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。     

木材热处理研究及产业化进展

热处理是在160℃以上低氧环境下进行的木材改性技术,可以改善木材的尺寸稳定性、生物耐久性和机械振动性能,同时能调节木材的材色,并且具有良好的环境友好性。但是高温处理也降低了木材的力学性能,对抗弯强度和冲击韧性的影响尤为显著。半纤维素在高温下的热解是热处理材改性的主要原因,它减少了木材中亲水基团和营养物质的数量,降低了木材的韧性,同时也影响了木材的明度指标。纤维素和木素在热处理过程中的变化相对较小,纤维素的结晶度有所上升,进一步降低了木材的亲水性,并提高了木材刚度;木素的结构在处理过程中发生了重组,形成了更加稳固的网状结构,对细胞壁的膨胀具有抑制作用,同时也是木材材色变化的主要原因。热处理过程中产生的抽提物主要是半纤维素的降解产物,它们对木材的吸湿性和声学特性都有影响。热处理对木材性能的调节受诸多工艺参数影响,温度是对木材改性深度影响最大的因子,处理环境的压力和在最高处理温度下的处理时间也对改性效果产生影响。木材热处理目前已获得较为广泛的产业化应用,这一方面是得益于系统性的基础研究,另一方面是因为它具有环保、低成本、操作简便等优点。木材热处理目前已逐渐形成了一个较为完整的技术和理论体系,但在平衡性能提升与强度损失、保持材色稳定性等方面的研究仍具有持续深入和拓展的空间。     

糠醇改性处理对户外用木材耐老化性的影响研究

木材在户外使用过程中易发生材性劣化现象,糠醇改性是一种增强木材耐老化性能的环境友好型改性技术。总结了糠醇改性机理、工艺及糠醇改性处理对木材性能的影响;简述了户外用木材耐老化性研究,为糠醇改性材在户外的应用提供理论指导。     

沙浴热处理杉木及其物理力学性能研究

以杉木为材料,通过沙浴和气相介质进行热处理,检测其炭化木材物理、力学性能和颜色等,借助XRD和FTIR分析不同热处理方法致木材性能差异的原因,以期探索沙浴炭化木材的可能性。结果表明:当热处理温度和时间相同时,沙浴热处理试件尺寸稳定性高于气相介质热处理;处理温度为220℃,时间4 h时,两种介质处理试件的尺寸稳定性均达到了最好状态,其中气相介质热处理杉木弦向线湿胀率最小为1.885%,比未处理材降低35.45%,沙浴热改性处理杉木弦向线湿胀率最小为1.923%,比未处理材降低36.16%。沙浴热改性处理杉木木材强度折损较气相介质热改性处理材更多。热处理温度和时间相同时,气相介质处理材颜色变化小于沙浴热改性处理材。热改性处理导致杉木材结晶特性和三素成分发生变化,其中沙浴热处理导致杉木材中半纤维素发生明显降解。     

热处理升温速率对柞木微观结构和物理力学性能的影响

升温速率对木材热处理的产品性能和反应机制都会产生显著影响,对生产实践操作也具有重要作用,但相关研究十分缺乏。以柞木为试样,在常压过热蒸汽条件下以5,10,15,20和25℃/h的升温速率分别升温至200℃进行热处理。分析处理材的主要化学组分和结构,并测试其主要物理力学性能,探索升温速率对处理材结构和性能的影响,为木材热处理技术的优化应用提供参考。结果表明：热处理升温速率对柞木化学组成和结构都具有显著影响。细胞壁半纤维素含量随升温速率的减小而下降,而木素的相对含量则随着升温速率的减小而提高,纤维素含量受热处理影响很小,但微纤丝结构发生明显变化。不同升温速率水平下热处理柞木的主要性能也呈规律性变化。热处理后柞木的静态与动态弹性模量均有所增加,且都随着升温速率的下降先增大后减小,与微纤丝结晶度的变化趋势高度一致。热处理后柞木的吸湿性随升温速率的减小而逐步下降,并与半纤维素浓度的变化密切相关。综上可见,升温速率是调节热处理柞木性能的有效工艺参数,但试材性能的变化与升温速率之间并非都是线性关系,应根据木材热处理的主要性能需求,结合生产效率和安全性等综合因素确定木材热处理的升温速率。     

高温热处理对木材颜色变化影响综述

通过总结热处理对木材颜色变化的研究结果,分析热处理方式、热处理工艺参数包括温度和时间、树种与化学成分对热处理材颜色变化的影响,颜色变化与化学成分以及物理力学性能的相互关系,以及热处理材颜色光稳定性能。对今后研究提出几点建议。     

