Structure-property relationship of highly crosslinked rubber-iron oxide composite based on chloroprene rubber (CR) as well as on nitrile rubber (NBR); a comparative study using different models

Abstract

Highly crosslinked elastomer-iron oxide composite for grinding as well as for polishing application. With the recent introduction of organic acid-based coolants in polishing applications, the designed composites should have good resistance to oils. This investigation reports the preparation and properties of high crosslinked elastomer-iron oxide composites based on Chloroprene Rubber (CR) as well as on Nitrile Rubber (NBR) as main elastomer matrix and their comparative study. In NBR system, a small amount of natural rubber (NR) was used to improve the abrasion resistance. The crosslink density (CLD) was determined from the plateau modulus in DMA using Nielsen’s model. CLD was also determined based on the equilibrium-swelling ratio by using Flory-Rehner model. The CLD at lower cure time estimated by both methods was substantially different. Nevertheless, it converges to a common value at highly crosslinked state. Highly crosslinked CR shows 500% higher modulus at high temperature when compared to the NBR system.

Highly crosslinked elastomeric composites based on Chloroprene Rubber (CR) as well as Nitrile Rubber (NBR) with high iron oxide content were prepared. This investigation gives insights into the fabrication of composites and evaluates the network structure of highly crosslinked composites. Different models were used to characterize the elastomeric network structures in the composites.     

Synthesis of regenerated bacterial cellulose-zinc oxide nanocomposite films for biomedical applications

Regenerated bacterial cellulose (RBC) composites with zinc-oxide nanoparticles (ZnO) were prepared using a new strategy for enhanced biomedical applications of BC. Powdered BC was dissolved in N-methylmorpholine-N-oxide, and different concentrations of ZnO nanoparticles were mixed into the BC solution. RBC, RBC-ZnO1 (1 % ZnO) and ZnO-RBC2 (2 % ZnO) nanocomposite films were prepared by casting the solutions through an applicator. FE-SEM images confirmed the structural features and impregnation of the RBC films by nanoparticles. XRD analysis indicated the presence of specific peaks for RBC and ZnO in the composites. The RBC nanocomposites were found to have greatly enhanced thermal, mechanical and biological properties. Specifically, the degradation temperatures were improved from 334 °C for RBC to 339 and 344 °C for RBC-ZnO1 and RBC-ZnO2, respectively. The mechanical strength and Young’s modulus of the composites were also higher than those of pure RBC. The greatly improved antibacterial properties of the RBC-ZnO nanocomposites are the most striking feature of the present study. The bacterial growth inhibition measured for the RBC was zero, but reached up to 34 and 41 mm for RBC-ZnO1 and RBC-ZnO2, respectively. In addition to their antibacterial properties, the RBC-ZnO nanocomposites were found to be nontoxic and biocompatible with impressive cell adhesion capabilities. These RBC-ZnO nanocomposites can be used for different biomedical applications and have the potential for use in bioelectroanalysis.     

Morphology and thermal stability of bacterial cellulose/collagen composites

The aim of this paper was to prepare composites of bacterial cellulose (BC) and collagen to evaluate both the effect of collagen on the morphological, mechanical and thermal properties of BC and the effect of BC on the thermal stability of collagen for designing composites with increased potential biomedical applications. Two series of composites were prepared, the first series by immersing BC pellicle in solutions of collagen obtained in three forms, collagen gel (CG), collagen solution (CS) and hydrolysed collagen (HC), followed by freeze drying; and the second series of composites by mixing BC powder in solutions of collagen (CG, CS and HC), also followed by freeze drying. The properties of obtained composites were evaluated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), mechanical tests, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results revealed that BC acts as a thermal stabilizer for CS matrix, while with CG matrix it interacts synergistically leading to composites with improved properties. On the other hand, the BC sheet impregnated with collagen has a significantly improved thermal stability. Collagen (as HC, CS or CG) has also a positive influence on the mechanical properties of lyophilized BC sheet. A four times increase of modulus was observed in BC/HC and BC/CG composites. and an increase of 60 times for BC/CS. The spectacular increase of elastic modulus and tensile strength in the case of BC/CS composite was explained by the easier penetration of collagen solution in the BC network and impregnation of BC fibrils as revealed by SEM and AFM analyzes.

