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1.
Int Orthop ; 2024 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-38942964

RESUMO

PURPOSE: Meniscal wrapping is a fully arthroscopic technique that involves enhanced meniscal repair with a tissue-engineered collagen matrix wrapping. This study aims to investigate the feasibility of using the meniscal wrapping technique for the treatment of chronic or complex meniscal tears. The primary objective is to assess its failure rate. The secondary objectives are to analyse complication rate, functional outcomes and overall patient satisfaction. METHODS: This retrospective case series study included patients who sustained chronic and complex tears undergoing meniscal wrapping with autologous liquid bone marrow injection. Failure rate was considered if the patient underwent partial or complete meniscectomy or knee replacement during the follow-up, while other unexpected knee reoperations were considered as complications. Clinical outcomes were evaluated through the IKDC score, Tegner Activity Score and Short Assessment of Patient Satisfaction. RESULTS: Twenty-one patients were included (15 non-acute bucket-handle tears, three non-acute horizontal tears and three non-acute complex injuries). The failure rate was 9.5% at 33 months. The rate of other unplanned reoperations was 14.3%, but none of these complications were apparently directly related to the wrapping technique. The average postoperative IKDC was 73.3/100. No statistically significant difference was encountered between preinjury and postoperative Tegner Activity Score. The mean overall patient satisfaction was 88.3/100. CONCLUSIONS: Meniscal wrapping can be safely used as an adjunctive technique to meniscal repair in such difficult-to-treat cases to preserve the meniscus. The technique achieves a low failure rate and promising results of knee function, and patient satisfaction.

2.
Biomacromolecules ; 24(8): 3872-3886, 2023 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-37523756

RESUMO

Lignin-containing cellulose nanofibrils (LCNFs) have attracted great attention because the presence of lignin brought additional merits to cellulose nanofibrils including hydrophobicity, ultraviolet (UV)-shielding capacity, and reduced water sensitivity. In the present work, LCNFs with lignin content up to 21 wt % were prepared with a high yield exceeding 70 wt %, from neat date palm waste, by a hydrothermal treatment (HTT) at 120-150 °C in the presence of 20-30 wt % maleic acid, followed by high-pressure homogenization. The chemical composition, degree of polymerization, morphology, and colloidal and rheological properties of the LCNFs were investigated to understand how the HTT in the presence of MA affected the properties of the resulting LCNFs. Nanopapers prepared from the LCNF suspensions exhibited mechanical properties lower than those from lignin-free CNF-based nanopapers, yet with decreased hydrophilicity. A mechanism explaining how the HTT in the presence of MA facilitated the disintegration of the biomass into nanoscale material was proposed. Overall, the present work demonstrated a feasible and scalable approach for the sustainable production of LCNF suspensions from neat agricultural residues, with a high yield and a high lignin content, without any need to perform a preliminary partial delignification.


Assuntos
Nanofibras , Phoeniceae , Celulose/química , Lignina/química , Suspensões , Nanofibras/química
3.
Environ Sci Technol ; 49(20): 12206-13, 2015 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-26425934

RESUMO

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.


Assuntos
Celulose/química , Nanofibras/química , Papel , Celulose/ultraestrutura , Eletricidade , Lignina/química , Nanofibras/ultraestrutura , Reciclagem , Termodinâmica
4.
Artigo em Inglês, Espanhol | MEDLINE | ID: mdl-39069070

RESUMO

BACKGROUND AND OBJECTIVES: Total hip arthroplasty (THA) is an effective surgery for treating hip osteoarthritis, but access is limited in Sub-Saharan Africa due to multiple challenges. This article describes the implementation of a THA program at Monkole Hospital in the Democratic Republic of Congo, focusing on the technical challenges and surgical complications. The objective is to share our experience to assist other professionals and organizations in similar settings. MATERIALS AND METHODS: Eight THA surgery campaigns were conducted between July 2019 and February 2023. Most patients presented with femoral head necrosis secondary to sickle cell anemia. Demographic and surgical data, technical difficulties, and complications were prospectively collected, and follow-up was conducted by a local orthopedic surgeon. RESULTS: Seventy-three surgeries were performed on 63 patients with a mean age of 34 years and an average follow-up of 24 months. Seventeen intraoperative technical incidents (23.2%) were observed. The postoperative complication rate was 9.5%, and three patients required revision surgery due to complications. CONCLUSIONS: The THA program at Monkole Hospital demonstrates that it is feasible to perform complex surgeries in developing countries and that it is a cost-effective procedure that improves patients' quality of life, provided there are adequate hospital infrastructures, team training, availability of implants, and ensured proper care and follow-up. Training local surgeons and investing in resources are key to the sustainability of the program and the improvement of surgical care.

