Study On The Crystallization Of Polymers/Montmorillonite Nanocomposites After Drawing

In this dissertation,two types of semicrystalline polymer/montmorillonite nanocomposites were prepared to study the crystalline morphology,melting behavior and orientation of nanocomposites after drawing and orientation.This dissertation consists of two parts:(1) crystalline morphology,melting and orientation behavior of polypropylene/montmorillonite nanocomposites after drawing;(2) crystalline morphology of polyvinylidene fluoride/montmorillonite electrospinning fibers.Polypropylene/organically modified montmorillonite(PP/OMMT) nanocomposites were prepared by melt intercalation using twin-screw extrusion.The dispersion morphology of OMMT in the matrix and crystallization properties of composites was studied by WAXD,DSC and TEM.The crystalline morphology, melting behavior and orientation of the nanocomposites drawn at different temperatures and drawing ratios were studied.It was found that increasing the draw ratio and draw temperature and lowering MMT content had the similar impacts on the crystalline morphology and melting behaviors of PP/OMMT composites after drawing.The orientation of PP/OMMT composites after drawing was analogous to the behavior after shearing in melting state that nanoclays could retard both the orientation and disorientation of PP chains,and at a higher temperature the retardance of disorientation prevailed.Poly(vinylidene difluoride)/organically modified montmorillonite(PVDF/OMMT) nanocomposites were prepared by a solution blending and co-precipitation method. The impacts of OMMT concentration,thermal treatment and organically modification of OMMT on the crystallization behavior of PVDF/OMMT nanocomposites were studied.Neat PVDF and PVDF/OMMT solutions in DMF were electrospun and the composite nanofibers were collected using an aluminum foil.It was found that the non-polarαphase was completely absent in the electrospun PVDF/OMMT composite nanofibers,while it was still present in the neat PVDF electrospun fibers and in the thin films of PVDF/OMMT nanocomposites.The stabilization effect of OMMT on the long trans conformation of PVDF was revealed by a carefully designed by melting-recrystallization experiment.A simple model was proposed to describe the synergistic effect between electrospinning and nanoclay on formation of polarβandγcrystalline phases.