Experimental Study On Birefringence Of Injection-molded Amorphous Polymers

Injection molding is one of the most widely employed method of polymer processing. Every particle in the material experiences a complex thermal-mechanic history since the viscoelastic nature of the polymer, which results in development of residual stress and molecular orientation and they have a great influence in the mechanical, optical performance and dimension stability. For transparent amorphous polymers, birefringence can be treated as a method to characteristic residual stress and frozen orientation and also a character of microstructure of products. Birefringence represents the anisotropy of products. So it is one of hot pot in the field of polymer processing to study the ingredient and variety distribution of birefringence in injection molded products. and to realize the optimization and control of the system. It has a great meaning to molding process and product quality control.The present thesis concern measurement and characteristic of birefringence in injection productions. On the basis of a better understanding of mechanism of birefringence, residual stress in injection products, The effect of processing condition and complex flow behavior on the residual birefringence and molecular orientation of products was analyzed. The main work are as follows:1. The in-plane birefringence of PS plate products have been measured through photoelasticity experiment to verify the validity of photoelasticity method. Meanwhile, the influence of the processing parameters on birefringence distribution was investigated. It was concluded that melt temperature and packing pressure were the two most important factors which influence the birefringence2. the birefringence in the weld line area of different insert of PS products was measured through the photoelasticity experiment. It can be seen that complex flow behavior behind insert introduce the apparent anisotropy. And we also compared of birefringence distribution under different processing condition. Different insert and weld angle also influence the birefringence development.3. The result of SEM and photoelasticity experiment after layer removal of product indicate that there is a ill entangle region through the whole thickness direction in the weld line area ,and it also indicate that the weld line exist from the end of insert to the end of product.4. Wedge method was used to study the distribution of birefringence along thick direction. the molecular orientation in the weld line area was analyzed on the basis of birefringence measurement. It can be seen that there is a small anisotropic area behind the insert, in which the gradient of orientation is noticeable. And the orientation raise to maximum along the flow direction and then gradually reduced to its minimum. From the result of heat shrinkage and birefringence along the gapwise direction, it can be seen that there exist apparent orientation perpendicular to flow direction in the area near the insert...