Glue-line durability of organo-chemical/urea formaldehyde resin joints of Ceiba pentandra (L.) Gaertn. plywood

Abstract

Ceiba pentandra, a non-durable hardwood, is greatly patronized for plywood production. Urea–Formaldehyde (UF) adhesive-joints of plies are filled with toxic preservative-chemicals to extend their service-lives. These pose environmental anxieties. The strengths of C. pentandra ply glue-lines containing different concentrations of Erythrophleum suaveolens bark-extract/UF- and Fossect 88/UF-adhesives were compared. Controls comprised plies without preservative-chemicals at glue-joints. Bonds from dry-pressed plies were stronger (85.91 ± 3.80% for 3% E. suaveolens extract to 93.54 ± 3.79% for 2% extract) than the cold-pressed (68.51 ± 2.57 [1% extract]–84.53 ± 1.14% [2% extract]). Thus, 2% bark extract-UF bonds were the strongest. Glue-joints weakened after field exposure. However, the dry-treated ply bonds were equally more durable (29.55 ± 1.33 [Control]–62.84 ± 1.52% [Fossect 88]) than their respective cold-pressed ply-joints (22.99 ± 2.58–47.55 ± 1.55%). Steady decrease in bond strength occurred with prolonged outdoor exposure spanning 24 weeks. Visual durability rating for the entire plywood boards was in this decreasing order: Control (4) >1% extract (3) >2%, 3% extract and Fossect 88 (2), while that for the mass loss was: Control (46.79 ± 2.86%) >3% extract (7.80 ± 2.06%) >2% extract (10.98 ± 2.04%) >1% extract (13.10 ± 2.99%) >Fossect 88 (5.71 ± 1.15%). Industrially, organic preservatives (e.g. E. suaveolens bark extract) could substitute the conventional types in laminate glue-joints to reduce production costs and address ecological concerns without compromising bond performance.