Preparation And Properties Of Polypropylene Supercritical Foaming Material

Propylene butene copolymer(PPB),which is formed by the addition polymerization of propylene and butene,has been widely used because it improves the brittleness and poor impact resistance of polypropylene.Polyolefin foaming material is the fastest growing foaming product at home and abroad because of its light weight,high cost performance,excellent mechanical properties,heat resistance,chemical corrosion resistance,easy recovery and green environmental protection.It will gradually replace polystyrene(EPS)foaming material and become the mainstream foaming products in the domestic and foreign markets.Therefore,this paper systematically studied the thermal insulation,flame retardant and foaming properties of PPB/EPDM blends.Firstly,PPB/EPDM blends were prepared.PPB/EPDM supercritical foaming materials were prepared by sulfur vulcanization system,twice vulcanization process and supercritical nitrogen as physical foaming agent.The effects of PPB/EPDM blend ratio on phase structure,pre vulcanization time on foaming and processing times on the mechanical properties of PPB/EPDM were studied.The research shows that PPB has good compatibility with EPDM;When EPDM is 70 phr,EPDM changes from continuous phase to dispersed phase after melt processing;With the increase of pre vulcanization time,the density of PPB/EPDM foam decreased first and then increased,and the density was the lowest at 18 minutes(0.06 g/cm~3);With the increase of EPDM content,the hardness,tensile strength and strength decrease gradually,elongation at break increased,and the permanent compression resistance was the best when the EPDM content was 70 phr;PPB/EPDM foaming material can realize repeated processing and re-foaming,and has similar mechanical properties to TPV prepared by dynamic vulcanization process.Secondly,the low density PPB composite foam material was prepared by using PPB as the substrate,the low density PPB composite foam materials were prepared by the irradiation crosslinking technology and supercritical CO₂ as physical foaming agent.The mechanical properties and thermal insulation properties of PPB composite foam materials were studied by using radiation crosslinking technology and supercritical SiO₂ as physical foaming agent.The radiation dose,lignin fiber and SiO₂ aerogel content were also studied.The results show that with the increase of irradiation dose,the foaming effect of PPB composites first becomes better and then worse.The best foaming effect is obtained at 30 k Gy,and the cells are uniform and regular;The mechanical properties showed the same trend with the increase of radiation dose,and reached the optimal mechanical properties at 30 k Gy;Radiation crosslinking also improves the thermal properties of PPB,improves the temperature resistance of the material,enhances the melt strength,widens the melting range,and widens the foaming window of PPB composites;The addition of lignin fibers and SiO₂ aerogels further promoted the radiation crosslinking and provided more crosslinking points.The pore structure,mechanical properties and thermal insulation properties of the composites were 3 phr respectively.The combination of SiO₂ aerogels and lignin fibers could further reduce the thermal conductivity.When the blending number was 1.5 phr/1.5 phr,the thermal conductivity was the lowest(0.0268 W/m·K).Finally,PPB composite flame retardants material were prepared by lignin fibers,ammonium polyphosphate(APP),resorcinol diphenyl phosphate(RDP)and SiO₂aerogels.The flame retardant effect of the composite system on PPB composites was studied.The results showed that the filler was evenly dispersed in PPB substrate;The use of lignin fibers,APP,RDP and SiO₂ aerogels as flame retardants alone did not improve the flame retardancy of PPB composites.When APP was added with a higher fraction,the limit oxygen index still failed to reach the refractory grade(the limiting oxygen index was greater than 27%).The synergistic effect of the four could significantly improve the flame retardancy of PPB.The intumescent flame retardant system composed of lignin fiber/APP/RDP/SiO₂ aerogels can not only reduce the smoke release rate and heat release rate of combustion,but also form a compact carbon layer on the surface of the material to prevent the material from continuing to burn.Finally,after supercritical carbon dioxide foaming,the UL-94 vertical combustion grade of PPB flame retardant foaming material can reach V-0 and the limiting oxygen index is 29%.