Distribution of some physical properties in injection‐molded thermoplastic parts

During the injection molding process, moldings undergo shear and elongational stresses. They are also exposed to thermal gradients of varying intensity. Invariably, molded parts, or at least some sections thereof, freeze before the polymer chains can relax to a random, non‐oriented configuration. As a result, injection molded parts contain frozen strains and exhibit anisotropic physical properties. In the present work, a variety of experimental techniques have been employed to determine the three‐dimensional variation of the following properties of injection‐molded, thermoplastic, rectangular parts: density, heat shrinkage, birefringence, and tensile strength.