Research On The Preparation,structure And Properties Of High Performance Polypropylene

As the second largest polyolefin product in China,polypropylene is widely used in automobiles,household appliances,logistics,packaging and other fields.In recent years,with the improvement of people’s living standards,while ensuring the quality,it is possible to take into account the aesthetics and plasticity and become a new pursuit of products.At present,there are problems of low-end varieties and scarcity of high-end varieties in Chinese polypropylene market.Most of the polypropylene products on the market have single performance,and they have shortcomings such as low toughness、rigidity and optical,which greatly limits the application of polypropylene.Therefore,it is important to research on polypropylene products with high performance.This paper aims to research and develop high performance polypropylene materials.High-gloss and high-impact polypropylene was prepared by one-stage polymerization;high-impact and high-modulus polypropylene was prepared by two-stage polymerization.Through the study of PP/EPR/PE ternary blends,it was found that low-density polyethylene can effectively improve the gloss of the blends under the premise of ensuring the toughness.The main research work and research results of the thesis are as follows:(1)The effects of ethylene content and hydrogen content on the molecular chain structure,condensed structure,optical properties and mechanical properties of ethylene-propylene copolymer were investigated by a one-stage gas phase polymerization.The experimental results show that the increase of ethylene content in the copolymer gas increases the polymerization activity of the polymer and the molar content of ethylene.The formation of more ethylene-propylene random copolymer destroys the crystallization of the polymer,decreases the melting point、crystallinity,and increases the MFR.The increase of the hydrogen content in the copolymer gas increases the activity of the polymer,decreases the molar content of ethylene,increases the melting point、crystallinity and MFR.It was found that the ethylene-propylene copolymer produced by one-stage polymerization is a polypropylene segment formed by a propylene segment and a piece of ethylene-propylene random copolymer,which is a single phase.As the ethylene content of the ethylene-propylene copolymer increases,the gloss and impact resistance of the ethylene-propylene copolymer increase simultaneously.Polypropylene having excellent gloss(102.7%)and impact properties(8.43 KJ/m2)was prepared by polymerization at 0.02 bar of hydrogen and 0.60 bar of ethylene.(2)The effects of ethylene-propylene gas ratio,hydrogen content and reaction time on the molecular chain structure,condensed structure and mechanical properties of polypropylene alloy were investigated by two-stage polymerization.The experimental results show that the decrease of the ratio of ethylene to propylene in the copolymerization stage increases the polymerization activity,reduces the rubber phase content of the polymer,and increases the ethylene content,crystallinity and molecular weight of the polymer.The increase of hydrogen content increases the polymerization activity and the rubber phase content of the polymer,reduces the ethylene content,crystallinity and molecular weight of the polymer.The increase of reaction time reduces the polymerization activity and increases the rubber phase content,ethylene content,and molecular weight of the polymer.It was found that the polymer produced under the high ethylene-propylene ratio is an in-situ blends of polypropylene,ethylene-propylene copolymer and polyethylene.The mechanical properties show that the flexural properties of the polymer decrease with the increase of ethylene content in the copolymerization stage,and the impact resistance increases first,then decreases and then increases.Polypropylene having excellent bending properties(29.43 MPa)and impact resistance(6.67 KJ/m2)was prepared by polymerization at a copolymerization gas ratio of ethylene to propylene of 1:2.(3)The effects of the density and content of polyethylene in PP/EPR/PE ternary blends on the crystallization behavior,microstructure,gloss and mechanical properties of the blends were investigated.The experimental results show that the increase of PE content in the PP/EPR/PE ternary blend has little effect on the spherulite size,but increases the size of the dispersed phase.The lower the density of PE,the smaller the spherulite size.However,it has little effect on the size of the dispersed phase.It is found that the rigidity of the blend is related to the size and crystallinity of the bulk modulus.The toughness of the blend is related to the size and structure of the dispersed phase.When the size of the dispersed phase is between 2.5 and 3.0 μm,the toughness of the blend is the best.The gloss of the blend is related to its spherulite size and the size structure of the dispersed phase.Based on the analysis of gloss,a model of the influence of core-shell structure on gloss is proposed.The more uniform the dispersed phase structure,the weaker the light scattering ability,the less energy consumption,and the higher the gloss of the blend.Through the characterization and analysis of PP/EPR/PE ternary blends,it is found that by regulating the density and mass content of polyethylene in PP/EPR/PE blends,the rigidity,toughness and gloss of polypropylene can be adjusted,and the application range of polypropylene can be broadened..