Effects of Fire Retardant Treatment on Properties of Pinus kesiya var. langbianensis Plywood

Five phosphor-nitrogen-boron compound fire-retardants were used to treat Pinus kesiya var. langbianensis veneer under vacuum-pressure conditions for manufacturing of fire retardant plywood. The bond strength, burning property, hygroscopicity and leaching resistance of fire retardant P. kesiya var. langbianensis plywood were tested according to standard methods. The results showed that the average bond strength of fire retardant plywood could be≥1.15 MPa when the fire retardant content was 10%, surpassing the standard of 0.80 MPa required by class Ⅱplywood. The maximum oxygen index was over 38%, meeting the requirement of JIS fire retardant index of Japan. The maximum oxygen index of 3 types of fire-retardants reached 53%~59% when their content was 15% individually. It was showed that FR-a could significantly increase the hygroscopicity of the plywood, whereas the rest 4 types of fire retardants did not have much impact on hygroscopicity property. Consequently, the leaching resistance of FR-a and FR-b was comparatively poor, while FR-d and FR-e showed excellent leaching resistance, and the leaching resistance property of FR-c was intermediate. Among the five kinds of fire retardants, FR-c showed the best comprehensive properties.