injection moulding, crystallization, monitoring
Rosario Bretas, Alessandra Marinelli, Marcelo Farah
E. S.
Brazil

Keywords: injection moulding, crystallization, monitoring

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The characterization of the “in-situ” crystallization of polymers during their processing constitutes a challenging problem. Usually, this crystallization occurs under high gradients of temperature, pressure and deformation, which can produce two types of morphologies: quiescent and flow induced. Injection molded parts of crystalline polymers display these morphologies. In this work, the “in-situ” crystallization of three polyesters, polybutylene terephthalate, PBT, polytrimethylene terephthalate, PTT and polyethylene terephthalate, PET, during the packing stage of the injection molding, was monitored. This monitoring was made by using a laser beam conduit inserted in the mold. The laser beam was reflected by the opposite mold surface; calibration was made when no polymer was present, with an amorphous polymer, polystyrene, PS and with a crystalline one, polypropylene, PP. Evidently, this reflection changed during the polymer crystallization. The mold cavity, in the form of a disk, had also temperature and pressure transducers at different parts. The signal of the laser beam, during the filling and the crystallization stages of these three polyesters, was found to be reproducible. The measurements showed that this technique was sensible to different types of polymers under different processing conditions.