FTIR 光谱法检测木材初期腐朽的最新研究进展

傅里叶变换红外(FTIR)光谱技术作为一种先进的检测方法具有迅速、准确、无损等优点.介绍了 FTIR光谱技术在木材初期腐朽检测中的基本原理、特点以及最新研究进展,并在此基础上指出现存问题和今后的发展方向,旨在促进 FTIR 光谱技术在木材初期腐朽检测领域的进一步应用     

桦褐孔菌引起的腐朽木上真菌组成的研究

以桦褐孔菌寄生的白桦活立木为材料,研究了由桦褐孔菌引起的木材白腐病及其腐朽初期、中期和末期腐朽木上的真菌组成。结果表明,随着腐朽程度的增加,腐朽木上的真菌物种数量增多,桦褐孔菌分离到的次数也随之增加。腐朽初期、中期和腐朽末期优势真菌种类差别不明显。各个时期树皮上的真菌种类最多,变色区种类相对少。说明不同腐朽阶段腐朽木上的真菌群落存在差异,群落组成处于动态变化之中。     

木材腐朽机理研究现状及展望

木材在生产应用过程中易受真菌侵害导致木材性能劣化，极大地限制了木制品在户外推广应用。近年来，为了增强木材防腐技术开发的理论基础，木材腐朽机理得到普遍关注与研究。文中从以下3个方面梳理、归纳、总结木材腐朽机理研究现状:1）木材腐朽过程中结构成分与性能的变化规律；2）木材酶降解理论；3）木材非酶降解理论。在此基础上，阐明现有木材腐朽机理研究中存在的问题及今后重点研究方向，以期为绿色环保型木材防腐技术的研发提供理论指导，为2030年我国实现“碳达峰”提供战略技术支撑。     

怎样减少贮木场木材的腐朽?

林晓木博士：你好！我们林场贮木场的木材经常发生腐朽，特别是在湿热的气候条件下，为什么？有什么有效的办法来减少木材的腐朽吗？木奇２００１年１１月１０日木奇：您好！您在来信中所说的木材腐朽是由微生物中的真菌作用于木材引起的。木材是一种生物材料，能引起木材腐朽的真菌包括褐腐菌（如密粘褶菌）和白腐菌（如彩绒革盖菌），前者导致木材发生褐腐（褐色腐朽），或叫粉末状腐朽，破坏性腐朽，俗称红糖包型腐朽。其木材典型的症状是外观呈褐色或红色，有如烧焦的木材；质脆，出现垂直于木材纹理的裂纹（龟裂）并伴随着严重的收缩和…     

木材保护体系的发展(续)

1.23 4,5一二氯一2一正辛基一4一异噻唑啉-3-酮(DC01)该产品又称Kathon 930,是一种有机溶剂防腐剂,适合用作在地面以上和与地接触使用环境中保护木材免受真菌腐朽和昆虫侵害的防腐剂配方中的有效成分。在标准实验室和长期野外的试验中,都已表明该化合物对一些腐朽真菌和侵害木材的昆虫有广谱的抑     

电阻测试法在立木腐朽检测中的应用研究进展

我国的木材需求巨大,但是木材利用率有待提高.木材无损检测技术可以很好地提高木材利用率,增加经济效益.电阻测试法对于立木早期腐朽变色具有良好的检测效果,而且使用方便快捷.介绍电阻测试法的基本原理,对针式探测法、四点检测法和断层成像法3种电阻测试法的研究进展进行分析和总结,在此基础上对电阻测试法在立木腐朽检测中的应用可行性进行探讨.     

基于应力波与X射线二维CT图像原木内部腐朽无损检测

木材无损检测技术是在20世纪60年代后逐步兴起的对木材性质进行非破坏性检测的技术,如今该技术已多达几十种,产生了多种多样的木材无损检测方法。为了更好地运用这些方法,找出它们的优缺点,有必要对它们检测木材内部缺陷进行试验和评价。同时使用应力波和X射线两种方法对原木内部腐朽进行检测,结果表明：应力波和X射线二维CT图像都能检测出原木内部腐朽,显示出腐朽的区域,而且能利用图像计算出腐朽区域的面积。两种方法计算出的腐朽区域的面积准确度φ都较高,但是应力波二维CT图像在其他许多方面逊于X射线二维CT图像：应力波二维CT图像对腐朽区域形状的显示不够准确,不能根据图像辨别出腐朽的严重程度,利用图像确定腐朽面积效率很低;X射线二维CT图像对腐朽区域形状的显示与实际较吻合,可以根据图像辨别出腐朽的严重程度,利用图像确定腐朽面积效率高。但是X射线仪器笨重不便携,而应力波检测仪轻快便携。     

茯苓褐腐过程中木材化学成分的变化

用褐腐真菌茯苓按常规栽培方法对木材进行降解,对比研究了正常材和不同腐朽程度木材化学组成之间的差异,用傅立叶红外光谱仪(FTIR)对样品进行表征.结果发现,腐朽初期,综纤维素和戊聚糖的含量及纤维素结晶度随腐朽时间的延长逐渐降低,木质素和1%NaOH抽出物的相对含量却逐渐升高.当腐朽进行到15周时,综纤维素含量、戊聚糖含量和纤维素结晶度分别由正常材的72.80%、14.95%和40.3%下降到18.57%、8.58%和16.1%,木质素含量和1%NaOH抽出物含量分别从27.30%和12.89%增加到43.88%和70.07%.之后,随着腐朽时间的延长,木材的组成几乎保持不变.FTIR结果证实了相同的变化趋势.     

