压力蒸汽热处理木材生物耐久性的研究

通过对樟子松和柞木分别在常压和压力蒸汽下进行高温热处理,比较了两种热处理材与常规对照材生物耐久性的差异。结果表明,高温热处理特别是压力蒸汽处理,可以更显著地改善木材的耐腐性,耐腐等级可由对照材的Ⅳ级(不耐腐),提高为Ⅰ级(强耐腐,樟子松)和Ⅱ级(耐腐,柞木)。热处理可以有效减轻蓝变菌对木材的侵害,但不能防止或减轻木材表面的霉变。在热处理材表面涂刷油性防水涂料,是防止表面生霉的很有效的方法。     

杉木热处理材结晶度及力学性能的研究

热处理对木材力学性能的影响是多样的,这与热处理条件下木材的物理化学变化密切相关。本次研究将杉木板材在160℃、180℃和220℃常压蒸汽条件下进行热处理,考察处理材的结晶度、抗弯弹性模量、抗弯强度及相互可能的关联。结果表明,热处理使试材结晶度增加,有助于提高木材的刚性,使热处理材的抗弯弹性模量高于常规对照材;结晶度的提高对抗弯强度没有改善作用,热处理后试材的抗弯强度明显下降。     

基于FT-IR和XPS的热处理白蜡木材色变化机理

以白蜡木(Fraxinus americana)为试材,在常压过热蒸汽条件下进行热处理,对热处理材和对照材的明度(L*)和色度(a*,b*)指标进行比较,借助傅里叶红外光谱仪(FT-IR)和X射线光电子能谱仪(XPS)对试材细胞壁化学组分的主要基团和元素变化进行分析,以探索热处理对木材材色的调节机理。结果表明:随着处理温度的增加,热处理材和对照材的总体色差不断增大,色差值与木材内部C和O元素的浓度比高度相关,表明热处理材的材色能较为准确地指示木材内部化学组分的变化。热处理材的明度指标随热处理温度的升高呈阶梯式下降,明度值的变化与木材中羧基的浓度线性相关,表明半纤维素是影响热处理材明度的主要因素。热处理材的色度指标变化规律没有明度指标显著,随着处理温度的升高,a*值先增加后降低,试材的b*值随着处理温度的升高总体上呈下降趋势。热处理使木素中的羰基等发色基团数量发生变化,是使热处理材的色度指标发生变化的一个主要原因。     

基于拉曼光谱分析的热处理松木吸湿机理研究

木材热处理可以显著降低木材的吸湿性,是提高其尺寸稳定性的有效改性方法。以南方松热处理材和对照材为试材进行动态水蒸气吸附试验,并借助拉曼光谱对两种试材的化学组分进行比较,探索热处理对木材吸湿性能的改性机理。结果表明:在本试验条件下,热处理不仅降低了木材的吸湿量,也改变了其吸湿特性,表现为热处理材平衡含水率变化率的降低和吸湿滞后性的增强。在实际应用中,这表明热处理材即使在环境湿度变化较大的情况下也能保持较好的尺寸稳定性。拉曼光谱分析表明,木素的结构变化是热处理材形成其吸湿特性的主要内在原因之一。热处理后木素在细胞壁中的相对含量有所上升,结构发生了重组,使木材细胞壁结构变得更加稳固而缺乏弹性,对木材的吸湿和平衡起到了阻滞作用。     

热处理对三种木材尺寸稳定性的影响

以落叶松、红橡和奥克榄为研究对象,采用不同的常压蒸汽热处理工艺条件,对照未处理材,研究热处理温度和时间对木材尺寸稳定性的影响。结果表明:热处理温度和时间对木材的尺寸稳定性有显著影响;木材吸湿性随温度提高逐渐降低,当热处理温度上升到一定程度时,尺寸稳定性改善趋缓;随着热处理时间延长,木材尺寸稳定性提高;木材高温热处理后吸湿性和吸水性的改善与木材的密度、结构等物理性能相关。     

樟子松热处理材耐腐性的评价

热处理材由于高温处理改变了木材的成分,可抑制腐朽菌的生长和繁殖,从而提高木材的耐腐能力。根据国家标准,对樟子松热处理材和对照材进行室内耐腐性检测及野外埋地试验。检测结果表明,热处理材的耐腐等级达到Ⅰ级,耐腐性显著提高;在对照材野外埋地试验的耐腐朽等级为0级时,热处理材仍可保持9.5级。     

热处理改性木材的性能分析Ⅳ——热处理木材的防白蚁性能

对南方松、樟子松、水曲柳、柞木、斯文漆木五种木材的热处理材,进行室内防白蚁性能检测和评价.结果表明:5种热处理试材的防白蚁蛀蚀等级均在3～4级,热处理工艺未能改善试材的抗白蚁蛀蚀性.     

