SURFACE AND THERMAL STUDIES OF PULAI AND ITS POLYMER COMPOSITES

Abstract

Wood-Polymer Composite based on a local tropical hardwood, Pulai (Alstonia spp.), was prepared by the impregnation of monomers into wood followed by 'in situ' polymerisation using gamma irradiation from a Cobalt-60 source. The monomer systems used were acrylonitrile (AN), styrene (ST), 1:3, 1:1, and 3:1styrene-co-acylonitrile (STAN). The surfaces of wood subjected to air-oxygen, extraction, gamma irradiation, weathering and 'in situ' polymerisation were studied using ESCA (Electron Spectroscopy for Chemical Analysis). Weathered WPC and polymer were also characterised by ESCA. Preliminary studies on strength, dimensional and thermal behaviour of WPC and wood were investigated. ESCA results for Pulai showed that surface composition altered after the processes of weathering, after extraction and modification of wood with polymer. However, gamma-irradiation did not significantly change composition. From the ESCA studies of STAN copolymers. the polyacrylonitrile (PAN) weight fractions were calculated. It was found that both the P1:1 and P3:1 STAN surfaces had similar mole ratios as the theoretical values whereas P1:3 STAN surface had a different mole ratio of 1:2 from the theoretical one In ESCA characterisation of Pulai-AN composite, the concentration of PAN polymer was evaluated and compared with that based on weight. In all five composites, namely, Pulai-AN, Pulai-ST. Pulai-1:3 STAN, Pulai-1:1 STAN and Pulai-3:1 STAN composites, the surface composition differed form that taken from the inner portions. The polymer distribution in Pulai-STAN composites with similar polymer loadings were compared. The polymer distribution in Pulai-1: 1 STAN and Pulai-3: 1 STAN composites was rather uniform unlike that in Pulai-1 :3 STAN composite. Their end surfaces contained polymer which was not detected at the end surface of Pulai-1 :3 STAN composite. Results also showed that chemical composition of surfaces of wood, polymer and WPC after weathering differed from those of the samples before weathering. The composite specimens together with untreated ones were tested for hardness, dimensional stability and thermal degradation. In dimensional stability studies, it was found that Pulai-1 :3 STAN composite showed highest ASE(Anti-Shrink Efficiency), followed by Pulai-1:1 STAN and Pulai-3:1 ST AN compoistes. However, AAE (Anti-Absorption Efficiency) for these three composites did not differ significantly. All the STAN copolymer composites increased in end hardness over the untreated wood specimens. In general, Pulai 3: 1 STAN composite produced the largest increases and Pulai-1 :3 ST AN composite the least. The thermal behaviour of the three STAN composites, together with untreated wood and polymer, were investigated by thermogravimetry. It was found that Pulai-1:3 STAN composite was the most stable to thermal degradation. The results for Pulai-1:1 and Pulai-3:1 STAN composites showed that some interaction was present between polymer impregnants and wood components.