含水率对樟子松细胞壁弹性模量和硬度的影响规律

Influence Law of Moisture Content on Elastic Modulus and Hardness of Pinus sylvestris var.mongolica Cell Wall

为探明水分对木材细胞壁力学性能的影响,选取樟子松为对象,利用热水、1%氢氧化钠以及苯-乙醇溶液在80℃、6 h、固液比1∶20的工艺条件下对试样进行抽提处理,抽提后的木材样品加工成金字塔形,然后对试样进行吸湿处理并且调控试样含水率,借助纳米压痕测试研究含水率对木材细胞壁力学性能的影响,并建立机理模型做进一步分析。结果表明,随着含水率的增加,木材的纵向弹性模量与硬度,均出现了一定程度的下降。分析发现,水分子进入细胞壁后与游离羟基形成氢键,随着含水率增加,会被部分原有的氢键破坏,并与之前进入的水分子形成氢键,在内部形成水分子簇,增大了细胞壁分子链之间的距离,使空隙增多,进而降低木材的弹性模量,且水分会使木材细胞壁主成分逐渐软化,硬度降低。

In order to clarify the effect of water on the mechanical properties of wood cell wall,wood samples of Pinus sylvestris var.mongolica were selected as the research materials.Firstly,the samples were extracted with hot water,1%sodium hydroxide solution and benzene-ethanol solution at 80℃ for 6 hours,and the ratio of solid to liquid was 1∶20,then,the extracted wood samples were processed into pyramid shape,and to perform moisture absorption treatment,from which the sample moisture was adjusted.Nanoindentation test was carried out to investigate the effect of moisture content on the mechanical properties of wood cell wall,and to establish a mechanism model for further analysis.The results showed that the longitudinal elastic modulus and hardness decreased to some extents with the increase of moisture content.The analysis showed that water molecules entered the cell wall and formed hydrogen bonds with free hydroxyl groups.With the increase of water content,not only some of the original hydrogen bonds were destroyed,but also hydrogen bonds were formed with the water molecules entered before,and water molecules cluster was formed in the cell wall,the distance between the molecular chains of cell wall increased,the number of voids increased,and then the elastic modulus of wood decreased.The moisture would gradually soften the main components of the wood cell wall and reduce the hardness.