Luvuyo Tyhoda
Stellenbosch University, Forest and Wood Science, Faculty Member
Abstract Irvingia seed kernels have been identified as potential raw materials for a wide range of applications such as biodiesel, cosmetics, perfume, and soap. As a result, the Irvingia wood species is earmarked for domestication... more
Abstract Irvingia seed kernels have been identified as potential raw materials for a wide range of applications such as biodiesel, cosmetics, perfume, and soap. As a result, the Irvingia wood species is earmarked for domestication globally in order to commercially exploit these potential benefits. This study investigated the physical and mechanical properties of experimental panels made with pine (Pinus elliottii) wood particles, using modified Irvingia gabonensis (IG) and Irvingia wombolu (IW) extracts as a binder. The mean values of modulus of rupture (MOR) and modulus of elasticity (MOE) for the panels produced with this Irvingia-based adhesive were 5.8 and 1251 MPa, respectively. These values are within the minimum requirement for MOR and MOE (5.5 and 1034 MPa, respectively) for panel grade 1-L-1 as specified by the American National Standards Institute A208.1. The results from the study show that Irvingia kernel extracts may be considered as a potential environmentally friendly adhesive for wood composite manufacture.
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This study investigated the feasibility of utilizing paper sludge (PS) as feedstock in the production of composite boards that are lightweight, durable and environmentally friendly. PS samples were collected from recycled newsprint (RN),... more
This study investigated the feasibility of utilizing paper sludge (PS) as feedstock in the production of composite boards that are lightweight, durable and environmentally friendly. PS samples were collected from recycled newsprint (RN), corrugated recycled (CR) and virgin pulp (VP) pulping mills in South Africa. The PS was dried and mixed with magnesium phosphate cement to produce boards in a central composite design. Three different fillers including fly ash, calcium carbonate and silica fume were also added to the mix as binder replacement. The PS was characterized before use, and the produced composite board was evaluated for mechanical and physical properties. The boards produced had medium to high density (0.52—1.12 g/cm3) that could be used for non-structural interior applications. The results showed that boards containing RN had the highest mean value for modulus of elasticity (MOE) of 769 MPa. The mean MOE for boards containing CR- and VP-PS was 357 and 411 MPa, respectively. Calcium carbonate had the best effect on the board properties. Techno-economic analysis was simulated for four different types of feedstock scenarios at different locations including a combined scenario. Sensitivity analysis revealed that decreased feedstock cost resulted in decreased minimum required selling price. The analysis also revealed that the combined scenario proved to be the most cost-effective and profitable option for the future.
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Purpose This study investigated the ammoxidation of three industrial lignins of which two were respectively precipitated from kraft and soda liquors, and the third one, a filtered sodium lignosulfonate for the synthesis of soil... more
Purpose This study investigated the ammoxidation of three industrial lignins of which two were respectively precipitated from kraft and soda liquors, and the third one, a filtered sodium lignosulfonate for the synthesis of soil conditioning materials.Method The industrial lignins were characterized for structural properties and ammoxidized in a 1 L Parr reactor at 80 oC, 10 barg, for 4 hours, with 7 wt. % ammonia and 10 wt. % lignin in the reaction mixture. A plant trial assessment of the products was conducted over four weeks.Results N-lignins with C/N ratios of 12.30, 15.81, and 14.64 were obtained from kraft, soda and sodium lignosulfonate against a standard requirement of a C/N < 20. However, soda lignin and sodium lignosulfonate could not meet the criteria for N-lignins (C/N < 20) under standard reaction conditions, requiring an additional pre-oxidation with 5% hydrogen peroxide prior to ammoxidation. In the plant trial, N-modified kraft (3.50 t/ha) and soda lignin (3.21 ...
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The development of effective strategies for lignin valorization to valuable products is of high interest in various industries such as pulp and paper and the emerging bioenergy process. Indeed, the successful valorization of lignin could... more
The development of effective strategies for lignin valorization to valuable products is of high interest in various industries such as pulp and paper and the emerging bioenergy process. Indeed, the successful valorization of lignin could improve the profitability of these processes and their environmental performance. In this study, an original strategy involving the sequential application of enzymes and pyrolysis was explored for the conversion (i.e., valorization) of lignins to bio-oil rich in phenols. Methods Four technical lignins from different processes were pretreated for 24 h using the concerted depolymerization action of lignin peroxidase and quinone reductase enzymes. Pyrolysis was then performed on the pretreated and untreated (control) samples using a bench-scale tubular reactor at 550 ℃ for 30 min. Results Enzymatic pretreatment could contribute to a 17.5-82.3% increase in the bio-oil mass yield during subsequent pyrolysis. In some cases, enzymatic pretreatment also improved the production of total phenols in bio-oils by a maximum of 43%, with steam explosion (S-E) lignin showing the best performance. Of the four technical lignins, S-E and sodaanthraquinone lignins gave the highest production of monomeric phenols whereas the sulfite lignins were more challenging to valorize due to their high inorganic contents. Conclusion Enzymatic pretreatment could contribute to the valorization of some technical lignins to phenols during subsequent pyrolysis.
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In recent times, mass timber products have encouraged renewed interest in wood as raw material for more sustainable building and construction. However, durability concerns due to wood susceptibilit...
