Eucalyptus Pulp Research Articles

Environmental Sustainability Assessment of Tissue Paper Production

The environmental performance of tissue paper varies greatly based on factors such as the type of fibre used as the raw material, the production process and the fuels used to meet the energy requirements. One possible strategy to decrease greenhouse gas emissions in tissue production is the integration of pulp and paper mills and their energy systems at the same site. However, the environmental trade-offs associated with this strategy are still unclear. Therefore, this study aimed (i) to assess for the first time the environmental impacts of tissue paper produced at a typical industrial site in Portugal using slush and market pulp as the main raw material, and (ii) to assess the environmental effects of the integration of bioenergy produced in the pulp mill in tissue production. A life cycle assessment was conducted from cradle to gate using real data from the production of eucalyptus wood, eucalyptus pulp and tissue paper. The results showed that energy consumption in tissue paper production is the main hotspot for most impact categories. When bioenergy is used in tissue production, the environmental impacts decrease by up to 20% for categories other than marine eutrophication and mineral resource scarcity. These results are relevant to support decision making concerning sustainable practices not only for the pulp and paper industry but also for the authorities in charge of defining environmental policies, incentives and tax regulations.

Cellulose nanofibers-based UV resistant and hydrophobic wood coatings

Wood and wood-based products are regarded as sustainable building materials, nonetheless, they frequently need the addition of protective coatings due to their susceptibility to abiotic and biotic degrading elements. Among the coating systems, water-borne coatings are a better choice since the majority of popular wood coatings are solvent-based and release volatile organic chemicals (VOCs). In this study, cellulose nanofibers (CNFs) were isolated from eucalyptus wood pulp using a chemo-mechanical method and used as the base substrate for wood coatings. The effect of CNF dispersion with varying concentrations (0.5 and 1 wt.%) of zinc oxide (ZnO) nanoparticles on UV-resistance of Pinus radiata and Hevea brasiliensis after 500 hrs of exposure was assessed. Wood surfaces without coating exhibited severe discolouration after 500 hrs of UV exposure. Only CNF-coating results in slight protection of wood surfaces from weathering but significantly increased water wettability of the surface. The incorporation of ZnO nanoparticles significantly reduced the colour change of the wood surfaces. As the concentration of ZnO increased, the colour stability and hydrophobicity of both the wood increased.

Bleached cellulose biochars as a sustainable alternative for oilfield-produced water (OPW) treatment and environmental remediation

Eucalyptus, a renewable and fast-growing raw material widely used in the paper industry, has great potential for new applications beyond papermaking. Bleached eucalyptus pulp, traditionally used in the pulp industry, has proved to be a promising alternative for removing complex organic compounds such as naphthenic acids (NAs), often found in oil-produced water (OPW). This study aimed to optimize the production of biochars from bleached eucalyptus pulp through pyrolysis at 700, 800, and 900 °C and to correlate the resulting properties with the ability to adsorb NA at low concentrations and in acidic and alkaline media. The research explores realistic environmental scenarios where naphthenic acids may be present in dilute concentrations after initial treatments. The biochars were characterized by their micro and mesoporous structures, amorphous structures, and distinct functional groups and were evaluated in simulated effluents. Biochar B900 reached a maximum adsorption capacity of 35 mg/g at pH 4 and 25 °C, excelling in acidic environments, while at pH 8, biochar B700 showed better performance. The PVSDM model revealed that mass transfer and pore diffusion coefficients increased with increasing pyrolysis temperature. The Langmuir model was the best fit for the experimental data. The biochar produced at 900 °C had the highest specific surface area (1,041.55 m2/g) and pore volume (0.56 cm3 g−1), favoring its adsorption capacity. Although the biochar shows good initial efficiency, the progressive reduction in adsorption capacity over the cycles suggests limited reusability, highlighting the need for optimization in the regeneration process to improve its economic viability in wastewater treatment.

