Crystallization of poly(phenylene sulfide) in fiber-reinforced composites: Experimental characterization and computer simulation

The main objective of this research was to improve the understanding of crystallization processes that occur in fiber-reinforced composites based on crystallizable thermoplastic polymers. Differential scanning calorimetry and hot stage optical microscopy were used to study the effects that aramid, carbon, and glass fibers have on the isothermal crystallization kinetics of poly(phenylene sulfide) (PPS). Two types of base polymer were used: conventional Ryton{dollar}spcircler{dollar} PPS and the more linear Fortron{dollar}spcircler{dollar} PPS. It was determined that the influence of fibers on PPS crystallization depends on the type of fiber reinforcement as well as the polymer matrix. In general, fiber-reinforced Ryton{dollar}spcircler{dollar} crystallized faster than the corresponding unreinforced polymer, with aramid and graphitized carbon fibers causing the most pronounced rate enhancement, while reinforcing fibers had little or no effect on the rate of Fortron{dollar}spcircler{dollar} crystallization.; A computer simulation of spherulitic crystallization was created and developed in order to explain the wide range of effects that fibers can have on the crystallization of PPS. Although the simulation was applied specifically to PPS, it is general enough to treat any polymer that crystallizes by a process of primary nucleation followed by spherulitic growth. The simulation was used to predict the crystallization kinetics and crystalline morphologies that develop in two and three-dimensional systems of spherulites that were nucleated either instantaneously or at a constant rate. It was determined that reinforcing fibers have a dual effect on the crystallization process. Fibers can both depress the crystallization rate relative to an unreinforced polymer by an impingement mechanism which interferes with spherulitic growth, and enhance crystallization by providing additional nucleation sites on the fiber surface. It was demonstrated that the relative nucleation rates in the bulk polymer and on fiber surfaces control the crystallization process.; Finally, by applying the simulation to the experimental crystallization kinetic data, a new method of quantifying the nucleation process that occurs in fiber-reinforced composites was developed. The bulk nucleation density of Fortron{dollar}spcircler{dollar} was determined to be more than 10{dollar}sp4{dollar} times greater than that of Ryton{dollar}spcircler,{dollar} and the simulation was successfully used to quantify the effective fiber nucleation densities in PPS composites.