5.
Int J Biol Macromol ; 263(Pt 2): 130319, 2024 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-38387632

RESUMO

The antioxidant and antimicrobial properties of thyme essential oil (TEO) are useful for active food packaging, but its poor aqueous solubility restricts its applications. This work involves anionic cellulose nanofibers (CNFs) as the sole stabilizing agent for TEO-in-water emulsions, with oil concentrations ranging from 10 mL/L to 300 mL/L. A double mechanism was proposed: the adsorption of CNFs at oil/water interfaces restricted coalescence to a limited extent, while thickening (rheological stabilization) was required to avoid the buoyance of large droplets (>10 µm). Thickening effects comprised both higher viscosity (over 0.1 Pa·s at 10 s-1) and yield stress (approximately 0.9 Pa). Dilute emulsions had good film-forming capabilities, whereas concentrated emulsions were suitable for paper coating. Regarding antimicrobial activity, CNF-stabilized TEO-in-water emulsions successfully inhibited the growth of both Gram-negative (E. coli, S. typhimurium) and Gram-positive bacteria (L. monocytogenes). As for the antioxidant properties, approximately 50 mg of paper or 3-5 mg of film per mL of food simulant D1 were required to attain 50 % inhibition in radical scavenging tests. Nonetheless, despite the stability and the active properties of these bio-based hydrocolloids, providing this antioxidant and antimicrobial activity was incompatible with maintaining the organoleptic properties of the foodstuff unaltered.


Assuntos
Anti-Infecciosos , Celulose Oxidada , Nanofibras , Óleos Voláteis , Óleos de Plantas , Timol , Thymus (Planta) , Emulsões , Escherichia coli , Antioxidantes/farmacologia , Celulose , Óleos Voláteis/farmacologia , Anti-Infecciosos/farmacologia
6.
Sci Total Environ ; 919: 170413, 2024 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-38309365

RESUMO

New composite materials (suitable for automotive bumpers), composed of recycled high-density polyethylene (rHDPE) and leather buffing dust waste (BF) ranging from 20 to 50 wt%, were produced and investigated for mechanical properties. Optimal mechanical performance was achieved with composites containing 30 % wt BF. The environmental performance of automotive bumper production from both virgin and recycled HDPE reinforced with 30 % wt BF (HDPE-BF, rHDPE-BF) composites was compared to that of conventional polypropylene (PP) by performing a cradle to gate life cycle assessment. A component-based approach, instead of a comprehensive LCA assessment for the entire car was adopted using various functional units (FU) such as mass (FU1), volume (FU2), and volume of raw material fulfilling a specific impact strength requirement (FU3), thus enriching the paper with methodological discussions. The rHDPE-BF system provided better environmental performance compared to the virgin PP system, when considering both mass and volume-related functional units, mainly due to the avoidance of virgin polymer production. Even with the inclusion of the use phase in FU2 and a slightly higher density (+1.7 %) of composites than PP-based bumpers, the rHDPE system still provides better environmental performance (10 % less impact). The sensitivity analysis highlighted the significance of car type and final density of the bumper on the impact results. Finally, when using FU3, due to its higher impact strength, HDPE-BF system is clearly the best environmental alternative (50 % less impact) followed by rHDPE-BF system. In all cases, rising the content of recycled materials in the bumpers increases its circularity. The paper illustrates the importance of selecting a suitable functional unit, based on a specific application (i.e., automotive bumpers), to evaluate the environmental impact of new composite materials in comparison to traditional options. Expanding the assessment to encompass multiple functions provides a more accurate portrayal of reality but also introduces greater result uncertainty.

7.
Nanomaterials (Basel) ; 13(10)2023 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-37242009

RESUMO

The international research community has made significant efforts in the production, characterization, and application of cellulose nanofibers (CNFs) in many sectors [...].