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Fabrication and evaluation of bacterial cellulose-polyaniline composites by interfacial polymerization

The fabrication and evaluation of nanocomposites based on microbial cellulose and polyaniline (PANi) are described. Microbial cellulose, so called, bacterial cellulose (BC) was introduced to interfacial polymerization of aniline. Two different phases based on water and chloroform made it easy for nanosized PANi particles to be synthesized on BC. Without any help of a surfactant or templates, BC played a critical role of supporting the growth of PANi. As a function of aniline concentration, the corresponding PANi content and volume resistivity were checked. From morphological images observed by FE-SEM, PANi nanoparticles were densely arrayed along every fiber of BC. The conjugated backbone of PANi was thought to contribute to the improvements of thermal stability of PANi/BC composites. The stiffness and brittleness of PANi were compensated by more ductile BC, suggesting BC can be a promising substrate for it. By the simple and facile interfacial polymerization, the electrical conductivity of PANi/BC composites reached up to 3.8?×?10^?1?S/cm when 0.32?M of aniline was used. This PANi/BC nanocomposite can be useful in applications requiring biocompatibility and electrical conductivity such as biological and chemical sensors.     

Bacterial Cellulose as a Versatile Biomaterial for Wound Dressing Application

Chronic ulcers are among the main causes of morbidity and mortality due to the high probability of infection and sepsis and therefore exert a significant impact on public health resources. Numerous types of dressings are used for the treatment of skin ulcers-each with different advantages and disadvantages. Bacterial cellulose (BC) has received enormous interest in the cosmetic, pharmaceutical, and medical fields due to its biological, physical, and mechanical characteristics, which enable the creation of polymer composites and blends with broad applications. In the medical field, BC was at first used in wound dressings, tissue regeneration, and artificial blood vessels. This material is suitable for treating various skin diseases due its considerable fluid retention and medication loading properties. BC membranes are used as a temporary dressing for skin treatments due to their excellent fit to the body, reduction in pain, and acceleration of epithelial regeneration. BC-based composites and blends have been evaluated and synthesized both in vitro and in vivo to create an ideal microenvironment for wound healing. This review describes different methods of producing and handling BC for use in the medical field and highlights the qualities of BC in detail with emphasis on biomedical reports that demonstrate its utility. Moreover, it gives an account of biomedical applications, especially for tissue engineering and wound dressing materials reported until date. This review also includes patents of BC applied as a wound dressing material.     

Sustainable optically transparent composites based on epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC)

Production of transparent composites from totally renewable resources with extraordinary potential for different applications can be made possible using cellulose. Composites of epoxidized soybean oil (ESO)/bacterial cellulose (BC) nanofibers have been prepared with high fiber content. Due to the nano-order scale network-like structure of BC nanofibers, composite films present high transparency even at high BC content. Transparency of films has been analyzed by UV–visible spectroscopy observing that only 15% of matrix transmittance is lost in the nanocomposites. ESO/BC composites show better mechanical properties with increasing BC content. Composites combine high stiffness and good ductility due to the incorporation of BC network structure in ESO matrix.     

Tin Oxide Based Hybrid Nanostructures for Efficient Gas Sensing

Tin oxide as a semiconductor metal oxide has revealed great potential in the field of gas sensing due to its porous structure and reduced size. Especially for tin oxide and its composites, inherent properties such as high surface areas and their unique semiconducting properties with tunable band gaps make them compelling for sensing applications. In combination with the general benefits of metal oxide nanomaterials, the incorporation of metal oxides into metal oxide nanoparticles is a new approach that has dramatically improved the sensing performance of these materials due to the synergistic effects. This review aims to comprehend the sensing mechanisms and the synergistic effects of tin oxide and its composites in achieving high selectivity, high sensitivity and rapid response speed which will be addressed with a full summary. The review further vehemently highlights the advances in tin oxide and its composites in the gas sensing field. Further, the structural components, structural features and surface chemistry involved in the gas sensing are also explained. In addition, this review discusses the SnO₂ metal oxide and its composites and unravels the complications in achieving high selectivity, high sensitivity and rapid response speed. The review begins with the gas sensing mechanisms, which are followed by the synthesis methods. Further key results and discussions of previous studies on tin metal oxide and its composites are also discussed. Moreover, achievements in recent research on tin oxide and its composites for sensor applications are then comprehensively compiled. Finally, the challenges and scope for future developments are discussed.     

