Characterization of molecular orientation by differential scanning calorimetry
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Differential scanning calorimetry was used to study relaxations occurring above the glass transition, Tg for a number of characterized and fabricated polystyrenes. Part 1 of this study examines the liquid-liquid relaxation temperature, TLL; Part 2 the effects of injection moulding and biaxial orientation of polystyrene; and Part 3 deals with the effects of injection blow moulding.
The rubbery plateau region was found to be bounded by the glass transition, Tg, and a weak transition or relaxation, TLL, found above Tg as an endothermic slope change in the base line. In some cases, this transition could be enhanced as a step change when molten samples were quenched in liquid nitrogen.
The effect of molecular weight on Tg and TLL was similar, and had the relationships TLL/Tg=1.07+0.03 forMinw/Mn ≃1, and TLL/Tg=1.15 ± 0.01 for ¯Mw/¯Mn > 1.
KeywordsDifferential Scanning Calorimetry Polystyrene Glass Transition Calorimetry Base Line
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