Determination of Cellulose Degree of Polymerization in Historical Papers with High Lignin Content.

Jasna Malešič,Ida Kraševec,Irena Kralj Cigić

doi:10.3390/polym13121990

Jasna Malešič, Ida Kraševec + Show 1 more

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https://doi.org/10.3390/polym13121990

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Abstract

Determination of cellulose degree of polymerization (DP) is one of the most commonly used methods in paper degradation studies, performed either by a standardized method using viscometry (as average degree of polymerization (DPv)) or size-exclusion chromatography (SEC) (as weight average molecular mass (Mw)). Due to the insolubility of papers with high lignin content in cupriethylenediamine (CED), such as groundwood papers, viscometric determination is not possible; therefore, pretreatment is required to allow subsequent dissolution of the papers. In this study, the pretreatment of historical papers containing groundwood with sodium chlorite in acetic acid was investigated, which enables dissolution of the paper samples in CED and determination of the cellulose average degree of polymerization by viscometry (DPv). Kappa number was determined to estimate the lignin content in the papers. The suitability of SEC UV-VIS analysis for determination of Mw in papers with high lignin content had been verified before it was used as a comparative method for viscometry. Using SEC, changes in the weight average molecular mass (Mw) of cellulose tricarbanilate (CTC) derivative during delignification were evaluated. The results indicate that no significant depolymerization occurred in the selected samples under the studied delignification conditions, which was additionally confirmed with determination of monosaccharides by ion chromatography. The results of the Mw determinations by SEC and DPv by viscometry are in good correlation, justifying the use of viscometry after chlorite/acetic acid pretreatment to determine the cellulose average degree of polymerization in historical papers with high lignin content.

Highlights

Regardless of the complexity of paper material, the two main chemical degradation pathways are acid hydrolysis and oxidation
The results of the Mw determinations by size-exclusion chromatography (SEC) and degree of polymerization by viscometry (DPv) by viscometry are in good correlation, justifying the use of viscometry after chlorite/acetic acid pretreatment to determine the cellulose average degree of polymerization in historical papers with high lignin content
The Kappa number is based on the reaction of a highly oxidizing chemical, potassium permanganate, with lignin as well as a low content of certain other organic impurities that remain in the pulp at various stages of its processing

Summary

Introduction

Regardless of the complexity of paper material, the two main chemical degradation pathways are acid hydrolysis and oxidation. Both processes result in cellulose depolymerization, which leads to a loss of mechanical strength of the paper. Determinations are performed either by a standardized procedure using viscometry or size-exclusion chromatography (SEC). Both techniques require sample dissolution, which limits their application. In the pulp and paper industry, conventional viscometry is still the standard approach for the quality control of bleached pulp It is quite commonly used by laboratories interested in paper degradation. The most commonly used nonderivatizing cellulose solvents for viscometry include copper(II) complexes with ethylenediamine (CED) or with ammonia (cuoxam) and cadmium ethylenediamine hydroxide (cadoxen) [2]

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