Study On Preparation And Mechanical Properties Of Modified Polypropylene Foaming Materials

Polypropylene(PP)foams are widely used because of many advantages such as low density,good temperature resistance,environment-friendly,high cost performance,etc.However,the application of PP foams is limited in certain areas by its low toughness,poor impact resistance and low compression deformation recovery.In this paper,linear low-density polyethylene(LLDPE)and polyolefin elasticity(OBC)are introduced into PP materials to improve its mechanical properties.various PP based foams of PP/LLDPE,PP/OBC blend,PP/OBC crosslinked blend in different ways were prepared by using supercritical carbon dioxide(sc CO₂)batch foaming process.And the effects of blend types,blending ratios and cross-linking modification on the foaming process conditions,cell structure and mechanical properties were studied.Firstly,comparing with neat-PP foam,PP/LLDPE blend foam has lower foaming temperature,smaller cell size and higher cell density,and higher elongation at break and compression deformation recovery.However,the toughness of blend foam is not enhanced due to its low strength with the addition of LLDPE.Secondly,for PP/OBC blend foam,the cell size is the smallest and the cell density is the largest when the OBC content is 10wt%.And an open cell structure is formed when the OBC content is up to 30wt%.Although the strength of PP/OBC blended foamed material is reduced by 15%-19%compared with neat-PP foam,the breaking elongation is increased by 150%-250%,so its toughness is improved.and its compression recovery rate also improved significantly,when the OBC content was 30wt%,the compression recovery rate reached 94%.Thirdly,PP/OBC crosslinked blend material 1 is obtained by cross-linking OBC first and then blended with PP,and PP/OBC crosslinked blend material 2 is obtained by direct blending and crosslinking of PP and OBC.It was found that the crystallinity of the modified materials after crosslinking was significantly improved,and the crystal size was smaller than that of neat-PP.Compared with the uncross-linked modified PP foam material,the tensile strength of the crosslinked blended foams is significantly improved.Although the tensile strength of material 1is still less than that of neat one,its breaking elongation is the largest in the tested samples.Therefore,its toughness is significantly improved.On the other hand,the tensile strength of material 2 was higher than that of neat one,which reached 3.1Mpa,leading to the higher toughness.Crosslinking can also effectively improve the compressive strength of foams,and the durability and compression recovery of crosslinked blend foams are better than that of neat one.Among them,the loss of permanent compression deformation of material 1 is only 5%.Finally,the blend foams of PP/OBC crosslinking or not can improve the toughness and compression recovery more or less,comparing with neat PP foam.In our study,material 2 foam has the smallest cell size,the largest cell density,the uniform and complete cell morphology and the best comprehensive mechanical performance,comparing with other samples.