Study of Polymer Microstructure Under Rapid Compression and Tensile Deformation
|Course||Materials Processing Engineering|
|Keywords||Rapid compression In situ tension Crystal destruction Crystalorientation|
In this paper, we studied their effects of rapid compression and tensile process on the micro structure of the polymer.As a new method for preparation of materials, rapid compression has a very important research significance for polymer processing. This method could be used to obtain the large pieces of material with special performance, for example, amorphous material, metastable phase and supramolecular polymers. In addition, in situ tension plays a more important role in evolution of polymer structure in the process of tensile deformation. We could understand the microscopic structure of polymer better and provide theoretical support for industrial processes. In this thesis, we focus on the changes in the micro structure of the polymer under rapid compression and tensile deformation. The crystalline structure of polyethylene with different molecular weight and degree of branching was discussed. In addation, for isotactic polypropylene, the critical stress and strain of the crystal destruction were investigated under different thickness of crystal and different tensile rates. The main results are as follows:(1) The crystalline structure of polyethylene with different molecular weight was spherulite prepared under rapid compression and liquid nitrogen quenching cold. For rapid compression, the molecular weight has a marked influence on the crystal structure. The bigger molecular weight the polyethylene has, the smaller size the crystal will become. In addition, the rapid compression reduces the content of rigid amorphous and improves the degree of crystallization.(2) Rapid compression has a different influence on HDPE and LLDPE. For LLDPE low mobility of molecular chains, rapid compression hinders the crystallization of the polymer melt effectively comparing with liquid nitrogen quenching cold.(3) The crystallinity distribution of rapid compressing samples is more uniform regardless of low thermal diffusivity of polymers because there is no temperature gradient and cooling velocity gradient. (4) Due to the accumulation is in a different direction, Crystal of uneven deformation in the process of uniaxial tensile deformation is probably the generality of the material. In the curve of true strain and true stress, the yield point is the inflection point of crystal deformation from fast to slow transformation. The critical strain is not affected by thickness of crystal and strain rate, while the critical stress increases with the increase of thickness of crystal and strain rate. Meanwhile the yield point is the starting point of crystal orientation and destruction and crystal orientation and destruction occur at the same time.