showed microphase separation morphology, in which the PA6 phase was dispersed as ~200 nm particles in continuous EVM phase. The PA6 phase behaved heterogeneous nucleation crystallization behavior in a confined manner which is resulted from the microphase separation and the chemical linkages between EVM and PA6. The copolymer showed tensile strength of 12.7 MPa and elongation at break of 595%, and demonstrated a great potential for engineering thermoplastic elastomer applications.

Keywords: thermoplastic elastomers; ethylene-vinyl acetate rubber; polyamide; exchange reactions

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Biography:

    Yong Zhang,Professor ,School of Chemistry and Chemical EngineeringShanghai Jiao Tong University,Shanghai 200240, China Tel: 0086-21-54743257 Fax: 0086-21-54741297 Email: yong_zhang@sjtu.edu.cn Education September 1980-July 1984 BSc, Chengdu University of Science and Technology September 1984-June 1987 MSc, Chengdu University of Science and Technology September 1987-March 1992 PhD, Chengdu University of Science and Technology June 1990-April 1992 IPTME，Loughborough University of Technology Work Experience July 1992- December 1993 Lecturer, Department of Applied Chemistry, Shanghai Jiao Tong University (SJTU) December 1993-July 1997 Associate Professor, Department of Applied Chemistry, SJTU December 1993-now Professor, School of Chemistry and Chemical Engineering, Deputy Director of the Polymer Research Institute, SJTU August 1999~December 2001 Chairman of the Department of Polymer Science and Technology January 2002~March 2013 Vice Dean of the School of Chemistry and Chemical Engineering March 2005-December 2005 Visiting Professor, Institute fuer Kunststofftechnologie，Stuttgart Universitaet, Germany