Research On Microlayer Coextruded PP/(POE/LDPE) Sheets And Their Foaming

Microlayer coextrusion technology can be used to prepare novel products with alternate multilayered structure.In this dissertation,combining flow field of two inlet modes was simulated.Ethylene–octene copolymer/low-density polyethylene（POE/LDPE）blends and multilayered polypropylene（PP）/（POE/LDPE）sheets were prepared.Their rheological and mechanical properties were investigated.The blends and multilayered sheets were foamed in an autoclave to investigate the influence of foaming conditions and microlayer structure on the cell structures of foamed samples.The formation mechanism of different cell structures was analyzed in order to offer new ideas for the preparation of high-performance multilayered foamed materials.The simulated results of combining channels for two inlet modes showed that different inlet position changed the position of melt sections at the outlet,resulting in different thickness uniformity along the width direction of sheets.The characterized results of POE/LDPE blends with five different LDPE contents showed that POE and LDPE exhibited good compatibility.When the content of LDPE was 30 wt%,LDPE might form continuous phase in the blend,which was consistent with the theoretically calculated results.Under high pressure Sc-CO₂,the times for the blends reaching approximate saturation points decreased with LDPE content increasing.The melt strength and yield strength of the blends increased with the increase of LDPE content.The blend with 50 wt%LDPE had the highest melt strength（61.1 mN）.POE had an inhibited effect on the crystallization of LDPE.The characterized results of multilayered PP/（POE/LDPE）sheets showed that the interfacial interaction between microlayers decreased with the increase of LDPE content in the blend layers,and the elongation at break of multilayered PP/（POE/LDPE）sheets increased with the increase of layers.POE/LDPE blends and multilayered PP/（POE/LDPE）sheets were foamed based on the orthogonal design.The results showed that the saturation pressure was the main factor affecting mean cell diameter and cell density.The optimum foaming conditions were obtained by intuitionistic analysis,and the crystallization behavior of LDPE during foaming process was controlled by variable temperature modes.As the number of layers increased,the yield strength and compressive strength of multilayered PP/（POE/LDPE）foamed samples prepared under optimized foaming conditions increased,and the thermal conductivities decreased significantly(from 322.5 mW·K^-1·m^-1 of the blend foamed sample to a minimum of 47.2 mW·K^-1·m^-1).By analyzing cell structures of multilayered foamed samples,it was found that the thickness ratio of film layer to foam layer and the interfacial interaction had great influence on the cell structure for multilayered foamed samples.