书画修复中可替代明矾的施胶沉淀剂筛选研究

明矾是我国传统书画修复装裱中一种极其重要的材料,但明矾水解析出酸,会促使纸张纤维素发生酸性水解。研究对比了明矾和水解后具有高阳离子电荷的6种沉淀剂对宣纸施胶前后的pH值、疏水性、色差、力学性能变化和对国画颜料的固色效果,利用扫描电镜(SEM)和衰减全反射傅里叶变换红外光谱(ATR-FTIR)测试宣纸施胶后的化学键合状况(包括沉淀剂与胶料、纤维),结合高场~(27)Al核磁共振波谱(~(27)Al-NMR)测试了纸张施胶中铝盐沉淀剂的水解聚合形态,及其与胶料混合后对宣纸表面化学形态变化的影响。结果表明,白色聚合氯化铝(PAC)施胶宣纸pH值可达到7以上,作为沉淀剂的施胶液处理后的宣纸具有一定的疏水性,湿热老化过程中具有较高的耐折度和抗张强度,色差变化小,对颜料固色效果好。SEM分析表明,白色PAC可使胶料分布较均匀,能在一定程度上包覆、填充宣纸纤维和孔隙。~(27)Al-NMR、ATR-FTIR及固化性能分析表明,PAC多核铝AlO_4Al_(12)(OH)_(24)(H_2O)_(12)]~(7+)(Al_(13))含量相对较高,对明胶也具有促干剂作用,可和胶料产生键合,形成网状络合物,适合替代明矾作为施胶沉淀剂。

Study of substitute materials for the sizing precipitant, alum, in the restoration of calligraphy and painting

Alum is one of the most important materials in the restoration of calligraphy and paintings. However, easy hydrolysis of alum produces acid at high humidity, which can accelerate the hydrolysis and aging of paper cellulose. The pH value, hydrophobicity, color difference and mechanical properties of Xuan paper and color fixing before and after sizing with alum as well as six precipitants with high cationic charges (after hydrolysis) were studied. The surface condition after sizing, including the chemical bonding of precipitants with gelatin and fibers, were tested by scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometry. Also, the species distribution of precipitants after hydrolysis, mixing with glue and sizing on the surface of Xuan paper were studied using high-field ²⁷Al-nuclear magnetic resonance (²⁷Al-NMR) spectrometry. The results show that the pH value of Xuan paper sized by white polyaluminium chloride(PAC) could reach over 7 and the sizing material improved the hydrophobic property and mechanical strength of the paper and made pigments that have good color and no shading. SEM analysis shows that white PAC could cover and fill fibers and pores of Xuan paper uniformly. ²⁷Al-NMR, ATR-FTIR and a curing test show that the content of AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺(Al₁₃) in PAC was relatively higher, and it also had the effect of promoting the drying of gelatin. It could be bonded with gelatin to form a network complex, which was suitable to replace alum as a sizing precipitant.