热处理木材材色变化机理研究现状北大核心

热处理是一种应用广泛的木材改性方法,不仅能改善木材材色,还能提高木材的尺寸稳定性和生物耐久性。总结了热处理工艺对木材性能的影响,详述了热处理过程中木材化学组分变化。从处理过程和老化过程讨论了环境对处理材性能的影响,并概括了热处理木材材色变化机理。未来应深入解析热处理化学反应路径及其内在机理,建立木材材色与其他材性的关系,并通过联合改性处理提升热处理木材的耐久性。     

高温热处理对樟子松板材物理力学性能影响的研究

分别采用170、190、210℃三组处理温度对樟子松板材进行了高温热处理工艺试验,并对处理材和对照样进行了物理、力学性能测试:高温热处理工艺使樟子松木材的绝干密度下降、吸湿性降低,对其抗弯强度亦有较大影响,且此影响随温度升高而增大;对于抗弯弹性模量、顺纹抗压强度、表面硬度三项指标则基本无影响.在常规使用环境下,由于处理材与对照样之间存在含水率差异,除了210℃处理材的抗弯弹性模量、顺纹抗压强度、表面硬度比对照样略小外,170℃和190℃处理材的三项指标均不同程度高于对照样.     

人工林杉木木材力学性质对高温热处理条件变化的响应

以人工林杉木为试材,分别用空气和菜子油为介质,在温度为180,200和220 ℃对其分别热处理1,3和5 h,研究试材的抗弯强度(MOR)、抗弯弹性模量(MOE)、顺纹抗压强度、表面硬度对高温热处理条件变化的响应,同时对处理材的主要化学成分进行分析,用扫描电镜对处理材横切面微观结构进行观察.结果表明:人工林杉木试材的4种主要力学性质对不同条件热处理的响应程度不同.无论是空气热处理还是油热处理,试材的MOR,MOE,顺纹抗压强度与对照比有不同程度的降低,且随处理温度升高、时间延长,下降幅度增大,相比于时间,温度的影响更显著;180 ℃热处理1,3和5 h时,试材的MOR,MOE与对照比未发生明显变化(降幅在3%以内),而顺纹抗压强度则明显低于对照,两介质中降低幅度分别在3.29%～9.58%和3.89%～7.18%;200 ℃以上处理时,不同时间处理的3种主要力学性质不仅显著或极显著低于对照,且各性质问的差异也达显著或极显著水平;对硬度的测试结果表明:180 ℃热处理时,试件的径面硬度和弦面硬度均随时间的延长而增大;200 ℃热处理3 h时,试件的硬度达最大,与对照差异达显著水平;随后热处理试件的硬度开始降低,220 ℃热处理5 h后试件的硬度又明显低于对照.在隔氧的油介质中进行热处理,4种主要力学性质的变化程度低于空气介质处理材,当温度高于200 ℃时,两介质处理间的差异达显著水平.而热处理过程中木材主要化学组成与横切面微观结构变化的差异,反映了4种主要力学性质对不同条件热处理时表现出的响应差异.     

Effects of heat treatment on some properties of MDF (medium-density fiberboard)

This work investigated some mechanical, physical and free formaldehyde emission properties of heat-treated MDF. For this purpose, MDF panels were subjected to varying heat treatment temperatures (155°C, 165°C and 175°C), durations (2.5?h., 3.5?h. and 4.5?h.) and waiting times after hot pressing (30?min., 120?min. and 600?min). Thickness swelling (TS), water absorption (WA), free formaldehyde emission (FFE), bending strength (BS), modulus of elasticity (MOE), tensile strength perpendicular to fibers (TSPF) for treated and untreated samples were tested and evaluated statistically. Consequently, after the heat treatment values of tensile strength, bending strength and modulus of elasticity were almost negatively affected relatively, but the thickness swelling and water absorption and quantities of free formaldehyde were improved positively of MDF samples.     

超高温热处理实木地板的工艺及应用

对白蜡木、柞木、香樟、荷木等实木地板坯料进行了超高温热处理的研究.结果表明:与普通实木地板相比,热处理实木地板后吸湿性降低51.87%,尺寸稳定性提高42.36%,弦向弹性模量和顺纹抗压强度分别提高了1.15%和2.19%,(但弦向抗弯强度明显降低),导热效能超过实木复合地板.该技术已在工业上推广应用.     

