Fast growing sengon (Paraserianthes moluccana) is largely rotary-cut to produce veneer for core plywood production. In order to provide better information on veneer production and utilization, in ...this study the effects of wood juvenility and veneer thickness on lathe checks of rotary-cut sengon veneers were evaluated. Before veneer manufacturing, sengon logs were boiled at 50°C and 75°C for 4 and 8h, respectively. The boiled logs were peeled to produce veneer of 1, 1.5, and 2mm in thickness. Lathe checks of veneers were measured on the loosed side at every 5mm veneer length under an optical video microscope and their frequency, depth, and length were characterized. Twenty sampling points of 5mm veneer length were prepared from each segmented ring of 1cm width from pith to bark. Isocyanate resin adhesive were used to produce laminated veneer lumber (LVL) of 20mm thick, which consisted of 24-ply of 1mm veneer thick, 14-ply of 1.5mm veneer thick, and 11-ply of 2mm veneer thick, for glue bond and bending strength test. Results showed that wood juvenility and veneer thickness determined the frequency, depth and length of lathe checks for the sengon rotary-cut veneers. In general, the frequency of lathe checks of the veneer increases with increasing veneer thickness, and also increases from pith to bark. Boiling of logs before rotary-cutting could decreases the frequency of lathe check of the veneer. The results indicated that boiling of logs at 50°C for 8h and at 75°C at least 4h before peeling the logs could minimize the frequency of lathe check in manufacturing rotary cut veneer thickness of 1, 1.5, and 2mm from juvenile wood of fast growing sengon. The frequency of lathe check affects significantly the glue bond and bending strength, in which the glue bond, modulus of elasticity (MOE), and modulus of rupture (MOR) decrease as the frequency of lathe checks increases.
Papua New Guinea (PNG) has abundant natural forest resources but there are many constraints which need to be addressed to support the development of competitive value-added wood industries. There is ...a need to develop knowledge and capacity in wood science and processing technologies which support successful domestic value-adding wood processing enterprises. A comprehensive testing program has been developed to assess the glue‐bond strength and performance of selected commercial PNG timber species in various climatic conditions to simulate service conditions in potential market destinations. Two criteria namely shear strength and wood failure have been used to determine if a species can meet the minimum requirements for either dry use or wet use applications. The performance of 24 different PNG commercial timber species has been assessed using a one-component cross-linking polyvinyl acetate emulsion adhesive. The bondability of the selected species has been carefully estimated considering the wood density and wood moisture content for the strength and durability in dry- and wet-use conditions. The testing results show that as the wood density as a wood property factor and moisture content as a service condition factor increase, high shear strength with high wood failure become more difficult to achieve consistently. The highest shear strength and wood failure results were achieved by softwood plantation species and low-density hardwood species. Based on the testing results, the selected species have been classified into bondability classes (bond very well, bond well, bond with difficulty, very difficult to bond).
Veneer overdrying is a primary cause of poor plywood glue bond quality due to surface inactivation and its effect on glue transfer and penetration. The goal of this work is to investigate the ...feasibility of using atmospheric cold plasma to treat overdried hybrid poplar (Populus hybrids) veneers to improve wettability and plywood glue bond (shear) strength. The effectiveness of the plasma treatment using three veneer drying conditions, air drying, oven drying, and overdrying, were compared. It was found that the cold plasma treatment significantly enhanced veneer surface wettability under all three drying conditions. Compared to untreated controls, instantaneous surface contact angles of treated veneers decreased the most under the overdried condition, followed by the oven-dried and air-dried conditions, regardless of whether glycerin or urea formaldehyde (UF) was used. After a 5-s treatment, overdried veneers achieved complete wetting with both droplets. The results demonstrated that the atmospheric cold plasma was the most effective one to treat overdried poplar veneers to achieve the smallest contact angle, leading to the highest plywood glue bond (shear) strength. However, further research is still needed to understand the mechanism of the cold plasma treatment on veneers under different drying conditions.
For the development of a cost-effective melamine-modified urea formaldehyde resin (MUF), the study evaluated the effects of reaction pH and melamine content on resin properties and bond performance ...of the MUF resin adhesive systems. Eight resins, each with three replicates, were prepared in a factorial experiment that included two formulation variables: two reaction pHs (i.e., 4.5 and 8.0) and four molar ratios of formaldehyde to urea to melamine (i.e., 3/2.2/0.3, 3/2.2/0.2, 3/2.2/0.1, and 3/2.2/0.05). Variables in particleboard preparation were two hot-press cured times (2 and 4 min). Thus, with two panel replications, a total of 96 panels were fabricated. Melamine content significantly affected resin properties and glue bond quality: gel time decreased, solid content increased, internal bond strength increased, thickness swell and water absorption decreased, and formaldehyde emission decreased as melamine content increased. In general, the resins catalyzed under acidic conditions (pH 4.5) resulted in faster gel times, higher internal bond strengths, lower formaldehyde emissions, and lower thickness swell and water adsorption than those catalyzed under alkaline conditions (pH 8.0). Significant correlation between gel time with both internal bond strength and formaldehyde emission suggest that resins with fast curing speeds provided favorable conditions for attaining a higher degree of resin cure, and in turn led to better bond strength and lower formaldehyde emission. PUBLICATION ABSTRACT
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