Paper degradation on a macroscopic scale is characterised primarily by yellowing, an increase in brittleness, and other destructive changes caused by the hydrolysis of glycoside bonds and oxidation reactions. Until now, lignin has been believed to cause these changes. However, contemporary analysis has not confirmed this assumption and has attributed low paper resistance to ageing with acidification owing to the production in acid environments that involve aluminium sulfate. In view of the common belief this manuscript presents studies on the accelerated ageing of papers with different lignin contents that are produced in neutral environments. To achieve the objective, artificially aged papers under conditions of increased humidity and temperature were investigated using chromatographic (SEC) and spectroscopic (FTIR and UV–Vis spectroscopy) techniques. Mechanical tests were used to determine the decrease in tensile properties of the samples. We observed no effects of the lignin content on the ageing rate of paper produced at neutral pH. This work also reveals the extent to which spectroscopic methods are useful for studying the papers containing lignin.

For economic reasons, increasing the use of various fibrous pulps with high lignin contents—i.e., chemothermomechanical pulp (BCTMP and CTMP), thermomechanical pulp (TMP), and semichemical pulp—is desirable. The relatively good quality and increased efficiency of these pulps make them attractive paper semi-products. In particular, they could alleviate the severe shortage of paper semi-products. Although mechanical pulp and semichemical pulp are achieving increasing quality with substantially increased wood efficiency, their production is often characterised by high consumption of electricity to defibre chips or refine high-lignin-content fibrous pulps. Technological, environmental, and economic evaluations of the manufacture and application of increased efficiency cellulose pulps that take into account potential profits from increased cellulose pulp efficiency and losses due to energy costs and degradation in the properties of the resulting paper are relevant and essential to paper mills. This article reports such an analysis. The authors have analysed the usable properties of ten cellulose pulps with various degrees of digestion and identified the optimum pulp that yields the optimum product properties, considering the yield; pulp refining time, which determines the cost of paper manufacture; and strength properties of the obtained paper.

The aim of this work was to assess the utility of seven different kraft pulps produced from softwood (pine), hardwood (poplar, birch and beech), wheat straw and hemp (bast and harl) as potential sources of sugar feedstocks for fermentation processes. The pulps contained low amounts of hemicelluloses (1.9–8.2% d.w.) and lignin (1.7–15% d.w.). The crystallinity index values ranged from 55% (wheat straw pulp) to 79% (hemp bast pulp), while the average DP varied from around 230 (hemp bast pulp) to 1482 (poplar and birch pulps). The results of enzymatic hydrolysis showed that not only the residual lignin content but also the cellulose crystallinity index decided on the sugar yields while the average polymerization degree had a weak impact. More reducing sugars were obtained from the hardwood pulps and wheat straw pulp (100% d.w.) than from the pine pulp (around 89% d.w.) and two hemp pulps (40.5% d.w. and 44.7% d.w. from the bast and harl pulps, respectively). Glucose was the dominating (69–79% w/w) soluble sugar in enzymatic hydrolysates of the pulps. The sugar profiles of these hydrolysates make them suitable sugar feedstocks for fermentation processes.

The degradation of cellulose is an important factor influencing its mechanical, optical, physical, and chemical properties and, hence, the lifetime of paper in libraries and archival collections. Regardless of the complexity of the paper material, the main chemical pathways for its degradation are hydrolysis and oxidation. This study presents an overview of the analytical techniques employed in the evaluation of the hydrolysis and oxidation processes; these techniques include size-exclusion chromatography, Fourier-transform infrared and ultraviolet–visible spectroscopy, and X-ray diffraction. This paper aims to determine the extent to which these instrumental methods are useful for studying the aforementioned processes and for which lignin contents. It also highlights how atmospheric humidity could affect the cellulose structure in paper containing lignin. It was found that humidity causes significant changes in the cellulose chain lengths and that a high lignin content in paper could suppress some cellulose degradation pathways. This knowledge can be applied to developing strategies and selective chemical treatments preventing the consequences of paper ageing.

Paper degradation menaces the useful lifetime of books, manuscripts, and works on paper during storage, circulation, and display in libraries, archives, and museums. Severe damages such as embrittlement, decay, and mold often occur to the paper that might threaten to lose cultural heritage. However, the shelf life of papers stored in suitable conditions can be extended by hundreds of years. The most important external factors affecting the deterioration of paper-based materials include, in particular, changes in temperature and air humidity. In this study, the effects of accelerated aging under different conditions, including substantially different relative humidity, were considered relative to the strength properties of the paper sheets. These include the mechanical strength, such as breaking length, tear resistance, and bursting strength of the paper samples before and after dry heat aging and hydrothermal aging. Samples with various content of lignin produced in neutral pH were examined to exclude the adverse influence of acidity on paper properties. The results indicate that impact of moisture on tensile properties and pH-value of paper is much greater than the effect of increased temperature. The results of this work are intended to consolidate and expand the theoretical foundation and provide technical support for the conservators and library staff on the storage of paper cultural relics.

Yield of Pulp, Dimensional Properties of Fibers, and Properties of Paper Produced from Fast Growing Trees and Grasses