# Determination of Cellulose Degree of Polymerization in Historical Papers with High Lignin Content
## 1 Introduction
These advantages include the stability of the tricarbanulate, the complete substitution of the cellulose, the substitution reaction that usually does not cause depolymerization of the original cellulose, and the ready volubility of the carbinale. Various solvents were investigated as a medium for the reaction of phenylisocyanate with cellulose. No degradation of the cellulose was observed when the reaction was carried out in pyridine at 80 \({}^{\circ}\)C [10]. The derivatization with phenylisocyante also has the advantage that the cellulose derivative can be detected by UV detectors, which are more sensitive compared to RI detectors, and it could be employed advantageously when only a small amount of sample is available [11]. Prior to viscometric determination of average DP\({}_{\rm v}\), attempts were made to partially remove the lignin by chlorite treatment to allow subsequent dissolution of paper made from high-yield pulps [6,12]. It was reported that under the conditions of a modified chlorite method, significant depolymerization of cellulose is prevented, enabling viscometric determination of average DP\({}_{\rm v}\) in cadaver solution of cellulose [12]. Viscometry represents a robust, rapid, inexpensive, and efficient technique, but under certain conditions, such as delignification, it can provide data that are subject to systematic error, making it is necessary to compare the results with M\({}_{\rm w}\) determinations with SEC [13]. Cellulose is a natural macromolecular material; therefore, not all molecules have the same DP, and in complex paper samples where strong macromolecular associations of hemicelluloses and lignin with cellulose are present, an interpretation of the molecular mass distribution rather than an average DP\({}_{\rm v}\) value is required [14]. Since SEC can provide comprehensive information on the molecular mass distribution, it can be particularly effective in the assessment of the current condition of paper as well as in kinetic studies of cellulose degradation [1]. Different results were obtained when comparing mass average molecular mass determination by viscometry and different SEC methods for cellulose tricarbanulates (CTCs). Some authors describe a good correlation between DP\({}_{\rm v}\) determination by viscometry and SEC determination of M\({}_{\rm w}\) of cellulose tricarbanilates [15], while other authors find significant differences between these methods [16]. The degree of polymerization of cellulose is calculated from the intrinsic viscosity of solutions prepared by dissolving cellulose in a suitable solvent, such as CED or cadaveren. In addition to cellulose, paper usually contains other components as well, of which lignin is the most abundant in unbleached wood pulp papers. According to the standard SCAN-CM 15:88 [17], the method for viscometric determination of the degree of polymerization is applicable to all types of pulp that dissolve completely in the CED solution, which is not the case for papers with high lignin content. The applicability of the method is defined in more detail in the Tappi standard [18]. The viscosity of pulp using the capillary viscometer method can be used for conventional pulps with up to 4% lignin. The applicability of this method to pulps with extended delignification has not been determined. It is also noted that chlorite delignification may result in a lower determined viscosity [18]; therefore, the results should be considered approximate only. Pulps with Kappa number above 35 to 40 should be delignified by mild treatment with sodium chlorite or chlorine dioxide to obtain reliable results, as mild treatment minimizes cellulose degradation [18]. Extensive treatment of pure cellulose with the chlorite delignification process may affect the cellulose average DP\({}_{\rm v}\)[19], which is consistent with a study by [PERSON] et al. [20].