Experimental analysis demonstrates processing conditions and copolymer chemistry control optical anisotropy in injection-molded PET copolyesters, indicating pathways for low-stress optical plastics.
The optical anisotropy of transparent injection-molded poly (ethylene terephthalate) (PET)-based copolyesters, including a biomass-derived PET copolymer, was investigated through birefringence and retardation measurements. Injection molding simulation was also performed to predict residual stress distributions. The effects of molding conditions and copolymer composition on optical anisotropy were systematically evaluated. The average retardation decreased from 468.6 to 190.3 nm as the injection temperature increased from 260 to 280°C, whereas it increased from 226.6 to 347.6 nm as the packing pressure increased from 40 to 80 MPa. Birefringence increased in the order of PET, poly (ethylene terephthalate-co-1,4-cyclohexanedimethylene terephthalate) (PETG), poly (cyclohexanedimethylene terephthalate-co-ethylene terephthalate) (PCTG), and poly (ethylene terephthalate-co-isosorbide terephthalate-co-cyclohexanedimethylene terephthalate) (PEICT). Increasing the 1,4-cyclohexanedimethanol (CHDM) content increased birefringence, while the incorporation of isosorbide (ISB) further enhanced birefringence by restricting polymer chain mobility and stress relaxation during cooling. These results demonstrate that the optical anisotropy of transparent PET-based copolyesters can be effectively controlled through copolymer composition and injection molding conditions.
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Jeoung et al. (2026) studied this question.
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