Assessing the effect of processing variables on the mechanical response of polysytrene molded using vibration‐assisted injection molding process

Abstract

ABSTRACT:The present work is focused on the study of vibration-assisted injection molding (VAIM) process, using polystyrene as a model polymeric system. This recently developed polymer processing operation is based on the concept of using motion of the injection screw to apply mechanical vibration to polymer melt during the injection and packing stages of injection molding process, to control the polymer behavior at a molecular level, which would result in improvements/alterations to the mechanical behavior of molded products. In this study, the afore-mentioned concept was verified experimentally from monotonic tensile experiments and birefringence measurements of VAIM molded polystyrene in comparison with those of conventional injection molding process. The results of our study indicate that the actual degree of strength improvement depends on at least four parameters, namely, vibration frequency, vibration amplitude, vibration duration, and the delay time between the injection start and the vibration start. Furthermore, when these parameters were optimized, as much as a 28% strength improvement was observed, accompanied by an increase in toughness. Furthermore, birefringence measurements revealed that VAIM processing significantly altered the residual stress distribution throughout final products, but it did not, however, change the material density in the products.

Shish–kebab of polyolefin by “melt manipulation” strategy in injection-molding: A convenience pathway from fundament to application

“…''Melt manipulation'' can be as an efficient technique for control of the formation of oriented morphology in the molded bars. For the injection-molded bars of noncrystalline polystyrene (PS), it was indicated by birefringence patterns that the residual stress distribution in the whole bar processed by VAIM was more uniform than in the bar processed by conventional injection molding (CIM) [66], and that VAIM significantly promoted the orientation of PS chains [67]. For the injection-molded bar of glass-fibre reinforced polypropylene prepared through push-pull processing, orientation of fibres parallel to the flow direction was found in the push-pull layer, while fibres were oriented perpendicular to the flow direction in the core region [62].…”

Suppressing the skin–core structure in injection-molded HDPE parts via the combination of pre-shear and UHMWPE

“…From a practical and academic point of view, it is very interesting to enhance the orientation level in core region and thus reduce the difference of orientation level between the skin region and core region. 21 We have designed and built a mixing-injection molding machine recently. 7 With respect to the former strategy, the addition of special additives/llers will lower free energy barriers for stretching/ orienting molecules, 8-10 amplify shear effect 11 or suppress the relaxation of stretched/oriented molecules, 12,13 thus skin-core structure can be largely suppressed.…”

Influence of shearing on crystallization of polyoxymethylene/high density polyethylene blend

“…At present, the influence of the complicated external flow fields during polymer blending process on their various properties have also been widely reported . Multiple morphologies and structures can be induced by injection molding, such as, different dispersed phase morphologies (ellipsoid, fiber‐like, spherical, or laminar morphologies), different structures of the matrix (crystalline or oriented structures), and various co‐continuous phase morphologies (irregular or layered morphologies).…”