Fabrication of wood-inspired high-performance composites through fermentation routes

In this paper, we developed a microbial route to fabricate wood-inspired biomimetic composites comparable to natural wood. Focusing on the chemical composition of woody biomass, we performed in situ bioprocessing of bacterial cellulose (BC) imbibed in modified cationic lignin (Catlig), which exhibited significant bioactivity in improving the microbial growth dynamics. The structural and morphological characteristics were enhanced by the formation of hydrophobic and electrostatic interactions between BC and Catlig during biosynthesis. Microbially derived BC/Catlig composites exhibited enhanced thermal stability and crystallinity, with oriented cellulose fibers. The tensile properties, toughness, and specific strength of BC/Catlig composites were comparable to those of a heavy wood species (Zelkova serrata) under hydrated conditions and synthetic soft materials.

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Effects of cellulose nanofibrils on the structure and properties on PVA nanocomposites

A green method—joint mechanical grinding and high pressure homogenization—was used to defibrillate paper pulp into nanofibrils. The prepared cellulose nanofibrils (CNF) were then blended with PVA in an aqueous system to prepare transparent composite film. The size and morphology of the nanofibrils and their composites were observed, and the structure and properties were characterized. The results showed that CNFs are beneficial to improve the crystallinity, mechanical strength, Young’s modulus, T _g and thermal stability of the PVA matrix because of their high aspect ratio, crystallinity and good compatibility. Therefore, nano cellulosic fibrils were proven to be an effective reinforcing filler for the hydrophilic polymer matrix. Moreover, the green fabrication approaches will be helpful to build up biodegradable nanocomposites with wide applications in functional environmentally friendly materials.     

Biosynthesis, production and applications of bacterial cellulose

Bacterial cellulose (BC) as a never-dried biopolymer synthesized in abundance by Gluconacetobacter xylinus is in a pure form which requires no intensive processing to remove unwanted impurities and contaminants such as lignin, pectin and hemicellulose. In contrast to plant cellulose, BC, with several remarkable physical properties, can be grown to any desired shape and structure to meet the needs of different applications. BC has been commercialized as diet foods, filtration membranes, paper additives, and wound dressings. This review article presents an overview of BC structure, biosynthesis, applications, state-of-the-art advances in enhancing BC production, and its material properties through the investigations of genetic regulations, fermentation parameters, and bioreactor design. In addition, future prospects on its applications through chemical modification as a new biologically active derivative will be discussed.     

A review on environmental applications of chitosan biopolymeric hydrogel based composites

Abstract

Chitosan (CS) is being used for fabrication of low cost, biocompatible materials that have applicability in fields such as agriculture, biotechnology and environment. In Environmental research, one of the applications of CS based hydrogel composites are in form of biosorbents for eviction of toxic dyes, heavy metals and nutrients from effluent streams. The adsorption potential could be attributed to the reactive functional groups existing on the surface of CS. CS based materials can also be employed for oil/water separation, as a fertilizer carrier, in Microbial fuel cells as Electrolyte membrane and as Electrochemical/Biosensors for detecting and analyzing few environmental pollutants such as pesticides. The earlier review papers on the subject matter have concentrated mainly on dye and heavy metal removal without giving details of its utility in the field of electrochemistry and agriculture. Though the biopolymer holds numerous applications, it has not been discussed extensively. Thus, an attempt has been made to elucidate the current and potential applications of CS hydrogels and composites based on the efficacy it has shown in areas of removal of organic and inorganic contaminants such as dyes, heavy metals and nutrients, in agriculture, oil and water separation, Microbial Fuel cells and Electrochemical/Biosensors.

• HIGHLIGHTS

• Chitosan based hydrogel composites could be extensively used in the field of Environment Technology.

• The composites act as effective biosorbents for dye, heavy metal and nutrient removal because of the functional groups present on Chitosan’s surface.

• These can also be effectively used for oil/water separation and also as a fertilizer/pesticide carrier for their slow release.

