Phosphate bonded wood and fibre composites

Amiandamhen, Stephen Osakue (2017-03)

Thesis (PhD)-Stellenbosch University, 2017.

Thesis

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.

AFRIKAANSE OPSOMMING: In 'n wêreld voortdurend gedryf deur verandering, vereis die ontwikkeling van nuwe saamgestelde produkte ‘n buite die tradisionele benadering tot meer omgewingsvriendelike prosesse en produkte. Hierdie studie ondersoek die toepassing van magnesium-gebaseerde fosfaat sement en kalsium-gebaseerde fosfaat sement in die ontwikkeling van natuurlike vesel saamgestelde produkte. Die magnesium fosfaat sement is bereid van 'n swaar magnesiumoksied (MgO) en monokaliumfosfaat (KH2PO4), terwyl die kalsiumfosfaat sement is bereid om van ongebluste kalk (CaO), kalsium silikaat (CaSiO3) en monokaliumfosfaat (KH2PO4). Hierdie fosfaat sement is gebruik om saamgestelde panele met behulp van bio-gebaseerde industriële oorblyfsels te produseer. Die oorblyfsels sluit in Suikerriet bagasse (Saccharum officinarum), Hennep hurds (Cannabis sativa), Denne saagsels (Pinus elliottii), papierfabriek slyk en afval papier. Daarbenewens is bos afval van plaaslike uitheemse spesies, insluitend Swartwattel (Acacia mearnsii), Lang-blaar wattel (A. longifolia), Port Jackson (A. saligna), Rooikrans (A. cyclops) en Bloekomhout (Eucalyptus globulus), Sekelbos (Dichrostachys cinerea) en Deurmekaarbos (Ehretia rigida) gebruik. Die studie benut n sentrale saamgestelde statistiese ontwerp, waarin die volgende faktore in ag geneem was; KH2PO4: MgO verhouding, KH2PO4: CaO + CaSiO3 verhouding, CaO: CaSiO3 verhouding en die hoeveelheid van hout / vesel as 'n verhouding van hout / vesel tot die totale anorganiese inhoud. Daarbenewens was die gebruik van steenkool vliegas as 'n aanvullende materiaal in die saamgestelde produk ondersoek. Gepasde reaksie oppervlak metode areas is gebruik om die verhouding tussen die veranderlikes en die verlangde reaskies te toon. Die effek van die belangrikste faktore en hul interaksies op die gemete bord eienskappe is geëvalueer met behulp van die Pareto ontleding van variansie. Reaksie oppervlak modelle is ontwikkel om parameters te voorspel wat optimum bord eienskappe lewer. Terwyl die fisiese eienskappe van die panele aan die minimum vereistes vir sement gebinde spaanderbord (EN 634: 2007) en LD-1 graad spaanderbord (ANSI 208,1: 1999) voldoen, sal die sterkte eienskappe moet verbeter om meer buigsaamheid te bied in terme van toepassing . Drie biomassa materiale is gekies vir verdere ondersoek met die doel om die bord eienskappe te verbeter. Hierdie materiaal is onderwerp aan drie verskillende behandelings, naamlik alkalisasie, asetilering en warm water onttrekking. Die effek van elk van die behandelings op die vesel materiaal is geëvalueer met behulp van HPLC, SEM en FTIR. Hierdie materiaal is gebruik om saamgestelde panele te vervaardig en μCT is gebruik om die mikrostruktuur van die saamgestelde monsters te kenmerk. 'n Numeriese tegniek is gebruik om die fases te kwantifiseer in die samestellings, naamlik sement matriks, toevoeger en leë ruimtes. Alle behandelings het die vesel eienskappe verbeter en het nie die vesel opbrengs aansienlik verminder nie. In magnesium fosfaat gebinde panele, was die gemiddelde modulus van breking 0,74 MPa vir onbehandelde, 1.03 MPa vir warm water onttreking, 1.20 MPa vir asetilering en 1,66 MPa vir alkaliseerde swartwattel panele. In kalsiumfosfaat gebinde panele, was die gemiddelde modulus van breking 0,88 MPa vir onbehandelde, 0.83 MPa vir warm water onttreking, 0.73 MPa vir asetilering en 1.18 MPa vir alkaliseerde swartwattel panele. Borde gemaak van alkali behandelde vesel het die beste eienskappe. Die studie het bevind dat bio-gebaseerde oorblyfsels geïnkorporeer kan word in geformuleerde fosfaat sement binders om duursame produkte te produseer wat vergelykbaar is met die huidige sement gebinde produkte.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100912
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