Polymer Engineering Faculty Research


Evaluation of processing effects in injection-molded amorphous and crystalline thermoplastics using an excimer laser

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The ablation behavior of amorphous [polystyrene (PS), polycarbonate (PC)] and crystalline [PET, glass-filled poly(butylene terephthalate) (PBT)] polymers by 248-nm KrF excimer laser irradiation were investigated for different injection-molding conditions, namely, injection flow rate, injection pressure, and mold temperature, as a possible method for evaluating processing effects in the specimens. For this purpose, dumbbell-shaped samples were injection-molded under different sets of processing conditions, and weight loss measurements were carried out for the different injection-molding conditions. Some of the crystalline (PET) samples were annealed at different annealing times and temperatures. For PET, the weight loss decreased with increasing mold temperature and remained insensitive to injection flow rate. Annealing time and temperature significantly reduced weight loss in PET. For PBT, the weight loss due to laser ablation decreased with increasing material packing due to pressure, and it also showed some sensitivity to flow rate variation. The major effect was seen with glass-filled PBT samples. The weight loss decreased drastically with increasing glass fiber content. Laser ablation allowed us to observe process-induced fiber orientation by scanning electron microscopy in PBT samples. For PS and PC, the weight loss increased with increasing injection flow rate and mold temperature and decreased with increasing injection pressure. The position near the gate showed higher ablation than the position at the end for all the conditions. A decrease in the material orientation with injection speed and mold temperature led to an increase in the weight loss, whereas an increase in the injection pressure, and consequently orientation, led to a lower weight loss for PS and PC. Higher residual stress samples showed higher weight losses.

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Journal of Applied Polymer Science





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