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The prevailing approach of total clearing to contain the spread of invasive plants (IP) in South Africa is generating enormous lignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of... more
The prevailing approach of total clearing to contain the spread of invasive plants (IP) in South Africa is generating enormous lignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of geopolymer composites for use in outdoor environments. Untreated wood particles from Acacia mearnsii and A. longifolia , as well as sugarcane bagasse residues, were incorporated into a geopolymer matrix developed from a binary precursor system of 75% fly ash and 25% metakaolin. The variables considered included precursor-activator ratio (PA), curing pattern (CP), lignocellulosic material (LM), and alkali concentration (Mcon). The production process was established using a mixed factorial experimental design. PA and CP were considered at 2 levels, while LM and MCon were considered at 3 levels. The density of the boards exceeded 1 g cm −3 and are classified as high-density boards. The boards have comparable sorption properties to the cement-bonded particleboard according to the EN 632-2: 2007 standard. However, only A. longifolia boards produced with 12 M NaOH and PA ratio of 2:1 met the mechanical strength requirements. Thermogravimetric analysis revealed that the boards are thermally stable. These results have shown that South African woody IPs are suitable for geopolymer wood composites, but there is still concern about their durability in the alkaline matrix. Scanning electron microscopy micrographs indicated mineralization of the particles and a partial degradation of hemicellulose was confirmed by Fourier transform infrared spectroscopy. Although the degraded components did not prevent geopolymer setting, there is need to further investigate the extent and means of preventing degradation as this can derail the intended use of the product.
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The effect of combined quinone reductase (QR) and lignin peroxidase (LiP) on the depolymerization of technical lignins isolated from soda-anthraquinone (SAQ), steam explosion (S-E), and two sulfite processes (NaE and NaPE) was... more
The effect of combined quinone reductase (QR) and lignin peroxidase (LiP) on the depolymerization of technical lignins isolated from soda-anthraquinone (SAQ), steam explosion (S-E), and two sulfite processes (NaE and NaPE) was investigated. While LiP is best known for its ability to degrade lignins, it may also cause lignin re-polymerization due to the random coupling of phenoxy radicals and quinoid intermediates. This study evidenced that the addition of the bioreactor produced QR can to some extent limit the lignin re-polymerization by LiP. The synergistic application of QR and LiP lowered the molecular weights (Mw) of SAQ, NaE, S-E, and NaPE lignins by 31%, 34%, 41%, and 52%, respectively. The thermogravimetric analysis also showed that the thermal stability of the four lignins was reduced, whereas gas chromatography-mass spectrometry analysis showed that the degradation products included monomeric phenols. Therefore, the combined QR and LiP system is a promising approach for lignin valorization.
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Biocomposite materials manufactured from natural fibres and polymer matrix represent a group of engineered composite products with diverse applications. These materials continue to find increasing applications due to their design... more
Biocomposite materials manufactured from natural fibres and polymer matrix represent a group of engineered composite products with diverse applications. These materials continue to find increasing applications due to their design flexibility, superior properties and aesthetic appeal. The applicability of these biocomposites, however, depends on the interaction in the fibre-matrix interface. This paper reviews the state of the art research in fibre-matrix interfacial interaction based on published literature. A brief background on biocomposite materials is presented. The focus of this review is the modification of natural fibres and its effect on fibre-matrix interfacial adhesion and properties. In addition, the effect of chemical treatment on fibre composition and fibre-matrix interfacial bonding mechanism are discussed.
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Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on... more
Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on the utilization of kernel seed extract as a potential source of green wood adhesive. This study is focused on investigating the properties of adhesives produced from kernel seeds of two Irvingia wood species i.e. Irvingia gabonensis (IG) and Irvingia wombolu (IW), as well as investigating the improved properties derived from the effect of modification using a few selected modifying agents including glutaraldehyde, glyoxal, epichlorohydrin (EPI) and an acid/base type process modification. Polyethylene (PE) was used along with the glutaraldehyde, glyoxal and epichlorohydrin modifiers in the modification process. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and thermogravime...
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Hemicelluloses are located in the walls of vegetal cells and are the second most abundant macromolecules in the world. Thanks to the inherent chemical composition, hemicelluloses can be directly used as substrates for enzymes synthesis... more
Hemicelluloses are located in the walls of vegetal cells and are the second most abundant macromolecules in the world. Thanks to the inherent chemical composition, hemicelluloses can be directly used as substrates for enzymes synthesis and in film or polymer manufacture or turned into several products, which include among others biofuels, biopolymers, organic acids, sweeteners, and intermediate bioproducts. However, for the generation of such value-added bioproducts as mentioned above, to succeed, there is a requirement for the development of appropriate conversion paths and processes from hemicelluloses under the realm of the biorefinery concept. One of the major challenges in the conversion of hemicelluloses to bioproducts is due to the inherent links that exist between hemicelluloses and such cell wall components as lignin and cellulose. Due to these links, it is difficult to liberate hemicelluloses from biomass with most processes, most notably the pulping process, without incurring any losses or degradation of structural properties. With the selection and application of appropriate processing routes, most of the hemicelluloses can be recovered, and can serve as precursors or raw materials for the development of value-added products in a biorefinery scheme. The production processes for cellulosic bioethanol, particleboard, and pulp and paper are potential avenues where hemicelluloses can be recovered and upgraded without significant effects on the main process or
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The structural and physicochemical characteristics are associated with resistance of plant cell walls to saccharification by enzymes. The effect of physicochemical properties on glucose yield of bagasse from different varieties of... more
The structural and physicochemical characteristics are associated with resistance of plant cell walls to saccharification by enzymes. The effect of physicochemical properties on glucose yield of bagasse from different varieties of sugarcane at low and high enzyme dosages was investigated. The result showed that glucose yield at low enzyme dosage was positively linear correlated with the yield at high enzyme dosage, for both the untreated and pretreated materials. The pretreatment significantly increased the accessibility of substrates by enzyme due to the increase of internal and external surface area. Glucose yield also showed a linear correlation with dye adsorption. However, the increase in glucose yield as a result of pretreatment did not correlate with the increases in crystallinity index and decreases in degree of polymerization. The Principal Component Analysis of infrared data indicated that lignin was the main component that differentiated the varieties before and after pre...
