This study investigates the swelling and liquid retention properties of cellulosic pulp from cotton waste, cotton linters and conventional dissolving wood pulp in both neutral (water) and alkaline (sodium hydroxide) conditions in regard to the first phase of the viscose process (mercerization). The swelling of single fibers is investigated by microscopic observation of the diameter increase during immersion in the liquids, which resulted in a logarithmic trend over time. The retention properties are investigated by water and lye retention values, and the latter was coupled to the pressability of mercerized pulp through observation of the trend in press factor with increasing pressing times. The different materials behaved similarly in neutral conditions regarding single fiber swelling and retention properties. Alkaline conditions, on the other hand, resulted in increased swelling and retention properties for all materials compared to neutral conditions, and the cotton-based pulps showed higher single fiber swelling and retention of lye, accompanied by impeded pressability. Thereafter, several material properties were investigated; morphological fiber properties (fiber width, cell wall thickness and fiber coarseness), fines content, carbohydrate monomer composition, and charge density. The results indicate that a thin cell wall and large lumen of the cotton waste fibers affect their higher swelling and retention properties, but further investigation of other morphological, chemical and physical properties of the fibers and fiber networks in pulp sheets is necessary. However, these insights on the behavior of different pulps can already help industries with the optimization of implementation of cotton waste pulps for viscose production.

This study examines the impact of hornification on the strength of paper made from chemical pulps. Two key aspects are examined: how varying degrees of hornification influence the mechanical properties of paper sheets, and how temperature affects hornification in papermaking pulps when water remains within the fibre structure. Experiments were conducted on hardwood and softwood kraft pulps that were dried and heated under controlled conditions. The results revealed that hornification reduces the strength of paper made from three different types of pulp. A local minimum of hornification and local maxima of tensile strength occurred around 40–60 °C. A strong linear correlation was observed between decreased tensile strength, decreased water retention, and the hornification ratio. Temperature treatments applied without water removal did not affect the water retention value (WRV) or the strength of the paper. This confirms that water removal is essential for hornification and strength loss to occur. These findings refine our understanding of hornification, suggesting that careful process control during drying can exploit the positive effects of moderate drying while minimizing hornification, and thus, the risk of excessive fibre closure. Such control strategies could improve strength optimization in industrial pulp and paper manufacturing.

During kraft pulping of wood, a considerable part of biomass is solubilized, forming a black liquor from which material can be taken out as by-products. Of these, extractive-derived fractions such as tall oil and raw turpentine has long seen technical utilization, and presently, lignin degradation products have garnered a large interest. The carbohydrate degradation products, however, have seen considerably less focus. In this work, we have investigated the structure of a high molecular-weight fraction of the carbohydrate degradation products using nuclear magnetic resonance spectroscopy, finding it to be a conjugated aromatic structure rich in methyl, methylidine, alcohol and carboxylic acid groups. Based on this information, we suggest a structure based on hydroxymethylfurfural as the repeating unit, with sugar acid substituents providing additional functionality. Additionally, UV-vis data of the polymer is compared with data from the kraft cooking of cotton linters and other model systems to corroborate the hypothesis that this polymer is indeed present in black liquor and potentially responsible for some of its characteristic colour. It also reacts in the kappa number analysis, exhibiting 40 % of the permanganate consumption predicted for pure lignin. Finally, the technical significance of these carbohydrate degradation products is discussed based on the structural findings.

In the past decades, substantial research efforts have been directed towards increasing the availability of renewable and recycled raw materials. Lignin, one of the most abundant natural polymers, constitutes a vast, renewable, and largely untapped source of aromatic structures. In addition, it is one of the most abundant renewable sources of carbon. Despite the countless research projects aimed at valorizing kraft lignin, the largest source of industrial lignin, relatively few commercial kraft lignin products have emerged. Simultaneously, lignosulfonates represent a commercially successful range of products with a steady and growing global market. This paper reviews the current outlook of technical lignin research, including common misunderstandings, and discusses various factors that have hampered the use of lignin as a renewable source of materials and chemicals.

In the manufacturing of cellulose derivatives, improving cellulose accessibility is essential for achieving a high product quality. In this study, endoglucanase enzyme treatment was applied prior to the cationization reaction to enhance the accessibility of hydroxyl groups for the production of cationized dialdehyde cellulose (CDAC). A range of enzyme dosages (0.09–45.00 ECU/g) was tested, and their effects on the swelling behavior and surface charge density of the final product were evaluated. The surface charge density of the ultimate cellulosic derivative confirmed its cationization and was proven to enhance the charge density of cationized dialdehyde cellulose (35% increase) compared to untreated pulp with enzyme. Additionally, the modified cellulose exhibited a significantly higher swelling capacity than regular pulps. These findings suggest that enzymatic pretreatment can enhance fiber reactivity and support a more sustainable and efficient production of cellulose-based derivatives, offering a promising potential for commercial applications.

