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Cellulose nanomaterials from plant fibre provide various potential applications (i.e., biomedical, automotive, packaging, etc.). The biomedical application of nanocellulose isolated from plant fibre, which is a carbohydrate-based source, is very viable in the 21st century. The essential characteristics of plant fibre-based nanocellulose, which include its molecular, tensile and mechanical properties, as well as its biodegradability potential, have been widely explored for functional materials in the preparation of aerogel. Plant cellulose nano fibre (CNF)-based aerogels are novel functional materials that have attracted remarkable interest. In recent years, CNF aerogel has been extensively used in the biomedical field due to its biocompatibility, renewability and biodegradability. The effective surface area of CNFs influences broad applications in biological and medical studies such as sustainable antibiotic delivery for wound healing, the preparation of scaffolds for tissue cultures, the development of drug delivery systems, biosensing and an antimicrobial film for wound healing. Many researchers have a growing interest in using CNF-based aerogels in the mentioned applications. The application of cellulose-based materials is widely reported in the literature. However, only a few studies discuss the potential of cellulose nanofibre aerogel in detail. The potential applications of CNF aerogel include composites, organic–inorganic hybrids, gels, foams, aerogels/xerogels, coatings and nano-paper, bioactive and wound dressing materials and bioconversion. The potential applications of CNF have rarely been a subject of extensive review. Thus, extensive studies to develop materials with cheaper and better properties, high prospects and effectiveness for many applications are the focus of the present work. The present review focuses on the evolution of aerogels via characterisation studies on the isolation of CNF-based aerogels. The study concludes with a description of the potential and challenges of developing sustainable materials for biomedical applications.

Hydrophilic behaviour of carrageenan macroalgae biopolymer, due to hydroxyl groups, has limited its applications, especially for packaging. In this study, macroalgae were reinforced with cellulose nanofibrils (CNFs) isolated from kenaf bast fibres. The macroalgae CNF film was after that treated with silane for hydrophobicity enhancement. The wettability and functional properties of unmodified macroalgae CNF films were compared with silane-modified macroalgae CNF films. Characterisation of the unmodified and modified biopolymers films was investigated. The atomic force microscope (AFM), SEM morphology, tensile properties, water contact angle, and thermal behaviour of the biofilms showed that the incorporation of Kenaf bast CNF remarkably increased the strength, moisture resistance, and thermal stability of the macroalgae biopolymer films. Moreover, the films’ modification using a silane coupling agent further enhanced the strength and thermal stability of the films apart from improved water-resistance of the biopolymer films compared to unmodified films. The morphology and AFM showed good interfacial interaction of the components of the biopolymer films. The modified biopolymer films exhibited significantly improved hydrophobic properties compared to the unmodified films due to the enhanced dispersion resulting from the silane treatment. The improved biopolymer films can potentially be utilised as packaging materials.

The fabrication of superadsorbent for dye adsorption is a hot research area at present. However, the development of low-cost and highly efficient superadsorbents against toxic textile dyes is still a big challenge. Here, we fabricated hydrophobic cellulose nanofiber aerogels from cellulose nanofibers through an eco-friendly silanization reaction in liquid phase, which is an extremely efficient, rapid, cheap, and environmentally friendly procedure. Moreover, the demonstrated eco-friendly silanization technique is easy to commercialize at the industrial level. Most of the works that have reported on the hydrophobic cellulose nanofiber aerogels explored their use for the elimination of oil from water. The key novelty of the present work is that the demonstrated hydrophobic cellulose nanofibers aerogels could serve as superadsorbents against toxic textile dyes such as crystal violet dye from water and insulating materials for building applications. Here, we make use of the possible hydrophobic interactions between silane-modified cellulose nanofiber aerogel and crystal violet dye for the removal of the crystal violet dye from water. With a 10 mg/L of crystal violet (CV) aqueous solution, the silane-modified cellulose nanofiber aerogel showed a high adsorption capacity value of 150 mg/g of the aerogel. The reason for this adsorption value was due to the short-range hydrophobic interaction between the silane-modified cellulose nanofiber aerogel and the hydrophobic domains in crystal violet dye molecules. Additionally, the fabricated silane-modified cellulose nanofiber hydrophobic aerogels exhibited a lower thermal conductivity value of 0.037 W·m−1 K−1, which was comparable to and lower than the commercial insulators such as mineral wools (0.040 W·m−1 K−1) and polystyrene foams (0.035 W·m−1 K−1). We firmly believe that the demonstrated silane-modified cellulose nanofiber aerogel could yield an eco-friendly adsorbent that is agreeable to adsorbing toxic crystal violet dyes from water as well as active building thermal insulators.

