Prevulcanized natural rubber latex/clay aerogel nanocomposites

Knitting Elastic Conductive Fibers of MXene/Natural Rubber for Multifunctional Wearable Sensors

Wearable electronic sensors have recently attracted tremendous attention in applications such as personal health monitoring, human movement detection, and sensory skins as they offer a promising alternative to counterparts made from traditional metallic conductors and bulky metallic conductors. However, the real-world use of most wearable sensors is often hindered by their limited stretchability and sensitivity, and ultimately, their difficulty to integrate into textiles. To overcome these limitations, wearable sensors can incorporate flexible conductive fibers as electrically active components. In this study, we adopt a scalable wet-spinning approach to directly produce flexible and conductive fibers from aqueous mixtures of Ti3C2Tx MXene and natural rubber (NR). The electrical conductivity and stretchability of these fibers were tuned by varying their MXene loading, enabling knittability into textiles for wearable sensors. As individual filaments, these MXene/NR fibers exhibit suitable conductivity dependence on strain variations, making them ideal for motivating sensors. Meanwhile, textiles from knitted MXene/NR fibers demonstrate great stability as capacitive touch sensors. Collectively, we believe that these elastic and conductive MXene/NR-based fibers and textiles are promising candidates for wearable sensors and smart textiles.

Improved Heat Dissipation of NR/SBR-Based Tire Tread Compounds via Hybrid Fillers of Multi-Walled Carbon Nanotube and Carbon Black

The development of thermally conductive rubber nanocomposites for heat management poses a formidable challenge in numerous applications, notably within the realm of tire technology. Notably, rubber materials are characterized by their inherently low thermal conductivity. Consequently, it becomes imperative to incorporate diverse conductive fillers to mitigate the propensity for heat build-up. Multi-walled carbon nanotubes (MWCNTs), as reinforcement agents within the tire tread compounds, have gained considerable attention owing to their extraordinary attributes. The attainment of high-performance rubber nanocomposites hinges significantly on the uniform distribution of MWCNT. This study presents the influence of MWCNTs on the performance of carbon black (CB)-reinforced natural rubber (NR)/styrene butadiene rubber (SBR) tire compounds prepared via high shear melt mixing. Morphological analysis showed a good distribution of MWCNTs in the NR/SBR/CB compound. The vulcanization parameters, such as the maximum and minimum torque, cross-linking density, hardness, abrasion resistance, tensile strength, and Young modulus, exhibited a progressive improvement with the addition of MWCNT. Remarkably, adding MWCNT into CB improved the heat conductivity of the NR/SBR/CB compounds, hence decreasing the heat build-up. A percolation mode was also proposed for the hybrid carbon fillers based on the data obtained.

A comprehensive review on the recent advancements in natural rubber nanocomposites

Natural rubber (NR) is an eminent sustainable material and is the only agricultural product among various rubbers. Use of nanofillers in NR matrix as a reinforcing agent has gained huge attention because they offer excellent matrix-filler interaction upon forming a good dispersion in the NR matrix. Nanoscale dispersion of fillers lead to greater interfacial interactions between NR and fillers compared to microfillers, which in turn lead to a conspicuous reinforcing effect. Addition of various nanofillers into NR matrix improves not only the mechanical properties but also the electrical, thermal and antimicrobial properties to an extreme level. The current review describes the reinforcing ability of various nanofillers such as clay, graphene, carbon nanotube (CNT), titanium dioxide (TiO₂), chitin, cellulose, barium titanate (BaTiO₃) and lignin in NR matrix. Moreover, reinforcement of various hybrid nanofillers in NR is also discussed in a comprehensive manner. The review also includes the historical trajectory of rubber nanocomposites and a comprehensive account on the factors affecting the properties of the NR nanocomposites.

The Relationship between the Morphology and Elasticity of Natural Rubber Foam Based on the Concentration of the Chemical Blowing Agent

Concentrated natural latex was used to produce a rubber foam that is porous, elastic and well ventilated. The mechanical properties can be either soft or firm, depending on the formulation of the latex used. Briefly, concentrated natural latex was mixed with chemical agents to make the rubber foam on a laboratory scale using the Dunlop process. In this work, we changed the concentration of the chemical blowing agent in the latex. The morphological properties of the rubber foam were characterised using scanning electron microscopy, and the mechanical properties, or elasticity, were studied using compression experiments and the Mooney-Rivlin calculation. The results show that the concentration of the chemical blowing agent affects the morphological properties of the rubber foam but not the mechanical properties, indicating the heterogeneous structure of the rubber foam. The thermodynamic parameters (∆G and ∆S) and the internal energy force per compression force (F_u/F) of the rubber foam with various amounts of chemical blowing agent were also investigated. This study could be applied in the foam industry, particularly for pillow, mattress and insulation materials, as the present work shows the possible novel control of the morphological structure of the rubber foam without changing its mechanical properties. The difference in cell sizes could affect the airflow in rubber foam.

