Thermoplastic Polyolefins (TPOs) are widely used in the automotive sector due to their superior elastomeric properties compared to conventional polyolefins. TPOs are obtained by blending a polyolefin, typically copolymer polypropylene, with a plastomer in specific ratios to enhance elastomeric characteristics. A significant challenge in TPO production is controlling mold shrinkage, especially for parts with high aspect ratios, such as bumpers and exterior trims.
Therefore, this study aims to develop TPO formulations with minimum mold shrinkage by optimizing mechanical properties. To achieve this, TPO formulations were created by melt-blending plastomers with varying physical and mechanical properties into the polyolefin phase. To understand the coworking mechanism of polypropylene and plastomers and the effect of different types of plastomers yielding minimum mold shrinkage, the relationship between the structure of the plastomer and the performance of the final TPO product was investigated through structural characterization and molecular dynamic (MD) simulations.
The mechanical test results reveal that the ideal TPO compound, designated as "sample A," consists of 70% plastomer with medium crystallinity and 30% copolymer PP. This formulation demonstrates low mold shrinkage values both parallel (0.19%) and perpendicular (0.2%) to the flow direction, along with optimal mechanical properties, including tensile strength (13.4 MPa), tear strength (74.4 N/mm), and elongation at break (815%). These findings provide valuable insights into the micro-events occurring during the compound process of PP and plastomers and clarify the necessary PP-plastomer ratio to achieve the desired mechanical performance.