基于热重法的纸张热老化特性分析及其评价模型

对纸张进行人工加速热老化,利用热重分析法(TG)对纸张热解过程进行分析,探讨了纸张在老化过程中的热失重特性.结果表明,纸张热解失重过程可分为纸张失水和纤维素热裂解失重两个阶段.TG动力学分析表明:未老化纸张的活化能最小,随着老化程度的加剧,活化能先增大后减小;随老化时间的延长和老化温度的升高,纸张的热稳定性变差,纸张热解转化率达0.5时的温度(θ0.5)逐步下降,纸张老化前后的θ0.5差值(Δθ0.5)逐步变大;纸张聚合度相对值(DP/DP0)与Δθ0.5存在指数量化关系,因此Δθ0.5可作为衡量纸张老化程度的一个参量.利用TG建立了一个快速量化评价纸张老化的模型,检验结果显示所得模型与实验数据吻合很好,模型具有较好的预测性.

Characteristic Analysis and Evaluation Model of Thermal Aging of Paper Based on Thermogravimetry

In this paper,first,an accelerated thermal aging of paper was carried out,and the corresponding pyro-lysis process was analyzed via the thermogravimetry.Then,the thermogravimetric characteristics of the paper during the aging were investigated,finding that the weight loss in the pyrolysis process contains two stages,namely the dehydration of paper and the weight loss caused by cellulose pyrolysis.TG kinetic analysis shows that the nonageing paper has the lowest activation energy,that the activation energy first increases and then decreases during the aging,and that,with the increases in aging time and temperature,the thermal stability of paper degrades,the temperature corresponding to a pyrolysis conversion rate of 0.5,namely θ0.5,gradually decreases,while the gap Δθ0.5 between the θ0.5 values of aging and nonageing paper progressively increases.Moreover,it is found that there is a quantitative exponential relationship between the relative polymerization degree DP/DP0 and Δθ0.5,which means that Δθ0.5 can be used as a parameter to evaluate the aging degree of paper.Based on the above-mentioned fin-dings,a model to rapidly and quantitatively evaluate the paper aging can be established by means of thermogravimetry,which is proved effective by the accordance between the evaluated and the experimental results.