亮果桉皱缩材汽蒸恢复过程研究OA

To address the problem that Eucalyptus nitens is prone to collapse during drying,which seriously degrades drying quality and hinders subsequent processing and utilization,kiln-dried quarter-sawn boards with a thickness of 45 mm and severe collapse were selected as test materials.Steam treatment at 92.7℃with 100%relative humidity was adopted for re-covery.Three methods were applied to evaluate the collapse degree and recovery rate from multiple perspectives:vernier caliper measurement(Method 1),ImageJ-based thickness difference method(Method 2),and ImageJ-based area differ-ence method(Method 3).Meanwhile,the recovery process of cellular structure in collapsed regions was observed via opti-cal microscopy and scanning electron microscopy(SEM).The results showed that steam treatment for 6 h could signifi-cantly restore the collapsed areas of wood specimens,and the cross-sections of specimens became basically flat.The varia-tion trends of collapse recovery rates obtained by the three methods were generally consistent,with the ranges of 57.1%-90.5%,46.2%-68.1%,and 38.6%-73.8%,respectively.Method 1 mainly characterizes the recovery effect of the most severely collapsed regions,while Method 2 and Method 3(especially Method 3)better reflect the overall recovery level of specimen cross-sections.However,Method 1 and Method 3 are susceptible to artificial judgment errors.The com-bined application of multiple methods can improve the comprehensiveness and objectivity in evaluating collapse recovery degree.Microscopic observations revealed that most vessels in collapsed regions were flattened due to tangential compres-sion.The vessels directly beneath collapse grooves were radially compressed,changing from nearly elliptical shapes to ir-regular quadrilaterals.Vasicentric tracheids,fiber cells and ray cells around vessels suffered severe deformation,among which vasicentric tracheids exhibited the most dramatic deformation.With the progress of steam treatment,all types of cells gradually recovered to their normal morphology.Nevertheless,cells in collapse zones near the pith required distinctly longer recovery time than those near the surface,and their recovery lagged behind the surface cells at the early stage,which restricted the duration of steam treatment.