8.
Nanomaterials (Basel) ; 13(16)2023 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-37630938

RESUMO

Beeswax is a bio-sourced, renewable, and even edible material that stands as a convincing option to provide paper-based food packaging with moisture resistance. Nonetheless, the difficulty of dispersing it in water limits its applicability. This work uses oxidized, negatively charged cellulose nanofibers along with glycerol to stabilize beeswax-in-water emulsions above the melting point of the wax. The synergistic effects of nanocellulose and glycerol granted the stability of the dispersion even when it cooled down, but only if the concentration of nanofibers was high enough. This required concentration (0.6-0.9 wt%) depended on the degree of oxidation of the cellulose nanofibers. Rheological hindrance was essential to prevent the buoyancy of beeswax particles, while the presence of glycerol prevented excessive aggregation. The mixtures had yield stress and showed pseudoplastic behavior at a high enough shear rate, with their apparent viscosity being positively influenced by the surface charge density of the nanofibers. When applied to packaging paper, the nanocellulose-stabilized beeswax suspensions not only enhanced its barrier properties towards liquid water (reaching a contact angle of 96°) and water vapor (<100 g m-2 d-1), but also to grease (Kit rating: 5) and airflow (>1400 Gurley s). While falling short of polyethylene-coated paper, this overall improvement, attained using only one layer of a biobased coating suspension, should be understood as a step towards replacing synthetic waxes and plastic laminates.

9.
ACS Appl Mater Interfaces ; 15(9): 12580-12589, 2023 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-36821826

RESUMO

The use of dithizone (DTZ) for colorimetric heavy-metal detection is approximately one century old. However, its pending stability issues and the need for simple indicators justify further research. Using cellulose nanofibers, we attained DTZ-containing emulsions with high stability. These emulsions had water (at least 95 wt %) and acetic acid (1-8 mL/L) conforming the continuous phase, while dispersed droplets of diameter <1 µm contained chloroform-solvated DTZ (3 wt %). The solvation cluster was computed by molecular dynamics simulations, suggesting that chloroform slightly reduces the dihedral angle between the two sides of the thiocarbazone chain. Nanocellulose concentrations over 0.2 wt % sufficed to obtain macroscopically homogeneous mixtures with no phase separation. Furthermore, the rate of degradation of DTZ in the nanocellulose-stabilized emulsion did not differ significantly from a DTZ/chloroform solution, outperforming DTZ/toluene and DTZ/acetonitrile. Not only is the emulsion readily and immediately responsive to mercury(II), but it also decreases interferences from other ions and from natural samples. Unexpectedly, neither lead(II) nor cadmium(II) triggered a visual response at trace concentrations. The limit of detection of these emulsions is 15 µM or 3 mg/L, exceeding WHO limits for mercury(II) in drinking water, but they could be effective at raising alarms.

10.
Polymers (Basel) ; 15(12)2023 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-37376332

RESUMO

Bio-based polymers, with any of their constituents based on nonrenewable sources, can answer the demands of society and regulations regarding minimizing the environmental impact. The more similar such biocomposites are to oil-based composites, the easier the transition, especially for companies that do not like the uncertainty. A BioPE matrix, with a structure similar to that of a high-density polyethylene (HDPE), was used to obtain abaca-fiber-reinforced composites. The tensile properties of these composites are displayed and compared with commercial glass-fiber-reinforced HDPE. Since the strength of the interface between the reinforcements and the matrix is responsible for the exploitation of the strengthening abilities of the reinforcements, several micromechanical models were used to obtain an estimation of the strength of the interface and the intrinsic tensile strength of the reinforcements. Biocomposites require the use of a coupling agent to strengthen their interface, and once an 8 wt.% of such coupling agent was added to the composites, these materials returned tensile properties in line with commercial glass-fiber-reinforced HDPE composites.

