Gamma-radiation effect on mechanical properties of Pp/Epdm polymeric blends

Abstract

Thermoplastic elastomers (TPEs) are provided with many properties of elastomeric or rubbery materials, but can be processed with the thermoplastic processing methods; they are one of the fastest growing polymers materials which combine the elastic and mechanical properties of crosslinked rubbers with the melt processability of thermoplastics. In addition, TPEs find a lot of applications in automotive, buildings and construction, wires and cables, etc.; besides their ability to reuse and recycle the production scrap and waste. Polypropylene (Pp) is a commodity, with high melting point, high chemical resistance, low density, with a balance between physical and mechanical properties and easy processing at low cost. Nevertheless, Pp shows limitations for some special applications, in terms of impact resistance; in order to minimize this characteristic, an impact modifier, as Ethylene Propylene Diene Terpolymer (Epdm) can be used. Due to different polarity and structure between the thermoplastic and elastomeric phases, most thermoplastic elastomers are incompatible. Poor interfacial adhesion and high interfacial tension between rubber and thermoplastic phases are main reasons for incompatibility of these systems; in case of Pp and Epdm, there is a relatively low interfacial tension (driving force for the transformation of a co-continuous structure into a dispersed one) between Pp and Epdm (approximately 0.3 mN/m), reducing the rate of breakup and facilitating the formation of a continuous structure. Pp/Epdm blends are completely recyclable and reusable, safe to the environment, thus improving the overall profitability of the process. Besides a higher impact resistance shown by Pp/Epdm blends, it is possible that Epdm incorporation in Pp causes a reduction in tensile resistance. In order to eliminate this interference and assuring a more comprehensive application in automotive, buildings and construction, Pp/Epdm blends, rubber contents ranging from zero to 30% (thirty percent), were subjected to gamma-irradiation, within doses from 5 to 20 kGy. Isotactic Pp was considered for this work. Characterization assessments included mechanical, thermal and rheological essays.