In situ processing of cellulose nanocomposites

Nanocellulose has gained attention in recent times due to their light weight, high strength, stiffness, biodegradability and renewability. Natural fibres have been used as reinforcement in composites for past many years, but the use of nanocellulose as reinforcement in composites is relatively new. The main challenges of preparing nanocellulose based composites include (i) generation of nanocellulose from natural resources, (ii) production in larger scale, (iii) enhancing compatibility with hydrophobic polymers, and (iv) achieving uniform dispersion in polymer matrices. These challenges have encouraged researchers to innovate efficient processes and techniques to utilise the maximum benefit of such green nanoscopic materials. In situ fabrication of cellulose nanocomposites is one such technique of achieving uniform nanocellulose dispersion in polymer matrices and obtaining a stronger filler/matrix interface. This review summarises the recent progress in the field of in situ processing of cellulose nanocomposites.     

Preparation of silane precursor microencapsulated intumescent flame retardant and its enhancement on the properties of ethylene–vinyl acetate copolymer cable

Silane precursor microencapsulated intumescent flame retardant (IFR) was prepared by sol–gel process and then modified with vinyltrimethoxysilane (A-171) with the goal of that the vinyl group functionalized silica microcapsule could be introduced into EVA matrix through crosslinking, which will enhance the compatibility and dispersion between EVA matrix and microencapsulated IFR. The effects of silane precursor microencapsulation technology on the mechanical, electrical, thermal, interfacial adhesion and flame retardant properties of intumescent flame-retardant EVA cable were investigated by mechanical test, resistance meter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI) and UL-94 test. The Fourier transform infrared (FTIR) results indicated silane precursor microencapsulated IFR were successfully prepared, and the water contact angle (WCA) results indicated that silane precursor results in the transformation of hydrophilic to hydrophobic of IFR surface. The characterization for the various properties of EVA composites demonstrated that silane precursor microencapsulation technology enhanced the interfacial adhesion, mechanical, electrical, thermal stability and flame retardancy of EVA/MCAPP/MCPER system. Furthermore, the water resistance test results demonstrate that EVA/MCAPP/MCPER composites have good water durability. This investigation provides a formulation for the industrial application as insulated materials of EVA cable with excellent properties.     

Extraction of cellulose nanocrystals from plant sources for application as reinforcing agent in polymers

In the last few decades, the usages of plant sources-based stiff fillers as reinforcement material in polymer composites have attracted significant interests of researchers. The crystalline part of the semicrystalline cellulose chains as found in the plant cell walls represents the most highly potential reinforcing agents for polymer. This review systematically covers the extraction of nano-sized cellulose crystals from plant cell wall which involving the applications of several highly effective techniques. The topic about the derivation of products functionality at each stage as well as their influences on the final reinforcing capability is also covered. Apart from these, a detailed overview of current knowledge on the surface modification of nanocellulose has been provided also. Inasmuch, this paper is desired to encourage the emergence of preparation of cellulose derivative nanocrystals with controlled morphology, structure and properties, so that enable positive development of biocompatible, renewable and sustainable reinforcing materials for polymer composites field.     

Novel bacterial cellulose–acrylic resin nanocomposites

The preparation and characterization of new nanocomposite films based on two acrylic emulsions, composed of random copolymers of butyl acrylate and methyl methacrylate, and bacterial cellulose is reported. The new composite materials were obtained through a simple and green approach by casting water-based suspensions of the acrylic emulsions and bacterial cellulose nanofibrils. The excellent compatibility between these matrices and the natural reinforcing fibers, observed by scanning electron microscopy (SEM), was reflected in the enhanced thermal and mechanical properties of the ensuing composites. Thus, an increase of around 30 °C in the maximum degradation temperature was observed for a 10% content of bacterial cellulose. The new composites showed glass–rubber transition temperature profiles comparable to those of the pristine matrices, as shown by DMA, and increasing elastic moduli with increasing the bacterial cellulose content. The tensile tests revealed a substantial increase in Young’s modulus and tensile strength and a corresponding decrease in elongation at break with increasing bacterial cellulose load.     

