尾巨桉木材冷冻干燥特性
Freeze-drying properties of Eucalyptus urophylla×E.grandis wood
杨琳 1马青原 1刘洪海 1廖晓梅 1吴智慧1
作者信息
- 1. 南京林业大学家居与工业设计学院,江苏 南京210037
- 折叠
摘要
对尾巨桉(Eucalyptus urophylla×E.grandi)试件分别进行冷冻干燥(-50℃)和常规干燥(60℃、相对湿度66％),利用扫描仪结合ImageJ软件测定了干燥过程中木材的干缩率,检测了试件分层含水率,并对木材皱缩及回复情况进行SEM镜像观测.对不同含水率阶段试件在两种干燥条件下的干燥速度、含水率分布、干缩率及细胞的微观结构等进行了对比分析.结果表明:冷冻干燥的含水率-时间变化曲线与常规干燥类似,纤维饱和点(FSP)以上干燥快,FSP以下干燥慢.冷冻干燥能够形成并保持良好的水分迁移通道,导致干燥速度在FSP上下均快于常规干燥.在干燥初期及高含水率阶段,冷冻干燥试件的表心层含水率差异大,干燥梯度大.FSP以下两种试件含水率分布类似,含水率梯度趋于均匀,没有明显差别.冷冻干燥全干面积收缩率小于常规干燥,且受试件长度影响.对试件微观结构的扫描电子显微镜(SEM)观察发现,冷冻干燥皱缩细胞的数量及程度远小于常规干燥.冷冻干燥能够最大限度地保持细胞形态,显著减小木材皱缩程度,但不能完全避免木材皱缩.
Abstract
Eucalyptus urophylla×E.grandis samples were dried by freeze-drying(FD)(-50 ℃)and conventional kiln drying(CKD)(60 ℃,66％)respectively,the shrinkage curve was measured by scanner and ImageJ software,layered moisture content distribution was measured,collapse and recovery were mirror observed by SEM,and then the drying rate,moisture content(MC)distribution,shrinkage in area and the morphological feature of collapsed cells were compared and the effects of FD on the collapse was investigated as well.The results indicated that the curve of moisture-time of FD was similar with that of CKD,drying rate was fast above fiber saturated point(FSP)and became slow below FSP.Moisture migration channels were created and maintained during FD process and these new channels resulted in high drying rate at about FSP level.In the early stage of FD,the MC distribution was quite different from surface to middle and core layer and with great MC gradient compared with that of CKD.Below FSP,MC distribution of FD became even and the MC distribution was same with that of CKD.The total shrinkage rate of FD was smaller than that of CKD and which is affected by sample length.The quantity and extent of collapsed cells in FD were smaller than that of CKD through SEM observations.Freeze-drying could not avoid the collapse entirely,but it could maintain the shape of cells and decrease the cell collapse significantly.
关键词
冷冻干燥/木材皱缩/干燥特性/尾巨桉Key words
freeze-drying/wood collapse/drying properties/Eucalyptus urophylla×E.grandis引用本文复制引用
基金项目
国家自然科学基金青年项目(31500479)
国家自然科学基金面上项目(31570558)
南京林业大学高层次人才科研启动基金(GXL010)
青蓝工程资助项目(164104841)
南京林业大学大学生创新训练计划项目(2017NFUSPITP333)
出版年
2018
国家科技期刊平台
NSTL
维普
万方数据