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This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties.... more
This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties. Four South African pulping-based lignins were used to synthesize these lignin-phenol formaldehyde resins (LPF100 resins), namely Eucalyptus Kraft lignin, Pine Kraft lignin, Bagasse Soda lignin, and Bagasse Steam Exploded lignin. Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry were used to determine structural and curing properties. These resins were then used directly (unmodified) as adhesives to test shear bonding strength (R0 LPF100 adhesives). To improve the bonding properties of the unmodified LPF100 adhesives, the LPF100 resins were modified via the addition of a crosslinker (hexamine) as well as a hardener (either glyoxal, R1, or epichlorohydrin, R2). All R0 LPF100 adhesives fell below th...
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Today there is renewed interest in using soil improvers with fertilising capability as the use of inorganic fertilisers results in ground water pollution through leaching and formation of nitrates in plant materials. Lignin is an... more
Today there is renewed interest in using soil improvers with fertilising capability as the use of inorganic fertilisers results in ground water pollution through leaching and formation of nitrates in plant materials. Lignin is an important precursor of humic material in soils and with modification, can be used as a raw material for producing slow release nitrogenous fertilisers. This project focussed on the use of industrial residues such as technical lignins which are produced by the South African pulping industry as well as low grade coals such as lignite occurring in South Africa, for the production of high-grade humic substances like Novihum TM, using the special technology developed by the Institute of Plant and Wood Chemistry of the Technical University of Dresden in Germany. Technicallignins derived from kraft lignin, sugar cane baggase, autohydrolysis lignin with a trade name Sucrolin, a calcium lignosulphonate and South African lignites mined in the Kraaifontein and Braeken...
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The development of effective strategies for lignin valorization to valuable products is of high interest in various industries such as pulp and paper and the emerging bioenergy process. Indeed, the successful valorization of lignin could... more
The development of effective strategies for lignin valorization to valuable products is of high interest in various industries such as pulp and paper and the emerging bioenergy process. Indeed, the successful valorization of lignin could improve the profitability of these processes and their environmental performance. In this study, an original strategy involving the sequential application of enzymes and pyrolysis was explored for the conversion (i.e., valorization) of lignins to bio-oil rich in phenols. Methods Four technical lignins from different processes were pretreated for 24 h using the concerted depolymerization action of lignin peroxidase and quinone reductase enzymes. Pyrolysis was then performed on the pretreated and untreated (control) samples using a bench-scale tubular reactor at 550 ℃ for 30 min. Results Enzymatic pretreatment could contribute to a 17.5-82.3% increase in the bio-oil mass yield during subsequent pyrolysis. In some cases, enzymatic pretreatment also improved the production of total phenols in bio-oils by a maximum of 43%, with steam explosion (S-E) lignin showing the best performance. Of the four technical lignins, S-E and sodaanthraquinone lignins gave the highest production of monomeric phenols whereas the sulfite lignins were more challenging to valorize due to their high inorganic contents. Conclusion Enzymatic pretreatment could contribute to the valorization of some technical lignins to phenols during subsequent pyrolysis.
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Purpose The current study investigated to which extent phenol could be replaced by lignins to produce lignin phenol formaldehyde (LPF) resins, utilising soda lignin and sodium lignosulphonate as by-products from the South African pulping... more
Purpose The current study investigated to which extent phenol could be replaced by lignins to produce lignin phenol formaldehyde (LPF) resins, utilising soda lignin and sodium lignosulphonate as by-products from the South African pulping industry.Method The lignins were characterised and soda lignin indicated the highest reactivity. It was therefore utilised to produce LPF resins at 60%, 80%, and 100% phenol substitution, using central composite designs to maximise the adhesive strength. A one-pot method allowing direct transition from phenolation to resin synthesis was used for the first time with a pulping lignin at 60% and 80% substitution.Results Plywood made with LPF60, LPF80, and LPF100 resins attained their highest shear strengths of 0.786, 1.09, and 0.987 MPa, respectively, which adhered to the GB/T 14732-2013 standard (≥ 0.7 MPa). A substitution level of 68% produced the highest shear strength of 1.11 MPa. High-density particleboard made with this LPF68 resin gave a MOR and...
