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Nanofibrillated cellulose as an additive in papermaking process: A review

During the last two decades, cellulose nanofibres (CNF) have emerged as a promising, sustainable reinforcement with outstanding potential in material sciences. Though application of CNF in papermaking is recent, it is expected to find implementation in the near future to give a broader commercial market to this type of cellulose. The present review highlights recent progress in the field of the application of cellulose nanofibres as additives in papermaking. The effect of CNF addition on the wet end process is analysed according to the type of pulp used for papermaking. According to the literature consulted, improvement in papers overall properties after CNF addition depended not only on the type and amount of CNF applied, but also in the pulps origin and treatment. Bulk and surface application of CNF also presented significant differences regarding papers final properties. This review also revises the mechanisms behind CNF reinforcing effect on paper and the effect of chemically modified CNF as additives.

Suitability of wheat straw semichemical pulp for the fabrication of lignocellulosic nanofibres and their application to papermaking slurries

The present work studies the feasibility of wheat soda pulp as a raw material for the fabrication of cellulose nanofibres and their application as an additive in papermaking. Wheat straws were cooked under alkaline conditions and the resulting pulp was used as a raw material for the production of lignocellulosic nanofibres (LCNF). Nanofibres were fabricated by intense mechanical beating followed by high-pressure homogenization. The produced LCNF were characterized and applied to papermaking slurry based also on wheat straw soda pulp. Paper sheets made thereof were analysed for their physical and mechanical properties. The results indicated that paper strength was improved after addition of LCNF, whereas density increased and porosity was reduced. These improvements in properties (except the Tear Index) are significant because they were achieved using LCNF with lower fibrillation degree compared to previous works where chemically pre-treated LCNF were used as reinforcement.

Are Cellulose Nanofibers a Solution for a More Circular Economy of Paper Products

This paper presents the study of the feasibility of incorporating lignocellulosic nanofibers (LCNF) to paper in order to maintain the relevant physical properties and increase the number of cycles that paper can be recycled in the technosphere in a more circular economy. For that purpose, the effect of mechanical refining in recycling processes was compared with that of the novel LCNF addition. In this sense, the behavior of a bleached kraft hardwood pulp when recycled was investigated, as well as the effects of each methodology. Since there are many issues to be considered when trying to replace a technology, the present paper analyses its feasibility from a technical and environmental point of view. Technically, LCNF present greater advantages against mechanical refining, such as higher mechanical properties and longer durability of the fibers. A preliminary life cycle assessment showed that the environmental impacts of both systems are very similar; however, changing the boundary conditions to some feasible future scenarios, led to demonstrate that the CNF technology may improve significantly those impacts.

The feasibility of incorporating cellulose micro/nanofibers in papermaking processes: the relevance of enzymatic hydrolysis

Cellulose nanofiber (CNF) is becoming a topic of great interest among the industrial and academic communities, mainly due to their potential applications in very well-differentiated industrial sectors. Among this wide range of applications, papermaking is one of the most accepted and studied. However, it is widely known that the papermaking sector is forced to compete in markets where products do not have huge added value and production margins are very low. Therefore, papermakers are constantly looking for new technologies that balance efficiency and production costs. In line with this, the present work attempts to assay the enzymatic hydrolysis of cellulose fibers to obtain CNFs. Accordingly, pH, pulp consistency, treatment time, enzyme dosage and temperature were varied to find a combination of parameters that could lead to highly efficient CNF in terms of the mechanical properties of paper enhancement and production costs. For this, CNFs were applied to unrefined and refined bleached kraft pulps and their properties were assessed. The obtained results demonstrated that it is possible to obtain highly efficient CNFs from bleached pulp at affordable costs for papermakers. Moreover, it was found that the treatment time has a key role during the production of this CNF but at low enzyme dosages since the obtained results, in terms of intrinsic properties and reinforcing potential, for high enzyme charges did not vary significantly as time was increased. In sum, the present work offers a cost-efficient solution for the application of CNF in the production of paper from bleached pulp as well as a promising alternative to those conventional processes from a technical point of view.

Effective and simple methodology to produce nanocellulose-based aerogels for selective oil removal

Spilled oil in seas has a direct impact on the environment and biodiversity. Moreover, there is no clear relationship between the amount of oil in the aquatic environment and its impact, since it mainly depends on the time and season that the oil is spilled. Nowadays, there are several techniques to clean up and recover oil from the sea, including the use of microorganisms, chemicals, controlled burning, dispersants and solidifiers, among others. Sometimes, unfortunately, the best option is to watch and wait for natural attenuation. Cellulose nanofibers have potential environmental applications due to their availability, light weight, mechanical and optical properties, and renewability. Several studies have dealt with modification of their hydrophilic character through silanation and acetylation. Both treatments, despite having a significant impact on the environment, are not plausible on a large scale because of the cost of chemicals and complexity of the modification. In this sense, the present work aims to develop hydrophobic nanocellulose-based aerogels from bleached kraft eucalyptus fibers modified with alkyl ketene dimers. For this, an experimental batch of 24 aerogels was prepared, including three types of CNF (TEMPO-oxidized, enzymatically hydrolyzed and mechanical) and eight modification degrees. The obtained aerogels were characterized in terms of morphology, hydrophilicity and water–oil absorption capacity under static and dynamic conditions, as well as their suitability for recycling and reuse for selective oil removal. The results showed that it is possible to obtain 3D-structured aerogels with a high oil absorption capacity by a simple and presumably low-cost methodology.

