老化竹纸的微观结构变化对性质的影响分析

Effects of micro-structural changes on properties of aged bamboo paper

我国大量的竹纸文物面临严重的老化糟朽问题,为进一步探讨竹纸的老化行为,对采集的传统手工竹纸进行人工加速老化处理,结合傅里叶变换红外、X射线衍射、扫描电子显微镜、抗张强度测试、热重分析以及动态水分吸附等多种方法,研究老化竹纸的微观结构变化对纸张性质的影响.结果表明,竹纸老化后内部–OH、C–O–C等基团的红外吸收峰强度下降,纤维分子链降解断裂产生了C=O等新基团.老化过程中竹纸的纤维结构受损使纤维素结晶度指数CrI呈现先升后降的趋势,与纤维素结晶区和无定形区对老化作用的敏感差异有关.竹纸老化后出现纤维断裂、粉化等微观形貌变化是纤维结构遭受破坏的直观表现.由于老化竹纸的纤维分子链降解断裂使纤维的自身强度降低,纸张的力学性能下降.纤维素结晶区受损使纸张的热稳定性变差,表现为老化竹纸的热解特征温度T0.05、T0.5及Tmax整体降低.毛细结构受损、羟基等亲水基团的含量降低是老化竹纸吸湿性下降的主要原因.纸张的性质劣化与其微观结构的改变密切相关,在科学制订纸质文物的保护方案以及评估保护效果时,需注重检测纸张的内部结构,有助于在古籍文物的修复实践中达到最佳保护效果.

Traditional handmade bamboo paper has a long history.Since the Song Dynasty,bamboo paper has been widely used in writing and printing.Bamboo paper comprises a large proportion of paper cultural relics,which have precious cultural value.However,many bamboo paper relics are degraded by factors such as temperature,humidity,acid,and alkali in the environment,resulting in aging and the paper becoming yellow and brittle during long-term storage.The aging mechanism of paper is a complex issue in cultural heritage conservation,which hinders the protection of paper cultural relics.Therefore,studying the mechanism of paper aging is the basis for implementing effective protection measures,which are crucial for effectively preserving bamboo paper cultural relics.This study examined the aging behavior of bamboo paper.Traditional handmade bamboo paper samples from Zhejiang Province,whose production technology is listed in the first batch of national intangible cultural heritage in China,were aged artificially by exposure to dry-heat conditions.The microstructure and micro-morphology of the aged bamboo paper were investigated via Fourier transform infrared spectroscopy,X-ray diffraction,and scanning electron microscopy.The tensile strength was tested,and the thermal stability was detected by thermogravimetric analysis.The moisture absorption ability was measured by dynamic vapor sorption.The relationship between the effects of aging on the microstructure of paper and performance degradation was revealed.The chemical structure of bamboo paper changed after aging,including the decreased relative intensities of the OH and C–O–C stretching vibrations,and new functional groups for C=O generated by the fiber molecular chain were broken.The fiber surface of aged bamboo paper becomes fragmented after prolonged aging,eventually leading to the collapse of the fiber structure.The crystallinity of cellulose increases initially and then decreases due to damage to the fiber structure,suggesting that the crystalline and amorphous regions of cellulose are affected differently by aging.The changes in the microstructure of aged bamboo paper also affect some of its properties.Aged bamboo paper gradually loses its mechanical strength due to degradation of the molecular chains inside the fiber.A persistent decrease in the characteristic pyrolysis temperature of bamboo paper after aging was observed due to damage in the cellulose crystallization region:The initial pyrolysis temperature of 5%mass loss(T0.05),the temperature of 50%mass loss(T0.5),and the temperature of maximum mass loss(Tmax).Therefore,the thermal stability of bamboo paper deteriorated.Furthermore,the capillary structure,hemicellulose,and amorphous regions of the aged bamboo paper were damaged,decreasing the ability of moisture absorption.The deterioration of the tensile strength,thermal stability,and moisture absorption of aged bamboo paper was caused by the destruction of the chemical structure and crystallinity of the paper fibers.These findings will promote research aimed at protecting aged paper cultural relics.Therefore,in addition to the macroscopic properties of aged paper,more attention needs to be paid to analyzing the microstructure of paper when planning a protection plan for paper cultural relics and evaluating the protection effect,which is vital for achieving a better protection effect.