Processing of single polymer composites with undercooled polymer melt

An approach of applying undercooled polymer melt to prepare single polymer composites (SPCs) was investigated. The fibers were introduced into the liquid matrix at a temperature well below the matrix melting temperature. The method was demonstrated using polypropylene (PP) as an example. The degree of supercooling of PP was determined by differential scanning calorimetry and rheological measurement. The processing temperature window was determined to be from 125 °C to 150 °C, within which PP SPCs were successfully prepared by compression molding. The crystalline orientation of PP fibers was characterized by X-ray diffraction, and no significant change was found before and after compression molding. The SPC molded at 150 °C containing 50% by weight of PP fabric achieved tensile strengths of approximately 220 and 180 MPa in the weft and wrap directions, much higher than the value of 30 MPa for the non-reinforced PP. The effect of processing temperature on tensile strength of PP SPCs was also investigated. The results showed that, as the processing temperature decreased, the tensile strength decreased in both weft and warp directions. This reduction in tensile strength was correlated with the increased viscosity of the matrix and consequently poor wetting of the PP fabric at reduced processing temperature.