Study On Micro-foaming Of Polyethylene High Pressure Fluid

In this paper three kinds of polyethylene resins,HDPE,LDPE and LLDPE,with similar chain structure and different melting finger.They were used to prepare polymer bead foams by using a green and environmental CO₂ gas as a physical foaming agent.The effects of isothermal treatment temperature and saturation pressure on the expansion of PE bead foams were studied,and three kinds of polyethylene were discussed.The influence of melt index and POE blending on the foaming behavior of PE autoclave foaming is revealed.Three kinds of PE autoclave foaming of HDPE,LDPE and LLDPE were studied,and the characteristics of three kinds of PE foaming behaviors were found;The LLDPE with different melt index was studied.It was found that the foaming temperature window of the resin broadens as the melt index decreases;using DSC to study and simulate the evolution of thermal behavior of PE foam beads and PE pressure foaming process;it was found that there were two peaks,one is the low melting peak T_mlow and the other is the high melting peak T_mhigh.When the treatment temperature is not high than the melting point,the peak value of T_mlow increases with the increase of the temperature.The peak value of T_mhigh is always near 126℃above the melting point about 4℃.When the treatment temperature is higher than the melting point,there is only one melting peak T_mc.And the effect of blending POE on the foaming behavior of LDPE was studied.It was found that the addition of POE increased the foaming rate of PE.We added POE components with different blending ratios into the LDPE/POE system.We also added POE components with different blending ratios into the LDPE system.The experimental results showed when the POE components of the LDPE/POE system was below 20%,the POE components gradually increased for LDPE/POE foam as the expansion rate increased.When the POE components reaches15%,a shoulder peak appears on the right side of the T_mhigh peak in the DSC curve,because the melting point of POE and LDPE is different.When the POE component content reaches a certain value,the shoulder peak appears.At last,LDPE/POE bead foam and thermal simulation was tested by DSC.It was found that CO₂ could induce a small melting peak of T_mi near 85℃.