11.
Polymers (Basel) ; 15(5)2023 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-36904336

RESUMO

The use of bio-based matrices together with natural fibers as reinforcement is a strategy for obtaining materials with competitive mechanical properties, costs, and environmental impacts. However, bio-based matrices, unknown by the industry, can be a market entry barrier. The use of bio-polyethylene, which has properties similar to polyethylene, can overcome that barrier. In this study, composites reinforced with abaca fibers used as reinforcement for bio-polyethylene and high density polyethylene are prepared and tensile tested. A micromechanics analysis is deployed to measure the contributions of the matrices and reinforcements and to measure the evolution of these contributions regarding AF content and matrix nature. The results show that the mechanical properties of the composites with bio-polyethylene as a matrix were slightly higher than those of the composites with polyethylene as a matrix. It was also found that the contribution of the fibers to the Young's moduli of the composites was susceptible to the percentage of reinforcement and the nature of the matrices. The results show that it is possible to obtain fully bio-based composites with mechanical properties similar to those of partially bio-based polyolefin or even some forms of glass fiber-reinforced polyolefin.

12.
Nanomaterials (Basel) ; 13(17)2023 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-37686928

RESUMO

This study aims to provide a comprehensive understanding of the key factors influencing the rheological behavior and the mechanisms of natural polyelectrolyte complexes (PECs) as flocculation agents for cellulose microfibers (CMFs) and nanofibers (CNFs). PECs were formed by combining two polyelectrolytes: xylan (Xyl) and chitosan (Ch), at different Xyl/Ch mass ratios: 60/40, 70/30, and 80/20. First, Xyl, Ch, and PEC solutions were characterized by measuring viscosity, critical concentration (c*), rheological parameter, ζ-potential, and hydrodynamic size. Then, the flocculation mechanisms of CMF and CNF suspensions with PECs under dynamic conditions were studied by measuring viscosity, while the flocculation under static conditions was examined through gel point measurements, floc average size determination, and ζ-potential analysis. The findings reveal that PEC solutions formed with a lower xylan mass ratio showed higher intrinsic viscosity, higher hydrodynamic size, higher z-potential, and a lower c*. This is due to the high molecular weight, charge, and gel-forming ability. All the analyzed solutions behave as a typical non-Newtonian shear-thinning fluid. The flocculation mechanisms under dynamic conditions showed that a very low dosage of PEC (between 2 and 6 mg PEC/g of fiber) was sufficient to produce flocculation. Under dynamic conditions, an increase in viscosity indicates flocculation at this low PEC dosage. Finally, under static conditions, maximum floc sizes were observed at the same PEC dosage where minimum gel points were reached. Higher PEC doses were required for CNF suspensions than for CMF suspensions.

13.
Int J Biol Macromol ; 253(Pt 4): 127054, 2023 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-37769759

RESUMO

Enzymatic pretreatment plays a crucial role in producing cellulose nanofibers (CNFs) before fibrillation. While previous studies have explored how treatment severity affects CNF characteristics, there remains a lack of suitable parameters to monitor real-time enzymatic processes and fully comprehend the link between enzymatic action, fibrillation, and CNF properties. This study focuses on evaluating the impact of enzyme charge (using a monocomponent endoglucanase) and treatment time on cellulose fiber morphology and reducing sugar generation. For the first time, a random forest (RF) model is developed to predict reducing sugar concentration based on easily measurable process conditions (e.g., stirrer power consumption) and fiber/suspension characteristics like fines content and apparent viscosity. Polarized light optical microscopy was found to be a suitable technique to evaluate the morphological changes that fibers experience during enzymatic pretreatment. The research also revealed that endoglucanases initially induce surface fibrillation, releasing fine fibers into the suspension, followed by fiber swelling and shortening. Furthermore, the effect of enzymatic pretreatment on resulting CNF characteristics was studied at two fibrillation intensities, indicating that a high enzyme charge and short treatment times (e.g., 90 min) are sufficient to produce CNFs with a nanofibrillation yield of 19-23 % and a cationic demand ranging from 220 to 275 µeq/g. This work introduces a well-modeled enzymatic pretreatment process, unlocking its potential and reducing uncertainties for future upscaling endeavors.


