Sixteen fresh and recycled particleboard furnishes were characterized for pH, acid buffer capacity, base buffer capacity and total buffer capacity. Mechanical and physical properties of particleboard prepared from heat-treated (kiln drying) particles were also correlated with the wood chemical properties. It was found that the wood chemical characteristics of both fresh and recycled materials were influenced by heat treatment time (4 minutes and 24 hours), temperature (105o and 150oC), and particle size (coarse face and fine core particles). In general, the recycled material resulted in lower pH values than fresh material at 105oC, which was probably attributed to the residual acids from cured urea-formaldehyde resin in the recycled particles. The pH values of both fresh and recycled materials increased as treatment time increased at 105oC. Increasing the treatment temperature from 105o to 150oC at 24-hour treatment time did not seem to affect the pH of recycled material but reduced the pH of fresh material. The decrease in pH of fresh material at 150oC/24 hours might be related to the release of organic acids from the wood particles via the initial decomposition (hydrolysis and/or pyrolysis) of wood extractives and components. No influence of treatment temperature on the pH of recycled material observed from 105o to 150oC at 24 hours could be resulted from the interaction between wood and cured resin after heat treatment. The acidity of wood due to the initial decomposition of wood extractives and chemical components might offset the alkalinity of wood caused by the generation of ammonium hydroxide via decomposition of cured UF resin. A higher temperature and longer heat treatment time generally resulted in higher acid, base, and total buffer capacities; the extent of the increase depended on face and core particles.
Particleboard was disintegrated using both BTCA (butanetetracarboxylic acid) treatment and cold water soaking (24 hours overnight), combined with hammer milling. BTCA treatment of particleboard resulted in decreased pH values in the particles due to the acid contained in the BTCA solution. Particles disintegrated with 1.0% BTCA solution yielded pH levels similar to the pH levels in particles treated with water soaking. In addition, BTCA treatment of particleboard yielded higher wood acid and base buffer capacities compared to water soaking.
A regression analysis indicated that some correlations existed between wood chemical characteristics and particleboard properties: internal bond (IB) strength strongly correlated with the pH value, but modulus of elasticity (MOE), thickness swelling (TS), and water absorption (WA) correlated with the base buffer capacity of core material. In addition, MOE and TS well correlated with the pH values of face materials, while modulus of rupture (MOR) and formaldehyde emission (FE) well correlated with the base buffer capacity of core material.