Anisotropic Shrinkage in Injection Moldings of Semicrystalline Polymers: Simulation and Experiment

A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using the flow-induced crystallization, frozen-in molecular orientation, elastic recovery and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen-in orientation function and the elastic recovery were used to obtain the in-plane anisotropic shrinkages. The elastic recovery and frozen-in stresses and birefringence were obtained by a non-linear viscoelastic model. The flow-induced crystallization was described via the elevated melting temperature affected by entropy production with modified kinetics of the crystallization. Numerous injection molding runs on polypropylene were carried out by varying packing time, flow rate, melt temperature and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data