Assuntos
Celulase , Nanofibras , Celulose , Açúcares , Carboidratos , Suspensões
14.
Polymers (Basel) ; 16(1)2023 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-38201704

RESUMO

Biocomposites from poly-(lactic acid) (PLA) and jute strands were prepared, and their flexural strength was analyzed. Jute strands were submitted to a progressive delignification process and the resulting morphology, composition, and crystallinity index were evaluated. Then, PLA biocomposites comprising 30 wt% of jute strands were produced and characterized under flexural conditions. The delignification processes decreased the lignin content and progressively increased the cellulose content. All this resulted in an enhancement of the composite flexural strength. A modified rule of mixtures, and the relation between tensile and flexural properties were used to determine the intrinsic flexural strength (of the jute strands) and their correlation with their physic-chemical characteristics. Equations correlating the intrinsic flexural strength with the crystallinity index, the cellulose content, and the microfibril angle were proposed. These equations show the impact of these properties over the intrinsic properties of the fibers and can help researchers to select appropriate fibers to obtain accurate properties for the composites. Jute strands show their value as reinforcement by increasing the flexural strength of the matrix by 70% and being less expensive and more environmentally friendly than mineral reinforcements. Together with the profitability and the environmental advantages, the mechanical results suggest that these PLA biocomposites are suitable for specific products of different market sectors.

15.
Polymers (Basel) ; 15(4)2023 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-36850185

RESUMO

Composites from polypropylene (PP) reinforced with hemp strands (HS) are prepared in the current work with the aim of deepening on the influence of this reinforcement on the impact performance of these specific composites. Despite all the research conducted in this field, the effect of this natural reinforcement on the absorbed energy during crack formation and propagation is not fully tackled in previous research works. From the methodology and samples' geometry, the results concluded that the quality of the interface has a noticeable role in the impact resistance of these materials. The interface strength, fiber dispersion and fiber pullout are the main contributors to crack formation, whereas fiber pullout is the main one responsible for crack propagation. Maximum values of absorbed energy were found for PP composites comprising 20-30 wt% of HS and 8 wt% of the coupling agent for the un-notched samples, whereas maximum absorbed energy values corresponded to PP composites with 40 wt% of HS and 4 wt% of coupling agent for the notched samples. The water-absorption behavior in different humid environments is also examined. From the kinetic study, the water diffusion followed a Fickean behavior showing low-diffusion coefficients, increasing with fiber content. This systematic investigation represents a contribution to the analysis of the potential of reinforcing conventional polymers with natural materials, as a strategy towards more sustainable development.

16.
Sci Total Environ ; 874: 162482, 2023 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-36858230

RESUMO

Cellulose micro- and nanofibers (CNFs) are commonly regarded as "greener" than petro-based materials. The high energy input that their production still demands, along with the use of chemicals or heat in some pretreatments, asks for a critical view. This paper attempts a life cycle assessment of CNFs produced from bleached hardwood kraft pulp via three different pre-treatments before mechanical homogenization. First, a fully mechanical route, based on a Valley beating pre-treatment. Second, an enzymatic route, based on endoglucanases and requiring certain temperature (~50 °C). Third, a TEMPO-mediated oxidation route, considering not only the impact of the chemical treatment itself but also the production of TEMPO from ammonia and acetone. The main output of the study is that both, mechanical and TEMPO-mediated oxidation routes, present lower impacts than the enzymatic pre-treatment. Although the mechanical route presents slightly milder contributions to climate change, acidification, eutrophication, and other indicators, saying that TEMPO-mediated oxidation is environmentally unfeasible should be put under question. After all, and despite being disregarded in most assessment publications up to date, it is the only well-known way to selectively oxidize primary hydroxyl groups and thus producing kinds of CNFs that are unthinkable by other ways.


Assuntos
Celulose , Nanofibras , Animais , Oxirredução , Tecnologia
17.
Polymers (Basel) ; 15(13)2023 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-37447605

RESUMO

Composite materials containing natural reinforcement fibers, generally called biocomposites, have attracted the interest of both researchers and manufacturers, but the most environmentally advantageous combinations include a bio-based matrix, as well. With this in mind, a poly(lactic acid) (PLA) matrix was reinforced with natural fibers from hemp, both untreated strands (UHSs) and soda-bleached fibers (SBHFs). The preparation of the subsequent fully bio-sourced, discontinuously reinforced composites involved kinetic mixing, intensive single-screw extrusion, milling, and injection molding. Up to a fiber content of 30 wt%, the tensile modulus increased linearly with the volume fraction of the dispersed phase. Differences between SBHFs (up to 7.6 Gpa) and UHSs (up to 6.9 Gpa) were hardly significant (p = 0.1), but SBHF-reinforced composites displayed higher strain at failure. In any case, for the same fiber load (30 wt%), the Young's modulus of PLA/hemp biocomposites was greater than that of glass fiber (GF)-reinforced polypropylene (5.7 GPa), albeit lower than that of PLA/GF (9.8 GPa). Considering all the measurements, the contribution of each phase was analyzed by applying the Hirsch model and the Tsai-Pagano model. As a concluding remark, although the intrinsic tensile modulus of SBHFs was lower than that of GF, the efficiency of those natural fibers as reinforcement (according to the rule of mixtures) was found to be higher.

