Gmelina arborea (Roxb. ex. Sm.) wood samples were thermally modified at 180 °C, 200 °C and 220 °C for 3 h, by employing a process similar to ThermoWood®. The resulting effects on the basic chemical composition and mechanical properties were determined. The results were analyzed statistically with ANOVA, and Least Square Deviation was used to compare means. Generally, after the thermal modification (TM) process, the cellulose, hemicelluloses and extractives content decreased significantly. By contrast, lignin proportions increased significantly. Untreated wood and samples modified at 180 °C indicated comparable modulus of elasticity (MOE), modulus of rupture (MOR), degree of integrity (I), fine fraction (F) and resistance to impact milling (RIM). Noteworthy reductions however occurred at 200 °C and 220 °C. Significant increases in Brinell hardness (BH) took place at 180 °C, recording a high decrease at 220 °C. Gmelina arborea could be modified suitably at 180 °C for structural and other purposes. To take advantage of other improved properties, modification at 200 °C could be employed for non-structural uses.
Poor machining of wood generates more residues which leads to low recovery in wood processing. Therefore, the availability of appropriate wood machining techniques would promote efficient utilization of logs. This study looked at the shaping and sanding properties of Gmelina arborea - a lesser-known species in Ghana - in order to promote its efficient utilization. Six trees from plantations at the Wet Evergreen and Dry Semi-Deciduous Forest Zones were extracted and processed into lumber using LT 15 horizontal wood-mizer. The average moisture content of samples just before the test was 14.57%. Specimens were prepared in accordance with ASTM D 143-83 and ASTM D 1666-87 (2004) for the sanding and shaping tests. The effects of tree location, grit size and spindle speed on sanding and shaping properties of Gmelina arborea wood were assessed using the visual approach. For the sanding test, grit size P80 was the best sandpaper to remove chipped and torn grain defects from the surfaces of Gmelina arborea lumber after planing. Spindle speed 10,000 rpm gave the best shaping output so it was recommended for shaping Gmelina arborea timber grown in Ghana. For the shaping operation, wood samples obtained from the Dry Semi-Deciduous Forest Zone had better surface quality than those obtained from the Wet Evergreen Forest Zone. A similar trend was obtained for the sanding test. The most common defects observed during grading of the shaped specimens were raised, chipped and fuzzy grains and those observed for the sanded specimen were fuzzy and scratchy defects. At 5% level of significance, tree location and spindle speed had significant effect on the surface quality of the shaped specimen.
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