The effect of fiber concentration on mechanical and thermal properties of fiber-reinforced polypropylene composites

A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene-co-ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP-PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%., 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber-matrix interaction. A higher concentration of long fibers (> 50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox-Krenchel and Haplin-Tsai equations were used to predict tensile modulus of random fiber-rein forced composites. A Cole-Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time-temperature superposition (ITS) by using data over the temperature range from -50 to 90 degrees C, which allowed for the prediction of very long and short time behavior of the composite.