The corrected H/G factors for accurately describing the delignification and depolymerization of industrial hemp stalks

Establishment of precise kinetic models is beneficial for the control of the degree of delignification and carbohydrate degradation in the pulping process. However, most kinetic models judge the degree of delignification and depolymerization only by holding time or fluctuating temperature, ignoring the effects of temperature and heating-up stage. Thus, this study explored in depth the delignification and depolymerization kinetic behaviors of the kraft pulping process of alkali-extracted hemp stalk material (HSM-AE). The chemical composition characteristics of the HSM-AE were firstly studied, followed by the investigation of the HSM-AE kraft pulping under different conditions. The H/G factor of the wood raw material was not suitable to describe the delignification and depolymerization behaviors during HSM-AE kraft pulping and needs to be corrected. Based on the corrected H/G factors, kinetic models of delignification and depolymerization were established. The parameter fitting results showed that the delignification and depolymerization were mainly dominated by sulfide cleavage and alkaline hydrolysis respectively. The activation energies of delignification caused by alkaline- and sulfide- cleavages were 66.8 and 72.7 kJ/mol; and the activation energies of cellulose depolymerization caused by peeling reaction and alkaline hydrolysis were 111.7 and 120.5 kJ/mol, respectively. Compared with eucalyptus kraft pulping, the activation energy ratio of delignification to cellulose depolymerization decreased, indicating that under the same delignification degree, the cellulose in HSM-AE was easier to alkaline degrade. At present, the process described in this experiment was more suitable to prepare dissolving-grade pulp for further production of viscose staple fiber.

Wheat straw as base paper for barrier coating

A smooth and dense surface of the base paper is advantageous when the goal is to apply a liquid coating as a barrier layer. For such a base paper, non-wood fibers derived from wheat straw could be an alternative to wood fibers. In this research paper, wheat straw pulp was refined with different beating levels (up to 600 revolutions) followed by different calendering pressure loads (up to 50 N/mm) to test its influence on mechanical and surface properties. Alkyl ketene dimer (AKD) was used as sizing agent with concentrations up to 0.2 wt% followed by a mineral-based precoating to test its influence on the smoothness. Eucalyptus pulp was chosen as a benchmark. After beating, the initial Schopper-Riegler degrees of 28 °SR increased to 56 °SR. Beating also increased the tensile index from 24 to 49 Nm/g, the burst index from 1.2 to 2.8 kPa·m²/g, and the tear index decreased from 3.3 to 2.8 mN·m2/g. Calendering reduced the initial roughness of 370 mL/min to 30 mL/min. When precoated and calendered again, the value was lowered to 15 mL/min. In summary, wheat straw paper is a relevant alternative to wood-derived base paper to produce barrier papers. Compared to eucalyptus, wheat straw paper showed better smoothness and much lower air permeability indicating excellent suitability for barrier coating.

Optimizing hemicelluloses pre-extraction in eucalyptus kraft pulping: A pathway towards enhancing pulp mill biorefineries

A critical pathway towards enhancing pulp mill biorefineries is to integrate the extraction and utilization of hemicelluloses into the pulping processes. Hence, an industrial pre-extraction strategy for hemicelluloses targeting eucalyptus kraft pulping process was developed. Alkaline solution or pulping white liquor was used to pre-extract hemicelluloses before the actual pulping process. The response surface methodology (RSM) technique was applied to investigate the most suitable conditions to maximize the yield of these hemicelluloses while simultaneously minimizing the damage to pulp yields and properties. Temperature (105 to 155 °C), alkali concentration (3 to 8%), sulfidity (20 to 30%) and retention time (19 to 221 min) were combined to evaluate their effects on hemicellulose yields and chemical structures. The optimal pre-extraction conditions identified in this work (5.75% NaOH concentration, 25% sulfidity at 135 °C for 60 min) successfully allowed recovering 4.8% of hemicelluloses (based on the wood dry mass) and limited damages to pulp yields and properties. The cellulose content in pulp can even be increased by about 10%. Hemicellulose emulsification properties were also evaluated, which were comparable to synthetic emulsifiers. This study provides an industrial pathway to effectively separate and utilize wood hemicelluloses from the pulping process, which has the potential to improve the economy and material utilization of pulp and paper mills.