Abstract The production of phenols through catalytic pyrolysis of different types of lignin was investigated. Samples from eucalyptus (hardwood), pine (softwood), and sugarcane bagasse (herbaceous) were impregnated with the catalysts,... more
Abstract The production of phenols through catalytic pyrolysis of different types of lignin was investigated. Samples from eucalyptus (hardwood), pine (softwood), and sugarcane bagasse (herbaceous) were impregnated with the catalysts, Al2O3, ZnO, NaOH and KOH, in quantities equivalent to 1% of the lignin mass. Pyrolysis was conducted using thermogravimetric analyser (TGA), and the released phenols were captured in thermal desorption (TD) tubes for quantification by gas chromatography/mass spectrometry (GC/MS). From the TGA profiles, some modifications in the primary mechanisms were observed, especially with the hydroxide catalysts. In comparison to non-catalysed lignin pyrolysis, KOH produced the most statistically significant effect on the total phenols yields from sugarcane bagasse (S-S) lignin, with increases up to +26%, while NaOH increased the yield from Eucalyptus (E-K) lignin by +40%. Syringol was the main S-type phenol product, with the highest yield increase by NaOH from E-K lignin (+90%) and a final yield of 1.86 wt.%. NaOH also produced the highest yield increases of G-type phenols from E-K lignin, especially 4-vinylguaiacol (+39% and yield of 2.80 wt.%). The increased production of primary compounds (S-type and G-type) by these hydroxides was probably correlated with the enhanced depolymerisation in the first decomposition stages, as observed by TGA. Oxide catalysts had limited effects on the production of S-type and G-type compounds but were more selective towards the production of P-type phenols, especially ZnO with S-S lignin (+36%) due to the enhancement of demethoxylation reaction.
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Abstract The structural nature of lignin renders it suitable as a renewable source of phenolic compounds. The production of phenols from pyrolysis of sugarcane lignins with impregnated catalysts was investigated by screening of twelve... more
Abstract The structural nature of lignin renders it suitable as a renewable source of phenolic compounds. The production of phenols from pyrolysis of sugarcane lignins with impregnated catalysts was investigated by screening of twelve catalysts (Al2O3, CaO, Fe2O3, TiO2, ZnO, MgO, CuO, MoO3, NiO, Ni/Al2O3-SiO2, NaOH, and KOH) at 1 wt.% content. Sugarcane bagasse lignins were isolated after soda-pulping (SD), soda-anthraquinone-pulping (SAQ) and steam explosion pre-treatment followed by enzymatic hydrolysis (SEH). Pyrolysis was conducted using a thermogravimetric analyser (TGA), and captured volatiles were quantified by thermal desorption (TD) gas chromatography–mass spectroscopy (GC–MS). The TGA results showed that the degradation profiles and char yields were influenced by the presence of catalysts, through modifications in conversion mechanisms. The highest increases in the total yield of phenols were obtained with KOH for SD lignin (+25.7%), CaO for SAQ lignin (+59.7%), and Fe2O3 for SEH lignin (+43.0%). Due to the enhancement of depolymerisation at low temperature (
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Covalent lignin-carbohydrate linkages between lignin and carbohydrates have been suggested to be a major obstacle to complete delignification of biomass feedstocks during chemical processing, e.g. pulping or enzymatic hydrolysis of the... more
Covalent lignin-carbohydrate linkages between lignin and carbohydrates have been suggested to be a major obstacle to complete delignification of biomass feedstocks during chemical processing, e.g. pulping or enzymatic hydrolysis of the biomass to release sugars for ethanol production. The current study is aimed at developing an understanding of the structural composition and the behaviour of lignin carbohydrate complexes (LCCs) in sugarcane bagasse, a potential raw material for bio-ethanol production. Hemicelluloses were pre-extracted prior to soda AQ pulping with the aim of preserving it for further use instead of losing it in the black liquor (Value Prior Pulping or VPP). LCCs from the hemicelluloses pre-extracted soda AQ pulps as well, as non-extracted materials i.e. controls, were isolated and quantified. Mainly, two types of LCCs were identified: the xylan-lignin and glucan-lignin-xylan complexes. FTIR and GPC analyses of LCC fractions confirmed that the ester bonds of LCCs wer...
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In recent times, mass timber products have encouraged renewed interest in wood as raw material for more sustainable building and construction. However, durability concerns due to wood susceptibility to biodegradation could curtail this... more
In recent times, mass timber products have encouraged renewed interest in wood as raw material for more sustainable building and construction. However, durability concerns due to wood susceptibility to biodegradation could curtail this interest. Hence, there is a need for more durable wood products in emerging structural applications including the use of preservative-treated wood for composite and mass timber products. This is particularly crucial in tropical and subtropical environments where wood products are highly vulnerable to biodeterioration. Unfortunately, preservation treatment often adversely affects other wood properties such as the surface adhesion characteristics and adhesivebond performance. Therefore, this review focused on the adhesion characteristics of wood, the impact of preservative impregnation, and the resultant effect on adhesive-bond performance. The aim is to draw attention to the challenges with bonding preservative-treated wood, and possible areas for research targeting bonding improvements.