Cellulosic fibers from rice straw and bamboo used as reinforcement of cement-based composites for remarkably improving mechanical properties

The cement-based composites reinforced with cellulosic fibers isolated from rice straw were fabricated by a slurry vacuum de-watering technique. The physical structures and mechanical properties of the composites with fiber contents ranging from 2% to 16% by weight (wt.%) were investigated. Moreover, the composites reinforced with bamboo cellulosic fibers and the control cement paste, sample without cellulosic fibers, were also fabricated as reference materials. As a result, the cement-based composites reinforced by cellulosic fibers showed a remarkable improvement in the mechanical properties. The measurements of the flexural strength and the fracture toughness of the optimal sample were found to be increased by 24.3% and 45 times, respectively. The bulk density of the composites was decreased by 12.4–37.3% as a result of the introduction of cellulosic fibers. Additionally, the field emission scanning electron microscope (FSEM) observations and energy dispersive spectroscopy (EDS) analyses revealed that the hydration products of Portland cement migrated to the fiber lumens, resulting in mineralizing the cellulosic fibers and decreasing the fracture toughness of the composites.     

Effects of hemicellulose extraction on properties of wood flour and wood-plastic composites

Hygroscopicity, low durability, and low thermal resistance are disadvantages of lignocellulosic materials that also plague wood-plastic composites (WPCs). Hemicellulose is the most hydrophilic wood polymer and is currently considered as a sugar source for the bioethanol industry. The objective of this research is to extract hemicellulose from woody materials and enhance the properties of WPC by diminishing the hydrophilic character of wood. Hemicellulose of Southern Yellow Pine was extracted by hot-water at three different temperatures: 140, 155, and 170 °C. Wood flour was compounded with polypropylene in an extruder, both with and without a coupling agent. Injection molding was used to make tensile test samples. The thermal stability of wood flour was found to have increased after extraction. Extraction of hemicellulose improved the tensile strength and water resistance of composites, which may indicate a decrease in the hygroscopicity of wood flour, better compatibility, and interfacial bonding of the filler and matrix.     

Modification of dielectric and mechanical properties of rubber ferrite composites containing manganese zinc ferrite

Spinel ferrites constitute an important class of magnetic materials. Polycrystalline ferrites are a complex system composed of crystallite grain boundaries and pores. Manganese zinc ferrites have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. Composite materials are ideally suited for many modern applications where ceramic materials have some drawbacks. The mouldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ (MZF) were synthesized for different ‘x’ values in steps of 0.2. These pre-characterized ceramic ferrites were then incorporated in a natural rubber matrix. The dielectric properties of the ceramic manganese zinc ferrite and RFC were also studied. A program based on G programming was developed with the aid of LabVIEW package to automate the dielectric measurements. The dielectric permittivity of the RFC were then correlated with that of the corresponding dielectric permittivity of the magnetic filler and matrix by a mixture equation, which helps to tailor properties of the composites.     

Novel nanocellulosic xylan composite film

Nanocellulosic-xylan films were prepared employing oat spelt xylan, cellulose whiskers and a plasticizer. The mechanical properties of the films were evaluated using tensile testing under controlled temperature and humidity conditions. The tensile data showed that the addition of sulfonated cellulose whiskers lead to a substantial improvement in strength properties. Addition of 7 wt% of sulfonated whiskers increased the tensile energy absorption of xylan films by 445% and the tensile strength of the film by 141%. Furthermore, films to which 7% cellulose whiskers were added showed that nanocellulose whiskers produced with sulfuric acid (sulfonated whiskers) were significantly better at increasing film strength than cellulose whiskers produced by hydrochloric acid hydrolysis of cellulosic fibers.     

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

The effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites was evaluated. Alkali treatment of the fibers and reaction with organosilanes as coupling agents were applied to improve fiber–matrix adhesion. Fiber loadings of 1, 3, 5, and 7 wt% were incorporated to the phenolic matrix and tensile, flexural, morphological and thermal properties of the resulting composites were studied. In general, mechanical properties of the composites showed a maximum at 3% of fiber loading and a uniform distribution of the fibers in such composites was observed. Silane treatment of the fibers provided derived composites with the best thermal and mechanical properties. Meanwhile, NaOH treatment improved thermal and flexural properties, but reduced tensile properties of the materials. Therefore, the phenolic composite containing 3% of silane treated cellulose fiber was selected as the material with optimal properties.     

Fracture mechanisms of epoxy-based ternary composites filled with rigid-soft particles

Epoxy composites filled with different amounts of aggregate-free silica nanoparticles and phase-separated submicron rubber particles were fabricated to study the synergistic effect of multi-phase particles on mechanical properties of the composites. Compared with binary composites with single-phase particles, the ternary composites with both rigid and soft particles offer a good balance in stiffness, strength and fracture toughness, showing capacities in tailoring the mechanical properties of modified epoxy resins. It was observed that debonding of silica nanoparticles from matrix in the ternary composites was less pronounced than that in the binary composites. Moreover, the rubber particles became smaller and their shape tends to be irregular, affected by the presence of rigid silica nanoparticles. The toughening mechanisms in the epoxy composites were evaluated, and the enlarged plastic deformation around the crack tip, induced by the combination of rigid and soft particles, seems to be a dominant factor in enhancing fracture toughness of the ternary composites.     