Feasibility of Energy Self-Sufficiency by Biomass Production in A Brazilian State

Objective: This study aims to analyze the potential of using industrial black liquor or black lye residue from the eucalyptus pulp and paper production process as an alternative source of energy, in order to alleviate the current energy crisis. Theoretical framework: The study is based on literature regarding energy generation from biomass, focusing on the utilization of black liquor residue in thermoelectric power generation. Therefore, the thermoelectric generation from black liquor or black lye, cellulose biomass residue as an alternative source in energy generation, characterizes an important electrical feedback path in pulp production processes, also generating surplus energy for the supply network, relief of demand in the face of the current energy crisis. Method: The methodology employed in this study entails applied research, that investigates energy generation from black liquor in integrated plants of eucalyptus forest biomass, in reforestation areas for pulp production. Results and conclusion: The results indicate that energy generation from black liquor is a viable alternative to mitigate the current energy crisis, contributing to regional sustainable development. Projections suggest that by 2024, 85% of bioenergy can will be generated from this source in in the micro-region of Brazil. Therefore, adequate planning brings great expectations for regional sustainable development. Implications of the research: The research contributes to advancing scientific knowledge in the field of energy generation from biomass, demonstrating the potential of black liquor residue as an alternative energy source. Originality/value: The research contributes to advancing scientific knowledge in the field of energy generation from biomass, demonstrating the potential of black liquor residue as an alternative energy source.

A novel AA14 LPMO from Talaromyces rugulosus with bifunctional cellulolytic/hemicellulolytic activity boosted cellulose hydrolysis

BackgroundThe recently discovered PcAA14A and B from white-rot basidiomycete Pycnoporus coccineus enriched our understanding of the oxidative degradation of xylan in fungi, however, the unusual mode of action of AA14 LPMOs has sparked controversy. The substrate specificity and functionality of AA14 LPMOs still remain enigmatic and need further investigation.ResultsIn this study, a novel AA14 LPMO was characterized from the ascomycete Talaromyces rugulosus. TrAA14A has a broad substrate specificity with strong oxidative activity on pure amorphous cellulose and xyloglucan. It could simultaneously oxidize cellulose, xylan and xyloglucan in natural hemi/cellulosic substrate such as fibrillated eucalyptus pulp, and released native and oxidized cello-oligosaccharides, xylo-oligosaccharides and xyloglucan oligosaccharides from this substrate, but its cellulolytic/hemicellulolytic activity became weaker as the contents of xylan increase in the alkaline-extracted hemi/cellulosic substrates. The dual cellulolytic/hemicellulolytic activity enables TrAA14A to possess a profound boosting effect on cellulose hydrolysis by cellulolytic enzymes. Structure modelling of TrAA14A revealed that it exhibits a relatively flat active-site surface similar to the active-site surfaces in AA9 LPMOs but quite distinct from PcAA14B, despite TrAA14A is strongly clustered together with AA14 LPMOs. Remarkable difference in electrostatic potentials of L2 and L3 surfaces was also observed among TrAA14A, PcAA14B and NcLPMO9F. We speculated that the unique feature in substrate-binding surface might contribute to the cellulolytic/hemicellulolytic activity of TrAA14A.ConclusionsThe extensive cellulolytic/hemicellulolytic activity on natural hemi/cellulosic substrate indicated that TrAA14A from ascomycete is distinctively different from previously characterized xylan-active AA9 or AA14 LPMOs. It may play as a bifunctional enzyme to decompose some specific network structures formed between cellulose and hemicellulose in the plant cell walls. Our findings shed new insights into the novel substrate specificities and biological functionalities of AA14 LPMOs, and will contribute to developing novel bifunctional LPMOs as the booster in commercial cellulase cocktails to efficiently break down the hemicellulose-cellulose matrix in lignocellulose.

Chemical induces microstructural transformation of pulp fibre to colloidal cellulose for sustainable plant protection.

