Impregnation of southern pine wood and strands with low molecular weight phenol-formaldehyde resins for stabilization of oriented strandboard

Low molecular weight phenol-formaldehyde (PF) resins were impregnated into southern pine wood using a vacuum/pressure method and the specimens were hot-pressed in the radial direction. Anti-swelling efficiency (ASE) values of treated specimens were up to 26% and 45%, respectively, for 1.0% and 5.0% resin solids loading levels in the first water-soak/dry cycle. The high ASE values were due to reduction in the irreversible swelling in radial and tangential directions of wood in spite of some negative effects that occurred in the reversible swelling. In the second and third water-soak/dry cycles, the ASE values were reduced mostly due to increased swelling of irreversible components in the radial direction with the tangential direction components little affected. Vacuum impregnation of southern pine/hardwood strands with 1.0% or 2.0% PF resin solids levels and hot-pressing gave strandboards with ASE values up to 45% in 24-h water-soak tests. ASE and board strength values of boards were higher for 2.0% resin solids loading level, higher hot-pressing temperatures, and longer press times. The high ASE values of boards arose from both irreversible and reversible swelling components and also increased adhesive bonds due to impregnating PF resins. The results would be useful for manufacturing oriented strandboard with reduced swelling if a low-cost resin impregnation process can be found.