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This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties.... more
This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties. Four South African pulping-based lignins were used to synthesize these lignin-phenol formaldehyde resins (LPF100 resins), namely Eucalyptus Kraft lignin, Pine Kraft lignin, Bagasse Soda lignin, and Bagasse Steam Exploded lignin. Fouriertransform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry were used to determine structural and curing properties. These resins were then used directly (unmodified) as adhesives to test shear bonding strength (R 0 LPF100 adhesives). To improve the bonding properties of the unmodified LPF100 adhesives, the LPF100 resins were modified via the addition of a crosslinker (hexamine) as well as a hardener (either glyoxal, R 1 , or epichlorohydrin, R 2). All R 0 LPF100 adhesives fell below the GB/T 17657-2013 plywood standard of 0.7 MPa, with the Bagasse Soda LPF100 adhesive recording the highest bonding performance of 0.5 MPa, and the lowest curing temperature of 688C. From the modified adhesives, the best performing were the Pine Kraft (R 1) and the Eucalyptus Kraft (R 2) LPF100 adhesives, recording 1.4 and 1.3 MPa, respectively. The curing temperatures of both these resins were 718C and 808C, respectively. Ultimately, the results of this study indicated that favorable adhesive properties may be obtained with the use of South African pulping-based lignins as a 100 percent phenol substitute in PFRs.
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The prevailing approach of total clearing to contain the spread of invasive plants (IP) in South Africa is generating enormous lignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of... more
The prevailing approach of total clearing to contain the spread of invasive plants (IP) in South Africa is generating enormous
lignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of geopolymer
composites for use in outdoor environments. Untreated wood particles from Acacia mearnsii and A. longifolia, as well as
sugarcane bagasse residues, were incorporated into a geopolymer matrix developed from a binary precursor system of 75%
fly ash and 25% metakaolin. The variables considered included precursor-activator ratio (PA), curing pattern (CP), lignocellulosic
material (LM), and alkali concentration (Mcon). The production process was established using a mixed factorial
experimental design. PA and CP were considered at 2 levels, while LM and MCon were considered at 3 levels. The density
of the boards exceeded 1 g cm−3 and are classified as high-density boards. The boards have comparable sorption properties
to the cement-bonded particleboard according to the EN 632-2: 2007 standard. However, only A. longifolia boards produced
with 12 M NaOH and PA ratio of 2:1 met the mechanical strength requirements. Thermogravimetric analysis revealed that
the boards are thermally stable. These results have shown that South African woody IPs are suitable for geopolymer wood
composites, but there is still concern about their durability in the alkaline matrix. Scanning electron microscopy micrographs
indicated mineralization of the particles and a partial degradation of hemicellulose was confirmed by Fourier transform infrared
spectroscopy. Although the degraded components did not prevent geopolymer setting, there is need to further investigate
the extent and means of preventing degradation as this can derail the intended use of the product.
lignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of geopolymer
composites for use in outdoor environments. Untreated wood particles from Acacia mearnsii and A. longifolia, as well as
sugarcane bagasse residues, were incorporated into a geopolymer matrix developed from a binary precursor system of 75%
fly ash and 25% metakaolin. The variables considered included precursor-activator ratio (PA), curing pattern (CP), lignocellulosic
material (LM), and alkali concentration (Mcon). The production process was established using a mixed factorial
experimental design. PA and CP were considered at 2 levels, while LM and MCon were considered at 3 levels. The density
of the boards exceeded 1 g cm−3 and are classified as high-density boards. The boards have comparable sorption properties
to the cement-bonded particleboard according to the EN 632-2: 2007 standard. However, only A. longifolia boards produced
with 12 M NaOH and PA ratio of 2:1 met the mechanical strength requirements. Thermogravimetric analysis revealed that
the boards are thermally stable. These results have shown that South African woody IPs are suitable for geopolymer wood
composites, but there is still concern about their durability in the alkaline matrix. Scanning electron microscopy micrographs
indicated mineralization of the particles and a partial degradation of hemicellulose was confirmed by Fourier transform infrared
spectroscopy. Although the degraded components did not prevent geopolymer setting, there is need to further investigate
the extent and means of preventing degradation as this can derail the intended use of the product.
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This study investigated the feasibility of utilizing paper sludge (PS) as feedstock in the production of composite boards that are lightweight, durable and environmentally friendly. PS samples were collected from recycled newsprint (RN),... more
This study investigated the feasibility of utilizing paper sludge (PS) as feedstock in the production of composite boards that are lightweight, durable and environmentally friendly. PS samples were collected from recycled newsprint (RN), corrugated recycled (CR) and virgin pulp (VP) pulping mills in South Africa. The PS was dried and mixed with magnesium phosphate cement to produce boards in a central composite design. Three different fillers including fly ash, calcium carbonate and silica fume were also added to the mix as binder replacement. The PS was characterized before use, and the produced composite board was evaluated for mechanical and physical properties. The boards produced had medium to high density (0.52-1.12 g/ cm 3) that could be used for non-structural interior applications. The results showed that boards containing RN had the highest mean value for modulus of elasticity (MOE) of 769 MPa. The mean MOE for boards containing CR-and VP-PS was 357 and 411 MPa, respectively. Calcium carbonate had the best effect on the board properties. Techno-economic analysis was simulated for four different types of feedstock scenarios at different locations including a combined scenario. Sensitivity analysis revealed that decreased feedstock cost resulted in decreased minimum required selling price. The analysis also revealed that the combined scenario proved to be the most cost-effective and profitable option for the future.
