P35: Characterization and Comparison of Thermoplastic Material Performance Using Pressure-Volume Relationships

Abstract

Purpose: Characterizing mechanical performance of finished materials can be challenging due to geometric constraints and the effects of downstream processing on raw material behavior. The following describes a more sensitive test method to accurately characterize the performance of a thin polymeric sheet material. Methods: Two different polymers, Thermoplastic Polyurethane, TPU, and Thermoplastic Elastomer, TPE, were selected for characterization. Each was molded and assembled into a manifold. Both polymers were under a constant pressure load over time, as a control and measurement technique. Fluid was injected incrementally into the assembly and the resulting injectate volume was measured by mass difference up to a limit volume to understand material behavior post processing. Results: The plotted pressure-volume relationships were distinct between TPU and TPE at two time intervals, as shown in Figure 1. A reduced pressure response to the same volume at test repetition demonstrated that both materials showed permanent set over time. Volume offset between sample runs illustrated reduced mechanical performance over time due to material creep. Conclusion: The pressure-volume testing method successfully characterized performance of the materials over time to discriminate the material set properties between two thin polymeric sheet material, which could not be detected for a finished component using traditional tensile test methods. This repeated method can be used during material selection in various applications for materials with a manufactured finished component, especially for the medical device industry where polymers are carefully chosen and designed for a specific function.