Polymer Engineering Faculty Research


Birefringence in gas-assisted tubular injection moldings: Simulation and experiment

Document Type


Publication Date

Fall 2009


The influence of the processing variables on the birefringence and polymer/gas interface distribution is analyzed for polystyrene moldings obtained by gas-assisted injection molding (GAIM) under various processing conditions. The processing variables studied were: melt and mold temperatures, shot size, gas pressure, injection speed, and gas-delay time. Measurements and viscoelastic simulations of the radial distribution of birefringence components, Δn and nrr − nθθ, the variation of the average birefringence, 〈nzz − nθθ〉, along the molding and polymer/gas interface along the length of spiral-shaped tubular moldings are presented. The polymer/gas interface distribution and flow stresses were simulated using a numerical scheme based on a hybrid finite element/finite difference/control volume method. The birefringence was calculated from the flow-induced stresses using the stress-optical rule. Simulations qualitatively agreed with measurements and correctly described theeffect of the processing variables on the birefringence andthe polymer/gas interface distribution in GAIM moldings.



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