Cellulose, an environmentally friendly material, is abundantly available in Thailand as pulp and has significant potential for use in sustainable plant protection; however, the raw material is not directly suitable for such applications. To address this, colloidal cellulose with high water dispersibility was synthesised by treating Eucalyptus pulp with sulphuric acid (H2SO4). The optimised conditions involved a 24 hour treatment, producing colloidal cellulose with an average particle size of 0.57 ± 0.03 μm, the smallest size achieved. The cellulose morphology, consisting of submicron and nanoscale fragments and particles, was confirmed by transmission electron microscopy, field-emission scanning electron microscopy, and dynamic light scattering analyses. This microstructural transformation, driven by H2SO4-induced gelatinization and regeneration, led to decreased crystallinity, as observed in X-ray diffraction patterns and infrared spectra. The formation of colloidal cellulose as a film with adhesive properties on complex plant surfaces is facilitated by hydrogen bonding and hornification mechanisms. Additionally, colloidal cellulose demonstrated high compatibility with cuprous oxide, which was used as a model agricultural protective agent, showing a reduction of over 99% in E. coli and S. aureus abundance, highlighting the potential of colloidal cellulose as a sustainable coating agent or adjuvant in agricultural protection strategies.

Use of iron ore tailings as partial replacement for cement on cementitious composites production with vegetable fibers

The mining industry has been expanding and consequently increasing the associated environmental impacts, especially regarding this process's high volume of iron ore tailings (IOT) disposal. The best way to solve the problems caused by IOT is to develop large-scale utilization technologies that may consume large quantities of it. This study aims to evaluate the influence of incorporating IOTs on the mechanical, physical, microstructural, and morphological properties of extruded fiber-cement reinforced with eucalyptus cellulose pulp. For its use, IOT was characterized by the inhibition index, pozzolanic test, and granulometric, chemical, morphological, and X-ray diffraction analyses. The fiber-cement flat slabs were prepared by replacing cement using 10%, 20%, 30%, and 40% of IOT and the control treatment, generating specimens measuring 20x30x200mm (height x width x length). The composites were characterized for physical, mechanical, and microstructural properties before and after exposure to weathering by accelerated aging test. This study showed an improvement in fiber durability with the increase in IOT content as a function of the waste’s pozzolanic activity and an improvement in physical properties using 10% cement replaced by IOT. All treatments tested at 28 days presented values within trading standards limits. However, the treatments with 10% and 20% of IOT met the most demanding criteria. Thus, using iron ore waste as a substitute for raw materials in cementitious composites may reduce the difficulties of IOT disposal and save natural resources, leading to more sustainable constructions.

Hemicellulose-rich paper-grade pulp as raw material for regenerated fibres in an ionic liquid-based process

Hemicellulose-rich pulp raw materials are avoided in the production of man-made cellulosic textile fibres due to hemicellulose reactivity with the currently used industrial solvent systems. Incorporation of hemicelluloses in regenerated fibres could, however, increase the share of used wood biomass and thus improve the environmental footprint of regenerated fibre products. Superbase ionic liquids have shown potential in dissolving and regenerating all the major wood polymers i.e. cellulose, hemicellulose and lignin into regenerated products. In this work, regenerated fibres were spun from hemicellulose-rich softwood and eucalyptus paper-grade pulps and eucalyptus dissolving pulp using a superbase ionic liquid [mTBNH][OAc]. Before dissolution and spinning, intrinsic viscosities of the paper-grade pulps were adjusted either enzymatically or by using a mild acid-treatment to improve dope rheology for dry-jet wet spinning. In fibre spinning, hemicellulose was found to regenerate in high yield and the obtained regenerated fibres had high dry tenacities (5.3 to 15 cN/dtex). The best mechanical properties were measured from fibres with high hemicellulose content (17.3% (w/w)). Pulp pretreatment was found to be critical for achieving good mechanical properties. Acid-pretreatment, which modified both cellulose and hemicellulose, yielded regenerated fibres with better mechanical properties compared to an enzyme-pretreatment which did not alter the hemicellulose structure. Removal of hemicellulose substituents and hydrolysis of hemicellulose backbone in acid-pretreatment may be the key to improved mechanical properties in hemicellulose-containing regenerated fibres. Enzymatic peeling and imaging with a xylan-specific monoclonal antibody (CCRC-M138) suggest that hemicelluloses were enriched to the outermost layers of the regenerated fibres.