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The effect of combined quinone reductase (QR) and lignin peroxidase (LiP) on the depolymerization of technical lignins isolated from soda-anthraquinone (SAQ), steam explosion (S-E), and two sulfite processes (NaE and NaPE) was... more
The effect of combined quinone reductase (QR) and lignin peroxidase (LiP) on the depolymerization of technical lignins isolated from soda-anthraquinone (SAQ), steam explosion (S-E), and two sulfite processes (NaE and NaPE) was investigated. While LiP is best known for its ability to degrade lignins, it may also cause lignin re-polymerization due to the random coupling of phenoxy radicals and quinoid intermediates. This study evi-denced that the addition of the bioreactor produced QR can to some extent limit the lignin re-polymerization by LiP. The synergistic application of QR and LiP lowered the molecular weights (M w) of SAQ, NaE, S-E, and NaPE lignins by 31%, 34%, 41%, and 52%, respectively. The thermogravimetric analysis also showed that the thermal stability of the four lignins was reduced, whereas gas chromatography-mass spectrometry analysis showed that the degradation products included monomeric phenols. Therefore, the combined QR and LiP system is a promising approach for lignin valorization.
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Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on... more
Irvingia tree species have been earmarked for domestication in many countries due to their potential as raw materials for various applications, which include biodiesel, cosmetics, perfume, soap, etc. Presently, there is no information on the utilization of kernel seed extract as a potential source of green wood adhesive. This study is focused on investigating the properties of adhesives produced from kernel seeds of two Irvingia wood species i.e. Irvingia gabonensis (IG) and Irvingia wombolu (IW), as well as investigating the improved properties derived from the effect of modification using a few selected modifying agents including glutaraldehyde, glyoxal, epichlorohydrin (EPI) and an acid/base type process modification. Polyethylene (PE) was used along with the glutaraldehyde, glyoxal and epichlorohydrin modifiers in the modification process. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were conducted to study the effect of modification on adhesive properties. The glycosidic carbon of the unmodified extracts and that of the EPI modified sample were not sensitive to chain conformations. Principal components (PC) 1 and 2 explained 85.19 and 9.54%, respectively, of the total variability in FTIR spectra among the modified and unmodified adhesives. The unmodified samples for IG and IW exhibited one peak with crystallization temperatures of 18.7 and 14.4 °C, respectively, indicating only one component exhibits some low degree crystallinity. The adhesive properties of the modified extracts were tested on wood veneers according to ASTM standard. The shear strength of the modified adhesives ranged from 1.5 to 3.93 MPa and 1.7 to 4.05 MPa for IG and IW, respectively. The modified samples containing PE showed marked improvement in the shear strength. The highest values were about 63% higher than the shear strength of unmodified samples with least shear strength. The results indicated that the modification of Irvingia-based adhesives had a great contribution to their performance as natural wood adhesives.
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Plant biomass residues are renewable sources for the production of biofuels and high-value macromolecules. Sugarcane bagasse is one such plant biomass residue that is available from the sugar-processing industry. It is used as a raw... more
Plant biomass residues are renewable sources for the production of biofuels and high-value macromolecules. Sugarcane bagasse is one such plant biomass residue that is available from the sugar-processing industry. It is used as a raw material for biobased ethanol production. However, some of its properties and its behavior during processing have a major inhibitory effect on its successful conversion. Chief among these inhibitory properties are the lignin content, its distribution in plant tissues, and its chemical properties. These make the materials naturally resistant to bioconversion processes. Further, lignin and carbohydrate degradation products can be formed during acid pretreatment, which is one of the major steps during biomass conversion to bioethanol. These products negatively affect the liberation of fermentable sugars and the yield of ethanol during the fermentation stage of the conversion process. Other factors that also have an influence on the production of fermentable sugar are related to the different structural arrangement of plant tissues (cane fractions of the node, internode, and external fraction), as well as biomass variety. Biomass varieties with low lignin content result in an improved yield of fermentable sugars, which in turn contributes to improved viability of the second-generation bioethanol production processes. By selecting sugarcane varieties with the best properties, ethanol production can be increased without increasing the total area under cultivation. Efforts have been dedicated to reducing biomass recalcitrance by classical and precision breeding. Genetic modification of sugarcane alters the genes responsible for the encoding enzymes for lignin biosynthesis, generating sugarcane with low recalcitrance.
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There is renewed effort in reducing the carbon footprint of conventional building materials by employing novel phosphate cements. This study investigates the influence of industrial aggregates, namely fly ash, silica fume and calcium... more
There is renewed effort in reducing the carbon footprint of conventional building materials by employing novel phosphate cements. This study investigates the influence of industrial aggregates, namely fly ash, silica fume and calcium carbonate on biocomposite properties. The biomaterials used included pine, bagasse and wattle. The density of the boards produced ranged from 0.82 to 1.16 g/cm 3 , and the MOE ranged from 410.57 to 1737.87 MPa. The study concluded that biomass type, curing temperature and aggregates have significant effects on the biocomposite properties. The boards produced met the physical property requirements for use as non-load-bearing structures in humid and external conditions.
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Over the last few decades, innovative wood composite products and processes have created markets for new and existing products. Inorganic bonded fibre composites have been developed for high performance applications using conventional... more
Over the last few decades, innovative wood composite products and processes have created markets for new and existing products. Inorganic bonded fibre composites have been developed for high performance applications using conventional cement and concrete. The demands for wood based composites along with increasing economic and environmental concerns on conventional wood products necessitate moving beyond the traditional processing methods to more cost-effective and environmentally friendly approaches. In the wake of the twenty-first century, a fast-setting phosphate binder with a low carbon footprint was developed, which can alternatively be utilized in wood composite development. This paper reviews the recent progress in phosphate bonded composite products, based on published literature from the last two decades. A brief background on Portland cement based natural fibre composites is presented. In addition, the mechanism of the formulation of phosphate binders, the effect of aggregates in the materials and the environmental benefits accruable to such materials are discussed.
