故宫养心殿区古建筑望板老化状况分析

Analysis of the Deterioration Condition of Roof Boarding of Ancient Buildings in the Hall of Mental Cultivation of the Forbidden City

以养心殿修缮为契机,对拆卸下的望板木构件在材种鉴定的基础上,对其进行化学组分定量分析,测定各化学成分相对含量的状况;采用X射线衍射(XRD)、红外光谱(IR)以及热重(TG)等表征手段,分析了望板木构件的相对结晶度及组分中化学基团的变化;结合力学性能试验评价望板的力学强度变化;比较老化材与现代材的测试结果分析和评价望板的老化状况。结论如下:①望板综纤维素含量降解严重,仅为现代材的1/2,而相对结晶度较高,推断该木构件降解机制为以多糖类化学组分为营养源的寄生性昆虫以及褐腐菌为主;②随着腐朽程度的增加,由于多糖类组分的严重降解,构成望板高分子化合物之间的结合作用降低,热稳定性降低,热解温度范围变窄,且残炭率大幅增加,约为现代材的2倍;③由于纤维素的降解,望板脆性增加,强度和弹性模量大幅低于现代材。

Taking the repair of the Hall of Mental Cultivation as an opportunity,this paper involves quantitative analysis of the chemical composition of the removed roof boarding components based on the wood species identification of the wooden components,and determination of the relative content of each chemical composition.By means of characterization methods such as X-ray diffraction(XRD),infrared(IR)and thermal gravimetric(TG),the relative crystallinity and change of chemical group in the composition of roof boarding wooden components were analyzed.The mechanical strength variation of roof boarding was evaluated coupled with the mechanical properties,with the experimental results of aging wood and modern wood compared to analyze and evaluate the aging condition of roof boarding,with conclusions as follows:severe degradation of holocellulose was found in the roof boarding,of which the content of cellulose was only 1/2 that of modern wood while the relative crystallinity of aging wood was relatively higher than that of modern wood,based on which it was inferred that the deterioration mechanism of roof boarding wooden components mainly consisted of parasitic insects using the chemical components of polysaccharides as nutrition sources and brown-rot fungi.With the degree of decay increasing,due to the severe degradation of polysaccharide components,the binding effect between the macromolecular compounds constituting the roof boarding decreased,the thermal stability decreased,the range of pyrolysis temperature became narrow and the rate of carbon residue increased dramatically,about twice as much as modern wood.to be about with increasing deterioration degree.With the degradation of cellulose,the brittleness of roof boarding increased while the strength and the modulus of elasticity were significantly lower than those of modern wood.Due to the degradation of cellulose,the brittleness of the roof boarding increased,with the strength and elastic modulus significantly lower than those of modern wood.