Crystallization, morphology, and thermal behavior of poly(p-phenylene sulfide)

Abstract

This article deals with the structure, crystallization, morphology, and thermal behavior of poly(p‐phenylene sulfide) (PPS) with low‐molecular mass, probed by DSC, optical, and electron microscopy. The growth rates of spherulites were measured over the temperature range 235–275°C. A regime II–III transition was found at T = 250°C. The regime transition was accompanied by a morphological change from sheaflike structure to classical spherulites. The Avrami equation poorly described the isothermal crystallization of PPS, for the occurrence of mixed growth mechanisms and secondary crystallization, in agreement with the morphology and the thermal behavior. Two melting peaks were detected on DSC curves and attributed to the melting of crystals formed isothermally at Tc by primary and secondary crystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 415–424, 2001

A Review of the Measurement and Development of Crystallinity and Its Relation to Properties in Neat Poly(phenylene Sulfide) and Its Fiber Reinforced Composites

“…Multiple melting peaks are commonly observed in PPS. 23,24,25 In the case that amorphous PPS samples were annealed at a temperature and time sufficient to eliminate the cold crystallization in the DSC scan, a small endotherm is often observed at a temperature somewhat above the annealing temperature (often about 15°C above the annealing temperature). 26,27 This endotherm is thought to be associated with melting of small crystals formed during the annealing process, probably associated with secondary crystallization effects.…”

“…The value of n is a function of the nucleation and growth rate of the spherulites formed during crystallization. Most investigators have found values of n between 2 and 3 for PPS isothermal crystallization 24,25,35,36,[41][42][43]48,50,56 with crystallization from the melt giving values nearer 3 and cold crystallization giving values nearer 2. The values for crystallization from the melt have generally been interpreted to indicate three-dimensional growth of predetermined nuclei.…”

“…25,35,36 The spherulites consist of lamellae and/or fibril shaped crystals growing radially outward from the primary nucleation site. 25,35,36 It has been established that the growth direction of the crystals is along the b-axis of the unit cell.…”

“…Many investigators [23][24][25]35,36,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] studied the crystallization kinetics of PPS and its composites. Most of these studies were reviewed previously, 3,6 so the approach taken here will be an overview of the most important observations.…”

“…For PPS, depending on the molecular architecture (linear versus branched, crosslinked, molecular weight) and crystallinity, the glass transition typically occurs in the range 80°-95°C and the equilibrium melting temperature is typically in the range 298°-330°C. 25,42,43,50,51 (Note that this temperature range is higher than the observed DSC melting range, Tm = 280°-295°C.) This suggests that the maximum crystallization rate should be in the neighborhood of 180°-190°C.…”