Effect of Melting–Recycling Cycles and Mechanical Fracture on the Thermoplastic Materials Composed of Thermoplastic Polyurethane and Polypropylene Waste Blends

With appropriate conditions, thermoplastic materials possess a good reversible ability. They are prone to exceed the reversibility range when being repeatedly processed as they cannot bear high temperatures. Therefore, this study aims to explore the impacts of the melting–recycling cycles and the presence of a compatibilizer on the omnipresent thermoplastic materials. Additionally, the tensile properties, morphology, and thermal properties are studied. The feasibility of multiple utilizations and differentiation effects are examined afterward. In this study, recycled or mechanically damaged thermoplastic polyurethane (T)/polypropylene (P) waste blends are used as the raw materials for the hot-pressing cycle, while maleic anhydride grafted polypropylene (MA) is used as the compatibilizer, thereby simulating the waste compounds. Next, the T/P/MA blends that undergo post-2nd and post-3rd recycling are evaluated for comprehensive change. The test results indicate that without MA, T/P blends exhibit significant differentiation effects due to an increase in the polypropylene content and multiple melting–recycling cycles. By contrast, the presence of MA mitigates the overall differentiation effect of T/P blends. The ultimate purpose of this study is to treat waste compounds via a simple hot-pressing approach to produce useful materials that can be used again. As a result, this study attenuates the negative influences of plastic waste on the environment while achieving sustainable development.