Texture of injection‐molded polypropylene

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Abstract
Injection‐molded specimens of polypropylene were examined by x‐ray diffraction for texture and orientation patterns as a function of the distance from the surface and of molding conditions. At least three distinct layers in the surface region whose texture patterns differ and an isotropic core of the moldings have been identified. These layers show preferred orientations; the axes of symmetry of the oriented textures lie in a plane passing through the direction of flow and perpendicular to the mold surface, but are inclined to the mold surface at a small angle. Some of these layers may be missing in conditions of either very high or very low shear during the injection‐molding flow. A tentative explanation of the formation of the texture patterns is proposed.