Structure, physical properties, and flame retardancy of POE/NR/EG blend foams: Effect of crosslinking

Abstract

Elastomeric foams were produced by melt-mixing of polyethylene-octene elastomer (POE), natural rubber (NR), and expandable graphite (EG) in an internal mixer. The blend was later foamed by compression-molding method. EG was used as a filler to enhance flame retardancy of the blend foams. Dicumyl peroxide (DCP) was used as curative to crosslink the blend foams. The influence of DCP content (0.5, 0.7, 0.9, and 1.0 part(s) by weight, pbw) on rheological properties, structure, density, mechanical properties, thermal conductivity, and flame retardancy of the POE/NR/EG blend foams was investigated. The rheological analysis showed that the melt strength/viscosity of the POE/NR/EG blend foams increased with more DCP addition due to promoted crosslinking in the blend foams. The cellular structural observation by SEM technique revealed that the POE/NR/EG blend foams had close-cell structure. Increasing DCP content, the blend foams had smaller cell and narrower cell size distribution. The degree of porosity, however, was highest for the foamed blends added with 0.7 pbw DCP, which brought about the lowest thermal conductivity. Furthermore, it was found that the density, tensile strength, elastomeric recovery, and compressive strength increased with increasing content of DCP, but the elongation at break decreased. The POE/NR/EG blend foams reached the horizontal burning level of HF-1, and their oxygen index increased in accordance with an increase of DCP content. The results indicated that an appropriate use of DCP was critical for the crosslinked POE/NR/EG blend foams with optimum cellular structure, providing the best improvement in thermal insulation properties and good flame retardancy.