The Effects of Chromated Copper Arsenate and Ammoniacal Copper Zinc Arsenate on Shear Strength Development of Phenolic Resin to Sitka Spruce Bonds

T. R. Narayana Prasad, Philip E. Humphrey, Jeffrey J. Morrell

Abstract


Preservative treatment of whole, wood-based composite products (mainly panels) has disadvantages; problems largely stem from swelling, strength loss, and incomplete or inappropriate penetration during treatment, and distortion during redrying. Pretreatment of comminuted wood prior to mat lay-up is one alternative, though the addition of chemicals may affect bonding during subsequent pressing. With this possibility in mind, the strength accumulation of small test bonds (15 x 4 mm) between variously treated thin wood pieces was investigated. Pieces of Sitka spruce (sliced 0.8 x 15 x 150 mm) were treated with one of four concentrations (0.25 to 1.50% oxide basis) of either chromated copper arsenate or ammoniacal copper zinc arsenate. An automated device was used to form and test lap-shear specimens from matched pairs of variously treated wood and a phenol-formaldehyde adhesive. Each specimen was pulled immediately after pressing to measure the accumulated shear strength of the bond. Pressing times ranged from 10 to 300 sec at 95 C and 1.5 MPa, and this enabled near-isothermal strength-development plots to be constructed for each level of pretreatment. The plots suggested that preservative pretreatment did not significantly affect shear strength development rates at the chemical retention levels and pressing and testing conditions employed.

Keywords


Wood-based composites;preservative pretreatment;hot-pressing;bond-strength development;chromated copper arsenate;ammoniacal copper zinc arsenate;phenol-formaldehyde

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