摘要
古籍、档案、书画、碑帖等纸质文物记录了人类社会的历史发展,是不可再生的文化遗产。然而,大量纸质文物在长期保存过程中发生了老化劣化现象,甚至造成纸质文物的永久失传。值得注意的是,部分颜料与墨水中含有的铁铜金属物种会引起纸张较为严重的腐蚀降解,使得色块或墨迹周围的纸张明显泛黄,甚至在着墨位置形成空洞。铁铜颜料引起纸质文物损害的原因复杂且多样,在其作用下纤维素高分子的反应路径与降解机理值得深入研究。本研究介绍了纸质文物中常见的铁基与铜基颜料,包括铁盐墨水、普鲁士蓝、赭石、蓝铜矿、孔雀石、醋酸铜等。总结了纸张纤维素的酸性水解、碱性降解和氧化降解反应路线,探索了金属物种作用下纸张纤维素的酸碱反应与氧化还原反应机理。其中含铁颜料的纸张纤维素主要经历芬顿(Fenton)氧化降解和酸性水解,含铜颜料腐蚀纸张纤维素的主要途径为菲林(Fehling)氧化降解和碱性降解。本研究聚焦于铁基与铜基颜料对纸质文物腐蚀降解的化学反应机理,总结出铁铜离子参与的氧化反应是纸张纤维素加速降解的主要因素。在此基础上,提出了添加抗氧化剂以减缓氧化反应发生的纸质文物保护策略,包括预防性抗氧化剂与断链性抗氧化剂。重点介绍了络合剂配位铁铜金属离子的预防性抗氧化保护法,如使用植酸/植酸盐、溴化铵、明胶蛋白等络合剂与铁铜离子络合,以减缓氧化降解反应的发生。同时也分析了络合剂方法存在的一些问题,如植酸只能在酸性条件下使用、苯并三唑会造成颜料变色、部分抗氧化剂具有毒性等。最后,本研究针对铁基与铜基颜料腐蚀降解纸张的机理研究与保护策略提出展望。在机理研究方面,过渡金属游离态与络合态的分布情况、过渡金属引发氧化反应的条件控制、氧化降解反应与纤维素超分子结构的相互关系等仍有待研究。在保护策略方面,所选择的保护方法应当不仅可以有效减缓过渡金属对纸张的降解,而且不会对纸张纤维与颜料墨迹造成损坏。本研究从化学角度对过渡金属颜料所导致的纤维素降解演化机理提出更深刻的认识,为含有过渡金属颜料纸质文物的多方位保护提供引导和借鉴。
As the carriers of human wisdom and civilization,paper cultural relics such as manuscripts,documents and artistic works are non-renewable cultural resources and extremely valuable treasures of mankind.Unfortunately,a large number of long-stored paper cultural relics have been undergoing serious deterioration and discoloration due to the endogenous(pH,lignin,degradation products)and exogenous(light,heat,humidity,pollutant gases)factors.It is worth noting that the iron and copper metal species contained in some pigments and inks can cause serious corrosion and degradation of the paper.For example,the use of iron gall ink often produces perforation in inked areas due to the severe corrosion of paper.Moreover,the use of malachite(basic cupric carbonate)in traditional Chinese painting causes the yellowing or even embrittlement of nearby paper substrates;a remarkable yellowish-brown deteriorating edge can usually be observed near the green-blue pigment,which directly affects the readability and appreciation value of the art or even its stability in long-term preservation.The reasons for the damage of paper cultural relics containing iron/copper pigments are complex and diverse,and the reaction pathway and mechanism of degradation of cellulose polymers with iron/copper pigments are worthy of in-depth investigation.This article introduces the iron-based and copper-based pigments which are commonly used in paper cultural relics,including iron gall ink,Prussian blue,ocher,azurite,malachite,copper acetate,etc.We summarize three common routes of paper cellulose degradation,including acid hydrolysis,alkaline degradation and oxidative degradation.Then,we discuss the mechanism of acid-base reaction and redox reaction of paper cellulose under the participation of transition metal species.Among them,paper containing iron pigments mainly undergo Fenton oxidative degradation and acid hydrolysis.Correspondingly,the main pathways of paper corrosion by copper-containing pigments are Fehling oxidative degradation and alkaline degradation.This article focuses on the chemical reaction mechanisms of iron-based and copper-based pigments on the corrosion degradation of paper cultural relics,and concludes that the oxidation reaction involving iron and copper ions plays the main character in the accelerated degradation of paper cellulose.For this reason,adding antioxidants—including preventive antioxidants and chain-scission antioxidants—is proposed as a protection strategy to slow down the oxidation reaction of paper-based cultural relics.We focus on the use of complexing agents,such as phytic acid/phytate,ammonium bromide,protein gelatin and others,to coordinate the active iron/copper metal ions and slow down the oxidative degradation reaction.At the same time,some problems in the complexing method are revealed,e.g.,phytic acid should be used under acidic condition,pigment discoloration will be caused by using benzotriazole,and some antioxidants may be toxic.Finally,this article proposes a prospect for the space to be explored in mechanism research and protection strategies of paper containing iron-based and copper-based pigments.With regard to mechanism research,the distribution of the free state and the complex state of the transition metal,the conditions for transition metal to initiate the oxidation reaction,and the relationship between the oxidation degradation reaction and the supramolecular structure of cellulose remain to be studied.With regard to protection strategies,the selected protection agents should not only effectively slow down the degradation rate of paper cellulose,but also not cause damage to paper fibers and pigments.This article proposes a more profound understanding of the mechanism of cellulose degradation and evolution caused by transition metal pigments from a chemical point of view and provides guidance and reference for the multi-directional protection of paper cultural relics containing transition metal pigments.
作者
于一平
张旭
张昊诚
闫玥儿
唐颐
YU Yiping;ZHANG Xu;ZHANG Haocheng;YAN Yue’er;TANG Yi(Department of Chemistry, Fudan University, Shanghai 200433, China;Institute for Preservation and Conservation of Chinese Ancient Books, Fudan University Library, Fudan University, Shanghai 200433, China)
出处
《文物保护与考古科学》
北大核心
2021年第6期52-60,共9页
Sciences of Conservation and Archaeology
基金
国家自然科学基金项目资助(21805042)
上海市浦江人才计划资助(2020PJC003)
上海市科委扬帆计划项目资助(18YF1401400)
文化和旅游部文化行业标准化研究项目资助(WH/Y08-2018)。
关键词
铁铜颜料
纤维素腐蚀
氧化降解
络合保护
Iron/Copper-based pigment
Cellulose deterioration
Oxidative degradation
Complexing for stabilization