Department of Forest and Wood Science

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Browsing Department of Forest and Wood Science by Author "Amiandamhen, Stephen Osakue"

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    Phosphate bonded wood and fibre composites
    (Stellenbosch : Stellenbosch University, 2017-03) Amiandamhen, Stephen Osakue; Meincken, Martina; Tyhoda, Luvuyo; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: In a world constantly driven by change, developing new composite products requires moving beyond the traditional approach to more environmentally benign processes and products. This study investigates the application of magnesium-based phosphate cement and calcium-based phosphate cement in the development of natural fibre composite products. The magnesium phosphate cement was prepared from a heavy magnesium oxide (MgO) and monopotassium phosphate (KH2PO4), while the calcium phosphate cement was prepared from unslaked lime (CaO), calcium silicate (CaSiO3) and monopotassium phosphate (KH2PO4). These phosphate cements were used to produce composite panels using bio-based industrial residues. The residues utilized include sugarcane bagasse (Saccharum officinarum), hemp hurds (Cannabis sativa), pine sawdust (Pinus elliottii), paper mill sludge and waste paper. Additionally, forest biomass waste from the clearing of locally occurring invasive alien species including Black wattle (Acacia mearnsii), Long-leaved wattle (A. longifolia), Port Jackson (A. saligna), Rooikrans (A. cyclops), Blue gum (Eucalyptus globulus), Sekelbos (Dichrostachys cinerea) and Deurmekaarbos (Ehretia rigida) were used. The study utilized a central composite statistical design, whereupon the following factors were considered i.e. KH2PO4: MgO ratio, KH2PO4: CaO + CaSiO3 ratio, CaO: CaSiO3 ratio and the amount of wood/fibre as a ratio of wood/fibre to the total inorganic content. Additionally, the use of coal fly ash as a complementary material in the composite was investigated. Fitted response surface methodology plots were used to show the relationship between the variable factors on the desired responses. The effect of the main factors and their interactions on the measured board properties were evaluated using Pareto analysis of variance. Response surface models were developed to predict the parameters yielding the optimum board properties. While the physical properties of the panels met the minimum requirements for cement bonded particleboard (EN 634-2:2007) and LD-1 grade particle board (ANSI A208.1:1999), the strength properties needed to be improved to offer more flexibility in terms of application. Three biomass materials were selected for further study aimed at enhancing the properties of the boards. These materials were subjected to three different treatments, namely alkalization, acetylation and hot water extraction. The effect of each of the treatments on the fibre materials was evaluated using HPLC, SEM and FTIR. These materials were used to manufacture composite panels and μCT was used to characterize the microstructure of the composite samples. A numerical technique was used to quantify the phases in the composites, namely cement matrix, filler and void spaces. All treatments improved the fibre characteristics and did not significantly reduce the fibre yield. In magnesium phosphate bonded panels, the mean modulus of rupture was 0.74 MPa for untreated, 1.03 MPa for hot water extracted, 1.20 MPa for acetylated and 1.66 MPa for alkalized black wattle panels. In calcium phosphate bonded panels, the mean modulus of rupture was 0.88 MPa for untreated, 0.83 MPa for hot water extracted, 0.73 MPa for acetylated and 1.18 MPa for alkalized black wattle panels. Boards made with alkali treated fibres had the best properties. The study concluded that bio-based residues can be incorporated into formulated phosphate cement binders to produce durable products that are comparable to current cement bonded products.