• Chitosan based electrolytes can become a promising ecofriendly substitute for synthetic polymers in fuel cells.

• These biopolymers have also been researched upon as electrochemical/biosensors in recent years for detecting environmental pollutants.

     

Calix[4]arene-based crab-like molecular sensors for highly selective detection of mercury and copper ions

In this work, two novel chemosensors based on calix[4]arene bearing (thio)barbituric acid groups (BC1 and BC2) were synthesised, and their structures were characterised by HRMS, NMR and FTIR. Furthermore, their binding properties towards various biologically relevant metal ions were studied by fluorescence titrations, ¹H NMR spectroscopies and Job’s plot evaluations. The chemosensor BC1 displayed excellent binding affinity and selectivity towards Cu²⁺, which was characterised using fluorescence spectroscopy. On the other hand, BC2 exhibited a very remarkable fluorescence enhancement as well as visible colour change from pale green to sunset yellow, in presence of Hg²⁺ ions. Finally, Job’s plot method revealed 1:1 binding stoichiometry for both BC1:Cu²⁺ complex and BC2:Hg²⁺ complex.     

Polylactide (PLA) and Highly Filled PLA - Calcium Sulfate Composites with Improved Impact Properties

Summary: Starting from gypsum as by-product of lactic acid fabrication process, novel high performance composites have been produced by melt-blending PLA and this filler after a previous specific dehydration performed at 500 °C for min. 1h. Due to PLA sensitivity towards hydrolysis, the utilization of β-anhydrite II (AII) as filler is a prerequisite. Characterized by attractive mechanical and thermal properties due to good filler dispersion throughout the polyester matrix, these composites are interesting in biodegradable rigid packaging or technical applications. Interestingly, tensile strength of PLA – AII composites proved remarkably high, e.g. higher than 35 MPa at 50 wt-% filler content. However a decrease of impact properties has been recorded. To increase the toughness of these composites while preserving high stiffness an impact modifier based on ethylene copolymer has been mixed with both the polymer matrix and AII by melt-compounding. The effectiveness of the impact modifier was confirmed in both neat PLA and AII-based composites. Addition of 5-10 wt-% impact modifier into highly filled composites (30 to 40 wt-% filler) leads to an attractively threefold increase of impact strength with respect to the compositions without modifier, remarkable thermo-mechanical performances and good filler dispersion.     

Monolithic polyimine vitrimer/graphene aerogel composites

Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes. Herein, we report the first example of cylindrical monolithic polyimine vitrimer/graphene composites with excellent mechanical, compressive, rehealable and recyclable, and piezoresistive properties via simple infiltration of polymer monomers into the pores of graphene aerogel followed by thermal curing. The composites exhibit excellent durable compressibility (negligible reduction in the compression properties even after 3000 consecutive compression cycles), rapid recovery to the original size upon stress released, high compressive strength (up to 1.2 MPa), and high conductivity (up to 79 S/m). Excellent piezoresistive properties were observed, displaying consistent and reliable change of the electrical resistance with the compression ratio. Furthermore, rehealing with ～100% recovery of the compressive strength and electric conductivity was achieved under mild rehealing conditions, which is highly desired but has rarely been reported for electronic materials. The facile strategy for fabrication of rehealable monolithic polymer/GAs can open new possibilities for the sustainable development of composites with high electrical conductivity for various applications such as sensing, health monitoring, and movement detection.     

A review of bacterial cellulose: sustainable production from agricultural waste and applications in various fields

Bacterial cellulose (BC) is a polymer with interesting conformation and properties. BC can be obtained in different shapes and is easily modified by chemical and physical means, so its applications in the production of new materials and nanocomposites for different purposes have been in the focus of many research projects. However, one of the major challenges to address in bacterium-derived polymer technology is to find suitable carbon sources as substrates that are cheap and do not compete with food production for achieving large scale industrial applications. Agricultural wastes are defined as the residues from the growing and processing of raw agricultural products such as crops, fruits, vegetables and dairy products. Their composition can vary depending on the type of agricultural activity and harvesting conditions, but these residues are suitable for the production of BC. The aim of this review is to give insight into the production of BC using agro-wastes and an overview of the most interesting and novel applications of this biopolymer in different areas i.e. environmental applications, optoelectronic and conductive devices, food ingredients and packaging, biomedicine, and 3D printing technology.

