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.

The objective of this work was to investigate the influence of hydrogen bonds between fibres on static and dynamic strength properties of paper. A commercial bleached pinewood kraft pulp was soaked in water, refined in a PFI, and used to form paper webs in different solvents, such as water, methanol, ethanol, n-propanol and n-butanol, to determine the effect of their dipole moment on static and dynamic strength properties of resulting paper sheets. Paper which was formed in water, being the solvent of the highest dipole moment among the tested ones, showed the highest breaking length and tear resistance. When paper webs were formed in n-butanol, which was the least polar among the solvents, these parameters were reduced by around 75%. These results provide evidence of the importance of water in paper web formation and strong impact of hydrogen bonds between fibres on strength properties of paper.

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.

Results of enzymatic hydrolysis of pine kraft cellulosic pulps (Kappa numbers ranging from 17.2 to 86.2) and waste fines from paper production line suggest that they are potential feedstocks for biofuel production. Glucose (61-68 % d.w.) and reducing sugars (around 90 % d.w.) yields from the pine cellulosic pulps with Kappa numbers ranging between 17.2 and 47.7 were higher than from the two pulps with Kappa numbers of 60.9 and 86.2. Glucose and reducing sugars yields from the latter pulps were around 54 and 45 % d.w. and 78 and 67 % d.w., respectively. The highest yields of glucose and total reducing sugars on a pine wood dry weight basis (29.3 and 43.1 %, respectively) were derived from the pulp with the Kappa number of 47.7. Thus the complete lignin removal from pine wood was not necessary to obtain maximum yields of glucose and other reducing sugars. Enzymatic hydrolysis of the fines from pine wood processing in a paper mill yielded around 75 % glucose and 78 % total reducing sugars on a dry weight basis that corresponded to around 34 and 36 % on a pine wood dry weight basis.

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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.

Typical bleached pinewood kraft pulp from a paper mill was immersed in either water or different alcohols, such as methanol, ethanol, n-propanol, and n-butanol, and then refined in a PFI mill. After refining, changes in the internal fibrillation of the fibres were evaluated by measurements of water retention values (WRV), while fibre shortening was determined by measurements of the average weighted fibre length. The objective of this study was to determine the influence of a liquid used for refining on the principal refining effects such as the internal fibrillation and fiber shortening. The highest increase in the internal fibrillation was observed for the pulp samples refined in water, which has the higher dipole moment than the alcohols. For these samples, WRV increased from 93% to 201%, while the average weighted fiber length was reduced by only 0.6 mm. When the pulp was beaten in n-butanol, which was the least polar liquid among the liquids investigated, liquid retention value increased by only 23.5%, while the average weighted fibre length was reduced by 1.37 mm. These results showed the importance of water in the beating of cellulose fibres and demonstrated that the outcomes of this process depended on the dipole moment of the fiber immersion liquid.

In the 21st century, numerous economic and environmental initiatives have significantly increased paper recycling, which continues to expand due to environmental awareness. With increasing recycling rate, low-quality paper fractions may be included in the process, leading to the overproduction of very low-value papers that cannot be reprocessed. Moreover, the production of paper from poor-quality wastepaper can result in the introduction of chemicals from the recycled paper into the recycling loop and unintended spread of chemical substances. Therefore, reliable and conscious selection of recycled pulp is imperative. To this end, the present study verified the properties of recycled pulp critical for the assessment of its papermaking ability for the production of high-quality sanitary paper. Following an examination of samples, it was found that the key parameters that influence the papermaking ability of wastepaper include presence of impurities, content of extractive substances, freeness, and length of fiber. On this basis, types of wastepaper that, at the very beginning, did not portend well for obtaining paper products with high potential for utility were eliminated.