纤维素导电基底及其柔性电子器件的研究进展

纤维素是自然界中含量丰富且可再生、可降解的天然材料。本文综述了物理、化学、生物或相结合的技术对纤维素的影响作用及可制备的纤维素基元材料,例如纤维素纤维、纳米纤维素和纤维素分子。基于纤维素纤维,利用湿法造纸技术可以生产具有高孔隙率的纤维素纸张基底;基于纳米纤维素,利用真空抽滤或涂布等方式可制备具有低表面粗糙度及高透明度的纳米纤维素膜基底;基于纤维素分子,利用涂布或铸涂等方式可生产具有均一的表面形态及高透明度的再生纤维素膜基底。本文进一步分析了常用的导电材料(金属导电材料、聚合物导电材料及碳基导电材料等)及其与纤维素基底结合的方法(涂布、沉积、原位聚合、自组装等),进而可以制备柔韧轻质的纤维素导电基底。基于高性能的纤维素导电基底可以组装柔性电子器件,在光电转化、能量储存及电磁屏蔽等领域展现了广阔的应用前景。总之,利用天然纤维素制备柔性电子器件对于扩大纤维素的应用范围、提升纤维素的利用价值及推动柔性电子器件的进一步发展具有重要意义。      

高岭土/白炭黑并用填充天然橡胶复合材料的性能

以高岭土和白炭黑作为增强剂,采用熔融共混法制备了一系列的天然橡胶(NR)复合材料,并对其微观结构、气体阻隔性能和力学性能进行了表征.结果表明,改性高岭土(MK)以片层结构,白炭黑(PS)以球状结构,均匀分散于NR基体之中;MK与PS单独填充NR时,随着MK填充量的增加,NR复合材料的气体阻隔性能逐渐提高,而且MK的增强...     

Cellulose diacetate reinforced with electrospun cellulose fiber: A new route to prepare an all cellulose-based composite

An all cellulose-based composite was produced by applying cellulose diacetate (CDA) and electrospun cellulose fibers (ECFs) as a matrix and reinforcing fibers, respectively. The ECFs were prepared by electrospinning CDA followed by alkali treatment. The alkali treatment of the electrospun CDA fibers removes acetyl groups and creates new crystalline domains similar to cellulose fibers, which may result in increased mechanical properties. The physical properties of ECFs are highly correlated with the acetyl content. The mechanical properties of the CDA/ECF composites were evaluated by measuring the tensile strength and Young’s modulus as a function of the hydrolysis time. The results showed that the integration of the CDA matrix with 15% weight/weight (w/w) ECF7, which was alkali-treated for 7 h, was optimal, resulting in an improved tensile strength and Young’s modulus by factors of 1.7 and 2.2, respectively. This study demonstrates that the increased mechanical properties are attributed to the reinforcement of ECFs as well as good interfacial adhesion.     

Dimensional stability and mechanical behaviour of wood–plastic composites based on recycled and virgin high-density polyethylene (HDPE)

This paper investigated the stability, mechanical properties, and the microstructure of wood–plastic composites, which were made using either recycled or virgin high-density polyethylene (HDPE) with wood flour (Pinus radiata) as filler. The post-consumer HDPE was collected from plastics recycling plant and sawdust was obtained from a local sawmill. Composite panels were made from recycled HDPE through hot-press moulding exhibited excellent dimensional stability as compared to that made from virgin HDPE. The tensile and flexural properties of the composites based on recycled HDPE were equivalent to those based on virgin HDPE. Adding maleated polypropylene (MAPP) by 3–5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. Dimensional stability and strength properties of the composites can be improved by increasing the polymer content or by addition of coupling agent. This project has shown that the composites treated with coupling agents will be desirable as building materials due to their improved stability and strength properties.     

Effect of phenoxy-based coating resin for reinforcing pitch carbon fibers on the interlaminar shear strength of PA6 composites

Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics followed by being pressed. In order to improve the interfacial adhesion, phenoxy resin-based materials were coated on the surface of the fiber. The surface analyses of the fiber were carried out by XPS, TGA and dynamic contact angle method. Interlaminar shear strength (ILSS) of the composites was measured to evaluate the effect of the coating materials. The results showed that the composites with the coated pCF had higher ILSS than that with neat pCF by more than 20%. This indicated that a proper coating material can improve mechanical properties of the PA6 composites, which can be applied to the structural parts.     

