Time-temperature and stress dependent behaviors of composites made from recycled polypropylene and rubberwood flour

The effects of time, temperature, and stress on the flexural creep of composites from recycled polypropylene (rPP) and rubberwood flour (RWF) were experimentally investigated and numerically modeled. Creep of rPP/RWF composites increased with an increase of time, temperature, and stress. A critical temperature of rPP composites containing 44.5 wt% RWF is 65 °C. Burger, Power law, and HRZ models fit the creep profiles well in general, but at high temperature and stress levels the Power law and HRZ models performed poorly. However, the HRZ model interpolated creep well across the applied stresses, or across the temperatures. The time-temperature superposition (TTS) and time-stress superposition (TSS) principles were used to model long-term creep. The master curves from TTS and TSS principles were in good agreement with each other. They predicted that the lifetime limitation by long-term creep exceeds 10 years for 15 MPa stress at 25 °C. All these results pertain to a specific formulation of rPP/RWF composites.