Phase Coarsening in Polycarbonate and Amorphous Copolyester Blends
Vol. 57, No. 4, pp. 199-209,
Aug. 2020
10.12772/TSE.2020.57.199
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Abstract
Phase behaviors of the blends of bisphenol A polycarbonate (PC), copolyesters (TR) of 1,4-cyclohexanedimethanol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol
(CBDO) with terephthalic acid were investigated through dynamic mechanical analysis, differential
scanning calorimetry, and scanning electron microscopy. When the blends were
prepared using an internal mixer at low shear condition, TR-1 with a CBDO content of
27 mol% exhibited miscibility with the PC in the melt-mixed state, whereas TR-2, with a
CBDO content of 38 mol% did not. However, a 50/50 PC/TR-2 blend prepared using a twinscrew
extruder subjected to high shear rates formed a single phase. Its morphology
became a modulated structure and returned to the homogeneous phase during thermal
annealing at the melt-mixing temperature. This morphological change is likely owing to
shear-induced mixing and ester-carbonate intermolecular exchange during annealing,
although no new peaks caused by the exchange reaction were observed in the 1H-NMR
spectrum. The effect of CBDO content on the miscibility of PC/TR blends were interpreted
in through a binary interaction model. The blends prepared in this study exhibited a transparency
close to 90%, a refractive index ranging between 1.550 and 1.586, Tg in the range
of 110 to 145 °C and a positive birefringence in its stretched state. The PC/TR blends prepared
in this study are expected to be used as matrices for PEN fiber-impregnated reflective
polarizing sheets or retardation films.
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