文献类型：期刊文献

中文题名：木材塑性变形的湿热固定技术及机理研究进展

英文题名：Advances in Wood Plastic Deformation Fixation by Hygro-Thermal Treatments and the Fixation Mechanisms

作者：黄荣凤[1]

第一作者：黄荣凤

机构：[1]中国林业科学研究院木材工业研究所,国家林业和草原局木材科学与技术重点实验室,北京100091

年份：2022

卷号：58

期号：2

起止页码：206-216

中文期刊名：林业科学

外文期刊名：Scientia Silvae Sinicae

收录：CSTPCD;;EI(收录号：20222012128651);Scopus;北大核心:【北大核心2020】；CSCD:【CSCD2021_2022】；

基金：国家自然科学基金项目“基于过热蒸汽压力和介质组成的木材塑性变形永久固定机理及其适用”(32071690)。

语种：中文

中文关键词：塑性变形;永久固定;残余应力;应力释放;湿热处理

外文关键词：plastic deformation;permanent fixation;residual stress;stress release;hygro-thermal treatment

分类号：O636.1;TQ352

摘要：塑性变形永久固定是木材压缩密实化、弯曲等塑性改性的关键科学和技术问题之一。本研究针对塑性变形湿热固定技术,从塑性变形形成和回复机理入手,在全面分析木材塑性变形固定研究现状的基础上,重点阐述木材塑性变形的湿热固定技术和机理研究进展以及存在的问题,为突破该项技术的产业化应用瓶颈提供参考。湿热固定技术是以释放木材内应力方式固定塑性变形的方法,因处理方式不同,区分为常压热处理和加压热处理两大类。目前采用的所有处理方法,永久固定塑性变形的必要条件为温度达到180℃以上,加快热传递速度,并使板材厚度方向的中心温度快速达到180℃,能够有效缩短塑性变形永久固定时间。湿热处理永久固定塑性变形机理研究主要从热处理和饱和蒸汽处理2种过程中木材内应力释放与化学性质变化之间的关联性展开,多数研究支持3种基本机制,即基质分子间的交联反应形成稳定的结构;分子链断裂使微纤维和基质中应力松弛;亲水的细胞壁成分,特别是半纤维素形成聚合物阻止其再次发生水软化。但这些研究实际上只局限在2个极端,一端是干燥状态下依靠提高温度和延长时间释放木材内应力的热处理,另一端是接近饱水状态下依靠高温高压释放木材内应力的饱和蒸汽处理,而且这些研究均未涉及影响塑性变形固定和木材性能热、质传递等重要的过程因素,存在永久固定和木材性能变化的相互制约等适用性问题。虽然采用湿热处理方法理论上已经实现塑性变形的永久固定,但这些技术并未实现产业化应用,主要原因在于支撑湿热处理永久固定塑性变形的理论和技术体系不完整。要解决塑性变形的湿热固定技术应用问题,不能只关注最终条件,还有考虑如何有效实现这些条件,因此,需从湿热处理过程中水分的作用、热作用和氧化作用及其相互作用机理,热、质传递规律,湿热作用下木材内应力释放的作用机制等方面开展深入研究。
Permanent fixation of wood plastic deformation has been one of the key scientific and technologic issues for wood modifications such as densification and bending.This paper reviews plastic deformation fixation via hygro-thermal treatments from the perspectives of mechanisms for plastic deformation formation and set recovery.Recent research on fixation of solid wood plastic deformation,especially the advances and challenges in wood plastic deformation fixation by hygro-thermal techniques and the associated mechanisms,are overviewed,with the objective of providing a reference for breaking through the bottleneck of hygro-thermal treatment techniques scale-up to industrial level for wood deformation fixation.Hygro-thermal treatment is the main technique to fix plastic deformation by releasing wood interior stress.Depending on the treatment method,hygro-thermal treatments are categorized into heat treatment under atmospheric pressure and heated treatment under pressurized conditions.Currently,hygrothermal treatment requires the heating temperature to reach to over 180℃for the permanent fixation of wood plastic deformation.Thus,to accelerate the heat transfer rate and heat wood center to 180℃can effectively shorten the time required for wood plastic deformation fixation.Research on permanent fixation of wood plastic deformation is generally carried out by hygrothermal treatment in forms of heat treatment and saturated steam treatment,and was explained by the relationships between wood internal stress release and chemical changes.Three mechanisms for hygro-thermal treatment based permanent fixation of plastic deformation have been widely acknowledged.The first one is stabilized structures caused by the intercrossing of matrix molecules,the second one refers to molecular chains scission caused relaxation of stress in microfibril and matrix,the third is that polymerization of hydrophilic wood cell wall components especially hemicellulose and the resultant retardancy of the hydrophilic wood cell wall components to re-softening.However,research on hygro-thermal treatments for wood plastic deformation fixation is actually limited to two extreme conditions:one is the heat treatment under dry conditions,by applying elevated heating temperatures and extended heating time for internal stress release;the other is the heat treatment under almost water saturated conditions,by employing saturated steam at high temperatures under high pressure,to release wood interior stress.Neither of these involves processing variables/parameters of heat and mass transfer affecting wood plastic deformation fixation and wood properties,causing a contradiction between permanent fixation of wood deformation and wood properties deterioration.Even though permanent fixation of wood fixation has been theoretically realized by hygro-thermal treatment,it has not been completely applied in industry.The main reason for this is the immaturity of theories and technology system supporting hygro-thermal treatment based permanent fixation of wood deformation.To solve the application issues in hygro-thermal treatment based permanent fixation of wood deformation,more attention should be paid to how to make the hygro-thermal treatment conditions applicable rather the conditions themselves.Thus,research on hygro-thermal treatment for permanent fixation of wood deformation from the perspectives of functions of water and heat,oxidation and their interaction,as well as wood interior stress relaxation during hygro-thermal treatment should be carried out.