Hornification of cellulose-rich materials, particularly wood pulps, occurs when chemical bonds form between cellulose surfaces, along with intermolecular forces created during dewatering and drying, preventing the material from reswelling in water to its original structure. Hornification of pulps results in a reduced ability to form effective fiber networks and therefore weaker paper products. The objective of this work was to investigate the role of hornification in pelletized cellulosic biomass and materials in general to provide more information than can be obtained by measuring standard wet state properties, such as water retention. Pellets were produced from chemical pulps with different degrees of hornification, as indicated by the water retention value (WRV), and their mechanical performance was evaluated. The chemical pulps served as a model material for investigating hornification. Pulps with higher hornification produced pellets with inferior mechanical properties, which has not been shown before by such a test. This effect is attributed to increased fiber stiffness and reduced surface flexibility, which limits fiber-fiber bonding. In addition, high drying temperatures prior to pelletizing, and thus higher hornification, will increase compression energy and friction in the pelletizing process. A novel connection was observed between WRV and mechanical performance, highlighting the impact of hornification on the surface interactions of cellulose-based materials.

Kraft pulping of wood is based on efficient depolymerization and solubilization of lignin, while cellulose is relatively undamaged. Non-cellulose cell wall polysaccharides are however in some cases heavily degraded, especially pectin and to a lesser degree also glucomannan while, xylan is relatively stable. In this mini-review, the most important reactions in lignin and polysaccharide degradation in kraft pulping are described, both the technically favorable and the problematic reactions, and the chemical background to discuss the advantages and drawbacks of the process. An attempt to put the different reactions in the perspective of the goals of the pulping process is made and a special focus is on the development of color in the pulp fiber during the kraft pulping.

Hornification, a complex phenomenon occurring during drying of lignocellulosic materials because of formation of irreversible chemical bonds, remains a subject of scientific interest. This study aims to shed light on the underlying mechanisms of hornification by investigating interactions between the liquid and solid phases through a solvent exchange treatment. The treatment involved replacing water with various solvents in suspensions of never-dried cellulose samples, including alcohols (methanol, ethanol, isopropanol) capable of forming hydrogen bonds, albeit to a lesser extent than water, as well as non-alcohol solvents (acetone, ethyl acetate, toluene, heptane) that do not possess the ability to form chain of hydrogen bond, and no hydrogen bond between each other. The impact of solvents on the hornification process was evaluated using WRV measurements. Our findings reveal that water, as a solvent, plays a dominant role in the hornification process, primarily due to its excellent capability to form bridges of hydrogen bonds. In comparison, hornification with alcohols was considerably lower than with water, likely attributed to the smaller ability of alcohols to engage in such interactions. Furthermore, our results indicate a tendency for reduced hornification also when using non-hydrogen bond solvents with decreased polarity. This strengthens the hypothesis related to chains of hydrogen bonds. Additionally, the interaction between hydrophobic surfaces on cellulose through hydrophobic interactions could provide another plausible explanation.

Hornification is a well-known phenomenon describing what happens during the drying of lignocellulosic materials, often within and between cellulosic pulp fibers. For wood fibers used in papermaking, this phenomenon decreases fiber wall swelling, and internal and external fibrillation. It reduces flexibility of damp fibers, which leads to a diminished ability to form effective fiber networks, resulting in lower paper strength. This work investigates how drying temperature affects the changes in fiber morphology, connects this to the changes in sheet behavior, and proposes a combination of bonding mechanisms for hornification. Results show that hornification depends on drying temperature; higher temperature gives higher degrees of hornification with decreased WRV of about half the numerical value, from 1.5 g/g for never-dried pulp to 0.7 g/g for hardwood pulp samples. Higher temperatures, above 100°C, also change the pulp color, as measured by increased yellowness. Decreased swelling capacity and pulp yellowness are connected. This indicates parallel reactions, which both contribute to hornification. The mechanisms are proposed to be chains of hydrogen bonds, dominating at low temperatures and providing no color change, and dehydration reactions via pyrolysis, giving a yellow-to-brown color shift. Compression strength measurements show that major hornification adversely affects sheet strength due to poor network bonding. However, minor hornification can be beneficial for applications where compression strength is an important parameter.

Factors affecting the swelling of cellulosic fibers are considered in this review.  Emphasis is placed on aqueous systems and papermaking fibers, but the review also considers cellulose solvent systems, nanocellulose research, and the behavior of cellulosic hydrogels.  The topic of swelling of cellulosic fibers ranges from effects of humid air, continuing through water immersion, and extends to hydrogels and the dissolution of cellulose, as well as some of its derivatives.  The degree of swelling of cellulose fibers can be understood as involving a balance between forces of expansion (especially osmotic pressure) vs. various restraining forces, some of which involve the detailed structure of layers within the fibril structure of the fibers.  The review also considers hornification and its effects related to swelling. The expansive forces are highly dependent on ionizable groups, pH, and the ionic strength of solution.  The restraining forces depend on the nature of lignin, cellulose, and their detailed structural arrangements.