The research aims to ensure the structural stability of nanocellulose-based aerogels in humid environments while imparting flame-retardant properties, alongside their inherent thermal and acoustic insulation capabilities. Building on the established flame retardancy of citric acid-based nanocellulose, our study marks a significant advancement by employing a simple and efficient methodological approach. We introduce a simple and facile technique for crosslinking CNF aerogel using a single crosslinking agent for extraction and modification. The cross-linked CNF aerogel shows a 91% porosity with a low density (0.15 g/cm 3 ) which is also positively influenced by the morphological studies. In addition, the inclusion of citric acid into CNF improves water stability, mechanical performance (7.8 N/mm 2 for pure CNF and 8.9 N/mm 2 for cross-linked CNF aerogels), and thermal stability, while reducing the residue of the cross-linked material to 1.6% from 6.4% of pure CNF aerogel. The cross-linking of aerogel by citric acid could enhance fire resistance by lowering the production of hazardous and combustible gases. Furthermore, the cross-linked CNF aerogel was evaluated with a thickness of 40 mm, as the pure CNF aerogel demonstrated optimal sound absorption behavior at this thickness according to simulations conducted using COMSOL Multiphysics software. This work contributes to the broader understanding of how nanocellulose can be engineered for structural building applications, paving the way for further innovations in environmentally friendly aerogel technologies. Graphical Abstract

Biodegradable aerogels possessing flexibility and high strength are appealing for applications in construction, acoustic and thermal insulation. However, their susceptibility to flammability presents a significant challenge. Enhancing the flame retardancy of these aerogels has been a prominent focus of research, with the widespread use of inorganic fillers and layered materials for this purpose. In the current study, our objective is to fabricate cellulose nanofiber aerogels characterized by low density, exceptional flame retardancy, high mechanical properties, and thermal insulation. This is achieved through the cross-linking of melamine and formaldehyde under aqueous conditions using an eco-friendly freeze-drying process, followed by post-curing. The resulting aerogels demonstrate flexibility, effective sound absorption within the mid-frequency range, and outstanding flame retardancy (Limiting Oxygen Index ∼33%) with a non-flammable behaviour. The thermal conductivity of the fabricated melamine formaldehyde-modified cellulose nanofiber (MF-CNF) aerogels was 0.064 ± 0.014 W/m.K. MF-CNF aerogels exhibited a Time to Ignition (TTI) of 489 s, whereas pristine CNF aerogels only have 3 s. This improvement was attributed to the concurrent reductions in both the Peak Heat Release Rate (PHRR) and Fire Growth Rate (FIGRA) of MF-CNF aerogels. The straightforward melamine formaldehyde modification of CNF aerogels enhances their mechanical strength as well as fire resistance. These sustainable multifunctional aerogels hold great potential for a variety of real-life applications in the realm of buildings and its structures for ensuring fire safety and sound insulation.

This study aimed to compare the performance of fabricated microbially induced precipitated calcium carbonate– (MB–CaCO3) based red seaweed (Kappaphycus alvarezii) bio-polymer film and commercial calcium carbonate– (C–CaCO3) based red seaweed bio-film with the conventional biodegradable mulch film. To the best of our knowledge, there has been limited research on the application of commercial CaCO3 (C–CaCO3) and microbially induced CaCO3 (MB–CaCO3) as fillers for the preparation of films from seaweed bio-polymer and comparison with biodegradable commercial plasticulture packaging. The results revealed that the mechanical, contact angle, and biodegradability properties of the polymer composite films incorporated with C–CaCO3 and MB–CaCO3 fillers were comparable or even superior than the conventional biodegradable mulch film. The seaweed polymer film incorporated with MB–CaCO3 showed the highest contact angle of 100.94°, whereas conventional biodegradable mulch film showed a contact angle of 90.25°. The enhanced contact angle of MB–CaCO3 resulted in high barrier properties, which is highly desired in the current scenario for plasticulture packaging application. The water vapor permeability of MB–CaCO3 based seaweed films was low (2.05 ± 1.06 g·m/m2·s·Pa) when compared to conventional mulch film (2.68 ± 0.35 g·m/m2·s·Pa), which makes the fabricated film an ideal candidate for plasticulture application. The highest tensile strength (TS) was achieved by seaweed-based film filled with commercial CaCO3 (84.92% higher than conventional mulch film). SEM images of the fractured surfaces of the fabricated films revealed the strong interaction between seaweed and fillers. Furthermore, composite films incorporated with MB–CaCO3 promote brighter film, better water barrier, hydrophobicity, and biodegradability compared to C–CaCO3 based seaweed polymer film and conventional mulch film. From this demonstrated work, it can be concluded that the fabricated MB–CaCO3 based seaweed biopolymer film will be a promising candidate for plasticulture and agricultural application.