This study investigates the potential use of magnesium based phosphate cement prepared from a heavy magnesium oxide and monopotassium phosphate as a binder for the production of composite panels using bio-based industrial residues such as... more
This study investigates the potential use of magnesium based phosphate cement prepared from a heavy magnesium oxide and monopotassium phosphate as a binder for the production of composite panels using bio-based industrial residues such as bagasse, hemp hurds, pine sawdust, paper mill sludge and wastepaper as raw materials. These residues were used to produce lightweight and durable materials that can compare with current Portland cement based products. The phosphate binder is fast setting, cold curing and has a low carbon footprint compared to its Portland cement counterpart. The development of phosphate bonded board products promises to reduce the energy requirements in the manufacturing process of board products, and also provides an alternative route for disposal or value addition to bio-based residues by developing environmentally friendly products. The board manufacturing process was laid out on a central composite design (CCD) to model the response variable, utilizing as much residues as technically feasible. The design allowed for the production of low and medium density boards that can be used for non-structural interior finishes and partition boards. Response surface methodology (RSM) was used to show the relationships between the production variables and predict the board property by variable optimisation. Tests of mechanical and physical properties were conducted on the boards. The density of hemp boards ranged from 0.59-0.83 g/cm 3 , bagasse boards ranged from 0.54-0.78 g/cm 3 , pine boards ranged from 0.58-0.84 g/cm 3 , paper sludge boards ranged from 0.68-0.81 g/cm 3 and wastepaper boards ranged from 0.67-0.81 g/cm 3. The study has shown that it is feasible to produce phosphate based board products using bio based industrial and agricultural residues. The physical properties of the products met the minimum requirements for cement bonded particleboard (EN 634:2007) and LD-1 grade particle board (ANSI 208.1:1999).
There is renewed interest in the domestication of Irvingia tree species due to the potential use of various parts of the tree as raw materials for a wide range of applications such as biodiesel production, cosmetics, perfumes, soap,... more
There is renewed interest in the domestication of Irvingia tree species due to the potential use of various parts of the tree as raw materials for a wide range of applications such as biodiesel production, cosmetics, perfumes, soap, weight-loss supplement etc. The current study investigates the properties of extracts from the seed kernels of two Irvingia species-Irvingia gabonensis (IG) and Irvingia wombolu (IW) as natural wood adhesives. Three extraction methods using various solvent/solute media were compared in terms of yield, composition and mechanical properties. Statistically, the analysis revealed significant differences between the different extraction methods. The adhesion properties of the extracts were tested on wood veneers according to the American Society for Testing and Materials standard (ASTM D-906-64). The shear strength of the extracts ranged from 0.55 to 1.5 MPa and 0.86-1.7 MPa for IG and IW, respectively. The initial decomposition temperature of all Irvingia Kernel extract ranges from 138.3 to 149.11 °C for IG and 129.5-145.3 °C for IW. As a result, the hot melt temperature for the adhesive experiments was set around 150 °C. The results indicate that Irvingia kernel extract is a more promising source of non-formaldehyde based adhesives in wood composite production.
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Irvingia seed kernels have been identified as potential raw materials for a wide range of applications such as biodiesel, cosmetics, perfume, and soap. As a result, the Irvingia wood species is earmarked for domestication globally in... more
Irvingia seed kernels have been identified as potential raw materials for a wide range of applications such as biodiesel, cosmetics, perfume, and soap. As a result, the Irvingia wood species is earmarked for domestication globally in order to commercially exploit these potential benefits. This study investigated the physical and mechanical properties of experimental panels made with pine (Pinus elliottii) wood particles, using modified Irvingia gabonensis (IG) and Irvingia wombolu (IW) extracts as a binder. The mean values of MOR and MOE for the panels produced with Irvingia-based adhesives were 5.8 and 1251MPa respectively. The values are within the minimum required MOR and MOE (5.5 and 1034MPa respectively) for panel grade 1-L-1 as specified in the American National Standard (ANSI) A208.1. The results from the study show that Irvingia kernel extracts may be considered as a potential environmentally friendly adhesive for wood composite manufacture.
