Hydrostatically extruded glass‐fiber‐reinforced polyoxymethylene. I: The development of fiber and matrix orientation

This paper describes the determination of fiber and matrix orientation in oriented short‐glass‐fiber‐reinforced polyoxymethylene (POM) composites produced by hydrostatic extrusion. The starting material was random glass fibers (25 wt% and average length 150 μm) in an isotropic POM matrix, and the oriented composites were produced by extrusion through a reducing conical die at 15°C below the polymer melting point: after extrusion the average fiber length was reduced slightly to 133 μm. Fiber orientations were measured using an image analysis method developed at Leeds University, and the matrix orientation was determined using wide angle X‐ray diffraction. The development of fiber orientation with extrusion ratio was found to be close to that predicted by the pseudo‐affine deformation scheme although the fiber orientation was greater than that predicted by the model at low draw ratios and slightly less at the highest draw ratio. The development of the orientation of the crystalline portion of the matrix was found to be always significantly greater than that predicted by the pseudo‐affine scheme.