THE EFFECTS OF CHROMATED COPPER ARSENATE AND AMMONIACAL COPPER-ZINC ARSENATE ON SHEAR-STRENGTH DEVELOPMENT OF PHENOLIC RESIN TO SITKA SPRUCE BONDS

Preservative treatment of whole, wood-based composite products (mainly panels) has disadvantages; problems largely stem from swelling, stren gth loss, and incomplete or inappropriate penetration during treatment , and distortion during redrying. Pretreatment of comminuted wood prio r to mat lay-up is one alternative, though the addition of chemicals m ay affect bonding during subsequent pressing. With this possibility in mind, the strength accumulation of small test bonds (15 x 4 mm) betwe en variously treated thin wood pieces was investigated. Pieces of Sitk a spruce (sliced 0.8 x 15 x 150 mm) were treated with one of four conc entrations (0.25 to 1.50% oxide basis) of either chromated copper arse nate or ammoniacal copper zinc arsenate. An automated device was used to form and test lap-shear specimens from matched pairs of variously t reated wood and a phenol-formaldehyde adhesive. Each specimen was pull ed immediately after pressing to measure the accumulated shear strengt h 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 th at preservative treatment did not significantly affect shear strength development rates at the chemical retention levels and pressing and te sting conditions employed.