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The production of phenols through catalytic pyrolysis of different types of lignin was investigated. Samples from eucalyptus (hardwood), pine (softwood), and sugarcane bagasse (herbaceous) were impregnated with the catalysts, Al2O3, ZnO,... more
The production of phenols through catalytic pyrolysis of different types of lignin was investigated. Samples from eucalyptus (hardwood), pine (softwood), and sugarcane bagasse (herbaceous) were impregnated with the catalysts, Al2O3, ZnO, NaOH and KOH, in quantities equivalent to 1% of the lignin mass. Pyrolysis was conducted using thermogravimetric analyser (TGA), and the released phenols were captured in thermal desorption (TD) tubes for quantification by gas chromatography/mass spectrometry (GC/MS). From the TGA profiles, some modifications in the primary mechanisms were observed, especially with the hydroxide catalysts. In comparison
to non-catalysed lignin pyrolysis, KOH produced the most statistically significant effect on the total phenols yields from sugarcane bagasse (S-S) lignin, with increases up to +26%, while NaOH increased the yield from
Eucalyptus (E-K) lignin by +40%. Syringol was the main S-type phenol product, with the highest yield increase by NaOH from E-K lignin (+90%) and a final yield of 1.86 wt.%. NaOH also produced the highest yield increases of G-type phenols from E-K lignin, especially 4-vinylguaiacol (+39% and yield of 2.80 wt.%). The increased production of primary compounds (S-type and G-type) by these hydroxides was probably correlated with the enhanced depolymerisation in the first decomposition stages, as observed by TGA. Oxide catalysts had limited effects on the production of S-type and G-type compounds but were more selective towards the production of Ptype phenols, especially ZnO with S-S lignin (+36%) due to the enhancement of demethoxylation reaction
to non-catalysed lignin pyrolysis, KOH produced the most statistically significant effect on the total phenols yields from sugarcane bagasse (S-S) lignin, with increases up to +26%, while NaOH increased the yield from
Eucalyptus (E-K) lignin by +40%. Syringol was the main S-type phenol product, with the highest yield increase by NaOH from E-K lignin (+90%) and a final yield of 1.86 wt.%. NaOH also produced the highest yield increases of G-type phenols from E-K lignin, especially 4-vinylguaiacol (+39% and yield of 2.80 wt.%). The increased production of primary compounds (S-type and G-type) by these hydroxides was probably correlated with the enhanced depolymerisation in the first decomposition stages, as observed by TGA. Oxide catalysts had limited effects on the production of S-type and G-type compounds but were more selective towards the production of Ptype phenols, especially ZnO with S-S lignin (+36%) due to the enhancement of demethoxylation reaction
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Phosphate-bonded composites are an emerging class of building materials produced from natural fibres and phosphate based cement pastes. They are durable and possess mechanical properties similar to those of Portland cement. However, the... more
Phosphate-bonded composites are an emerging class of building materials produced from natural fibres and phosphate based cement pastes. They are durable and possess mechanical properties similar to those of Portland cement. However, the moisture absorption of natural fibre can lead to swelling which may result in the reduction in the mechanical strength properties and eventually negatively affect the long-term performance and dimensional stability of the products. This study was aimed at the modification of some properties of selected biomaterial residues in order to enhance the final properties of the phosphate-bonded composite product. Three different treatments were evaluated viz. 1% caustic alkali, 1% acetic anhydride and hot water on natural fibres derived from slash pine, black wattle and bagasse. The effect of the treatment on the fibres was evaluated via HPLC, SEM and FTIR. Further, the performance of the treated fibres was evaluated in composite panels bonded with magnesium phosphate (MgPO 4) and calcium phosphate (CaPO 4) cement pastes against the controls. The manufactured panels were tested for flex-ural properties and dimensional stability. In the MgPO 4-bonded panels, the MOR increased from 0.55 MPa for untreated bagasse panels to 0.79 MPa for alkalised panels. Similarly, the MOE increased from 150.04 MPa for untreated bagasse panels to 175.65 MPa for alkalised panels. In untreated MgPO 4-bonded panels, the mean density was 0.76, 078 and 0.75 g/cm 3 , while in alkalised panels, the mean density was 0.81, 0.81 and 0.81 g/cm 3 for wattle, pine and bagasse panels, respectively. In the bagasse panels, the water absorption was 54.61% for untreated, 48.74% for hot water extracted, 42.21% for acetylated and 36.44% for alkalised MgPO 4-bonded panels. This represents a percentage improvement of 11, 23 and 33%, respectively. Alkali-treated fibres had the best effect overall for all measured properties.
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Covalent lignin-carbohydrate linkages between lignin and carbohydrates have been suggested to be a major obstacle to complete delignification of biomass feedstocks during chemical processing, e.g. pulping or enzymatic hydrolysis of the... more
Covalent lignin-carbohydrate linkages between lignin and carbohydrates have been suggested to be a major obstacle to complete delignification of biomass feedstocks during chemical processing, e.g. pulping or enzymatic hydrolysis of the biomass to release sugars for ethanol production. The current study is aimed at developing an understanding of the structural composition and the behaviour of lignin carbohydrate complexes (LCCs) in sugarcane bagasse, a potential raw material for bio-ethanol production. Hemicelluloses were pre-extracted prior to soda AQ pulping with the aim of preserving it for further use instead of losing it in the black liquor (Value Prior Pulping or VPP). LCCs from the hemicelluloses pre-extracted soda AQ pulps as well, as non-extracted materials i.e. controls, were isolated and quantified. Mainly, two types of LCCs were identified: the xylan-lignin and glucan-lignin-xylan complexes. FTIR and GPC analyses of LCC fractions confirmed that the ester bonds of LCCs were degraded through hemicelluloses pre-extraction, leading to a significant change in their structure. This in turn resulted in more cellulose being more accessible to pulping and enzymatic hydrolysis respectively. The study showed that alkaline pre-extracted biomass materials have a more amenable structure to processing, as a result of the disruption of the unreactive LCCs in the residual lignin. Further, alkaline hemicelluloses pre-extraction in combination with soda AQ holds more promise for VPP due to reduced LCCs. This could have a positive impact in downstream processes such as bleaching.