Nanocelluloses: a new family of nature-based materials

Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.     

Cellulose nanomaterial reinforced polymer nanocomposites

Several forms of cellulose nanomaterials, notably cellulose nanocrystals and cellulose nanofibrils, exhibit attractive properties and are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, basis for low-density foams, additive in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic, and medical products. This entry focuses on cellulose materials as filler in polymer nanocomposites. The ensuing mechanical properties obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials that has not yet been properly resolved and remains a challenge.     

Nanofibrillated cellulose: surface modification and potential applications

Interest in nanofibrillated cellulose has been increasing exponentially because of its relatively ease of preparation in high yield, high specific surface area, high strength and stiffness, low weight and biodegradability etc. This bio-based nanomaterial has been used mainly in nanocomposites due to its outstanding reinforcing potential. Solvent casting, melt mixing, in situ polymerization and electrospinning are important techniques for the fabrication of nanofibrillated cellulose-based nanocomposites. Due to hydrophilic character along with inherent tendency to form strong network held through hydrogen-bonding, nanofibrillated cellulose cannot uniformly be dispersed in most non-polar polymer matrices. Therefore, surface modification based on polymer grafting, coupling agents, acetylation and cationic modification was used in order to improve compatibility and homogeneous dispersion within polymer matrices. Nanofibrillated cellulose opens the way towards intense and promising research with expanding area of potential applications, including nanocomposite materials, paper and paperboard additive, biomedical applications and as adsorbent.     

Elastomer Nanocomposite; Properties

Polymer nanocomposites represent a class of materials that have assumed great importance in recent years and are the focus of extensive research. Unlike plastomer nanocomposites, the elastomer nanocomposites are in the stage of infancy in respect to their applications.

In general, in polymer composites, the matrix and the filler are bonded to each other by weak intermolecular forces and covalent bonding are rarely involved. If the filler could be dispersed in the polymer matrix at the nanometre level and is able to interact with the matrix by chemical bonding, nanocomposites with significant properties improvement are obtained. These improvements can include mechanical properties (module, strength, etc.), thermal resistance, decrease in gas permeability (barrier), flammability, etc.

This paper is a review of the property improvements of different elastomers using nanofillers like silicates, carbon black, metallic powders, cellulose crystals, mixture of nanofillers, etc, with the intention of obtaining elastomer nanocomposites.     

Cellulose Nanocomposites

Cellulose is a linear polysaccharide and one of the world's most abundant biopolymers. It is one of the renewable biopolymers being studied to reduce the dependence on non-renewable mineral oil based products. Cellulose can be used in different kinds of composites, including the recent nanocomposites.The production of nanoscale cellulose fibers and their use in polymer composites gained increasing attention due to their interesting properties and potential applications. This review paper is trying to cover studies done to use various forms of cellulose as reinforcement for different polymers, as matrix, as reinforcement and matrix for the same nanocomposite and as a component in polyblend nanocomposites beside other polymers.     

The Microwave‐Assisted Ionic‐Liquid Method: A Promising Methodology in Nanomaterials

In recent years, the microwave‐assisted ionic‐liquid method has been accepted as a promising methodology for the preparation of nanomaterials and cellulose‐based nanocomposites. Applications of this method in the preparation of cellulose‐based nanocomposites comply with the major principles of green chemistry, that is, they use an environmentally friendly method in environmentally preferable solvents to make use of renewable materials. This minireview focuses on the recent development of the synthesis of nanomaterials and cellulose‐based nanocomposites by means of the microwave‐assisted ionic‐liquid method. We first discuss the preparation of nanomaterials including noble metals, metal oxides, complex metal oxides, metal sulfides, and other nanomaterials by means of this method. Then we provide an overview of the synthesis of cellulose‐based nanocomposites by using this method. The emphasis is on the synthesis, microstructure, and properties of nanostructured materials obtained through this methodology. Our recent research on nanomaterials and cellulose‐based nanocomposites by this rapid method is summarized. In addition, the formation mechanisms involved in the microwave‐assisted ionic‐liquid synthesis of nanostructured materials are discussed briefly. Finally, the future perspectives of this methodology in the synthesis of nanostructured materials are proposed.     

