Investigation of structure-morphology-function relationship of plastomers used to produce low mold shrinkage thermoplastic olefins

Abstract

Thermoplastic Polyolefins (TPOs) are one of the most commonly used polymeric materials in automotive industry due to their better elastomeric properties compare to commercial polyolefins. Thermoplastic polyolefin (TPO), or olefinic thermoplastic elastomers are prepared by mixing a polyolefin usually copolymer polypropylene and a plastomer in certain fraction in order to improve elastomeric properties. One of the most challenging problems in automotive industry during the production of these materials is to control the mold shrinkage of TPOs since the parts having very high aspect ratio such as bumper, exterior trims, glass run channel are produced by those materials. Therefore, this paper intends to produce TPO formulations with minimum mold shrinkage by focusing on to optimize the mechanical properties. For that purpose, TPO formulations were prepared by melt blending of plastomers having different physical/mechanical properties into a polyolefin phase. The relationship between structure of plastomer and the function of final product TPO was tried to be explained by structural characterization and molecular dynamic (MD) simulations. In terms of mold shrinkage values and mechanical properties the optimum TPO compound is found to be “sample A” containing 70% plastomer with medium crystallinity and 30% copolymer PP. It shows low mold shrinkage values in parallel (0,19%) and perpendicular (0,2%) to flow direction and optimum tensile strength (13,4 MPa), tear strength (74,4N/mm) and elongation at break (815%) results. Findings of this study is useful in understanding the micro-events taking place during compound process of PP with plastomers, and to explain the necessary PP-plastomer ratio with desired mechanical traits.