Preparation And Properties Of CO₂ Foamed Polypropylene Beads

Polypropylene foamed products not only have the advantages of traditional foaming,but also have degradability and recovery.They are widely concerned by researchers,but due to the late start of China,the technology is not mature enough,and the foaming rate is low.And the process depends on Japan,Europe and other issues.This paper starts with the preparation process of polypropylene,understands the influence of temperature,pressure and holding time on the preparation of beads,and improves the nucleation performance of the system by adding graphene and zeolite,adding low-melting polypropylene to adjust the viscosity of the system,using DSC,rotating The rheometer characterizes the melting crystallization behavior and rheological behavior of the system.The morphology of the cells is observed by SEM and the cell density and expansion ratio are calculated to prepare polypropylene beads with high expansion ratio.Firstly,the effect of foaming process on polypropylene foaming performance and melt crystallization behavior was studied by controlled variable method.The results show that the highest expansion ratio of 13.17 at 146°C and 8 MPa,the cell density at this time is 1.918×10~5/cm~3,and the pressure and temperature have the same effect to some extent.Both the elevated pressure and the elevated temperature cause The cell diameter is increased,the gas coating property is deteriorated;the dwell time has a limited effect on the polypropylene foaming,and the dwell time of 40 min is enough to dissolve the carbon dioxide into the polypropylene matrix;the bead prepared by the intermittent foaming method has a double melting peak Structure,bimodal ratio has a certain relationship with cell morphology.When the bimodal ratio is between 5.36 and 13.17,the cell morphology is better.Secondly,the effects of graphene addition on the melt crystallization behavior,rheological behavior and foaming behavior of polypropylene were investigated.Experiments show that the addition of graphene has no effect on the melting point and crystal form,but it will hinder the crystallization of the system,the crystallization temperature of the city will decrease,and the addition of graphene will decrease the viscosity of the whole system;the addition of graphene can significantly improve the cell density of polypropylene.The optimum expansion ratio occurs when 1 part of graphene,146°C,and 8 MPa is added.At this time,the cell density is 3.634×10~5/cm~3 which is about2 times that of pure polypropylene.Thirdly,the effect of the addition of 5A zeolite on the crystallization behavior,rheological behavior and foaming behavior of polypropylene was investigated.Experiments show that zeolite has little effect on the melt crystallization and rheological behavior of polypropylene,but the addition of zeolite has a good nucleating effect and the zeolite can broaden the temperature range of foaming.1 part of zeolite was added at146°C,and the optimum foaming effect was obtained at 8 MPa,and the cell density was7.149×10~5/cm~3,and the expansion ratio at this time was 13.54.When the amount of zeolite added is 1%,the nucleation property is the best.In addition,the effect of zeolite modification at low pressure is better than that under high pressure.Finally,it was found that the low melting point polypropylene and the copolymerized polypropylene were blended and foamed,and the low melting point polypropylene was blended to make the foaming temperature advance.The maximum expansion ratio appeared at 143°C,and the expansion ratio at this time was 16.93 times.It is 28.5%higher than pure polypropylene and has a cell density of 6.15×10~5/cm~3.Excellent foaming when blending 20%low melting point polypropylene.