Influence Mechanism Of Weight Loss Rate And VOCs Release In Fast-growing Wood Heat Treatment

The functional modification of fast-growing wood by heat treatment is one of the most important methods to ease the wood supply-demand contradiction in China.However,the wood heat treatment process has problems,such as high treatment temperature and high and unclear VOCs emissions,which limits the environmentally friendly and sustainable development of wood heat treatment to some extent.In view of this phenomenon,this study took fast-growing Chinese fir and Eucalyptus as the research objects and began with the basic problems such as the weightlessness rate,VOCs release,and heat transfer during the heat treatment of fast-growing wood.By combining the heat treatment experiment with SPMEGC/MS and finite element analysis,the heat transfer process,and the weightlessness of heat-treated wood were studied.On this basis,from the perspective of reducing energy consumption and reducing pollutant emissions in the heat treatment process,we tried to achieve low-temperature heat treatment and control the VOCs release during heat treatment by zinc chloride impregnation treatment,ultrasonic-assisted extraction treatment,and combined treatment.This research not only has reference value and guiding significance for improving and optimizing the existing heat treatment process,but also plays an important role in promoting the transformation and upgrading of the wood thermal processing industry to low energy consumption and low emissions.The main conclusions and innovations of this study are as follows:(1)The weight loss models changed with the treatment temperature and holding time during the heat treatment process of 20 mm fast-growing Chinese fir and Eucalyptus were constructed in this study.(2)The VOCs number of Chinese fir was 63 under all the treatment conditions,mainly including terpenes,aldehydes and phenols,while the Eucalyptus VOCs number was 45 and mainly consist of aldehydes and phenols.The number of VOCs and the content of major degradation products of hemicellulose,cellulose,and lignin generally increased with the increase of the treatment temperature and the extension of the reaction time.However,the relative content of specific ingredients may fluctuate due to the influence of other components in the group.(3)Based on the internal temperature field of the heat-treated wood obtained by finite element simulation,the problem of that effective thermal conductivity of heat-treated wood changed with different thicknesses was solved by computer simulation correction,and the average thermal conductivity models of heat-treated wood under different thickness conditions were obtained in this study.(4)Zinc chloride impregnation pretreatment can effectively promote the thermal degradation reaction of samples at a lower temperature.When zinc chloride pretreated Chinese fir and Eucalyptus were treated at about 180? for 2 hours,the weight loss rate and dimensional stability were comparable to those of the 200?-2h control wood.In addition,the treatment temperature relationship between the zinc chloride-treated wood and control wood under the same weightlessness rate was obtained in this study,which can be used to determine the heat treatment conditions required by the zinc chloride-treated wood in an easier way.(5)Compared with the control heat-treated wood at 200?,the main VOCs number of 180?zinc chloride-pretreated Chinese fir and Eucalyptus was decreased from 19 and 23 to 12 and 16 respectively;the relative content of aldehyde compounds was increased significantly from 13.55% and 34.90% to 85.66%and 79.53%.Especially,the relative content of platform compounds such as furfural and vanillin rose sharply,which simplified the composition of heat treatment VOCs and facilitated their recovery and disposal.(6)Ultrasound-assisted extraction can significantly improve the extraction efficiency.Compared with the traditional extraction method,the yields of extractives from Chinese fir and Eucalyptus wood powder in ultrasound-assisted extraction reached 4.09% and 2.95% from 2.82% and 1.23%,respectively.At the same time,the weight loss rate of heat-treated Chinese fir and Eucalyptus plates increased,which helped reduce energy consumption in heat treatment.However,the impact of ultrasound-assisted extraction on the release of VOCs from plates was not obvious.(7)In the combined treatment of zinc chloride,ultrasound and coating,the catalytic effects of zinc chloride on wood heat treatment were enhanced by ultrasound-assisted treatment,and the release of VOCs during heat treatment was inhibited by the renewable vanillyl alcohol-based epoxy resin coating.