EFFECT OF INJECTION-MOLDING CONDITIONS ON THE CRYSTALLINITY, ORIENTATION GRADIENTS, AND MECHANICAL-PROPERTIES OF POLY(ARYL ETHER KETONE) .2. LARGE DUMBBELL PARTS

High-temperature thermoplastics such as poly(arylene ether ketone) form multilayer structures when they are molded at low mold temperatures. The cavity geometry, particularly the cavity thickness, plays an important role in forming these structural gradients. In this paper, we present our results on relatively thick large dumbbell specimens. Unlike the thin specimens (reported in Part I of this series of papers) that show structural gradients composed of amorphous skin-crystalline intermediate zone and amorphous core, thicker dumb-bell specimens exhibit structural gradients with increasing crystallinity from skin to core at low mold temperatures. Optical profiling on thin-sliced specimens indicate the presence of six layers from skin to core at low mold temperatures, and the number of layers decrease with the increase of mold temperature. As the mold temperature increases, the regions near the surface increase in crystallinity while the core crystallinities remain high and unaffected by the changes in the process variables. At very high mold temperatures where thermally activated crystallization is dominant, the crystallinities become uniform throughout the thickness of the specimens. Wide-angle X-ray pole figure investigations indicate that the skin layers possess high preferential orientation with uniplanar axial (200) [ 001] texture and the core regions possessing lower orientation levels exhibit simple uniaxial texture with the chain axes oriented primarily along the flow direction. Elongation to break, tensile strength, and impact strength increase with the decrease of injection speed. The implications of these structural gradients on the mechanical properties are discussed.