Reinforcement of Natural Rubber: The Use of in Situ Regenerated Cellulose from Alkaline–Urea–Aqueous System

Investigation of physicochemical and biological properties of bacterial cellulose & zein-reinforced edible nanocomposites based on flaxseed mucilage containing Origanum vulgare L. essential oil

In the present study, the effect of zein and different amounts of bacterial cellulose (BC; 1, 2 and 3 wt%) on the physical, mechanical and barrier properties of flaxseed mucilage/carboxymethyl cellulose (FM/CMC) composite was investigated. The appearance of the absorption band at 1320cm-1 in the ATR-FTIR spectra of nanocomposites indicated the successful introduction of zein into their structure. The characteristic peak at 2θ of 9° belonging to zein disappeared in XRD patterns of the prepared composites suggesting the successful coating of zein via hydrogen bonding interactions. SEM images proved the formation of semi-spherical zein microparticles in the FM/CMC matrix. TGA plots ascertained the addition of zein and nanocellulose caused a significant increase in the thermal stability of FM/CMC film, although zein showed a greater effect. The presence of zein and nanocellulose increased the mechanical strength of nanocomposites. The WVP of FM/CMC decreased after the incorporation of zein and nanocellulose, which created a tortuous path for the diffusion of water molecules. The zein particles exhibited a greater influence on improving the mechanical and barrier properties compared to nanocellulose. FM/CMC-Z film exhibited the highest mechanical strength (49.07 ± 5.89 MPa) and the lowest WVP (1.179 ± 0.076). The composites containing oregano essential oil (EO) showed higher than 60 % antibacterial properties. The bactericidal efficiency of FM/CMC/Z-EO and FM/CMC/Z-EO/BC1 nanocomposites decreased about 10% compared to FM/CMC/EO and FM/CMC-Z/BC1. This evidenced the successful encapsulation of EO molecules in zein particles. According to the in vitro release study, entrapment of EO into zein particles could delay the release and provide the extended antimicrobial effect.

Flexible, sensitive and rapid humidity-responsive sensor based on rubber/aldehyde-modified sodium carboxymethyl starch for human respiratory detection

Natural polymers with abundant hydrophilic groups are potential candidates for humidity sensor designing. Unfortunately, most of natural polymers lack essential stretchability and high conductivity, which hinder their development in the field of flexible humidity sensor. Cooperation with rubbers and conductive nanometer materials is an effective method to make the best use of natural polymers in flexible humidity sensor. In this paper, a flexible and sensitive sensor with rapid response to humidity change is fabricated based on aldehyde-modified sodium carboxymethyl starch (ACMS), carboxylated styrene-butadiene rubber (XSBR) and Ag nanoflakes through film-forming method. The pre-prepared ACMS owns a better dispersibility in the aqueous phase and serves as reducing agent for formation of Ag nanoflakes. After the film-forming process, the composite film shows a strength of 5.66 MPa and a high stretchability with strain of 367 %. Besides, our sensor shows a rapider response to humidity change than the commercial electronic hygrometer that it takes only 1 s to respond to the humidity change from 25 % RH to 27 % RH. Therefore, the XSBR/ACMS/Ag sensor possesses an impressive sensitive response to slight sweat on human skin and breath, which could find applications in monitoring people's health and distinguish their physical condition.

Rod-like Cellulose Regenerated by Bottom-Up Assembly in Natural Rubber Latex and Its Reinforcement

As a renewable biomass material, nano-cellulose has been investigated as a reinforcing filler in rubber composites but has seen little success because of its strong inclination towards aggregating. Here, a bottom-up self-assembly approach was proposed by regenerating cellulose crystals from a mixture of cellulose solution and natural rubber (NR) latex. Different co-coagulants of both cellulose solution and natural rubber latex were added to break the dissolution equilibrium and in-situ regenerate cellulose in the NR matrix. The SEM images showed that the sizes and morphologies of regenerated cellulose (RC) varied greatly with the addition of different co-coagulants. Only when a 5 wt% acetic acid aqueous solution was used, the RC particles showed an ideal rod-like structure with small sizes of about 100 nm in diameter and 1.0 μm in length. The tensile test showed that rod-like RC (RRC)-endowed NR vulcanizates with pronounced reinforcement had a drastic upturn in stress after stretching to 200% strain. The results of XRD and the Mullins effect showed that this drastic upturn in stress was mainly attributed to the formation of rigid RRC-RRC networks during stretching instead of the strain-induced crystallization of NR. This bottom-up approach provided a simple way to ensure the effective utilization of cellulosic materials in the rubber industry.

APPROACHING SUSTAINABILITY: NANOCELLULOSE REINFORCED ELASTOMERS—A REVIEW

Awareness of the environmental implications of conventional reinforcing fillers and the urge to reduce the carbon footprint have lead researchers to focus more on natural and sustainable materials. Nanocellulose from multitudinous sources finds use in elastomer engineering because of its distinctive properties, such as renewability, sustainability, abundance, biodegradability, high aspect ratio, excellent mechanical properties, and low cost. Green alternatives for conventional fillers in elastomer reinforcing have gained considerable interest to curb the risk of fillers from nonrenewable sources. The differences in properties of nanocellulose and elastomers render attractiveness in the search for synergistic properties resulting from their combination. This review addresses the isolation techniques for nanocellulose and challenges in its incorporation into the elastomer matrix. Surface modifications for solving incompatibility between filler and matrices are discussed. Processing of nanocomposites, various characterization techniques, mechanical behavior, and potential applications of nanocellulose elastomer composites are also discussed in detail.

