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.

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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 results of enzymatic hydrolysis of birch and beech kraft cellulosic pulps indicate that they may be promising feedstocks for fermentation processes including biofuel manufacturing. The aim of this study was to investigate whether birch and beech wood require the same degree of delignification by kraft pulping as pine wood. The differences observed in the efficiency of hydrolysis for the raw materials tested suggest that the differences in the anatomical structure of the examined wood in relation to pine wood is essential for the efficiency of the enzymatic hydrolysis process. The yields of glucose and other reducing sugars obtained from the birch and beech cellulosic pulps were similar (up to around 75% and 98.3% dry weight, and 76% and 98.6% dry weight, respectively). The highest glucose yields from cellulose contained in the birch and beech pulp were around 81.2% (at a Kappa number of 28.3) and 83.1% (at a Kappa number of 30.4), respectively. The maximum glucose yields and total reducing sugars of birch wood on a dry weight basis (39.8% and 52.1%, respectively) were derived from the pulp at a Kappa number of 28.3, while the highest yields of glucose and total reducing sugars of beech wood on a dry weight basis (around 36.9% and 48.2%, respectively) were reached from the pulp at a Kappa number of 25.3. To obtain the highest glucose yields and total reducing sugars of a wood on a dry weight basis, total lignin elimination from the birch and beech pulps was not necessary. However more in-depth delignification of birch and beech wood is required than for pine wood.

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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.

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