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A perspective on diamond composites and their electrochemical applications

Diamond composites have gained increasing interests because of their outstanding properties (e.g. robust mechanical properties, high conductivity and activity, good chemical and thermal stability, as well as excellent electrochemical properties) and their promising applications in a wide range of different fields. In this perspective, recent advances on the synthesis of diamond composites are summarized together with state-of-the-art progress in their electrochemical applications. Metal-diamond, alloy–diamond, oxide/carbide/nitride-diamond, sp² carbon/sp³ diamond, and organic-diamond composites are covered in the context of enhancing their performance of electrocatalysis, sensing, water treatment, supercapacitor, and photoelectrochemistry. Ongoing challenges and future perspectives of the synthesis and electrochemical applications of diamond composites are outlined and discussed.     

Multifunctionality in Epoxy Resins

Abstract

Epoxy resin will continue to be in the forefront of many thermoset applications due to its versatile properties. However, with advancement in manufacturing, changing societal outlook for the chemical industries and emerging technologies that disrupt conventional approaches to thermoset fabrication, there is a need for a multifunctional epoxy resin that is able to adapt to newer and robust requirements. Epoxy resins that behave both like a thermoplastic and a thermoset resin with better properties are now the norm in research and development. In this paper, we viewed multifunctionality in epoxy resins in terms of other desirable properties such as its toughness and flexibility, rapid curing potential, self-healing ability, reprocessability and recyclability, high temperature stability and conductivity, which other authors failed to recognize. These aspects, when considered in the synthesis and formulation of epoxy resins will be a radical advance for thermosetting polymers, with a lot of applications. Therefore, we present an overview of the recent finding as to pave the way for varied approaches towards multifunctional epoxy resins.     

Silica Aerogel-Rubber Composite: A Sustainable Alternative for Buildings’ Thermal Insulation

Silica aerogel composites with recycled tire rubber have been synthesized and evaluated for their potential use for thermal protection in buildings. The present work describes for the first time the preparation of silica-based aerogel composites containing recycled rubber tires reinforced with polyvinyl butyral (PVB) by hot pressing. The developed composite was extensively characterized regarding its physical, morphological, thermal and mechanical features, and the results showed their properties were relevant, leading to composites with different properties/performances. The obtained bulk density values were satisfactory, down to 474 kg·m⁻³, and very good thermal properties were achieved, namely, thermal conductivity as low as 55 mW·m⁻¹·K⁻¹ for composites with silica aerogel, recycled tire rubber and PVB. The most promising composites were those based on low bulk density and thermal conductivity values, and they were thermally stable, indicating their suitability for thermal insulation applications.     

A review on potential development of flame retardant kenaf fibers reinforced polymer composites

Kenaf fibers have been extensively explored from the past few decades in polymer composites industries owing to its extensive adaptations, excellent properties together with its comparable mechanical properties to traditional glass fibers polymer composites. The combustibility or lowered flame retardancy hampered the diverse applications of kenaf fibers reinforced polymer composites, as it affects the mechanical strength and stiffness of composites during fire. Current review article intended to be a comprehensive source of published literature involving the flame retardants (FRs), types and applications of FRs and the fabrication of kenaf fibers reinforced polymer composites. This article will also provide a perfect data on the recent development of the FR kenaf fibers polymer composites with different FRs and explored its structural and semi‐structural industrial application for performing further research in this topic. Copyright © 2016 John Wiley & Sons, Ltd.     

Versatile Lightweight Polymer Composites

Abstract

Knowledge of polymer composites goes back to antiquity, yet their most spectacular boom, from a scientific point of view, began during the 1960s when their microstructure was studied as it relates to their properties. Modern technology demands newer materials in place of conventional engineering materials. Although concrete is an excellent building material, its use is subject to certain limitations. These include its relatively low tensile strength, a tendency to crack with changes in temperature coupled with moisture absorption, and deterioration due to chemical and physical attack under various environmental conditions. Polymer composites, on the other hand, have outstanding strength and durability which offer several advantages over those of conventional materials.