The Analysis of Molecular Orientation in Injection Molded Polystyrene Using Laser Raman Spectroscopy

In this study, we analyzed the molecular orientation in injection molded polystyrene using laser Raman spectroscopy. We evaluated the degree of molecular orientation according to the peak intensity ratio at 1000 cm-1 and 620 cm-1 (I1000/I620), with the flow direction of the injection moldings set at 45° relative to the laser polarization plane in a crossed Nicols configuration. In addition, we determined whether the orientation was parallel or orthogonal to the flow by measuring I1000/I620 while varying the angle between the flow and the polarization plane of the Raman analyzer, with the flow direction set at 45° to the laser polarization plane. Furthermore, we analyzed the direction of molecular orientation in detail by measuring I1000/I620 in a crossed Nicols configuration while varying the angle between the flow and the laser polarization plane. These methods showed that the molecular orientation inside the polystyrene injection moldings was highest around 200μm from the surface, and the orientation gradually decreased from there to around 400μm. There was almost no change in the molecular orientation from 400μm to the center of the moldings. Overall, the orientation inside the moldings was almost parallel to the flow. The molecular orientation at a depth of 400μm or more from the surface was also relaxed through heat treatment below the glass transition temperature (Tg). We suggest that the relaxation of the residual molecular orientation at a depth of 400μm or more during heating below Tg affects dynamic viscoelasticity and thermal deformation.