The Preparation Of Microporous Polyethylene Using Hollow Glass Beads As Gas Carriers

In this paper, the idea was raised that preparing Microporous low density polyethylene(LDPE) by N2-filled hollow glass beads as novel gas carriers and LDPE as matrix, and by physics foam and compression molding. The effect of Ethylene propylene terpolymer(EPDM) and bromine fire-retardant system on the heat insulation performance, mechanics performance and fire retardance of microporous LDPE was studied.In the paper, the effect of the technical parameters and the content of the components on the performance of microporous LDPE was studied firstly. The test on samples by scanning electronic microscopy(SEM), mechanics performance and thermal conductivity test showed that the number of hollow glass beads cracked was little at 165℃ mixing temperature, the optimum compression temperature, time and pressure were 160℃, 8 minutes and 12 MPa, respectively, and the cooling method was quencher; the optimum contents of hollow glass beads and crosslinked agent, dicumyl peroxide(DCP), were 25% and 2.0%, respectively, the tensile strength, breaking elongation, impact strength and thermal conductivity of microporous LDPE prepared in the condition were 12.2MPa, 218.6%, 74.1 KJ/m2 and 0.050 W/m·K, respectively.In the paper EPDM was selected to improve the impact performance of microporous LDPE. Firstly, mechanics performance test, dynamic mechanical analysis(DMA), X radial diffraction(XRD) and SEM were used to analyze the mechanics performance, crystallinity and compatibility of the LDPE/EPDM blend. The results indicated that EPDM and LDPE have excellent compatibility, the tensile strength increased and crystallinity decreased with EPDM content increase, samples did not break when impacted. Gel rate test indicated that the gel rate of the system increased slightly with EPDM content increase. thermal conductivity test showed the thermal conductivity of microporous LDPE was 0.034 W/m·K and samples did not break when impacted when EPDM content was 30%.In the paper, decabromodiphenyl oxide(DBDPO), octabromodiphenyl oxide (OBDPO) and Sb2O3 were used to modify the fire retardance of microporous LDPE. Limiting oxygen index(LOI) and mechanics performance testing results indicated that the fire retardance of DBDPO to LDPE was better than that OBDPO, but it resulted in a greater decrease of the mechanics performance of microporous LDPE. Sb2O3 had a cooperative effect with DBDPO or OBDPO, which made the fire retardance ofmicroporous LDPE increase greatly, and the optimum ratios of DBDPO/ Sb2O3 and OBDPO/ Sb2O3 were 3:1 and 2.5:1, respectively. The compound fire-retardant system, DBDPO/OBDPO/ Sb2O3=35/15/17(named as fire-retardant system C in the paper), could give attention to the mechanics performance and the fire retardance of materials. The LOI of the microporous LDPE with 8% fire-retardant system C was 27.4, which met the standard of fire resistant materials. The LOI of the sample with 8% fire-retardant system C and 30% EPDM increased to 28.2, its thermal conductivity decreased to 0.044 W/m·K, and its tensile strength and breaking elongation increased to 14.8MPa and 220.4%, respectively, meanwhile it did not break when impacted.The microporous LDPE prepared by this technique possessed the cell diameter ranged from 0.1μm to 10μm and the cell density of about 10~9~10~11/cm3, and bubbles distributed equably, and it had excellent heat insulation performance, mechanics performance and fire retardance.