The effect of processing conditions and inner properties on the en- vironmental stress cracking resistance of polycarbonate

摘要

Environmental stress cracking (ESC) is the most common failure reason of plastic parts during their use. There are many factors that influence the resistance of plastic products that are affected by a combination of a mechanical load and a liquid medium which may lead to environmental stress cracking. The most obvious factor is the interaction between plastic and liquid which could be described by using the Hansen solubility parameters. Other parameters are the type and extent of the mechanical load, the applicationtime applying this load and the surrounding temperature. The influence of the processing conditions e.g. of the injection molding process has not been investigated yet. For this reason there are several tests carried out at the IKV. Test specimens are injection molded with different parameters for melt temperature, mold temperature and injection rate. These parametervariations cause variable inner properties of the molded parts, for example residual stresses and molecular orientations. Investigations show that the resistance against environmental stress cracking of specimens with different inner properties differs in a wide range. Lower values for melt temperature and mold temperature lead to a higher durability. The higher value is about twice as high as the lower value. Lower temperatures correlate with higher molecular orientations in the surface layer of the parts and higher residual stresses. So there is an interrelationship between inner properties and the environmental stress cracking resistance of injection molded parts made of polycarbonate. The results of the investigations are discussed in-depth.