Classifying health issues in Eucalyptus miniclonal gardens in Uruguay

Clonal propagation is extensively used in the Eucalyptus pulp industry in Uruguay. Mother plants are maintained in clonal minigardens and they constitute the source of cuttings that are harvested continuously and sent to shaded greenhouses for rooting. Environmental conditions within the minigarden are optimized for plant growth, but such conditions can also promote the emergence of pests and diseases which can affect the mother plants and impair cutting production. However, comprehensive studies on health status within minigardens are scarce in the country. We carried out a seasonal survey on three clonal minigardens along the country to check for epidemiological patterns connected to the time of the year, the conditions within the clonal garden and the genetic material in propagation. We visited each minigarden at least once per season during 2019 and the beginning of 2020. During each visit, we inspected all the mother plants along three transects (two on the edges and one in the centre of the minigarden). We counted the number of plants with symptoms of disease and of insect attacks, and collected samples of affected plants for further identification in the laboratory, if necessary. We looked for a way to classify nurseries and species all together, according to the incidence of the different health issues surveyed. Thus, the dataset obtained from the surveys was assessed under different classification algorithms based on machine learning: neural networks, discriminant analysis models, classification regression tree, support vector machine, and random forest. We observed attack by arthropods such as mites, whiteflies, scales and aphids and caterpillars. We also recorded powdery mildew and disease symptoms such as dead plants and dry shoots. The different materials assessed during the survey belonged to E. grandis, E. dunnii, and E. grandis × E. globulus hybrids. The most common symptoms observed in all the minigardens and throughout the entire survey period were powdery mildew and damage from mites. The support vector machine model performed best, being able to classify the dataset with an accuracy of 76%. We discuss the relevance of these findings within the context of miniclonal garden health management.

Nanocellulose Coating on Kraft Paper

Paper is a biodegradable material, but in food packaging, its hygroscopicity and porosity can cause food contamination due to the exchange of gasses and liquids with the environment. Therefore, it is important to use biodegradable materials for paper coatings, such as nanocellulose, which is chemically compatible with paper but less hygroscopic. The objective of this study was to evaluate the effectiveness of nanofibrillated cellulose (NFC) as a paper coating. NFC produced from bleached eucalyptus pulp was used as a coating on kraft paper sheets produced from Pinus pulp. To prepare the coating, two thicknesses of wet nanocellulose (1 mm and 2 mm) were tested, and two nanocellulose films made with the same thicknesses were evaluated. The morphological, physical, mechanical, and thermal properties of the composites were investigated. The presence of NFC improved the surface of the paper by filling the pores; consequently, the density and barrier properties were also improved. All mechanical properties were improved, with the highest increases observed for bursting and tensile strength; however, the films showed low bursting index values and null values for the tearing index. The thermal stability of the paper with NFC coatings met the minimum requirements for food packaging.

Influence of different curing regimes and accelerated carbonation on the physical, mechanical, and aging performances of fiber cement

The curing process in fiber cement is essential to improving the characteristics of the fiber-matrix interface, physic-mechanical performance, and durability. This work studied the effect of different curing regimes and accelerated carbonation on fiber cement to optimize these materials' production stages and physic-mechanical performance. The fiber cement flat sheets were produced with 10% bleached eucalyptus pulp by slurry-dewatering method to reproduce the commercial Hatschek process. Carbonated and non-carbonated samples were assessed at different regimes and curing ages to provide a comparative parameter. Thermal curing at 60 °C (7 days) and wet curing (28 days) was carried out after carbonation as supplementary curing. The accelerated carbonation was performed in a climatic chamber at 60 °C, 90% RH, and 20% CO2 concentration. Accelerated aging trials were also conducted for durability evaluation. X-ray diffraction, TGA, and scanning electron microscopy analyses determined the mineralogical composition, chemical components, and fiber cement microstructure. Mechanical results presented an average increase of 33% in resistance of carbonated samples compared to non-carbonated fiber cement. Additional curing increased the materials' hydration potential and demonstrated an 11% increase in calcium carbonate amounts. However, there was no statistically significant difference in fiber cement’ physic-mechanical performance with additional curing. The carbonated samples without supplementary curing presented a fiber-matrix interface like that observed in other curing regimes, even after being subjected to a shorter curing time (3 days) and accelerated aging cycles. The accelerated carbonation process enables the materials’ production at reduced ages, achieving physic-mechanical performance and durability like materials produced at more advanced ages with conventional curing regimes.

