The Influence Of Solid Phase Stretching On Microstructure And Physical Properties Of Polypropylene Sheet Containing β Nucleating Agent

The aggregate structure of isotactic polypropylene(iPP)determined the comprehensive properties of its final products.Adjusting the iPP aggregate structure through the external field to optimize the iPP performance had always attracted the attention of a large number of research teams,but most of the research work was focused on the toughening modification of the iPP film.Because the iPP products generally had a certain thickness,and under the external field,the iPP film was in a two-dimensional stress state,while the iPP sheet was in a three-dimensional stress state,the stretching of the iPP film was quite different from that of the iPP sheet.Therefore,it was of great theoretical significance and practical application value to study the effect of solid phase stretching on the microstructure and physical properties of iPP sheets.In this thesis,the effects of mixing process and β nucleating agent content on the mechanical properties and crystallization properties of iPP sheets containing β nucleating agent were studied based on a two-rotor continuous mixer.High-performance iPP sheet containing β nucleating agent was prepared by solid phase stretching and quenching by means of a tensile tester with high and low temperature test chamber.The mechanism for solid phase stretching to affect iPP sheets containing β nucleating agent was investigated.The model of the influence of solid phase stretching on the microstructure and physical properties of the iPP sheet containing β-nucleating agent was established,and the optimum solid phase stretching conditions were determined.Finally,the effect of annealing on the crystallization and mechanical properties of iPP sheet containing the β-nucleating agent was studied by means of an electrothermal constant temperature blast drying oven.The main research results were as follows:(1)The iPP sheet containing β nucleating agent was solid-phase stretched to form a regular microscopic morphology,which had a more significant effect on the physical properties of iPP sheet.A strengthening model for solid phase stretching of iPP sheet containing β nucleating agent was established by analyzing the changes of crystallinity and microstructure during solid phase stretching of iPP sheet.(2)The stretching strain was mainly to optimize the physical properties of the iPP sheet containing the β nucleating agent by adjusting the microstructure.The stretching temperature was to control the physical properties of the iPP sheet by controlling the structure of iPP sheet and the conversion amount of β crystal to a crystal.After the iPP sheet was subjected to solid phase stretching and strengthening under the optimum stretching conditions(stretching strain 15%,stretching temperature 130℃),the impact strength was nearly twice that of the unstretched iPP sheet containing β nucleating agent.(3)The iPP sheet containing β nucleating agent had a small residual stress after being directly stretched without annealing,and the orientation was relatively complete,and the residual β crystal was more,and the toughening effect was more obvious.If the iPP sheet containing β nucleating agent was annealed and then stretched,the toughening effect was not obvious since the a crystal was relatively hard and unfavorable for orientation;Although re-annealing after stretching was helpful for orientation and toughening,the process was more complicated and was not recommended.