Cellulose nanocrystals from lignocellulosic feedstock: a review of production technology and surface chemistry modification

Fossil fuel substitutes are being developed to combat the ecological impact and rapid exhaustion of petroleum-based products. Being the most abundant polymer on Earth, cellulose-based products are renewable and sustainable. Cellulose nanocrystals (CNCs) are derived from cellulosic-based materials, have good physicochemical properties, and can be used to produce numerous products. CNC synthesis and their applications have been extensively studied; however, they remain limited to laboratory-scale as several challenges hinder its commercial-scale production. Herein, the suitability of nanocrystalline isolation methods, including chemical, enzymatic, ionic liquids, and deep eutectic solvents, for mass production is evaluated. Poor re-dispersion of CNCs is a major challenge that hinders its utilization in many applications. Hence, surface chemistry modification of CNCs have also been reviewed. It has been concluded that the CNC isolation method and surface modification technique significantly impacts its cost, morphology, and physicochemical properties. This review paper presents the challenges often faced in the conversion of bench-scale studies into commercial production of nanocrystalline cellulose. Hence, this paper gives all the necessary information on the important aspects of raw material selection, nanocellulose isolation process selection, and suitable surface modification method together in a single review article. Readers will be able to identify the possible research gaps for future research studies.

     

High‐Strength and Tough Crystalline Polysaccharide‐Based Materials†

Due to the increasing public awareness of environmental issues and the shortage of resources, the focus on products made from renewable sources to fulfill the sustainable development of modern society has intensified. Natural crystalline polysaccharides have been studied for a long time and are among the most abundant renewable resources in the world. High‐performance materials have been fabricated using crystalline polysaccharides such as cellulose and chitin. For practical applications, the mechanical performance of polysaccharide‐based materials is critical. In this review, we focus on the methods for constructing high‐strength and high‐toughness crystalline polysaccharide‐based materials. This review elucidates the three approaches of aggregate structure regulation, bioinspiration and mineralization, and the use of crystalline polysaccharides as matrices for reinforcing the mechanical properties of nanocomposites.     

Crosslinked fibrous composites based on cellulose nanofibers and collagen with in situ pH induced fibrillation

Collagen and cellulose nanofiber based composites were prepared by solution casting followed by pH induced in situ partial fibrillation of collagen phase and crosslinking of collagen phase using gluteraldehyde. Microscopy studies on the materials confirmed the presence of fibrous collagen and cellulose nanofibers embedded in the collagen matrix. The cellulose nanofiber addition as well as collagen crosslinking showed significant positive impact on the nanocomposite’s mechanical behaviour. The synergistic performance of the nanocomposites indicated stabilization and reinforcement through strong physical entanglement between collagen and cellulose fibres as well as chemical interaction between collagen matrix and collagen fibrils. The mechanical performance and stability in moist conditions showed the potential of these materials as implantable scaffolds in biomedical applications. The collagen-cellulose ratio, crosslinking agent and crosslinking level of collagen may be further optimised to tailor the mechanical properties and cytocompatibility of these composites for specific applications such as artificial ligament or tendon.     

Liquid crystal templating of nanomaterials with nature's toolbox

Naturally occurring biomolecules are sustainable and green precursors for the development of new materials. Within this family of natural materials, cellulose nanocrystals (CNCs) have emerged as one of the most promising materials because of their outstanding physico-chemical properties and the possibility to produce them in large quantities. One key trait of CNCs is their ability to self-assemble into a chiral nematic liquid crystalline phase. In this review, we discuss how templating can be used to transfer the three-dimensional structure of liquid crystalline CNC phases onto solid materials. This is followed by examples that illustrate the fascinating properties and potential applications that arise from the resulting nanostructured materials such as sensing and catalysis. We then summarize efforts to use the liquid crystalline phase of a selection of other biopolymers for templating. While nanocrystalline chitin, having very similar properties to CNCs, has been successfully employed to make a variety of new materials, efforts to template liquid crystal phases of other biomolecules have been met with limited success. However, we discuss virus nanoparticles and collagen as examples to highlight further possibilities for materials research.     