Crosslinked natural rubber nanocomposites reinforced with cellulose whiskers isolated from bamboo waste: Processing and mechanical/thermal properties

Crosslinked natural rubber (NR) nanocomposites were prepared using cellulose nanowhiskers (CNWs) that were extracted from bamboo pulp residue of newspaper production, as the reinforcing phase. The coagulated NR latex containing bamboo nanowhiskers (master batch) was compounded with solid NR and vulcanizing agents using a two-roll mill and subsequently cured to introduce crosslinks in the NR phase. No evidence of micro-scaled aggregates of cellulose nanowhiskers in NR matrix was observed in Scanning Electron Microscopy (SEM) images. The addition of CNWs had a positive impact on the tensile strength, E-modulus, storage modulus, tan delta peak position and thermal stability of the crosslinked NR. Theoretical modeling of the mechanical properties showed a lower performance than predicated and therefore further process optimization and/or compatibilization are required to reach the maximum potential of these nanocomposites.     

Effect of cellulose nano fiber (CNF) on fatigue performance of carbon fiber fabric composites

The effect of cellulose nano fibers (CNF): micro-fibrillated cellulose and bacteria cellulose fibers were investigated on the fatigue life of carbon fiber (CF) fabric/epoxy (EP) composites. Epoxy used as the matrix was physically modified with CNF in advance before fabricating the laminates. The high cycle fatigue strength was significantly improved at 0.3 wt% CNF. There exists an appropriate CNF content which makes the fatigue life longest. An increase of adhesive strength between CF and matrix results due to physical modification with CNF. The adhesive strength much increases with increasing the CNF content. Almost no interfacial debonding occurs at 0.8 wt% CNF content when CF breakage takes place. On the other hand, some debonding occurs along CFs from the breaking point at 0.3 wt% CNF. Debonding is more significant in the case of no CNF addition to the matrix. An appropriate interfacial strength brought at 0.3 wt% CNF is the key of fatigue life extension.     

Nanocellulose as a natural source for groundbreaking applications in materials science: Today’s state

Nanocelluloses are natural materials with at least one dimension in the nano-scale. They combine important cellulose properties with the features of nanomaterials and open new horizons for materials science and its applications. The field of nanocellulose materials is subdivided into three domains: biotechnologically produced bacterial nanocellulose hydrogels, mechanically delaminated cellulose nanofibers, and hydrolytically extracted cellulose nanocrystals. This review article describes today’s state regarding the production, structural details, physicochemical properties, and innovative applications of these nanocelluloses. Promising technical applications including gels/foams, thickeners/stabilizers as well as reinforcing agents have been proposed and research from last five years indicates new potential for groundbreaking innovations in the areas of cosmetic products, wound dressings, drug carriers, medical implants, tissue engineering, food and composites. The current state of worldwide commercialization and the challenge of reducing nanocellulose production costs are also discussed.     

Effect of surface modification of bamboo cellulose fibers on mechanical properties of cellulose/epoxy composites

Bamboo cellulose fibers were treated with NaOH aqueous solution and silane coupling agent, respectively, before they were applied into epoxy composites. The effect of surface modification on mechanical properties was evaluated by tensile and impact tests under controlled conditions. Compared with the untreated cellulose filled epoxy composites, the NaOH solution treatment increased the tensile strength by 34% and elongation at break by 31%. While silane coupling agent treatment produced 71% enhancement in tensile strength and 53% increase in elongation at break. The scanning electron microscopy (SEM) was used to observe the surface feature of the cellulose fibers and the tensile fractures as well as cryo-fractures of the composites. The Fourier transform infrared (FTIR) was employed to analyze the chemical structure of the cellulose fibers before and after modifications. The results indicated different mechanisms for the two modifications of cellulose. The NaOH solution partly dissolved the lignin and amorphous cellulose, which resulting in splitting the fibers into smaller size. This led to easier permeating into the gaps of the fibers for epoxy resin (EP) oligmer and forming effective interfacial adhesion. Based on the emergence of Si–O–C and Si–O–Si on the cellulose surface, it was concluded that the enhancement of mechanical properties after coupling agent modification could be ascribed to the formation of chemical bonds between the cellulose and the epoxy coupled with the coupling agent.