Crystallization Behavior Of Mesophase Isotactic Polypropylene During Stretching And Preparation Of Mesophase Segregated Structure

Isotactic polypropylene(iPP)is one of the most widely used plastics due to its excellent mechanical properties,good heat resistance and processability.Generally,the structure of the polymer determines its performance,and iPP is a typical polycrystalline structure.Therefore,studying the crystalline structure of iPP helps improve the performance of the product.In addition to the common ?,?,and ? phases,the mesophase iPP has received extensive attention due to its special physical properties.As a metastable phase,the mesophase has an unstable structure and can crystallize under certain conditions.Therefore,one can precisely control the crystallinity and crystal structure by controlling the crystallization process of the mesophase,thereby improving the performance of iPP.In this paper,the mesophase iPP was first prepared by the rapid pressurization,and the phase transition behavior of the mesophase iPP at different temperatures was studied in combination with wide-angle X-ray diffraction(WAXD).Based on the above mechanical data,the ultra-high ductility of the mesophase gives us inspiration to improve the toughness of the segregated structure products.Therefore,this work further successfully prepared the mesophase iPP / CNTs with segregated structure,and carried out electrical and mechanical properties Test.The main research results are as follows:1.Crystallization behavior of iPP mesophase prepared by rapid pressurization during stretching(1)It was found that isothermal crystallization above 80 ? can induce the transformation of mesophase to ? phase,and the higher the temperature,the easier the transformation occur,and the transformation mainly consists of two-step crystallization.And the crystallization mainly comes from the mesophase,and the amorphous basically does not participate.(2)It was proved that stretching at above 40 ? can induce the transition of the mesophase to ? phase,which is fundamentally different from stretching the mesophase at normal temperature without phase transformation.The higher the temperature,the faster the transition occur.And the transition of the ? phase is mainly at the expense of the mesophase.It is found that the stretching transition below 50 ? is mainly due to stretching,while the effect of stretching temperature above 80 ? on the phase transition is more obvious.(3)When stretching above 40 ?,the stretching can promote the phase transition from mesophase to ? crystal,and the lower the stretching temperature,the more obvious the promotion effect.Under the double action of temperature and stretching,the intermediate phase iPP can be more easily transformed into the ? phase.2.Segregated structure of mesophase iPP/CNTs prepared by rapid pressurization(1)iPP/CNTs with segregated structure were successfully prepared for the first time by rapid pressurization.Through the tests of the electrical conductivity,it was found that although the electrical conductivity of the mesophase has decreased,it is still at the electrical conductivity level.The ? phase formed after annealing the mesophase has improved the conductivity compared to the mesophase.(2)Through mechanical tests,we compared the mechanical properties of three samples,namely the initial segregated structure of the ? phase,the segregated structure of the mesophase,and the segregated structure of the mesophase annealed to ? phase.Although the initial segregated structure has high modulus and strength,it shows brittle fracture.The mesophase and mesophase annealed to ? phase have outstanding toughness due to the unique nodule structure.This successfully solves the problem of poor toughness of traditional segregated structure.