Effect of heat treatment on hardness, density and color of Populus × canadensis ‘I-214’ wood

Abstract

Aim of study: To evaluate the effect of heat treatment (HT) on hardness, density and color of Populus × canadensis ´I-214´ (poplar) wood. Area of study: 15-years-old poplar wood from Pomona, Río Negro, Argentina. Material and methods: 352 samples were exposed to different HT schedules: 120ºC, 160ºC, 180ºC and 200°C for 45 min, 90 min, 135 min and 180 min. Hardness, density and color were determined before and after each HT combination. Hardness and density tests were performed following the specifications of IRAM standards and wood color was determined according to CIELab system. Main results: Hardness improved significantly at 160°C for 45 min and 90 min in comparison with control (14.34% and 9.08%, respectively) whereas this property was improved at 120°C in all cases without significant differences. The 200°C: 45 min schedule showed the worst performance with a 20.26% hardness loss. Density was lower than the control in all schedules with losses ranging from 2.50% to 10.00%. Color became darker (decrease in L value, increase in a and b values) as HT intensity increased (mainly temperature), with changes becoming evident at 180°C and 200°C. Research highlights: HT on P. × canadensis ‘I-214’ improved its hardness under two HT schedules, although was not enough to extend the feasible applications, since it still belongs to a category of “soft” wood. Hardness and density did not show a clear correlation and color of poplar wood became darker as HT intensity increased.