A system lock-in blocks the uptake of mixed sustainable Eucalyptus plantations in Brazil

Forest plantation areas across the globe are increasing in size and in 2019 Eucalyptus monocultures in Brazil covered 6.97 million hectares (0.8%). These monocultures hardly provide ecosystem services and do not support wildlife habitats. A transition towards more sustainable Eucalyptus plantations is urgently needed to support the provisioning of ecosystem services and conserve biodiversity. This transition requires the development of sustainable business models. We studied the upscaling of sustainable Eucalyptus plantation alternatives in Brazil, by analysing the potential barriers that need to be overcome using the Technological Innovation Systems perspective and semi-structured interviews of relevant stakeholders across the Eucalyptus value chain. Although the provisioning of ecosystem services is improved by alternative plantation management, we identified four blocking mechanisms that inhibit the functioning of the innovation system and as such hamper upscaling; 1) the productivist approach by incumbent actors on plantation management that is focussing only on short-term profit maximisation and results in a strong resistance to change current practices, 2) the weak societal and governmental vision that does not put sufficient pressure to change practices, 3) additional certification to support alternatives is in its infacy to develop niche markets which also hampers the development of financial support, and 4) failed demonstration projects in the past that have led to a lack of proof of concept for further experimentation and knowledge development. These barriers combined lead to a system lock-in, resistant to change and not capable for a diffusion of sustainable alternatives. We conclude that the directionality of a sustainability transformation should be enhanced by formulating long-term goals and strong commitment of public and private actors. We discuss how a mission oriented approach could foster such directionality for the urgently needed regime transformation in Eucalyptus paper and pulp production.

Assessing the Genotoxicity of Cellulose Nanomaterials in a Co-Culture of Human Lung Epithelial Cells and Monocyte-Derived Macrophages.

Cellulose micro/nanomaterials (CMNMs) are innovative materials with a wide spectrum of industrial and biomedical applications. Although cellulose has been recognized as a safe material, the unique properties of its nanosized forms have raised concerns about their safety for human health. Genotoxicity is an endpoint that must be assessed to ensure that no carcinogenic risks are associated with exposure to nanomaterials. In this study, we evaluated the genotoxicity of two types of cellulose micro/nanofibrils (CMF and CNF) and one sample of cellulose nanocrystals (CNC), obtained from industrial bleached Eucalyptus globulus kraft pulp. For that, we exposed co-cultures of human alveolar epithelial A549 cells and THP-1 monocyte-derived macrophages to a concentration range of each CMNM and used the micronucleus (MN) and comet assays. Our results showed that only the lowest concentrations of the CMF sample were able to induce DNA strand breaks (FPG-comet assay). However, none of the three CMNMs produced significant chromosomal alterations (MN assay). These findings, together with results from previous in vitro studies using monocultures of A549 cells, indicate that the tested CNF and CNC are not genotoxic under the conditions tested, while the CMF display a low genotoxic potential.

Epoxidized linseed oil as a plasticizer for All-Cellulose Composites based on cellulose acetate butyrate and micronized pulp fibers

All-Cellulose Composites (ACCs) with cellulose derivatives have been neglected in the composite industry due to their high brittleness, low impact strength, and flowability. Epoxidized vegetable oils are well-known plasticizers for several polymers and composites but have never been exploited on the production of ACCs. The present work investigates the potential of an epoxidized linseed oil (ELO) as a cost-effective additive to enhance the properties and processability of ACCs made with cellulose acetate butyrate (CAB) and micronized Eucalyptus pulp fibers. The thermo-mechanical characterization of the composites, obtained by melt-mixing, revealed that ELO significantly decreases the glass transition temperature (Tg) of the obtained composites without compromising their thermal stability. Moreover, an 84-fold improvement was achieved on the melt flow rate (MFR) with 30 wt% ELO, and growing amounts of this additive caused an augment on the elongation and flexural strains at break. High loads of ELO resulted also on a substantial improvement of the impact strength, with values raising from 5.3 ± 0.9 kJ.m−2 up to 29.5 ± 1.7 kJ.m−2. Furthermore, this eco-friendly plasticizer also led to higher water uptake values, as well as higher biodegradation rates than the non-plasticized ACCs. Therefore, these results evince a remarkable improvement on the ACCs processability, performance, and biodegradation upon addition of a bio-based and cost-effective plasticizer.

