Study The Physical Properties Of The Polymers Under Strain State

This thesis studies physical properties of polymer materials under strain state. Polycarbonate (PC), polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC) are selected for the study, and tensile and bending strains are applied on the samples of these materials to observe changes in properties of these materials with time. This study is divided into the following three parts.First, in order to compare the strained aging property and physical aging properties of the glassy PC, glassy polycarbonate (PC) samples of physical aging, samples quenched and aged under strains and samples annealed and aged strains were studied by testing of mechanical properties and the differential scanning calorimeter (DSC) measurement. The test results of mechanical properties show that, the yield stress σy and elastic modulus E of samples of strain aging get larger as time goes on, and in the same aging time, the yield stress σy and elastic modulus E of samples quenched and aged under tensile strains as well as samples annealed and aged under tensile strains are higher than those of samples of physical aging. It means that the property of polycarbonate material was changed from toughness to brittleness. The DSC measurement results shows that, around the glass transition temperature Tg, the heat absorption peaks of samples quenched and aged under tensile strains are larger than that of samples of physical aging. The similar DSC measurement results were obtained for the samples in the quasi-equilibrium state, namely the samples annealed and aged under tensile strains, regardless of strain amounts. These results of mechanical property tests and the differential scanning calorimeter (DSC) measurement indicate that the structure and aging mechanism of strain aging samples are different with that of physical aging samples.Secondly, changes in properties of amorphous polymer materials, PC and PMMA, under bending strain were studied with static mechanical property tests and DSC measurement. From the static mechanical property test results, it is clear that change in mechanical properties of these materials under bending strain state are very similar to change under tensile strain state, increasing with time. And the DSC results indicate that apart from that a condensation tangled structure is formed in the bending-strained specimen, some amount of energy is stored in condensed matter structures inside the molecular chain, and formation of this structure is irrelevant to material strain mode (tensile or bending strain).Finally, the plastic working for glassy polymer materials at low temperature was discussed. Non-equilibrium polymer structure of samples of PVC and PC were obtained by stretching them uniaxially to observe changes in their mechanical properties with time. In order to discuss effect of deformation amount and heat history on mechanical properties of materials, DSC analyses were carried out to the samples. The results show that the extent of thermodynamic non-equilibrium of polymer materials become higher, in a short time after deformation, and the polymer materials softened. Comparing with the state before deformation, the mechanical properties such as yield stress and elastic modulus after deformation become larger obviously. Thus, the results of this paper may become the experimental foundation for shaping of solid polymer materials at low temperature by utilizing the property that polymer structure softens in a short time after deformation, and strengthening polymer materials by utilizing the phenomenon that the polymer materials become harder in a long time after deformation.