MICROSTRUCTURE EVOLUTION DURING TENSION DEFORMATION OF SEMI-CRYSTALLINE POLYMER

Molecular dynamics simulation with coarse-grained model of polyvinyl alcohol was used to investigate the structure of semicrystalline polymer through melt-cooling process.The relationship between microstructure and macroscopic mechanical behavior was then investigated to reveal the microscopic mechanism of semicrystalline polymer during uniaxial tension.The stress-strain behavior comprised elastic stage, yield stage, strain softening stage and strain hardening stage.Several important structural evolution forms were investigated:reorientation of molecular chains, slipping of PVA molecules in crystalline region, disturbed crystalline region(crystal to amorphous) and disentanglement of PVA molecules in the amorphous region.The stress-strain behaviors in the crystal region and amorphous region were investigated respectively. The stress varied in two regions during uniaxial tension, which mainly caused by various microstructure evolution in different stages.In the elastic stage, the main microstructure evolution was the reorientation of molecular chains.In the strain softening stage, the slipping behavior of folded chains in the crystalline region and the disentanglement of the PVA molecules in the amorphous region were the main structural evolution forms.The stress in the crystal region in this stage was larger than that in the amorphous region, because keeping slipping behavior of folded chains in crystalline region was harder than to deform in the amorphous region.In the strain hardening stage, the deformation of amorphous region was more difficult than crystal slipping, in other words, the disentanglement of PVA molecules need more energy.The stress in this stage increased which mainly led to the mechanical behavior of strain hardening.In conclusion, the coordinated microstructure evolution contributed to macroscopic mechanical behavior during tension in spite of the variation of the main microstructure evolutions in different stages.