Milicia excelsa (Welw.) C. C. Berg sawdust as glue-extender in urea formaldehyde-adhesive in enhancing Ceiba pentandra (L.) Gaertn. veneer joint bonding strength

Abstract

Expensive adhesives and preservative-chemicals pose challenges to the wood composite industry. Adhesive-extenders reduce cost and enhance ply-joint bonding strength. Urea Formaldehyde (UF) extender was substituted with Milicia excelsa sawdust to formulate five extender-combinations: A (no sawdust), B (100% cassava flour); C (25% cassava flour, 75% sawdust); D (75% cassava flour, 25% sawdust); E (50% cassava flour, 50% sawdust) and F or control (100% cassava flour with 10 g Fossect 88 insecticide). Each glue-mixture contained 3 kg UF (primary resin), hardener (0.6 kg) and water (4.5 l). Ceiba pentandra ply-joint bond strength was subjected to knife-test under dry and cold/moist conditions. Glue-line durability was determined through outdoor exposure. Viscosities for the formulations ranged between 2600cps (for C) to 265cps (for B and F). C had the fastest spreadability(231.67 g/m2) and F the least (188.33 g/m2). Bond strength for D dry-pressed plies (88.750%)] was greatest and E’s (72.083%) the weakest. Bonds weakened under moist conditions; however, C plies’ (73.33%) remained strongest and F’s (67.083%) the weakest. C plies degraded most outdoors (mass loss: 54.434%); F (13.89%) and E (42.964%) performed well. Normal C. pentandra boards lost 28.975%. Visual durability rating followed similar pattern. Appropriately formulated, sawdust from other durable hardwoods has utilization potential as glue/adhesive-extender and would serve as durable in-line treatment for chemical protection of wood composites alongside conventional preservative-chemical in glue mixtures. These need be explored by the wood and other related industries to enhance timber recovery, efficient total utilization and ensure eco-friendliness.