Study On The Environmental Stress Cracking Behavior Of Polycarbonate Injection Molded Products

Environmental Stress Cracking (ESC) is a complicated failure behavior of polymer materials. It's also a serious problem when molding high quality polycarbonate (PC) products. But there are little researches about the effect of residual stress distribution and the inhomogeneous microstructure in injection molding caused by complicated thermal-mechanic history on ESC. Therefore, studying on the mechanisms and influence factors of PC injection-molded products can provide a theoretical basis and experimental evidence for prediction and improvement of Environmental Stress Cracking Resistance (ESCR) of molded parts. It's also has a significant academic meaning and practical engineering value.This study mainly researches on the ESC behavior of PC injection-molded parts. Based on the analysis of molded micro-structure, the paper emphasizes the effect of processed residual stress & molecular orientation, and the influence factors of processing parameters & solvent on ESC behavior. The main works are as follows:1. Wedge-method was used to study the birefringence along the thickness direction of PC plate. From the distribution of birefringence & molecular orientation under different processing parameters & different positions in the molded plate, it was found that an asymmetrical distribution of birefringence on the side-way of the plate; The pressure-effect in injection-molding on the tensile-stress distribution in the plate surface was also analyzed combined with simulation experiment.2. Based on the molded micro-structure analysis, the ESC behavior of PC injection-molded plate in carbon tetrachloride was studied. It was found that ESC of PC injection-molded plate in carbon tetrachloride is mainly due to the interaction of the surface residual tensile-stress, the molecular orientation distribution due to complicated thermal-mechanic history and the solvent-induced effect. The immersion experiment of annealed and layer-removed samples indicated that the residual tensile-stress in the surface of molded part can easily induce the appearance of ESC and determine the cracking depth. The discontinuous distribution of molecular orientation determined both the cracking position and the cracking development direction in the side-wall3. The effect of different processing parameters on carbon tetrachloride and the mixture (benzene/cyclohexane) immersion cracking was studied. The results showed that the set of processing parameters which can effectively reduce the molecular orientation & the surface residual tensile-stress were helpful to prevent appearance of ESC in PC injection molding. Cracks are apparent in molded parts under high packing pressure, and high melt temperature can improve the ESC resistance of PC injection-molded parts effectively. Crack can easily happen when the solubilityparameter difference of polymer & solvent is in a certain range.