Aging of Wood by Long-Term Heating at a Moderately High Temperature under Cyclic Humidity Changes

Abstract

In order to attain the fruitful effects of wood properties by aging, we conducted the thermal treatment at a moderately high temperature (85°C), which does not cause drastic thermal degradation, under a cyclic humidity changes between 30 and 80% R.H. for 3 months. For wood and cellulose samples, the weight losses were significantly accelerated by the existence of moisture, however the weight loss of cellulose was 1 order lower than wood sample. Loss tangent of wood specimens decreased for a few percent by the heating for 3 months without humidity change, whereas it increased under cyclic humidity changes. By the heating accompanied with humidity change, the degradation may excessively occur even only 1 month and as low as 85°C. The decrease of holocellulose content and relative increase of Klason lignin content were observed, which were remarkable under the heating with humidity change. Because plural factors may participate to the changes of equilibrium moisture content and crystallinity, the changing behaviors were complicated. In conclusion, it was proved that the existence of moisture merely accelerated the thermal degradation and positive effect was not virtually founded.