Hierarchical structure gradients developed in injection-molded PVDF and PVDF--PMMA blends. I. Optical and thermal analysis
The structural gradients developed along and across the flow direction of injection-molded PVDF and PVDF/PMMA parts were investigated by optical microscopy and thermal analysis techniques. The spatial variation of crystallinity across the thickness direction was found to be insensitive to the process variables: injection speed and mold temperature. This relatively flat crystallinity profile across the thickness of the parts was found to decrease with the increase of PMMA concentration. The blends become noncrystallizable beyond about 40–45% PMMA concentration. The influence of flow history on the structural evolution across the thickness was observed in the peak position of the cold crystallization region. This peak temperature showed a minimum at depths where shear effects are at their maximum. This was attributed to the increased levels of chain orientation frozen in the amorphous portions of these regions which crystallize at lower temperatures upon heating.
Journal of Applied Polymer Science
Wang, Y. D. and Cakmak, Mukerrem, "Hierarchical structure gradients developed in injection-molded PVDF and PVDF--PMMA blends. I. Optical and thermal analysis" (1998). Polymer Engineering Faculty Research. 283.