Nanocrystalline cellulose acetate (NCCA)/graphene oxide (GO) nanocomposites with enhanced mechanical properties and barrier against water vapor

Highly flexible nanocomposite films of nanocrystalline cellulose acetate (NCCA) and graphene oxide (GO) were synthesized by combining NCCA and GO sheets in a well-controlled manner. By adjusting the GO content, various NCCA/GO nanocomposites with 0.3–1 wt% GO were obtained. Films of these nanocomposites were prepared using the solvent casting method. Microscopic and X-ray diffraction (XRD) measurements demonstrated that the GO nanosheets were uniformly dispersed in the NCCA matrix. Mechanical properties of the composite films were also studied. The best GO composition of the samples tested was 0.8 wt%, giving tensile strength of 157.49 MPa, which represents a 61.92 % enhancement compared with NCCA. On the other hand, the composite films showed improved barrier properties against water vapor. This simple process for preparation of NCCA/GO films is attractive for potential development of high-performance films for electrical and electrochemical applications.     

Self‐Healing Polyester Urethane Supramolecular Elastomers Reinforced with Cellulose Nanocrystals for Biomedical Applications

Stretchable self‐healing urethane‐based biomaterials have always been crucial for biomedical applications; however, the strength is the main constraint of utilization of these healable materials. Here, a series of novel, healable, elastomeric, supramolecular polyester urethane nanocomposites of poly(1,8‐octanediol citrate) and hexamethylene diisocyanate reinforced with cellulose nanocrystals (CNCs) are introduced. Nanocomposites with various amounts of CNCs from 10 to 50 wt% are prepared using solvent casting technique followed by the evaluation of their microstructural features, mechanical properties, healability, and biocompatibility. The synthesized nanocomposites indicate significantly higher tensile modulus (approximately 36–500‐fold) in comparison to the supramolecular polymer alone. Upon exposure to heat, the materials can reheal, but nevertheless when the amount of CNC is greater than 10 wt%, the self‐healing ability of nanocomposites is deteriorated. These materials are capable of rebonding ruptured parts and fully restoring their mechanical properties. In vitro cytotoxicity test of the nanocomposites using human dermal fibroblasts confirms their good cytocompatibility. The optimized structure, self‐healing attributes, and noncytotoxicity make these nanocomposites highly promising for tissue engineering and other biomedical applications.     

Polymer Nanocomposites in Sensor Applications: A Review on Present Trends and Future Scope

Polymers are crucial constituents of modern electronic devices. They can be used in their pristine, composite or nanocomposite forms for several domestic and industrial applications with innumerable unique possibilities. Polymer nanocomposites have gained wide theoretical interest and numerous practical applications in diverse fields of science and technology as they bestow the materials not only with virtuous processability but also with exceptional functionalities. It is evidenced that the electrical conductance of polymer nanocomposite is governed by the conductive filler networks within the polymer matrix. Hence, insignificant variation in the conductive networks can result in noteworthy variations in the output electric signal of polymer nanocomposite. Exploiting this stimuli-responsive performance of conductive networks to the physical parameters, polymer nanocomposites can be harnessed to fabricate novel sensitive sensors to detect vital physical parameters viz.strain/stress, pressure, temperature, solvent or vapor. Technical and phenomenological studies on polymer nanocomposites are still enduring.Advanced explanations are being sought but the mechanisms governing the formation of several polymer nanocomposites are still topics of debate in the material science community. Their in-depth investigation requires copious scientific work. This review analytically sketches the synthesis, microstructures, physiochemical properties and the underlying mechanisms for stimuli-responsiveness to the physical parameters of the polymer nanocomposites as well as their applications in various sensitive sensors and detectors. Thus, it became evocative for this review to focus on their processing methodologies, physiochemical physiognomies, classification and probable potentials of polymer nanocomposites.This review primarily presents the current literature survey on polymer composites and the gap areas in the study encourages the objective of the present review article. Finally, the status, perspectives and the advantages of specific polymer nanocomposites at present are summarized. The attention of this review is drawn to the present trends, challenges and future scope in this field of study. Finally, the vital concern and future challenge in utilizing the stimulus responsive behavior of polymer nanocomposites to design versatile sensors for real time applications are elaborately discussed.     

