CHEMICAL FORCE MICROSCOPY ANALYSIS OF WOOD-PLASTIC COMPOSITES PRODUCED FROM DIFFERENT WOOD SPECIES AND COMPATIBILIZERS
Keywords:
Alien invasive species, compatibiliser, adhesive force, chemical force microscopy, tensile strengthAbstract
Alien invasive species are posing a serious and direct threat to biodiversity, water security, and productive use of land in South Africa. Most of these species need to be cleared and are therefore regarded as waste material, which could become raw material for wood-plastic composites (WPCs). WPCs containing wood from Pinus radiata, Eucalyptus grandis, Acacia mearnsii, Acacia longifolia, Acacia saligna, and Casuarina cunninghamiana trees, low-density polyethylene (LDPE) and three different compatibilizers: namely the commercially available ethylene vinyl alcohol (EVOH), polyethylene graft-maleic anhydride (PE-g-MA), and thermally degraded LDPE (dPE)—were studied. The determined properties included MC, density, tensile strength, and adhesive forces between the wood and compatibilizer components. The adhesive forces were determined using chemical force microscopy with functionalized, coated tips. WPC samples were compounded and injection molded. EVOH as compatibilizer proved to be very sensitive to the wood species incorporated into the WPC blend. Composites containing PE-g-MA and dPE as compatibilizer had a higher tensile strength for all the wood species. Composites containing dPE as compatibilizer showed less variation in all samples for tensile strength and adhesive force measurements. The densities and tensile strengths of the samples compares well with some commercial WPCs. The study shows that the inexpensive dPE outperforms commercially available compatibilizers and effectively promotes adhesion in WPCs. It was also shown that the studied invasive wood species can be incorporated into WPCs, if the correct compatibilizer is chosen. The differences in the results of the study seem difficult to relate due to the many factors such as the wood species, MC, density, compatibilizers, and processing method. However, the micro properties can give enough information regarding the macro properties of WPCs.
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