ANNEALING EFFECTS IN POLY(PHENYLENE SULFIDE) AS OBSERVED BY DYNAMIC-MECHANICAL ANALYSIS

Poly(phenylene sulfide) (PPS) is a semicrystalline engineering resin w ith exceptional solvent resistance and thermal performance. Properties such as these are directly related to the high crystallinity of PPS. In order to exploit its crystalline nature, PPS should be molded at a high tool temperature (hot oil tool) to allow for the highest crystall ization rate, and therefore the highest percent crystallinity. Alterna tely, if a low mold temperature is used, the molded parts should be an nealed. This latter process has been studied for injection molded neat PPS resin for various annealing temperatures. Two different grades of PPS were studied that represent cured and linear types. Samples were studied as-molded, and annealed at 160, 180, 200 and 220-degrees-C. In creases in glass transition temperature were noted upon annealing. An increase in storage modulus was also noted for annealed samples. This increase persisted up to approximately the annealing temperature. Diff erential scanning calorimetry has been used to show that annealing PPS allows for a secondary crystallization to occur whereby an endotherm appears that corresponds to the secondary crystalline phase melting ne ar the annealing temperature. As the annealing temperature is increase d, the area of the endotherm increases. The secondary crystallization explains the higher storage modulus that persists up to the annealing temperature. These results are discussed in terms of crystallinity and overall effect on heat distortion temperature.