白桦木材中总酚含量与抗木材腐朽菌的关系

腐朽是木材最严重的生物破坏,它能引起木材结构损坏,造成经济上的巨大损失.白桦(Betula platyphylla)是极易腐朽的树种(李坚,2002).本文利用5种木材腐朽菌对白桦进行生物降解,根据质量损失率筛选出易腐和抗腐植株,进一步研究易腐和抗腐白桦总酚含量的差异与木材腐朽抗性的关系.为今后在林木遗传改良中筛选适宜的天然抗腐朽植株提供理论基础,同时也为森林培育、木材利用等方面的研究提供相关信息,减少防腐剂的使用,降低防腐剂对环境的污染.     

有助于林业的真菌

木材腐朽主要是由于真菌和细菌这两大微生物侵害所致。而真菌对木材的破坏力、破坏速度要比细菌大得多。但是近年来的研究发现,称为菌根的某些真菌却有助于树木生长,对种在贫瘠土壤的树木特别有利。 菌根(也有称根瘤菌、菌根菌的)在优质土壤中天然出现,它们在树根内繁殖,或包围着树根生长,这些真菌从寄主树根那里取得碳水化合物,而树木则通过微细的根毛吸收水分和菌根排出土壤的有价值的营养     

Non-destructive monitoring of early stages of white rot by Trametes versicolor in Fraxinus excelsior

? Non-destructive detection of fungal decay in living trees is relevant for forest management of valuable species, hazard tree assessment, and research in forest pathology. A variety of tomographic methods, based on stress wave timing, radioactive radiation, or electrical resistivity have been used to detect decay in standing trees non-destructively. But apart from mobile gamma ray computed tomography (Habermehl and Ridder, 1993) which is virtually unavailable, the detection of incipient stages of decay is still not possible.

? Wood moisture and electrolyte content influence the electric resistivity of wood. Both are changed by fungal decay. Therefore electric resistivity tomography (ERT) should detect decay in its early stages. Then it could be used to monitor the spatial and temporal progress of degradation.

? We infected four Fraxinus excelsior trees with Trametes versicolor using wooden dowels and measured two-dimensional electric resistivity tomograms 3, 10, 13 and 21 months after infection. Immediately after the last electric resistivity measurement trees were felled for further analyses of stem cross-sections. Wood moisture content and raw density had significantly increased in infected areas, but dry density had not significantly changed after 21 months. Areas of very low electric resistivity around the infected wounds correlated very well with infected wood in the stem cross-sections. Increasing areas of low electric resistivity around the infected wounds during consecutive measurements indicate increasing areas of infected wood.

? We conclude that the growth of white rot by Trametes versicolor can be monitored with electric resistivity tomography (ERT) beginning from incipient stages, even before wood density decreases. ERT could therefore be a powerful research tool for decay dynamics as well as a method for diagnosing wood decay in forestry and arboriculture.

     

Vibrational and acoustical experiments on logs of spruce

Summary This paper presents the results of some vibro-acoustical experiments conducted on logs of spruce. The aim from this study was in the beginning to study the possibilities of investigating acoustically the presence of decay in the stems of standing trees, and for assessing the strength of wood in the shape of logs. First, a brief review is made for the different experimental techniques used in studying the response of mechanical systems in general with emphasis on an efficient technique used for evaluating the impulse response of vibrating systems. Then a literature survey on the effects of decay on the strength and on the damping properties of wood are presented with some practical general implications regarding decay inspection of wood composites. Lastly some experiments using vibrations and sound which were conducted on two specimens of wood logs, one sound and one decayed, are presented with some discussions regarding the implementations of these methods for the quality grading and defect detection in wood logs and standing trees. Received 16 July 1997     

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.     

介质对木材热处理的影响

文中总结了不同介质热处理的技术特点,介质对热处理材性能的影响,以及预处理和复合介质热处理的研究进展,认为采用油、预处理或复合介质等热处理可以进一步提高热处理材的尺寸稳定性,减小木材强度降幅,还能显著增强防腐性能等其他单纯蒸汽热处理无法实现的功能,建议今后进一步拓展热处理介质的范围,深化预处理和复合介质热处理研究,赋予热处理材更多、更好的性能,研发出更具有竞争力的热处理技术。     

Comparison of chitosans with different molecular weights as possible wood preservatives

Fungi cause serious problems in wood utilization, and environmentally benign wood protection is required as an alternative to traditional chemicals. Chitosan has shown promising antimicrobial properties against several microorganisms. In this study, we present the characterization of and antifungal properties of a commercial chitosan formulation developed for impregnation of wood. A broad range of chemical and mycological methods were used to evaluate the uptake, fixation, and antifungal properties of chitosan for wood preservation. The results show that the higher the uptake of chitosan the lower the relative recovery of chitosan in wood after leaching, and the higher the molecular weight of chitosan the higher the recovery. Chitosan with high molecular weight proved to be more efficient against decay fungi than chitosan with low molecular weight. The fungi tested on chitosan-amended nutrient agar medium were totally inhibited at 1% (w/v) concentration. In decay studies using small wood blocks, 4.8% (w/v) chitosan concentration gave the best protection against brown rot fungi.     

