This article describes how crystalline or fibrous nanocellulose influences the mechanical properties of paper substrate. In this context, we used commercially available cellulose nanocrystals, mechanically prepared cellulose nanofibers dispersed in water or ethanol, and carboxy cellulose nanofibers. Selective reinforcement of the paper treated with the nanocellulose samples mentioned above was observed. The change in the fibre structure was assessed using scanning electron microscopy, roentgenography, and spectroscopy techniques. In addition, the effect of nanocellulose coating on physical properties was evaluated, specifically tensile index, elongation coefficient, Elmendorf tear resistance, Bendtsen surface roughness, Bendtsen air permeability, and bending strength. It can be concluded that the observed decrease in the strength properties of the paper after applying some NC compositions is due to the loss of potential disturbances in hydrogen bonds between the nanocellulose dispersed in ethanol and the paper substrate. On the other hand, significantly increased strength was observed in the case of paper reinforced with nanocellulose functionalized with carboxyl groups.

Starch is an inexpensive, easily accessible, and widespread natural polymer. Due to its properties and availability, this polysaccharide is an attractive precursor for sustainable products. Considering its exploitation in adhesives and coatings, the major drawback of starch is its high affinity towards water. This study aims to explain the influence of the silane-starch coating on the hydrophobic properties of paper. The analysis of the organosilicon modified starch properties showed an enhanced hydrophobic behavior, suggesting higher durability for the coatings. Molecules of silanes with short aliphatic carbon chains were easily embedded in the starch structure. Longer side chains of silanes were primarily localized on the surface of the starch structure. The best hydrophobic properties were obtained for the paper coated with the composition based on starch and methyltrimethoxysilane. This coating also improved the bursting resistance and compressive strength of the tested paper. A static contact angle higher than 115° was achieved. PDA analysis confirmed the examined material exhibited high barrier properties towards water. The results extend the knowledge of the interaction of silane compositions in the presence of starch.

The objective of the presented research was to determine the influence of cellulose coating, obtained from the cellulose solution in N-Methylmorpholine N-oxide (NMMO), on the structural and mechanical properties of paper. The effect of heating time of paper samples coated with cellulose dissolved in NMMO was also investigated. Depending on the heating time of the coating, a continuous or porous layer was obtained. Coating without any heating stage yielded a continuous cellulose layer of hydrophobic properties (higher contact angle in comparison to base paper), and paper of higher smoothness and increased tear resistance. Analysis of the paper samples showed that cellulose coating not only changed the surface properties of paper, but also significantly improved paper strength properties, such as the tensile index, elongation, bursting strength index and double folds number. Despite the process’ limitations (e.g. necessity of removing the NMMO), this method can be considered as a novel approach for paper property modification.

Cellulose fines are—in general—small particles removed from natural cellulose fibres during refining process which is typically carried out in papermaking industry. Fines have been recognized as a separate component of papermaking fibrous raw material since their properties differ considerably from those of cellulosic fibres. Fines are characterized by low dewatering ability, very high specific surface area, and high swelling ability. Knowledge about the possibility of effective control over fines generation and swelling during refining process are nowadays of key importance. Beside its significance in papermaking process (e.g. impact on paper structure and mechanical properties and dewatering properties of the pulp), nowadays the cellulose fines fraction is considered as a raw material for the production of novel materials e.g. microfibrilled cellulose and nanocellulose. The main objective of the presented study was to determine the impact of the most important refining parameters (e.g. net refining energy, rotor speed, and pulp consistency) which could be used to control the fines development and their swelling degree. On the basis of presented research results it may be concluded that the amount of the fines generated during refining process was mainly affected by the effective refining power (net power) and the rotational speed of the refiner rotor. Also, the final swelling degree of fines varies depending on the refining operating conditions used. It was found that the swelling degree of fines was mostly influenced by the rotational speed of the refiner rotor, refined pulp consistency, and—for very low consistency (1–2%)—also pulp volumetric flow rate through the refiner. As a result, it could be concluded that—for more effective control of the refining process—greater attention to the control of these parameters should be paid.

Impact of Pulp Consistency on Refining Process Conducted under Constant Intensity Determined by SEL and SEC Factors

Cellulose fibres modified with the luminescent inorganic compound were obtained by using N-methylmorpholine-N-oxide as a direct solvent. The fibres were cut and introduced to the unrefined and refined paper pulp samples. Schopper-Riegler value of the pulps were measured and the laboratory paper samples were formed. Observations under UV radiation showed that the cellulose luminescent fibres were randomly and even scattered in the paper and were well visible. Measurements of the paper properties such as tensile index, Elmendorf tear resistance, Bendtsen air permeability, Bendtsen roughness, folding endurance, bursting strength and tensile energy absorption were carried out and the scanning electron microscopy (SEM) analysis was used for the assessment of the paper structure and the bonding properties of the luminescent fibres. SEM analysis showed that the cellulose man-made fibres create microfibril network and have excellent compatibility with the paper. The results showed that cellulose man-made fibres with luminescent properties express similar properties to natural cellulose fibres (e.g. external fibrillation and bonding properties) which are useful for the purpose of secure paper production. Cellulose man-made fibres introduced to the paper do not have any disadvantageous impact on paper properties.