木材硅化改性研究进展

通过木材改性实现人工林低密度软质木材的提质增效,高效利用人工林资源,对我国木材工业的可持续发展和生态建设具有重要意义。木材硅化改性可以有效提高木材性能,但改性材性较脆、工艺复杂、成本较高等问题限制了其实际应用。文中分别从木材硅化改性剂种类、改性方法、改性机理和改性材性能等方面综述了木材硅化改性的研究成果,讨论了目前木材硅化改性存在的主要问题。建议基于有机-无机杂化研制多效一体化木材硅化改性剂,改进工艺,提升性能,降低成本,从而推动硅化木的开发和利用;开展木材仿生硅化改性研究,促进组分界面结构性连接,全面提升木材性能。     

改性松香对速生杨木性能提升的研究

以精制松香(RR)、聚合松香(PR)和丙烯酸松香(AAR)为改性剂,无水乙醇为溶剂,配制质量分数为20%的浸渍液,采用浸渍法对速生杨木进行改性,得到精制松香改性材(RRMW)、聚合松香改性材(PRMW)和丙烯酸松香改性材(AARMW),并以无水乙醇浸渍得到对照木材(CW)。采用红外光谱(FT-IR)、扫描电镜(SEM)、激光共聚焦显微镜(CLSM)和X射线衍射(XRD)等方法对改性材进行了结构表征,并测试了改性材的耐水性和机械性能。研究结果表明:改性材的红外光谱在1691 cm^-1的■吸收峰显著增强,XRD分析发现晶面衍射峰没有明显变化,SEM和CLSM图中可清晰地观察到改性松香沉积在木材细胞腔且渗入了木质细胞壁,表明改性松香已经进入木材细胞,但对木材纤维素的结构没有影响。性能测定结果发现:3种改性材的性能均有所提高,其中AAR对速生杨木的性能提升最显著,AARMW的耐水性明显增强,其浸渍12 d后的吸水率为79.68%,而对照木材的吸水率则为186.28%;AARMW在180 s时的接触角为88.78°,相比15 s时的100.09°,仅下降12%,而对照木材接...     

自然老化对古建筑木材细胞壁结构与成分的影响

探究古建筑木材微观结构和化学成分的变化,有助于揭示自然老化作用下木材性质的演变机制和劣化机理。以古建和现代落叶松（Larix sp.）木材为研究对象,通过对两者微观构造、孔隙率、纤维素结晶度和化学成分进行测试,探究自然老化作用下古建材性质的变化。结果表明,古建材微观构造上存在显著的劣化特征,其中早材比晚材的劣化程度更严重;古建材孔隙的孔体积和孔径均显著大于对照材,古建材中大部分孔隙孔径在10 nm以上,而对照材中孔径10 nm以下的孔隙占比最高。古建材纤维素结晶度比对照材升高13.61%;傅里叶变换红外光谱显示古建材中木质素、半纤维素出现了一定程度的降解,峰强度比结果显示纤维素结晶区未发生明显变化,而纤维素无定形区发生了降解。基于微观结构和化学成分的变化,提出木材细胞壁化学成分的劣化模型,为自然老化作用下木材的劣化机理研究提供参考依据。     

木材塑化复合改性

木材塑化复合改性该工艺利用塑料单体对木材进行浸渍处理，使塑料单体渗入木材内部孔隙和细胞腔内，然后利用辐射交联技术。使单体与构成细胞壁的纤维素进行交联固化，形成网状结构，从而大大改善了木材的机械性能。经实测，木一塑复合材料在纯水中长期浸泡，其吸水变形很...     

木质材料激光表面处理研究进展

激光以其能量密度高、运行轨迹自如、方向性好等优点,被广泛用于木质材料切削加工以及表面处理等领域.其中,木质材料激光表面处理,即利用激光热/光电子效应促进材料发生物理、化学变化,以实现改性的目的.笔者对木质材料激光表面处理原理、激光类型与用途以及激光表面处理技术特点与应用领域等内容的研究现状进行了综述与分析.现有研究表明...     

Anatomical explanations for the changes in properties of western red cedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) wood during heat treatment

Thermal treatment is an alternative to the chemical treatment in wood preservation, which has been used to some extent in improving timber quality. Despite the enormous works done so far on the effects of heat treatment on wood properties, very little is known about the anatomical changes in the various wood species during the process. Wood samples from western red cedar (Thuja plicata) were heat-treated at a temperature of 220°C for 1 and 2 h. The anatomical structures were examined before and after the heat treatment process by using scanning electron microscope (SEM) and related to density, water uptake, thickness swelling and modulus of rupture of wood samples obtained from the same board. Heat treatment of red cedar wood resulted in the destruction of tracheid walls, ray tissues and pit deaspiration. The destroyed tracheid walls and ray tissues appeared to blow up, thus increasing the size of the specimen. The process of pit deaspiration also resulted in increasing size of the pits, thus creating more openings in the wood. These changes in wood anatomy indicate that the well-established chemical degradation is not the only reason for changes in wood properties during heat treatment. However, it is believed that the effects of the chemical changes still outweigh those of the anatomical changes based on the modification observed during the process of heat treatment.     