Natural fiber composites have been widely used for various applications such as automotive components, aircraft components and sports equipment. Among the natural fibers Typha spp have gained considerable attention to replace synthetic fibers due to their unique nature. The untreated and alkali-treated fibers treated in different durations were dried under the sun for 4 h prior to the fabrication of Typha fiber reinforced epoxy composites. The chemical structure and crystallinity index of composites were examined via FT-IR and XRD respectively. The tensile, flexural and impact tests were conducted to investigate the effect of the alkali treated Typha fibers on the epoxy composite. From the microscopy analysis, it was observed that the fracture mechanism of the composite was due to the fiber and matrix debonding, fiber pull out from the matrix, and fiber damage. The tensile, flexural and impact strength of the Typha fiber reinforced epoxy composite were increased after 5% alkaline immersion compared to untreated Typha fiber composite. From these results, it can be concluded that the alkali treatment on Typha fiber could improve the interfacial compatibility between epoxy resin and Typha fiber, which resulted in the better mechanical properties and made the composite more hydrophobic. So far there is no comprehensive report about Typha fiber reinforcing epoxy composite, investigating the effect of the alkali treatment duration on the interfacial compatibility, and their effect on chemical and mechanical of Typha fiber reinforced composite, which plays a vital role to provide the overall mechanical performance to the composite.

Oil palm ash (OPA) is an agro-industry waste and it has disposable problems. In the present study, an effort was made for value addition to OPA by incorporating it as a micro-filler in different concentration (0, 10, 20, 30, 40, and 50%) and sizes (100, 200, and 300 mesh size particles) in the epoxy matrix. Prepared micro OPA was having a crystallinity index of 65.4%, high inorganic elements, and smooth surface morphology. Fabricated composites had higher void content as compared to neat epoxy matrix. Mechanical properties of fabricated composites had a maximum value at 30% loading of 300 mesh-size filler due to its low void content and size as compared to filler of 100 and 200 mesh size. Further increase in the concentration of OPA filler after 30 wt% of loading leads to the agglomeration of OPA microparticles and thereby resulted in the reduction of mechanical characteristics such as tensile strength, tensile modulus, flexural strength and flexural modulus of the composites. However, elongation at break decreased with increase in filler content at all percentage. Thermal stability and char residue percentage of composite increased with the concentration of filler at all percentage. Surface morphology of composite showed that OPA incorporation lead towards its roughness and cracks were originated from the site of OPA embedded in the epoxy matrix. The 300 mesh- size particles were having the best effect on composite as compared to 100 and 200 mesh-size filler.

This study is aimed to fabricate and characterize the seaweed- biodegradable films incorporated with varying concentrations of microcrystalline cellulose (MCC) which was extracted from two bamboo sources: Schizostachyum brachycladum (BLMCC) and Gigantochloa scortechinii (BSMCC). Pure biodegradable seaweed film was directly fabricated from red seaweed (Kappaphycus alvarezii). In this demonstrated work, commercial MCC (CMCC), BLMCC and BSMCC were used to reinforce the pure seaweed bio-degradable film at different loading concentrations (0, 1, 3, 5, 7, 10 and 15%) based on the dried-weight of seaweed, for packaging applications. There was substantial improvement in the tensile strength and contact angle values while reduction in the water vapor permeability and elongation at break values with the incorporation of the CMCC, BLMCC and BSMCC into the seaweed pure film matrix, which is highly desirable for the packaging material in the current scenario. The morphology of the fabricated films confirmed that there was good dispersion of the 7% of CMCC, 5% of BLMCC and 3% of BSMCC in the pure seaweed films, which resulted in the enhanced mechanical properties. So far, this is the first report on the microcrystalline cellulose based seaweed films with excellent mechanical properties, which makes them suitable for packaging application. The demonstrated work proved that both BSMCC and BLMCC based seaweed composite films have the huge potential to be used as biodegradable packaging material for wide range of applications.Graphical Abstract

The conventional isolation of cellulose nanofibers (CNFs) process involves high energy input which leads to compromising the pulp fiber’s physical and chemical properties, in addition to the issue of elemental chlorine-based bleaching, which is associated with serious environmental issues. This study investigates the characteristic functional properties of CNFs extracted via total chlorine-free (TCF) bleached kenaf fiber followed by an eco-friendly supercritical carbon dioxide (SC-CO2) treatment process. The Fourier transmission infra-red FTIR spectra result gave remarkable effective delignification of the kenaf fiber as the treatment progressed. TEM images showed that the extracted CNFs have a diameter in the range of 10–15 nm and length of up to several micrometers, and thereby proved that the supercritical carbon dioxide pretreatment followed by mild acid hydrolysis is an efficient technique to extract CNFs from the plant biomass. XRD analysis revealed that crystallinity of the fiber was enhanced after each treatment and the obtained crystallinity index of the raw fiber, alkali treated fiber, bleached fiber, and cellulose nanofiber were 33.2%, 54.6%, 88.4%, and 92.8% respectively. SEM images showed that amorphous portions like hemicellulose and lignin were removed completely after the alkali and bleaching treatment, respectively. Moreover, we fabricated a series of cellulose nanopapers using the extracted CNFs suspension via a simple vacuum filtration technique. The fabricated cellulose nanopaper exhibited a good tensile strength of 75.7 MPa at 2.45% strain.