Chitosan-based membranes preparation and applications: Challenges and opportunities

Chitosan is an abundant natural biopolymer which finds a variety of applications due to its functionalization extending to pharmacology, controlled drug delivery, healing materials, biomedical engineering, food industry, agriculture, catalysis, biosorbents, wastewater treatment, etc. Chitosan can be transformed to distinct derivatives and composites and be modified and grafted for specific use. Many products like flakes, fine powders, beads, membranes, sponges, fibers, and gels can be formed from chitosan. Degradable membranes made of chitosan in conjunction with other materials have increased their scope and include adsorptive membranes for heavy metal and dyes, biomedical applications of chitosan electrospun nanofibers, metal complexation, polymer and modified chitosan-based nanocomposites, cellulose and chitosan composites in wastewater treatment, fuel cells and catalysis. The review has focused on a number of issues related to the said areas. Application of these composite membranes with real industrial effluents should be done with reference to the commercial adsorbents and then their application for removal of aromatics, oils, surfactants, etc. will become practical. The review covers existing gaps and gives future scope for research and innovation.     

Electroconductive Green Metal-polyaniline Nanocomposites: Synthesis and Application in Sensors

Polyaniline (PANI) is one of the most extensively used conducting polymer due to its fascinating properties including conducting, thermal, optical, magnetic and electrochemical properties, simple synthesis procedure and low cost of monomer. It has attracted major attention in a variety of applications including electrochemical sensors, catalysts, supercapacitors and biosensors. However, its limitations such as insolubility in common solvents, low process-ability and poor mechanical properties have led to the development of new approaches to improve it properties. Metal nanoparticles (MNPs) such as silver, gold, copper and palladium have been combined with PANI to improve on its properties which has led to a new class of materials known as metal/PANI nanocomposites. These hybrid nanocomposites incorporate advantages of both MNPs and polymers which effectively improves the properties of the individual materials. Various synthesis techniques including in situ polymerization, ɤ-radiolysis, electrodeposition, complexation, vacuum deposition and interfacial polymerization have been used in the formation of metal/PANI nanocomposites. These nanocomposites have been used in various sensor and biosensor applications due to their excellent conductivity, ease of synthesis, excellent redox potentials, chemical and thermal stability. This review highlights the various metal/PANI nanocomposites, their various synthesis techniques and their application in sensors and biosensors. The importance of these nanocomposites in sensing and signaling various toxic heavy metals such as mercury, lead and silver and toxic gases such as hydrogen sulphide, ammonia and chloroform has been discussed. In addition the review covers the applications of metal/PANI nanocomposites in biosensor systems for the detection of glucose, DNA, protein, cholesterol, drugs and hydrogen peroxide.     

Antifungal cellulose by capsaicin grafting

Cellulose is one of the most abundant materials in nature. Besides its biological function, cellulose can be extracted from the cell wall and used in several industrial applications. Thus, it can be used in papers, pharmaceuticals, food, cosmetics and innovative materials such as nanocomposites, packaging, coatings and dispersion technology. With the aim of extending cellulose applications and producing so-called “smart” materials, new functionality can be introduced by physical or chemical modifications. Taking into account that capsaicin, the active component of chili peppers, is an excellent antifungal agent, a potential new material could be obtained by chemical reaction between this active compound and cellulose. In this work, capsaicin grafting onto cellulose using polycarboxylic acid as linking agent is proposed. The reaction occurrence was corroborated by Fourier transform infrared spectroscopy and UV–Vis spectrophotometry in reflectance mode. Modified cellulose with <2 wt% of capsaicin shows a strong change in antifungal activity with respect to the unmodified one. This activity was evaluated by the fungal growth inhibition test with two different fungi, Trametes versicolor and Gloeophyllum trabeum. Modified cellulose samples showed a high percentage of fungal growth inhibition, demonstrating the success of the cellulose modification and high antifungal power of the grafting molecule.     