Lignocellulosic nanofibers from triticale straw: The influence of hemicelluloses and lignin in their production and properties

The present work aims to determine the influence of hemicellulose and lignin content in the production of lignocellulosic nanofibers (LCNF) from triticale straws. Triticale straws were digested and then gradually delignified, preserving as much hemicelluloses as possible. The obtained LCNF was characterized and used as paper strength additive, observing that hemicellulose and lignin have a key role on the final properties thereof, as well as on their reinforcing potential as paper additive, obtaining LCNF with the same paper reinforcing potential than CNF obtained by TEMPO ((2,2,6,6-Tetramethyl-piperidin-1-yl)oxyl) mediated oxidation.

Magnetic bionanocomposites from cellulose nanofibers: Fast, simple and effective production method

Nanocellulose is becoming a topic of great interest due to its lightweight, huge availability and its interesting properties. Among these properties, it is worthy to distinguish its specific surface and its strength. Both properties allow producing films with great mechanical properties able to retain nanoparticles which can provide the nanopaper of much functionality. Many applications for nanocellulose nanocomposites have been reported, demonstrating the interesting opportunities that this product has in a near future. In this sense, the present work attempts to produce membranes based on cellulose nanofibers (CNF) filled with magnetite nanoparticles with the purpose of developing membranes for loudspeakers. The main advantage of this is the avoiding of the iron core that one can find in any loudspeaker, since the membrane itself acts as that core. Bionanocomposites ranging from 10 to 70% of magnetite nanoparticles were produced by filtration in a nitrocellulose membrane with a pore size of 0,22μm. Tensile tests showed that mechanical properties were decreased as the amount of magnetite was increased. They were observed by FE-SEM to see the interactions between nanoparticles and CNF. Finally, a loudspeaker prototype was developed in order to evaluate the sonorous efficiency of the resulting membranes.

Evaluation of Thermal and Thermomechanical Behaviour of Bio-Based Polyamide 11 Based Composites Reinforced with Lignocellulosic Fibres

In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to α’ more stable phase, without any negative impact on the properties of the fibres.

Approaching a new generation of fiberboards taking advantage of self lignin as green adhesive

This study describes the use of lignin as natural adhesive for the production high density fiberboards (HDF) made from wheat straw. In the present work, this agricultural residue was used to produce thermomechanical pulp and the used lignin was obtained from the spent liquors generated in the same process. A hot pressing process was conducted to manufacture these fiberboards and different percentages of this green adhesive were targeted. The wheat straw raw material and its pulp were characterized. Apart from that, the chemical composition and the thermal properties of the lignin sample were evaluated. Physical and mechanical properties were assessed and the results revealed that the panels made only with wheat straw fibers had a flexural strength value (52.79MPa) even above the value corresponding to the commercial HDF (41.70MPa). Also, results showed that the incorporation of soda-lignin lead to lignocellulosic composites that, as lignin content was increased (from 0 to 15%), mechanical properties were enhanced. The highest mechanical performance was reached for fiberboards at 15% of lignin with a flexural strength of 96.81MPa, a flexural modulus of 3.55GPa, and finally an internal bond of 1.46MPa.

Bleached Kraft Eucalyptus Fibers as Reinforcement of Poly(Lactic Acid) for the Development of High-Performance Biocomposites

Poly(lactic acid) (PLA) is one of the most well-known biopolymers. PLA is bio-based, biocompatible, biodegradable, and easy to produce. This polymer has been used to create natural fiber reinforced composites. However, to produce high-performance and presumably biodegradable composites, the interphase between PLA and natural fibers still requires further study. As such, we aimed to produce PLA-based composites reinforced with a commercial bleached kraft eucalyptus pulp. To become a real alternative, fully biodegradable composites must have similar properties to commercial materials. The results found in this research support the competence of wood fiber reinforced PLA composites to replace other glass fiber reinforced polypropylene composites from a tensile property point of view. Furthermore, the micromechanics analysis showed that obtaining strong interphases between the PLA and the reinforcement is possible without using any coupling agent. This work shows the ability of totally bio-based composites that fulfill the principles of green chemistry to replace composites based on polyolefin and high contents of glass fiber. To the best knowledge of the authors, previous studies obtaining such properties or lower ones involved the use of reagents or the modification of the fiber surfaces.