Current challenges in thermodynamic aspects of rubber foam

Natural rubber (NR) foam can be prepared by the Dunlop method using concentrated natural latex with chemical agents. Most previous studies have focused on the thermodynamic parameters of solid rubber in extension. The main objective of this study is to investigate the effect of the NR matrix concentration on the static and dynamic properties of NR foams, especially the new approach of considering the thermodynamic aspects of NR foam in compression. We found that the density and compression strength of NR foams increased with increasing NR matrix concentration. The mechanical properties of NR foam were in agreement with computational modelling. Moreover, thermodynamic aspects showed that the ratio of internal energy force to the compression force, Fu/F, and the entropy, S, increased with increasing matrix concentration. The activation enthalpy, ∆Ha, also increased with increasing matrix concentration in the NR foam, indicating the greater relaxation time of the backbone of the rubber molecules. New scientific concepts of thermodynamic parameters of the crosslinked NR foam in compression mode are proposed and discussed. Our results will improve both the knowledge and the development of rubber foams based on the structure-properties relationship, especially the new scientific concept of the thermodynamical parameters under compression.

Effect of Fillers on the Recovery of Rubber Foam: From Theory to Applications

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (F_u/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆H_a) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading.

Chitosan and Natural Rubber Latex Biocomposite Prepared by Incorporating Negatively Charged Chitosan Dispersion

Generally, natural rubber/chitosan (NR/CT) biocomposites could be prepared by either mixing natural rubber latex (NRL) with CT acid solution or mixing dry NR with CT powder on mixing equipment. In the present work, a new mixing method has been proposed and properties of the obtained NR/CT biocomposites are investigated. CT particles were prepared to have a negative charge that could be dispersed in water by using a ball mill before mixing with NRL. The effects of CT loading varied from 0 to 8 phr on latex properties and physical properties of NR/CT biocomposite films were focused. The results showed that the viscosity of NRL increased with increasing CT loading. With increasing CT loading from 0 to 8 phr, 300% modulus of the NR/CT biocomposite film increased, whereas the opposite trend was found for elongation at break. Additionally, the presence of CT in the biocomposite resulted in an increased elastic modulus (E') in conjunction with enhanced antibacterial activity against Staphylococcus aureus (S. aureus).

Natural rubber modification as a pre-vulcanized latex impregnated with TiO2 for photo-catalytic degradation of gaseous benzene

Photocatalytic oxidation purposes an economical and environmental friendly process to remove benzene from indoor air pollution. However, the process efficiency is primarily dependent on catalytic-film. The main purpose of this study is to synthesize pre-vulcanized latex impregnated with TiO2 (PVL-TiO2 thin film) from natural rubber to be used in photo-catalytic oxidation for benzene removal in a reactor. PVL-TiO2 thin films were synthesized for 3 different dosages of TiO2, which were 5%, 15%, and 25% The outcome of this study offers the new application of modified natural rubber in terms of environmental and health care protection. Morphology of the synthesized films was analyzed by SEM. The results showed that TiO2 particles could be well dispersed all over the surface of the film, in which the best distribution could be found for the PVL-TiO2 15% thin film. Tensile stress of the films was analyzed using ASTM D412. Results showed that the stress of the films got higher with the increasing amount of TiO2 content. This indicates that TiO2 strengthened the PVL-TiO2 film because the uniformly distribution of TiO2 on the inner surface increased the strength of the film. The decomposition of PVL and PVL-TiO2 thin films was analyzed using thermo gravimetric analysis. The maximum weight loss rates in the range of 1.536-1.145 wt%/°C attained at between 380 - 382 °C TiO2 particles enhanced thermal stability of PVL-TiO2 thin films due to the high decomposition temperature of its properties and also acted as barrier for the heat transfer of the films. Specific surface area (SSA) of the films was analyzed using Brunauer-Emmett-Teller. Specific surface area increased as the increasing content of TiO2, which corresponded to the morphology analysis by SEM. The analysis of chemical functional group of thin films was performed using ATR-FTIR. The results of Crystal identification using XRD clearly showed good attachment of rutile TiO2 on the films. Finally, results of absorbance spectrums and band gap energy showed that PVL not only peg TiO2 particles but also reducing band gap energy which induced by S and ZnO. Therefore, PVL-TiO2 thin films could be used under visible light condition. The films were then used in the study of benzene removal in annular reactor. The highest removal efficiency (83%)for the PVL-TiO2 15% thin film was obtained. Comparing to the maximum removal efficiency for PVL film (28%), roughly 60% increase in efficiency was achieved. The PCO kinetics were well fit by a first order Langmuir-Hinshelwood model. The calculation of oxidation rate and percentage of residual intermediates indicated that accumulation of residual intermediates can occur on the active site and the gas phase, resulting in increasing of residual intermediates. The successful synthesis of PVL-TiO2 thin film provides new opportunity to use natural rubber in terms of environmental and health care protection.