Detection of incipient decay in tree stems with sonic tomography after wounding and fungal inoculation

Picus^® acoustic tomography was used to map incipient stages of fungal decay in the sapwood of standing Douglas fir, beech, oak, and sycamore trees 2, 16, and 27 months after wounding and artificial inoculation with brown-, soft-, and white-rot decay fungi. Some wood properties were additionally measured before (velocity of sound) and after (moisture content, weight loss, and density of sound, discoloured and/or decayed wood) tree felling (28 months). With the exception of Trametes versicolor in sycamore, wood decay was not evident from the tomograms in any host-fungus combination. In comparison to measurements after two months, the device recorded a reduction in sound velocity in some host-fungus combinations after 16 and 27 months. In beech, there was a significant reduction in sound velocity after inoculation with Ganoderma applanatum, Kretzschmaria deusta, and Trametes versicolor. Similarly, a reduction in sound velocity was recorded in sycamore inoculated with Kretzschmaria deusta and Trametes versicolor. In all these combinations, losses in wood weight and wood density were also found. Results showed that the detection of incipient fungal decay at the periphery of tree stems needs to be improved such that tomograms of the Picus^® acoustic tomograph are capable of identifying decay progressing from the sapwood inwards.     

Acoustic emission monitoring during partial compression to detect early stages of decay

Summary The acoustic emissions (AEs) under partially compression were monitored with two softwood and one hardwood specimens in very eary stages of decay by a brown- and a white-rot fungus. Even slightly decayed specimens emitted AEs immediately after beginning of loading, typically when partial compression stress was applied to brown-rotted wood with the flat-headed attachment. With sound specimens of three wood species, only a few AEs were generated until the load reached at the proportional limit. These results suggest that AE monitoring will be one of the feasible means to detect the incipient stages of decay in a field test.The authors thank the Weyerhaeuser Research Grants Program for its aid in this investigation     

Acoustic tomography in relation to 2D ultrasonic velocity and hardness mappings

Acoustic tomography is an emerging nondestructive testing (NDT) technology for tree decay detection in both urban community and production forest. Many field studies have been conducted to assess the applicability and reliability of the technique in such applications. Although investigations into urban trees showed great success using acoustic tomography to detect moderate to severe internal decay within the trunk, detection of early stage of decay using such technology still constitutes a challenge. This study was aimed to evaluate the capability of acoustic tomography by determining the relationships between acoustic tomograms and two-dimensional mappings of ultrasonic properties and end-hardness of the trunk cross sections. A freshly cut black cherry (Prunus serotina) log was used to simulate a tree trunk and tested in the laboratory. Time-of-flight (TOF) acoustic tomography measurements were conducted at three different heights (10, 30, and 50?cm). A disk was then cut from each height and subjected to ultrasonic and mechanical evaluations. The results indicated that the acoustic shadows in the tomograms revealed internal structural defects that were at the same locations and in similar magnitudes as the wood property mappings of the disks. However, no good correlations were found between apparent acoustic velocity of the tomograms and the measured ultrasonic velocity and end-hardness of small cubic samples. This analysis indicates that TOF acoustic tomography lacks the sensitivity to low-velocity features of decayed areas and thus has limited capability in detecting early stages of decay in trees.     

木材耐久性超疏水表面构建研究进展

木材作为一种天然可再生材料,富含亲水性基团且孔隙结构发达,因而具有很强的吸湿/水能力,易发生变形、开裂、腐朽等问题。基于“荷叶效应”原理,仿生构建木材超疏水表面是有效隔离木材与水分接触,赋予木材防水、防污、自清洁等优良特性的木材功能性改良新途径。然而超疏水木材在实际应用中不可避免地要受到刮擦磨损、阳光辐射、化学腐蚀等外界因素的影响,容易造成表面微/纳米粗糙结构的破坏或低表面能物质的降解,从而导致超疏水性能的降低或丧失,限制了超疏水木材的实际应用,因此设法提高木材表面超疏水涂层的机械稳定性和耐久性是亟待解决的关键问题。笔者首先分析了木材超疏水表面耐久性差的主要原因,介绍了木材超疏水表面耐久性能的测试方法,重点综述了木材耐久性超疏水表面的构建策略及其最新研究进展,最后对超疏水木材研究中存在的一些问题及发展趋势进行了总结和展望。