18.
Nanomaterials (Basel) ; 13(18)2023 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-37764564

RESUMO

The cost-effective implementation of nanofibrillated cellulose (CNF) at industrial scale requires optimizing the quality of the nanofibers according to their final application. Therefore, a portfolio of CNFs with different qualities is necessary, as well as further knowledge about how to obtain each of the main qualities. This paper presents the influence of various production techniques on the morphological characteristics and properties of CNFs produced from a mixture of recycled fibers. Five different pretreatments have been investigated: a mechanical pretreatment (PFI refining), two enzymatic hydrolysis strategies, and TEMPO-mediated oxidation under two different NaClO concentrations. For each pretreatment, five high-pressure homogenization (HPH) conditions have been considered. Our results show that the pretreatment determines the yield and the potential of HPH to enhance fibrillation and, therefore, the final CNF properties. These results enable one to select the most effective production method with the highest yield of produced CNFs from recovered paper for the desired CNF quality in diverse applications.

19.
Nanomaterials (Basel) ; 12(23)2022 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-36500912

RESUMO

Measurements of nanocellulose size usually demand very high-resolution techniques and tedious image processing, mainly in what pertains to the length of nanofibers. Aiming to ease the process, this work assesses a relatively simple method to estimate the dimensions of nanocellulose particles with an aspect ratio greater than 1. Nanocellulose suspensions, both as nanofibers and as nanocrystals, are subjected to dynamic light scattering (DLS) and to field-emission scanning electron microscopy (FE-SEM). The former provides the hydrodynamic diameter, as long as the scatter angle and the consistency are adequate. Assays with different angles and concentrations compel us to recommend forward scattering (12.8°) and concentrations around 0.05-0.10 wt %. Then, FE-SEM with magnifications of ×5000-×20,000 generally suffices to obtain an acceptable approximation for the actual diameter, at least for bundles. Finally, length can be estimated by a simple geometric relationship. Regardless of whether they are collected from FE-SEM or DLS, size distributions are generally skewed to lower diameters. Width distributions from FE-SEM, in particular, are well fitted to log-normal functions. Overall, while this method is not valid for the thinnest fibrils or for single, small nanocrystals, it can be useful in lieu of very high-resolution techniques.

20.
Nanomaterials (Basel) ; 13(1)2022 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-36616036

RESUMO

Lignin-containing cellulose nanofibrils (LCNFs) have emerged as a new class of nanocelluloses where the presence of residual lignin is expected to impart additional attributes such as hydrophobicity or UV-absorption. In the present work, LCNFs with a lignin content between 7 and 15 wt% were prepared via a TEMPO-mediated oxidation as chemical pretreatment followed by high-pressure homogenization. The impact of the carboxyl content (CC) on the properties of the resulting LCNF gel, in terms of lignin content, colloidal properties, morphology, crystallinity, and thermal stability, were investigated. It was found that lignin content was significantly decreased at increasing CC. In addition, CC had a positive effect on colloidal stability and water contact angle, as well as resulting in smaller fibrils. This lower size, together with the lower lignin content, resulted in a slightly lower thermal stability. The reinforcing potential of the LCNFs when incorporated into a ductile polymer matrix was also explored by preparing nanocomposite films with different LCNF contents that were mechanically tested under linear and non-linear regimes by dynamic mechanical analysis (DMA) and tensile tests. For comparison purposes, the reinforcing effect of the LCNFs with lignin-free CNFs was also reported based on literature data. It was found that lignin hinders the network-forming capacity of LCNFs, as literature data shows a higher reinforcing potential of lignin-free CNFs. Nonetheless, the tensile strength of the acrylic matrix was enhanced by 10-fold at 10 wt% of LCNF content.

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