太阳能预干联合热压干燥对桉木单板物理性能的影响

近年来木材太阳能干燥技术取得了一定的进展，但太阳能的不连续、不稳定性使其难以实现连续化干燥，因此联合干燥成为了发展热点。针对桉木单板探索了联合干燥对单板物理性能的影响，模拟太阳能将单板含水率由50%预干至25%~30%，然后联合热压干燥；设置热压温度为140℃、160℃、180℃、200℃，时间为2、3 min，压力为0.5 MPa。对联合干燥单板的压缩率，导热系数、表面颜色、平衡含水率进行测定，并采用扫描电子显微镜、傅里叶红外及XRD衍射光谱对微观层面变化进行分析。研究表明，太阳能预干联合热压干燥相比全程采用太阳能干燥节省时间约为50%；随着热压干燥温度的增加，单板厚度压缩率增大，导热系数增加率最大为14.6%，明度值L^*降低范围为0.4%~12.81%，表面颜色朝着暖色调方向发展；与未处理材相比，联合热压干燥后单板的平衡含水率呈降低趋势，最大减小约20%，且由XRD分析可知，联合热压干燥可使单板纤维素相对结晶度增加，能在一定程度上提高单板的尺寸稳定性；SEM显示热压处理改善了表面裂隙，有助于提高后期的胶合质量。因此太阳能预干联合热压干燥能够提高单板干燥效率与应用价值，在一定程度上可以改善单板干燥质量。

Effects of Solar Pre-drying Combined with Hot-pressing on the Physical Properties of Eucalyptus Veneer

In recent years,progress has made in wood solar drying technology,but its discontinuous instability makes it difficult to achieve continuous drying operation,so joint drying has become a hot spot for development.In this study,effects of joint drying on the physical properties of the veneer were explored.The veneer was dried under the simulated solar energy from 50% to 25%-30%,and then combined with hot-pressing;the hot-pressing temperatures were 140,160,180,and 200℃,the time durations were 2 and 3 min,and the pressure was 0.5 MPa.The compression,thermal conductivity,surface color,and equilibrium moisture content of the combined drying veneers were measured,and microscopic changes were analyzed by scanning electron microscopy,Fourier infrared and XRD diffraction spectroscopy.The results showed that the time of solar pre-drying combined with hot-pressing was saved about 50% compared with only using solar drying.With the increase of hot-pressing temperature,the compression of the veneer increased,and the thermal conductivity increasing rate was up to 14.6%.The value of L~* ranged from 0.4% to 12.81%,and the surface color developed to the warm color.Compared with the untreated material,the equilibrium moisture content of the veneer after the combined hot pressing decreased,and the maximum reduction was about 20%.XRD analysis showed that combined hot pressing could increase the relative crystallinity of veneer cellulose and improve the dimensional stability of veneers to some extent.SEM showed that hot-pressing treatment improved surface cracks and helped to improve the later stage.Therefore,solar pre-drying combined with hot-pressing could improve the drying efficiency and application value of the veneer,and also improve the drying quality of the veneer.