Impact of thermal modification on color and chemical changes of spruce and oak wood

Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and chemical changes in spruce (Picea abies L.) and oak wood (Quercus robur F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the L*a*b* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-O-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.     

辐射技术及其在木材科学研究中的应用

辐射化学是研究电离辐射与物质相互作用时产生的化学效应的化学分支学科.木材是一种天然生成的由几种高聚物(纤维素、半纤维素、木质素、抽提物)组成的有机复合体, 不同的高聚物在辐射过程中会产生辐射降解、交联等.文中主要概括了辐射加工的发展、特点、原理、辐射剂量, 并详细阐述了辐射加工在木材科学领域中的应用及进展, 主要包括木材辐射干燥、木塑复合材的辐射制备、射线辐射在木材改性中的应用、木材自由基对木材耐候性及辐射对木材各化学组分的影响; 分析了辐射技术在木材科学领域中的应用与发展趋势.     

Effect of fungal exposure on the strength of thermally modified Norway spruce and Scots pine

Abstract

Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself.     

木质材料等离子体改性研究进展

等离子体改性技术作为一种高效、绿色的处理工艺已广泛应用于催化剂合成、表面活化、化合物镀膜等研究及应用领域。其对木质材料改性研究从上世纪90年代至今已取得许多重要的实验及理论成果,可综述为:1）木质材料等离子体改性的特性; 2）木质材料等离子体改性的机理; 3）等离子体改性木质材料的设备及工艺。文中在整理近年文献资料的基础上分析了文献中相互矛盾的结论,并对未来等离子体改性木质材料的研究方向提出建议。     

木材压缩改性技术研究进展

为改善速生材自身固有的缺陷,提升其利用价值,需对速生材进行强化改性处理.木材压缩改性技术作为一种木材物理强化改性方法,具有生产效率高、无化学污染和易于产业化生产等优点,是扩展速生材应用范围最具潜在商业价值的木材改性技术之一,已成为木材改性研究领域的前沿和热点.笔者在广泛阅读文献的基础上,对木材压缩强化改性方面的代表性成...     

Detection of the effective refractive index of thermally modified Scots pine by immersion liquid method

The purpose of this study was to determine the effective refractive index of thermally modified Scots pine (Pinus sylvestris L.) wood specimens as a quantitative measure regarding the change of wood density which is due to the thermal modification. The refractive index of thermally modified Scots pine wood was obtained by introducing pine wood powder into an immersion liquid and measuring light backscattering with a homebuilt multifunction spectrophotometer. The present method provides useful information that in principle can be applied, for example, in the optimization of the thermal modification process and inspection of the quality of thermally modified wood.     

The influence of thermal-hydro-mechanical processing on chemical characterization of Tsuga heterophylla

Viscoelastic thermal compression (VTC) is a type of thermal-hydro-mechanical (THM) processing that requires only a short processing time. THM processing causes some chemical transformations, the nature and extent of hydro-thermolysis depends on the special treatment conditions and the chemical nature of wood species. In the present study, the chemical transformations of the cell wall components and wood extractives during VTC treatment were investigated, and correlation between chemical characterizations and observed property changes was analyzed. For this purpose, the content of extractives and pH values were determined, and FTIR analysis was performed on extractable substances, extract-free wood, holocellulose, α-cellulose and lignin. Two temperatures and two steam exposure times were adopted to determine the influence of processing conditions on chemical characterization of Tsuga heterophylla. The results revealed that THM treatment caused a series of chemical reactions in extractives. Treatment temperature and conditioning time have significant influence on chemical changes of extractives. For all of the VTC treatments used in this study, no significant changes occurred in the lignin and α-cellulose components. The only significant chemical changes occurred in the hemicelluloses, which were primarily reduction of carbonyl and acetyl functional groups. This study also confirmed that the chemical transformation of wood correlates with property changes of VTC wood.     

Structural Change of Wood Molecules and Chemorheological Behaviors during Chemical Treatment

It is very important to clarify the relationship of changes of molecular combinations in wood cell walls and the chemical rheological behavior during various chemical reagent treatments, for it would be helpful to develop new wood modification technologies and to enrich the theory of chemical rheology of wood. Based on previous investigations on the chemorheological properties of wood by chemical treatments and the applied methods in chemical rheology of wool fibers, this paper proposes thestudy of various additional reagents to wood saturated in water for long periods of time in order to investigate the chemical theology of wood, which can provide information about the character of combinations between wood molecules and the structural changes of molecules and further put forward the idea of modifying wood in a decrystallized state.