Foaming Properties Of Polypropylene Sheet With Supercritical CO₂

Polypropylene?PP?foams have been widely used in packaging,construction and automobile industry because of their excellent heat resistance,sound insulation,shock resistance and chemical corrosion resistance.At present,the research focus of PP foam industry is on the polypropylene foam beads?EPP?and research on the innovation of PP foam sheet is less.Polypropylene foam sheet was prepared through autoclave foaming process using CO₂ as the blowing agent and its performance is studied.The influence of foaming temperature,foaming pressure and foaming times on foaming properties and compression performance of Polypropylene foams were investigated.The results indicate that the cell diameter increases but cell density decreased with foaming temperature and foaming pressure,respectively.the cell structure is more uniform with longer foaming time which is beneficial to the full dissolution of CO₂.The foaming material that mean diameter and cell density is 3.743 ?m and 6.177×1010 cell/cm3 was obtained when the foaming temperature,foaming pressure and foaming tine are 165?,7 MPa and 120 min.The compression performance of Polypropylene Foams obtained at different conditions consistent with its foaming properties,which has a direct relationship with the size and shape of bubble.The foam which has better bubble size and morphology has better compression performance too.Polypropylene was modified by ultra-high molecular weight polyethylene?UHMWPE?.The influence of UHMWPE on rheological properties and crystallization characteristics of PP were investigated.Furthermore,the foaming properties of PP/UHMWPE composites and compression performance of its foaming material were investigated.The results indicate that the addition of UHMWPE can improve the melt strength of PP and improve its foaming properties.The foaming material that average cell size is smallest and the cell density is maximum was obtained when the content of UHMWPE is 20%.In addition,the static compression properties of the blends are directly related to the foaming properties,the foaming material with better cell morphology has better compression characteristic also.The compressive properties of foamed materials increased firstly and then decreased with the increase of UHMWPE content,and the compressive properties of the foamed materials are the best when the content of UHMWPE is 20%.The rheological properties and melt crystallization behavior of PP/ wood flour composites and the effects of the content of wood flour on the foaming properties and compressive properties were studied.The results indicate that the viscosity increase and the melting temperature and crystallization temperature will also increase with the addition of wood flour,A proper amount of wood powder can be dispersed uniformly in PP matrix,which is helpful to improve its foaming properties.But excessive wood flour had negative effect on the bubble shape because wood flour is easy to gather together to form a large group.The compression property of foamed material was gradually increased with the increase of wood flour content,but lower than that of pure PP,and the compressive property when the wood powder content is 30% is the best.