Paper number 1203
|CRYSTAL FORMS AND MELTING BEHAVIOR IN COLD-CRYSTALLIZED VS. MELT-CRYSTALLIZED SYNDIOTACTIC POLYSTYRENE|
Ya Sen Sun and E. M. Woo
Department of Chemical Engineering, National Cheng Kung University
Tainan, 701-01, Taiwan
|Summary||Syndiotactic polystyrene has been known to possess polymorphic crystals. Normally, alpha and beta forms are obtained with melt-processed s-PS. Combination of various fractions of alpha-type (hexagonal) and beta-type (orthorhombic) crystals exists in melt-crystallized syndiotactic polystyrene (s-PS) if crystallized at lower temperatures (240°C or lower), or majority of beta-type if at temperatures higher than 260°C. Slow-cooled s-PS samples in simulation of typical processing cycles were investigated in this study. The DSC results revealed that there are three (or fewer depending on the temperature of melt-crystallization) sharp melting peaks (labeled as Peak-1, -2, and -3, respectively) for the s-PS sample melt-crystallized. The first two peaks are relatively minor while the highest peak is prominent. With annealing at higher temperatures for various times, the first peak (Peak-1) was elevated to a higher temperature and increased in intensity rapidly while Peak-2 was also elevated to higher temperatures but its intensity decreased. Peak-3 remained at the same temperature regardless annealing but decreased in intensity rapidly. X-ray result suggested that beta-type crystal is largely associated with the melting entity of Peak-1, and alpha-type is associated with Peak-2 and Peak-3. Crystal forms in cold-crystallized sPS were compared to those in melt-crystallized one. sPS is commonly used in galss-reinforced forms. Investigation on possible effects of glass fiber on morphology, polymorphism, and properties of sPs is in progress and will be reported in the meeting.
||Keywords|| crystal structure, DSC, crystallization, s-PS, crystal forms.
Theme : Matrices ; Polymer Matrices
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