Electrochemical biosensors based on Ti3C2Tx MXene: future perspectives for on-site analysis

MXenes are recently developed two-dimensional layered materials composed of early transition metal carbides and/or nitrides that provide unique characteristics for biosensor applications. This review presents the recent progress made on the usage and applications of MXenes in the field of electrochemical biosensors, including microfluidic biosensors and wearable microfluidic biosensors, and highlights the challenges with possible solutions and future needs. The multilayered configuration and high conductivity make these materials as an immobilization matrix for the biomolecule immobilization with activity retention and to be explored in the fabrication of electrochemical sensors, respectively. First, how the MXene nanocomposite as an electrode modifier affects the sensing performance of the electrochemical biosensors based on enzymes, aptamer/DNA, and immunoassays is well described. Second, recent developments in MXene nanocomposites as wearable biosensing platforms for the biomolecule detection are highlighted. This review pointed out the future concerns and directions for the use of MXene nanocomposites to fabricate advanced electrochemical biosensors with high sensitivity and selectivity. Specifically, possibilities for developing microfluidic electrochemical sensors and wearable electrochemical microfluidic sensors with integrated biomolecule detection are emphasized.     

可降解聚合物/层状硅酸盐纳米复合材料的研究进展

作为一类性能优良的环保功能材料，生物降解性聚合物/层状硅酸盐（BPLS）纳米复合材料正日益引起人们的关注。本文综述了BPLS纳米复合材料的制备途径、结构表征方法及其性能特点，同时对其应用前景作了展望。     

Thermal and mechanical properties of chitosan nanocomposites with cellulose modified in ionic liquids

In this paper, ionic liquid treatment was applied to produce nanometric cellulose particles of two polymorphic forms. A complex characterization of nanofillers including wide-angle X-ray scattering, Fourier transform infrared spectroscopy, and particle size determination was performed. The evaluated ionic liquid treatment was effective in terms of nanocrystalline cellulose production, leaving chemical and supermolecular structure of the materials intact. However, nanocrystalline cellulose II was found to be more prone to ionic liquid hydrolysis leading to formation larger amount of small particles. Each nanocrystalline cellulose was subsequently mixed with a solution of chitosan, so that composite films containing 1, 3, and 5% mass/mass of nanometric filler were obtained. Reference samples of chitosan and chitosan with micrometric celluloses were also solvent casted. Thermal, mechanical, and morphological properties of films were tested and correlated with properties of filler used. The results of both, tensile tests and thermogravimetric analysis showed a significant discrepancy between composites filled with nanocrystalline cellulose I and nanocrystalline cellulose II.     

Role,effect, and influences of micro and nano‐fillers on various properties of polymer matrix composites for microelectronics: A review

Ever since the discovery of polymer composites, its potential has been anticipated for numerous applications in various fields such as microelectronics, automobiles, and industrial applications. In this paper, we review filler reinforced polymer composites for its enormous potential in microelectronic applications. The interface and compatibility between matrix and filler have a significant role in property alteration of a polymer nanocomposites. Ceramic reinforced polymeric nanocomposites are promising candidate dielectric materials for several micro‐ and nano‐electronic devices. Because of its synergistic effect like high thermal conductivity, low thermal expansion, and dielectric constant of ceramic fillers with the polymer matrix, the resultant nanocomposites have high dielectric breakdown strength. The thermal and dielectric properties are discussed in the view of filler alignment techniques and its effect on the composites. Furthermore, the effect of various surface modified filler materials in polymer matrix, concepts of network forming using filler, and benefits of filler alignment are also discussed in this work. As a whole, this review article addresses the overall view to novice researchers on various properties such as thermal and dielectric properties of polymer matrix composites and direction for future research to be carried out.