The effect of fines on the consolidation of Eucalyptus/PLA fiber air-laid sheets

Bio-based nonwoven products are potentially more sustainable with a lower environmental impact than the current generation of petrochemical nonwovens. This work aims to examine the structure and performance of an air-laid sheet composed of defibrated Eucalyptus pulp and polylactic acid (PLA) fibers. In this work, Eucalyptus pulp dry fibers were prepared through two different methodologies, yielding fibers with distinct morphological properties. In an air-laid former, specially conceived for this work, sheets with a grammage of 100 g m−2 were prepared from fiber blends with moisture to aid in the consolidation. The resulting air-laid sheets were characterized by their structural, mechanical, and water sorption properties. The results showed that Eucalyptus fibers with fewer fines and fiber deformations yielded more absorbent sheets. The high fines group gave higher sheet strength. 30% of PLA fiber gave the best combination of strength and absorption capacity and stretch at break. The improvement in bulk, dry and wet strength was possible for air-laid sheets produced from the Eucalyptus/PLA mixture. The results showed that PLA has a strong interaction with the sheet fines, affecting consolidation and performance of the final product.

Characterizing lignin-containing microfibrillated cellulose based on water interactions, fibril properties, and imaging

Morphological characterization of microfibrillated cellulose (MFC) is critically important to process control in production and product specification for trade and product development yet is extremely difficult. This study evaluated several indirect methods for relative comparison of the morphology of lignin-free and lignin-containing ((L)MFCs). The (L)MFCs studied were produced using a commercial grinder through different passes from a dry lap bleached kraft eucalyptus pulp, a virgin mixed (maple and birch) unbleached kraft hardwood pulp, and two virgin-unbleached kraft softwood (loblolly pine) pulps with one bleachable grade (low lignin content) and one liner grade (high lignin content). The (L)MFCs were indirectly characterized using techniques based on water interactions, i.e., water retention value (WRV) and fibril suspension stability, as well as fibril properties, i.e., cellulose crystallinity and fine content. Optical microscopy and scanning electron microscopy were also applied to directly visualize the (L)MFCs to provide some objective measure of the morphology of the (L)MFCs. The results indicate that most measures such as WRV, cellulose crystallinity, fine content cannot be used to compare (L)MFCs from different pulp fibers. Measures based on water interactions such as (L)MFC WRV and suspension stability appeared can provide some degree of indirect assessment. This study provided the utilities and limits of these indirect methods for relative comparison of the morphologies of (L)MFCs.

Innovative system based on natural polyelectrolyte complex and cellulose micro/nanofibers to improve drainability and properties of recycled paper

In this work, the efficiency of a polyelectrolyte complex (PEC) to retain different cellulose micro/nanofibers (CMNFs) during paper formation and to improve the physical properties of recycled unbleached fiber paper was analyzed. CMNFs were obtained from a commercial bleached eucalyptus pulp (BEP) using a PFI refiner followed by a chemical treatment with oxalic acid at two different concentrations. Finally, the pulp was fibrillated using a high-pressure homogenizer at three different intensities. The PEC was formed by addition of the xylan (Xyl) solution on chitosan (CH) solution with a Xyl/CH mass ratio of 80/20. The required dosages of PEC solution to neutralize the charges of different nanocellulose fractions were determined by ζ-potential measurements, and the CMNF retentions on recycled unbleached fibers were evaluated in a Britt Dynamic Drainage Jar. The results showed that the maximum retention was obtained when the neutral PEC-CMNF system was added to pulp. Besides, a significant decrease on °SR was observed when PEC and PEC-CMNF systems were added to the untreated pulp, limiting the negative effects of nanocellulose addition on pulp drainability. The incorporation of PEC-CMNF systems to the handsheets increased the tensile index (up to 28%), Mullen index (up to 40%) and internal bonding (up to 255%). Finally, the compressive strength of the handsheets, namely SCT and CMT, increased up to 30 and 70%, respectively. These simultaneous improvement on drainability and mechanical properties makes the proposed PEC-CMNF system a promising solution for the production of packaging paper.