褐腐杨木微观结构、力学性能与化学成分的关系研究

Relationship among microstructure,mechanical properties and chemical compositions in Populus cathayana sapwood during brown-rot decay

为了探究褐腐对阔叶材主要材性的影响规律,对杨木边材试件进行室内褐腐培养,为期12周,每周抽样分别测试健康和腐朽木材的微观结构、力学性能及化学成分,并分析其随褐腐程度的变化情况,研究力学性能和化学成分之间的关系。结果表明:随褐腐程度的加深,木材细胞腔内的菌丝越来越多,纹孔膜和纹孔边缘的细胞壁分别于质量损失率为10%、16%时出现开裂;质量损失率为24%时,细胞壁严重溃烂。褐腐培养时间和质量损失率都对力学性能影响极显著;冲击韧性和抗弯强度的损失率随褐腐程度呈对数函数变化趋势,抗弯弹性模量和顺纹抗压强度的损失率呈线性变化趋势。各力学指标对褐腐的响应速度以及受褐腐影响的程度均呈如下规律:冲击韧性>抗弯强度>抗弯弹性模量>顺纹抗压强度。不同褐腐程度试样中的综纤维素、半纤维素以及抽出物含量差异极显著,纤维素和木质素差异不显著。腐朽过程中褐腐菌最先主要降解半纤维素,质量损失率为20%左右时,转为以分解纤维素为主。冲击韧性的快速显著降低与半纤维素的降解有关,抗弯强度的变化与综纤维素含量有关,抗弯弹性模量和顺纹抗压强度的线性降低是由纤维素的缓慢降解决定的。总之,在褐腐过程中,木材微观水平上化学成分的降解和细胞壁结构的破坏从根本上导致了宏观力学性能的降低。

In order to study the influence of brown-rot decay on main properties of hardwood, Populus cathayana sapwood specimens（ 20 mm × 20 mm × 300 mm） were made and brown-rot decay was incubated on the specimens in laboratory with brown-rot fungus Gloeophyllum trabeum for 12 weeks. The mechanical properties,microstructure and chemical compositions of both healthy wood and decayed wood were investigated once a week. And then changes of all indexes during decay processing and the correlation between mechanical properties and chemical compositions were contrastively analyzed. The research results showed that more and more hyphae were found in wood cell lumina under scanning electron microscopy（ SEM） with decay degree increasing. Pit membrane and the cell wall on the edge of pit were successively broken up at a wood weight loss of 10% and 16% respectively. Finally,the cellwall was ulcerated seriously while the wood weight loss increased to 24%. Both degradation time and weight loss had extremely significant influence on wood mechanical properties（ P 〈0. 01）. The loss of impact bending strength（ IBS） and modulus of rupture（ MOR） increased in forms of logarithmic function with decay degree changing（ R2= 0. 922＊＊,0. 830＊＊）,while the loss of modulus of elasticity（ MOE）and the compressive strength parallel to grain（ CSⅡ） increased slowly in linear trends（ R2= 0. 991＊＊,0. 986＊＊）. Whether the response speed to decay or the influenced degree by decay,the ranking of four mechanical properties were IBS〉 MOR〉 MOE〉 CSⅡ. Holocellulose,hemicellulose and extractions of specimens varied significantly at different decay degrees（ P 〈0. 01）,but cellulose and lignin had no significant variance（ P 〉0. 05）. During the decay processing,hemicellulose was first and mainly degraded by brown-rot fungus. The prominent degradation of cellulose began when the weight loss was about 20%. A strong relationship between the loss of wood IBS and the degradation of hemicellulose was found. The variation of MOR was dependent on holocellulose content. And the linear decreasing trends of MOE and CSⅡwere determined by cellulose＇s slow degradation. In conclusion,during the brown-rot decay processing,the degradation of chemical compositions and the structural failure of wood cell wall at the micro level fundamentally resulted in the decrease of macroscopical mechanical properties.