Doctoral Degrees (Forest and Wood Science)

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Browsing Doctoral Degrees (Forest and Wood Science) by Subject "Building materials -- Thermal properties -- South Africa"

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    Properties of wood-plastic composites made from alien invasive tree waste and recycled low-density polyethylene for interior use in social housing
    (Stellenbosch : Stellenbosch University, 2022-11) Mohammed, Abubakar Sadiq; Meincken, Martina; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACTS: Low-cost wood plastic composites (WPCs) were developed from the entire biomass of invasive trees and recycled low-density polyethylene. The aim was to produce affordable building materials for low-cost social housing in South Africa. Both raw materials are regarded as waste materials and the subsequent product development adds value to these resources, while simultaneously reducing the waste stream. The entire biomass of Acacia saligna salvaged from clearing operations was utilised as received, without any prior processing to minimise associated processing costs. Low-grade recycled low-density polyethylene (rLDPE) was used as the matrix to make the WPCs without any additives as an additional cost-cutting measure. The WPCs were at three different biomass content (50, 60 and 70 wt%), with two wood particle sizes (0.3 and 0.5 mm), and at different hot press times (10 and 30 min) and temperatures (150 and 180 °C) to obtain boards with optimum mechanical, physical and insulation properties for use in social housing in South Africa. The water absorption, dimensional stability, moduli of elasticity (MOE) and rupture (MOR), tensile strength and modulus were found to be better at longer press times and higher temperatures for all blending ratios. An increased biomass content and particle size were positively correlated with water absorption and thickness swelling and inversely related to MOR, tensile strength and density due to discontinues plastic matrix formation. A heat flow meter (HFM) and an acoustic impedance tube were designed and built to measure the thermal transmission and sound transmission loss (STL) properties of the WPCs. Boards from larger sized particles generally showed lower conductivity. The boards pressed with 70 wt% biomass and lower press temperature and time had the lowest heat conductivity value (0.044 W/m‧k), which can be attributed to higher incidence of lattice defects and vacancies due to a higher proportion of thermally modified biomass. The boards pressed with 50 wt% biomass at 150 °C for 10 min possessed a higher mass/stiffness ratio, which resulted in improved STL via reflection and absorption of acoustic energy in the mid-frequencies (500-2000 Hz). Boards produced with 60 wt% biomass exhibited the best noise attenuation level (8-14 dB) and thermal insulation with a heat conductivity around 0.048-0.056 W/m‧k, making them best suited as insulation boards to improve living conditions in Reconstruction and Development Programme (RDP) houses. The low proportion of non-woody biomass (leaves and bark) in the WPC formulation did not entirely inhibit mould growth on the WPC surfaces immediatly, even though the growth was slowed across all samples in no particular order. The fire tests showed that the WPCs composed with 70 wt% biomass pose the lowest fire hazard as they possess higher flammability and self-ignition temperatures and are also the most thermally stable with the highest melt-deflection temperature. This study demonstrates the feasibility of utilising low-grade recycled polyethylene and whole-tree biomass of A. saligna to manufacture WPC boards, without the need for pre-processing, or the addition of expensive compatibilisers, to produce boards with properties that satisfy the minimum South African Bureau of Standards (SABS) requirements for interior wall or ceiling cladding.