【作者】 杨亮庆；

【导师】 刘一星； 蔡英春；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2011， 博士

【摘要】 圆盘是通过将原木横截制得,在其横截面上展现出的独特美学特性和可观赏性,得到越来越多人的喜爱。同时,圆盘是木材(尤其是弯曲木、小径木)利用的新途径,利于提高木材的单位经济效益和产品附加值。美中不足,圆盘干燥要远困难于锯材的干燥,因为干燥过程中存在着严重的开裂问题。因此有必要开展圆盘干燥的研究。本论文以东北地区蓄积量较大的枫桦木材为研究对象,进行圆盘的常规干燥和高频真空干燥的研究,研究干燥方式、工艺条件等对干燥特性、干燥缺陷等影响,确定较适宜的工艺基准；系统研究了干燥前预处理对枫桦圆盘常规干燥特性的影响、预处理抑制圆盘开裂的机理以及预处理对干燥成本影响等方面的内容,将氯化钠和PEG400应用于圆盘的预处理,并首次将“二元协同思想”引入木材预处理研究中来,就解决氯化钠预处理中存在的小足进行探索,采用扫描电镜(SEM)、傅里叶红外变换光谱(FTIR)、X-射线衍射仪(XRD)等手段研究了处期物质与术材的作用机理；分析了不同干燥方式及不同预处理时圆盘的干燥成本。工作的主要内容如下(1)通过大量实验结果的分析,根据圆盘干燥独有特点,建立了圆盘弦向干燥应变模型和干燥应力与圆盘径向干缩关系模型,确定圆盘‘开裂势’,为影响圆盘开裂因素的确定及干燥应力变化的判断提供依据。弦向干燥应变模型表明：弦向干燥应变取决于弦、径向的干缩差和圆盘的半径大小,在圆盘直径一定的情况下,引起圆盘开裂的弦向干燥应变与弦、径向的干缩差密切相关,并由此将弦、径向的干缩差确定为圆盘的‘开裂势’。干燥应力与圆盘径向干缩关系模型表明：干燥应力可通过圆盘径向卜约束干缩和自由干缩之比值体现…来。通过不同干燥方式和预处理干燥实验证实了上述模型的正确性。(2)根据圆盘在干燥中的特点,首先提出运用间歇低温的常规干燥方法来干燥枫桦圆盘,取得了较好的干燥质量。进而通过在快速干燥基准下对圆盘干燥特性及开裂产生含水率点研判的实验分析,提出了快速-低温间歇式干燥的干燥工艺,缩短了干燥周期。(3)采用高频真空的方法干燥圆盘,获得了较好的干燥质量,提高了干燥效率。确定含水率梯度和‘开裂势’的降低为高频真空干燥抑制圆盘开裂的主要原因。从力学角度出发,通过建立“木材内外作用力影响干缩模型”对高频真空干燥降低木材干缩率和开裂势的机理进行了分析。(4)提出使用氯化钠、PEG400两种无毒、无环境污染、适于生材处理的方法来处理枫桦圆盘。就预处理因素(包括处理时间、处理溶液浓度)对木材物理特性的影响进行了显著性分析。就预处理对圆盘物理特性径向各部位变化规律的影响进行了分析,为分析圆盘开裂的原因提供了依据。(5)建立微毛细管内处理物质及水分子存在状态模型,对预处理圆盘的干燥特性和机理进行分析。在保证干燥质量的前提下,处理后的干燥周期明显缩短,干燥速率大幅度提高,PEG400提高尤为明显。对处理前后圆盘干燥后心表层含水率差、横纹抗拉强度、约束干缩等影响圆盘开裂因素的分析表明：两种处理均通过降低弦径向干缩差来抑制圆盘的开裂,由此也证实了圆盘弦向理论干燥应变模型的正确性。采用SEM、XRD、FTIR等方法分析了两种处理物与木材的复合机理,结果表明：氯化钠可以进入到纤维素的无定形区且.其在木材内的存在使游离羟基受到结合力的作用,PEG400则更多为在木材内的机械沉积,并解释了两种处理对抗拉强度、干燥速率产生影响及存在差异的原因。(6)针对氯化钠预处理圆盘吸湿性较大的实际问题,引入NaCI/SiO2"二元协同作用”思想。尝试采用可控低温水热法和溶胶-凝胶法来实现NaCI/SiO2的协同作用,并采用SEM、XRD、FTIR等方法分析协同处理试件,结果表明：上述两种方法均可使木材的吸湿性对照氯化钠单独处理的情形大为降低,其机理为前者通过改变氯化钠的晶体形貌来降低吸湿性,后者通过疏水性二氧化硅对氯化钠的包裹来降低吸湿性。(7)从流动资产、固定资产、干燥周期、适用范围以及干燥质量等与干燥成本相关的几个方面对圆盘干燥成本进行行了综合分析,结果表明：圆盘经氯化钠预处理干燥成本最低,而PEG400处理后干燥成本较高,但与处理后干燥周期短、干燥质量好、适于较大径级圆盘干燥,是圆盘干燥的最优选择；之后顺次为高频真空干燥、联合干燥；最后为间歇式低温干燥,干燥成本较高、干燥周期最长,且仅适用于小径级圆盘干燥。考虑到我国木材干燥行业的现状,圆盘预处理干燥中工序稍有复杂等因素的影响,因此,可根据不同预处理及干燥方式的特点,以及应用方面的需求对这些方法有针对性的选择。更多还原

