THE EFFECTS OF THERMAL HISTORY ON THE STRUCTURE-PROPERTY RELATIONSHIP IN POLYPHENYLENESULFIDE CARBON-FIBER COMPOSITES

The purpose of this investigation was to examine the effects of thermal history during cooling from the melt on the degree of crystallinity, morphology, and mechanical properties of polyphenylenesulfide (PPS)/carbon fiber composites. Three thermal treatments were employed in this study: isothermal crystallization from the melt at 140, 160, 180, 200, and 220-degrees-C, quenching from 315-degrees-C and then annealing at 160 and 200-degrees-C; and nonisothermal crystallization from the melt at rates varying from 0.4-degrees-C/min to 68-degrees-C/s. The effect of varying the thermal history of the sample on the degree of crystallinity developed in the matrix polymer was determined using differential scanning calorimetry (DSC). The effect of thermal history on and the resulting matrix morphology was examined by scanning electron microscopy (SEM). The subsequent effects of the degree of crystallinity and the morphology on the mechanical behavior of the samples were monitored by transverse tensile tests and flexural tests. In all cases, the transverse tensile and flexural moduli increased as the amount of crystallinity in the samples increased. However, samples with greater amounts of crystallinity did not always yield higher transverse tensile or flexural strengths. Upon examination of the composite samples by electron microscopy, it was observed that large increases in the values of the transverse tensile and flexural strengths could be correlated with structural changes in the matrix.