High-temperature creep behavior of wheat straw isotactic/impact-modified polypropylene composites

Abstract

Short-term creep behavior of wheat straw composites made with either polypropylene homopolymer or impact-modified copolymer was studied at elevated temperatures (50–90°C). Various mineral fillers were tried to enhance creep resistance in the composite materials among which wollastonite was found to be the most effective one. All formulations exhibited higher creep deformations at higher temperatures where the effect of temperature was more pronounced for composites containing the impact-modified copolymer as the matrix. Short-term creep was successfully modeled using a three-parameter power law and Burgers model, and the dependence of the power law model parameters on temperature was evaluated to quantify temperature dependence of creep behavior. Long-term creep at 50°C was predicted based on the short-term data using the time–temperature superposition (TTS) principle, the power law model, and the Burgers model, and the results were compared with actual long-term data. While TTS was found to be the best method to accurately extrapolate short-term data, the failure of the two other methods was found to be related to the time scale of the deformation in short-term creep tests. The results of this study will provide a basis for the design of natural fiber thermoplastic composites to be used in under the hood applications in auto industry.