【Abstract】 The tree disk, which is cross cut from a log, for making wood artifacts and material for home-decorating, is a wood product with unique aesthetics character and artistic value, and also is one way to effectively utilize wood(especially crooked wood, small-diameter log etc.). to improve timber unit economic benefit and additional value. However, disk drying is much more difficult than drying lumber because of severe check problems. Therefore it’s necessary to research the problem of disk drying. The thesis with resourceful B.costata of Northeast China Region as the object of study, put forward research method of special drying and preprocessing of disk, systematically researched drying properties of RF/V, the influence of preprocessing for conventional drying properties and drying cost, the mechanism of restrained cracking of disk. It’s first time to research the application of NaCl. to introducing "dual cooperation thought" to solve deficiency in in preprocessing of disk. The thesis researched mechanism of action between preprocessing chemicals and wood by SEM. FTIR and XRD instrument. The main research contents were as follows:(1) Through the analysis of experimental results and unique features of disk, put forward the cracking potential of disk and the model about drying strain of disk in circumference direction, which indicated that drying strain depends on disk radius and difference of drying shrinkage in circumference and radial direction.Put forward the relational model between drying stress and radial shrinkage. which indicated that:drying stress closed related with the ratio of restrained shrinkage and free shrinkage in radial direction.When disk radius is unchanged. the relationship between drying strain and difference of drying shrinkage in circumference and radial direction has positive correlation. therefore put forward difference of drying shrinkage as the cracking potential of disk. The correctness of the models had been confirmed through drying experiments.(2) Dependding on disk characteristic, the thesis first put forward low-temperature intermittent drying method, which could ensure the drying quality of disk; and then researched when the cracks produced and changed in rapid drying schedule, finally raised "rapid-low temperature intermittent combinated drying" to obviously shorten drying period.(3) Drying quality and efficiency of disk were satisfactory, the reducing of MC gradient and’cracking potential’restrained the cracking of disk in RF/V. The mechanism of restrained cracking in RF/V was analysed by the model, which describes the relationship between drying shrinkage and resultant force inside and outside cell wall.(3) The thesis put forward to processing B.costata disk with NaCI and PEG400, which are pollution-free, non-toxic for people, livestock and environment, are suitable for processing of green wood. The thesis analysed the influence of preprocessing factor for physical properties and the influence of preprocessing for radial change trend of physical property in wood. All of the work provided basic for analyzing the reason of restrained cracking.(5) The thesis analysed dyring character of preprocessing disk by the model of existential state of chemicals and hydrone in micro-capillary. Preprocessing obviously shortened drying period, especially processing by PEG400. The analysis indicated that reducing of ’cracking potential’ was the main reason to restrain the cracking of disk, which also confirmed that model about drying strain of disk in circumference direction was right. The analysis of compound mechanism between processing chemicals and wood by SEM. XRD and FTIR showed:NaCI could enter the amorphous region of cellulose and combined with free hydroxyl by hydrogen bonding; a PEG400 mainly mechanically deposited in wood, it also explained the influence of preprocessing for tensile strength and drying rate.(6) The thesis introduced dual cooperative processing of NaCI/SiO2 to resolve the deficiency of higher avsorb moisture of disk processing by NaCI. The synergy of NaCI/SiO2 was realized by using the methods of controlled low-temperature hydro therman and sol-gel. The analysis of SEM, XRD and FTIR showed:the first method reduced hygroscopic by change of crystal morphology of NaCI, the second method reduced hygroscopic by cover of SiO2 for NaCI(7) The thesis analysised drying cost from current assets, fixed assets, drying period, scope of application and drying quality. The results showed:the drying cost by processing of NaCI was lowest, and then PEG400, the preprocessing has advantages for example:drying cycle is shortest, drying quality is best, scope of application is wide, therefore, preprocessing was the best method for disk drying. Drying methord in RF/V was taked second place. The last was united drying and intermittent low temperature drying, which has shortage for example:drying cycle is longest; it was only suitable in small diameter disk. Therefore we should pertinently choose suitable drying methord of disk according to actual demand and characteristic of preprocessing and drying methord.更多还原