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A Review of Rubber Biocomposites Reinforced with Lignocellulosic Fillers

Lignocellulosic fillers have attracted considerable attention over the years as a promising alternative to conventional petroleum-based fillers (carbon black) in rubber composites due to their renewability, biodegradability, availability, high mechanical properties, low density and low cost. Based on the literature available, a comprehensive review is presented here of rubber biocomposites reinforced with plant-based fillers. The study is divided into different sections depending on the matrix (natural or synthetic rubber) and the type of lignocellulosic fillers (natural fiber, microcrystalline cellulose, lignin and nanocellulose). This review focuses on the curing characteristics, mechanical properties and dynamic mechanical properties of the resulting rubber biocomposites. In addition, the effect of hybrid filler systems, lignocellulosic filler surface modification and modification of the rubber matrix on the properties of these rubber biocomposites are presented and compared. A conclusion is finally presented with some openings for future works.

Recent Developments in Nanocellulose-Reinforced Rubber Matrix Composites: A Review

Research and development of nanocellulose and nanocellulose-reinforced composite materials have garnered substantial interest in recent years. This is greatly attributed to its unique functionalities and properties, such as being renewable, sustainable, possessing high mechanical strengths, having low weight and cost. This review aims to highlight recent developments in incorporating nanocellulose into rubber matrices as a reinforcing filler material. It encompasses an introduction to natural and synthetic rubbers as a commodity at large and conventional fillers used today in rubber processing, such as carbon black and silica. Subsequently, different types of nanocellulose would be addressed, including its common sources, dimensions, and mechanical properties, followed by recent isolation techniques of nanocellulose from its resource and application in rubber reinforcement. The review also gathers recent studies and qualitative findings on the incorporation of a myriad of nanocellulose variants into various types of rubber matrices with the main goal of enhancing its mechanical integrity and potentially phasing out conventional rubber fillers. The mechanism of reinforcement and mechanical behaviors of these nanocomposites are highlighted. This article concludes with potential industrial applications of nanocellulose-reinforced rubber composites and the way forward with this technology.

Mechanically Strong, Heat-Resistant, Water-Induced Shape Memory Poly(vinyl alcohol)/Regenerated Cellulose Biocomposites via a Facile Co-precipitation Method

In this work, poly(vinyl alcohol) (PVA) biocomposites with regenerated cellulose-softwood pulp (RC-SP) as a green reinforcement were prepared via co-precipitation method. Simultaneous precipitation of the two components promotes uniform dispersion of the RC-SP and constructs strong molecular chain entanglements and hydrogen bonding network inside the composites. This physical cross-linking network reduces the water absorption and improves the water resistance of the composites. The incorporation of RC-SP not only improves the thermal decomposition properties of the composites, but also enhances the mechanical properties and dynamic mechanical properties, attributed to the strong interaction between the filler and the matrix. Moreover, the fabricated PVA/RC-SP composites exhibit good water-induced shape memory effect, and shape recovery rate of 10% RC-SP reinforced composite reaches 95.3% after immersing for 35 min. This work provides useful information for the implementation of co-precipitation method and the application of renewable cellulose resources.

Self-Healing and Recyclable Hydrogels Reinforced with in Situ-Formed Organic Nanofibrils Exhibit Simultaneously Enhanced Mechanical Strength and Stretchability

In this work, self-healing and recyclable polymer hydrogels with simultaneously enhanced mechanical strength and stretchability are fabricated through the complexation of poly(acrylic acid) (PAA) with complexes of branched poly(ethylenimine) and 1-pyrenybutyric acid (PEI-PYA) to generate PAA/PEI-PYA complexes, which are further molded, dried, and rehydrated. The in situ-formed PYA nanofibrils with aggregated structures during the complexation process enable the simultaneous enhancement of the tensile strength and stretchability of the PAA/PEI-PYA hydrogels. The PAA/PEI-PYA hydrogels have a tensile strength of 1.13 ± 0.04 MPa and stretchability of 2970 ± 154%, which are 2.2 and 2.1 times higher than those of the PAA/PEI hydrogels. Meanwhile, the damaged PAA/PEI-PYA hydrogels can be efficiently healed or recycled at room temperature to regain their original mechanical strength and integrity because the dynamic nature of hydrogen-bonding and electrostatic interactions among PAA, PEI, and PYA endows the hydrogels with excellent healing and recycling capacity. This strategy of using aggregated nanofibrils to simultaneously enhance the tensile strength and stretchability of hydrogels can be extended to PAA/PEI hydrogels reinforced with aggregated nanofibrils of 9-anthracenecarboxylic acid and N,N'-di(propanoic acid)-perylene-3,4,9,10-tetracarboxylic diimide, demonstrating its generality for fabricating hydrogels with enhanced mechanical properties.

Immobilization of rubber additive on graphene for high-performance rubber composites

It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.