C. Antwi-Boasiako

Suitability of sawdust from three tropical timbers for wood-cement composites

ABSTRACT Construction material rising cost and global demand for economically-sustainable and environmentally-friendly building resources have necessitated the use of sawdust-cement composite. Wood constituents and cement incompatibility hinder its production and need careful selection of the timber. Sawdust suitability from Triplochiton scleroxylon, Entandrophragma cylindricum and Klainedoxa gabonensis for wood-cement composite was determined by identifying their chemical constituents and their composites’ physico-mechanical properties. T. scleroxylon recorded the minimum total extractive (6.12%), lignin (29.89%) and holocellulose (56.38%) and K. gabonensis the maximum (9.31, 31.59 and 57.5% respectively). Ash content was higher for T. scleroxylon (7.6%) but lower for K. gabonensis (1.53%). T. scleroxylon boards were stronger [Modulus of Elasticity (MOE) = 696.1 N/m2] and more moisture-resistant [Moisture Absorption (MA) = 8.8%] than E. cylindricum (MOE = 625.9 N/m2; MA = 9.5%). K. gabonensis boards crushed after manufacturing due to its incompatibility with cement. T. scleroxylon sawdust is suitable for wood-cement composites due to its more compatible chemical constituents (i.e., lower extractive, lignin, holocellulose contents and more ash) and its boards’ excellent physico-mechanical properties than those for the other timbers. Its sawdust-cement composites could be utilized for cladding and walling. The use of sawdust would increase green building resource base and reduce environmental pollution.

Assessment of the bending strength of mortise-tenon and dovetail joints in leg-and-rail construction using Klainedoxa gabonensis Pierre Ex Engl. and Entandrophragma cylindricum (Sprague) Sprague

ABSTRACT Mortise-tenon joints for working chair construction fail under bending stresses. Dovetail joints could offer an alternative due to their resistance to bending. However, furniture joint strength depends on the design of the parts and appropriateness of the timber for the construction. Information on timber-joint design combination that would improve joint strength is lacking for most secondary timbers with prospects for joinery-making. This study assessed the bending strengths of two joint designs (dovetail and mortise-tenon) for leg-and-rail construction from Klainedoxa gabonensis (a secondary timber) and Entandrophragma cylindricum (popularly used for furniture). Dovetail joints were stronger than those of mortise-tenon. For both joints, the design with longer, wider and thicker tails and tenons [large-sized (Type LS)] was stronger than its counterpart [small-sized (Type SS)]. Joints manufactured from K. gabonensis were also stronger than those from E. cylindricum. Thus, K. gabonensis could be an appropriate material for joinery/furniture production. This would broaden the raw material base for the furniture sector. However, its working chairs designed with Type LS dovetail joints would resist bending forces better and ensure stronger furniture than mortise-tenon. To offset frequent furniture breakdown, this study provides designers with reliable information regarding joint strength from different timbers to guide selection.

Termite resistance of Klainedoxa gabonensis (kruma), a tropical lesser-utilised-species for commercial utilisation

ABSTRACT The paper describes the testing for termite resistance of a lesser-utilised tropical species known as kruma (Klainedoxa gabonensis) in order to evaluate its potential for the building, construction and related wood-consuming industries. Results suggest that kruma heartwood can be rated as very durable and the sapwood as durable. It is concluded that utilisation of this wood species could reduce over dependence on traditional primary species.

Solvent extraction of inhibitory substances from three hardwoods of different densities and their compatibility with cement in composite production

Chemical pre-treatment of wood to remove extractives improves timber’s compatibility with cement and produces strong composites. The chemicals often used are expensive and environmentally-destructive. Data on eco-friendly solvents for such extraction are deficient, which makes it difficult to recommend the most effective solvent for wood pre-treatment. This study compared the extracting potentials of three readily available and environmentally friendly solvents (i.e. ethanol, hot and cold water) and their influence on the thickness swelling, modulus of rupture and shear strength of composites produced from three hardwoods of different densities [Klainedoxa gabonensis (high), Entandrophragma cylindricum (medium) and Triplochiton scleroxylon (low)]. Hot water removed more extractives (e.g. 2.21 ± 0.07% from T. scleroxylon) than ethanol (0.925 ± 0.02% from T. scleroxylon) and cold water (0.865 ± 0.02% from T. scleroxylon). Composites from hot water-extracted sawdust least swelled and were stronger than those produced from the ethanol-, cold water- and non-extracted sawdust. T. scleroxylon boards from both extracted and non-extracted sawdust had the lowest thickness swelling and greatest strength. Hot water was found to be more effective than cold water and ethanol for pre-treating the sawdust, especially those from the light timbers (e.g. T. scleroxylon) before mixing with cement in producing strong and dimensionally stable composites. Utilization of sawdust, especially from these timbers, would contribute to increasing the raw material base for the wood–cement board manufacturing or the composite industry.

Mechanical properties of coppiced and non-coppiced Pterocarpus erinaceus boles and their industrial application

Rosewood (Pterocarpus erinaceus Poir.) is valued for flooring, ornaments, musical instruments and furniture-making due to its durability, strength, beauty and acoustic properties. It coppices easily which could boost its continual supply. Compression parallel to grain, Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) within coppiced and non-coppiced boles were determined. These properties decreased along both types of boles. Strength values for the heartwood were also greater than those for the sapwood of each type of bole. MOE, MOR and compression for non-coppiced stems were greater than those from the coppiced stems. The differences were significant (p < 0.05). Mechanical properties from the coppiced and non-coppiced boles are comparable. Both have strength properties comparable with those of species widely used for railway sleepers, structural supports, flooring, veneer, furniture, cabinetry, truss and mine props. Therefore, coppiced wood could supplement non-coppiced wood for industrial applications which require strength.