热处理材的铣削加工性能分析

考察热处理对木材机械加工性能的影响,为优化热处理材的加工工艺提供借鉴,在本试验确定的加工参数条件下,对热处理柞木进行了铣削加工。试验结果表明,相比对照材,铣削加工热处理材时刀体的温度更低,在加工过程中排放的较小粒径粉尘的比例增加,热处理材加工面的粗糙度与对照材并没有显著差异。     

热处理改性木材的性能分析Ⅲ——热处理材的防霉性能

检测了4种热处理材的防霉性能,以及桦木和樟子松热处理材中还原糖的含量。结果表明,热处理材的含糖量升高,且表面部分比中间部分高。故热处理材比其素材更易长霉,尤其是木材表面部分。清漆处理可避免木材霉变。     

Study on the effect of nano-silver impregnation on mechanical properties of heat-treated <Emphasis Type="Italic">Populus nigra</Emphasis>

The present study is aimed at investigating the effect of heat treatment of nano-silver-impregnated Populus nigra on weight loss, modulus of rupture (MOR), modulus of elasticity (MOE), and compression parallel to grain. Specimens were impregnated with 200 PPM water-based solution of nano-silver particles at 2.5 bar in a pressure vessel. For heat treatment, both nano-silver-impregnated and simple specimens were kept for 24 h at 45°C and then further for 24 h at 145°C and finally for 4 h at 185°C. MOR decreased from 529 to 461 kg/cm² in heat-treated specimens; MOE and compression parallel to grain were though improved. Also, comparison between heat-treated and nano-silver-impregnated heat-treated specimens showed that there was a decrease in MOR and MOE in nano-silver-impregnated heat-treated specimens. This shows that nano-silver impregnation facilitates transfer of heat in wood and it may increase the process of degradation and pyrolysis of wood structures in deeper parts of specimens.     

Optimization of processing variables during heat treatment of oak (Quercus mongolica) wood

The properties of oak heat treated at temperatures of 160–220 °C, oxygen concentrations of 2–10 %, steam pressures of 0.1–0.4 MPa and treatment time of 2–4 h were investigated. Although modulus of elasticity (MOE), modulus of rupture (MOR) and equilibrium moisture content (EMC) of the heat-treated wood (HTW) were reduced, the value of $ \Updelta E^{*} $ was increased, and the dimensional stability [anti-swelling efficiency in radial (ASE-R), anti-humidity efficiency (AHE)] was improved considerably. Six regression equations (temperature, oxygen concentration, steam pressure and time as functions of MOE, MOR, ASE-R, AHE, EMC and $ \Updelta E^{*} $ ) were developed for the estimation and a nonlinear programming model was derived with operation research theory to obtain the most desirable HTW properties under some production constraints.     

基于近红外光谱技术的热处理竹材物理力学性能

探讨了近红外光谱(NIRs)技术对实现热处理毛竹分选和性能在线检测的可能性。采集了3种不同温度(150,180和210℃)热处理及未处理毛竹的径切面近红外光谱信息,应用主成分分析方法与偏最小二乘法对竹材进行分类,并建立了热处理竹材的材色、密度以及力学性能预测模型。结果表明:1)近红外光谱二阶导数谱图在7 004和6 452 cm-1等吸收带处很好地反映了竹材热处理对应化学成分的变化,表明了近红外光谱变化与化学成分变化的一致性,也说明了NIRs用于快速分析热处理竹材材性的可能性; 2)热处理竹材在主成分得分图中呈明显的聚类分布特征,说明了NIRs技术对于热处理竹材良好的分类能力; 3)材色预测模型的模型参数R2≥0.93、RPD均大于3.90,表现出了非常好的材色预测性能。气干密度、绝干密度以及抗弯强度预测模型的R2分别为0.83,0.85和0.82,RPD分别为2.42,2.59和2.34,能够满足竹材性能的评估精度要求。     

处理时间对热改性橡胶木物理力学性能的影响

采用过热蒸汽作为传热介质和保护气体热改性橡胶木,分别于185℃条件下热改性处理2、3、4、5h,于200℃热改性处理1、2、3、4h,主要分析了处理时间对橡胶木热改性材物理力学性能的影响。结果表明:在200℃条件下,处理时间对质量损失率、颜色的影响均较185℃更显著。在两个温度条件下,处理时间对MOE的影响均不显著。在185℃温度条件下,MOR从3h开始即无显著变化;在200℃温度条件下,MOR在前3h内无显著变化,第4h开始显著降低。     

Bending strength and toughness of heat-treated wood

The load-deflection curve for static bending and the force-time curve for impact bending of heat-treated wood were examined in detail. The effect of oxygen in air was also investigated. Sitka spruce (Picea sitchensis Carr.) was heated for 0.5–16.0h at a temperature of 160°C in nitrogen gas or air. The dynamic Young's modulus was measured by the free-free flexural vibration test, the static Young's modulus and work needed for rupture by the static bending test, and the absorbed energy in impact bending by the impact bending test. The results obtained were as follows: (1) The static Young's modulus increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. (2) The bending strength increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. (3) The work needed for rupture decreased steadily as the heating time increased. It decreased more in nitrogen than in air. It is thought that heat-treated wood was more brittle than untreated wood in the static bending test because W₁₂ was reduced by the heat treatment. This means that the main factors contributing to the reduction of the work needed for rupture were viscosity and plasticity, not elasticity. (4) The absorbed energy in impact bending increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. It was concluded that heat-treated wood became more brittle in the impact bending test becauseI ₁₂ andI ₂₃ were reduced by the heat treatment.