Oxidative degradation of non-recycled and recycled paper

Abstract

The degradation of paper-based materials involves several and complex mechanisms, such as hydrolysis and oxidation. The behaviour of different types of pulps can be very variable. In this study, the difference upon oxidation of contemporary non-recycled and recycled papers, which now constitute a considerable fibre source, is investigated. A 0.015 M potassium periodate solution is used to oxidise five types of paper, two non-recycled and three recycled, for 0.5, 1, 2 and 4 h. The effects of such oxidation treatments are evaluated in terms of carbonyl content and degree of polymerisation (DP). A modified procedure of the Szabolcs’s method and viscometry are used to measure the carbonyl content and DP, respectively. The carbonyl groups are found to increase more rapidly in the recycled papers than in the non-recycled ones. On the contrary, oxidation causes a larger decrease of the DP values in the non-recycled papers, the paper made of pure cellulose being the most sensitive in terms of depolymerisation. The DP values measured for pure cellulose paper are in line with previously reported data. Moreover, in accordance with the Ekenstam equation, the plots of the reciprocal of DP as a function of oxidation time show good linear correlations for all types of paper investigated. Pseudo rate constants are thus calculated from the slopes of these plots, those of the non-recycled papers being found to be higher than those of the recycled papers. Graphic abstract

Improvement on Measuring the Intrinsic Viscosity of Cellulose by the Copper Ethylenediamine Method

“…度或分子量决定了高分子的加工和使用性能。测定高分子聚合度的方法包括凝胶色谱法、端基测定 法、光散射法、渗透压法和粘度法等。粘度法具有设备简单、操作便利、测定和数据处理周期短的 优势，目前已被国内众多物理化学实验教材大量采用 [1][2][3] 。粘度法可分为三类：毛细管粘度法、落球 式粘度法、旋转粘度法等，其中毛细管粘度法是使用最广泛的。但该方法只适用于稳定、可溶的纯 净高分子溶液，所测分子量称为粘均相对分子质量。而在实际高聚物聚合度测量中，也有很多高分 子由于不易溶解、溶解后不稳定或含有杂质等问题，难于直接使用粘度法测定相对分子量。本文将 选择中国手工纸为测定对象，针对其含有较多木质素杂质以及纤维素难溶解、易氧化降解等问题， 发展适合于化学类或纸质文物保护类本科生或者研究生实验课程的研讨型综合实验。 中国手工纸是通过传统工艺制备的以天然纤维素为主要成分的纸张，其分子量测定是推断其使 役寿命和力学强度的基本参数，对解决古籍断代、修复及再造意义重大。由于其主要成分纤维素纤 维含有大量氢键，最常用的方法是采用铜乙二胺解氢键来制得适合粘度法测定的稀溶液 [4] 。但在手 工纸的传统制备工艺中，为了获得高纤维素得率和聚合度，通常采取条件缓和的处理方法，往往残 留一定量的木质素，导致测定纤维素聚合度常用的铜乙二胺粘度法难以适用，例如目前造纸领域的 现行国家标准要求所测纸浆木质素质量分数低于0.5% [5] 图3 木质素含量对纤维素铜乙二胺法所得特性粘度的影响 [6] • 表观特性粘度；◆ 校正特性粘度 5.2 纸张样品特性粘度讨论 本实验选择了3种木质素含量不同的纸样，并基于上述方法测定了纸样中纤维素的校正特性粘 度，进一步根据方程(2)获得了纸样纤维素的聚合，所得结果列于表1中。这一方法不仅降低了木质素 的影响，同时获得了更加准确的特性粘度值和聚合度，能够降低由木质素影响而导致的纤维素聚合 度偏差，进而为纸张的寿命预测提供更好的依据 [7,8] 。 表1 3种纸样铜乙二胺法特性粘度和聚合度的测试结果 [6] 纸张种类 木质素含量/% 表观特性粘度/(mL…”