Effects of thermal treatment on deformation fixation and properties of surface densified wood

ObjectiveThermal treatment at high temperature is a widely used method for deformation fixation of compressed wood. Wood is always treated as a whole in previous studies, but wood treated as a whole takes a long time and wastes a lot of energy, and only a few millimeters of surface densified layer need to be fixed. Therefore, it is necessary to explore a method for deformation fixation of surface densified wood.

MethodIn this study, hot press was used for surface thermal treatment of surface densified wood, then spring-back, surface hardness, abrasion resistance, wood color and chemical composition of the specimens treated by different conditions were measured, effects of thermal treatment on deformation fixation and properties of surface densified wood were discussed.

ResultThe results showed that: effects of thermal treatment on deformation fixation of surface densified wood were significant, spring-back of moisture absorption, water absorption and water boiling absorption all decreased with the increase of processing temperature and the extension of processing time. Surface hardness and abrasion resistance would be reduced when processing temperature was above 200℃ and processing time was extended. With the increase of processing temperature and the extension of processing time, the absolute value of brightness, red green ratio index and yellow blue ratio index increased, chromatic aberration also increased, wood color got darker. Absorbance of each absorption peak decreased after thermal treatment, and the decrease was more obvious with the increase of processing temperature and the extension of processing time. Cellulose, hemicellulose and lignin of wood were reduced because of pyrolysis reaction, and the number of hydroxyl groups and carbonyl groups affecting the dimensional stability of wood also correspondingly decreased under high temperature.

ConclusionThermal treatment could effectively fix the deformation of surface densified wood, however, increasing processing temperature and extending processing time would lead to the decrease of hardness and abrasion resistance of wood surface, and the change of wood color.