可视化热重分析技术对宣纸热分解形态的研究

Study on morphology characteristics during thermal decomposition of Xuan paper by visual thermogravimetric analysis

为研究宣纸形态在受热过程中的实时变化特征,使用高清摄像系统原位记录宣纸样品在氮气和空气中热分解的图像序列,并结合红外光谱测试宣纸在不同温度时对应的结构状态以分析相关热解过程。结果表明,宣纸在氮气热分解中颜色逐渐变黑,直径尺寸随着温度增加而减小,这与宣纸纤维逐渐降解炭化有关;在空气热分解中,宣纸颜色出现先黑后白的现象,是由炭化物在空气中氧化分解引起。亮度变化率(ΔL)和收缩率(Δd)可量化宣纸形态在热分解过程中的变化程度,其亮度约在150℃后逐渐降低,在氮气热分解中最终下降62.2%,尺寸收缩25.0%;在空气热分解中,宣纸的亮度下降63.2%后开始回升最终高于初始亮度,其尺寸收缩了50%。宣纸的颜色变化与内部纤维的热分解程度密切相关,将ΔL与热解转化率(α)进行回归分析,两者存在指数量化关系。基于所得指数模型,可根据宣纸的ΔL计算α值,进一步无损评估宣纸老化后其内部纤维组分的降解情况,为珍贵纸张的老化研究提供参考。

In this study,the morphology characteristics of Xuan paper during high purity nitrogen and air thermal decomposition were investigated.The image sequences of samples heated from room temperature to 800℃were collected in situ by high-definition camera system.Then,combined with infrared spectroscopy,the corresponding structural state of paper at different temperatures was detected to analyze the relevant pyrolysis process.The results revealed that during nitrogen thermal decomposition,the color of Xuan paper gradually darkened,and its diameter decreased with increasing temperature,which was attributed to the gradual degradation and carbonization of rice paper fibers.In air thermal decomposition,the color of Xuan paper first darkened and then turned white,resulting from the oxidation and decomposition of carbonized substances in the air.The brightness change rate(ΔL)and shrinkage rate(Δd)could quantify the degree of morphological changes in Xuan paper during thermal decomposition.Specifically,its brightness gradually decreased after 150℃,ultimately declining by 62.2%and 25.0%in diameter in nitrogen thermal decomposition.In air thermal decomposition,the brightness of paper dropped by 63.2%before starting to rebound,ultimately exceeding its initial brightness,while its size shrunk by 50%.The color changes in rice paper were closely related to the degree of thermal decomposition of its internal fibers.Regression analysis betweenΔL and pyrolysis conversion rate(α)revealed an exponential quantitative relationship between the two.Based on the obtained exponential model,theαvalue could be calculated usingΔL,further enabling non-destructive assessment of the degradation of internal fiber components in aged Xuan paper.