A Facile Pathway to Modify Cellulose Composite Film by Reducing Wettability and Improving Barrier towards Moisture

The hydrophilic property of cellulose is a key limiting factor for its wide application. Here, a novel solution impregnation pathway was developed to increase the hydrophobic properties of cellulose. When compared with the regenerated cellulose (RC), the composite films showed a decrease in water uptake ability towards water vapor, and an increase of the water contact angle from 29° to 65° with increasing resin content in the composites, with only a slight change in the transmittance. Furthermore, the Young's modulus value increased from 3.2 GPa (RC film) to 5.1 GPa (RCBEA50 film). The results indicated that the composites had combined the advantages of cellulose and biphenyl A epoxy acrylate prepolymer (BEA) resin. The presented method has great potential for the preparation of biocomposites with improved properties. The overall results suggest that composite films can be used as high-performance packaging materials.

Efficient approach to improving the flame retardancy of poly(vinyl alcohol)/clay aerogels: incorporating piperazine-modified ammonium polyphosphate

Ammonium polyphosphates (APP) modified with piperazine (PA-APP) was used to improve the flame retardancy of poly(vinyl alcohol) (PVA)/montmorillonite (MMT) aerogels, which were prepared via an environmentally friendly freeze-drying method. The thermal stabilities of the samples were evaluated by thermogravimetric analysis (TG); the flammability behaviors of samples were investigated by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CC) tests. TG test results showed that the 5% weight loss temperature (T5%) of PVA/MMT/PA-APP was 10 °C higher than that of PVA/MMT/APP. In combustion testing, all of PVA/MMT/PA-APP aerogels achieved V-0 ratings and have a higher LOI values than the unmodified PVA/MMT aerogel. Moreover, the aerogel with 1% PA-APP5, which means that the content of piperazine is 5% in PA-APP, decreased the cone calorimetry THR value to 5.71 MJ/m(2), and increased the char residue to 52%. The compressive modulus of PVA/MMT/PA-APP was increased by 93.4% compared with PVA/MMT/APP because of the increase in interfacial adhesion between matrix and PA-APP fillers. The densities of the PVA/MMT/PA-APP samples were slightly lower than those of the unmodified aerogels because of reduced shrinkage in the presence of PA-APP. All the tests results indicated that the incorporation of PA-APP not only improved the thermal stability and flame retardancy of aerogels but also maintained their mechanical properties.

Reduction of the water wettability of cellulose film through controlled heterogeneous modification

A facile method had been applied to introduce hydrophobic properties to cellulose materials by incorporation of polyurethane acrylate (PUA) prepolymers into the porous structured cellulose matrix through dip-coating; then, PUA prepolymers were cured around interconnected cellulose fibers under UV light, encapsulating a cellulose matrix with a hydrophobic polymer shell. The characterization of the composite films confirmed the success of the heterogeneous modification, and the chemical structure of the cellulose matrix was preserved. The composite films integrated the merits of cellulose and PUA resin, but the highly hydrophilic behavior of cellulose has been reduced. Contact angle measurements with water demonstrated that the composite films had obvious hydrophobic properties and an obvious reduction in the water uptake and the permeability toward water vapor gas at different relative humidity was also observed. The transmittance of the composite films at 550 nm was about 85%. The thermal and mechanical properties of the composite films were improved when compared with that of PUA resin. The obtained composite based on cellulose and UV curing technology was a good choice for the development of biomass materials with modified surface properties.

MIXING SEQUENCE IN NATURAL RUBBER CONTAINING ORGANOCLAY AND NANO–CALCIUM CARBONATE TERNARY HYBRID NANOCOMPOSITES

Rubber nanocomposites containing one type of nanofiller are common and are widely established in the research field. In this study, natural rubber (NR) based ternary nanocomposites containing both calcium carbonate and organoclay have been characterized on the basis of morphology, cure characteristics, and physico-mechanical behavior. Natural rubber nanocomposite samples containing modified silicate (Cloisite 15A) and also nano-carbonate calcium were prepared using a laboratory internal mixer. The effect of the mixing sequence on the morphology and mechanical properties of the samples was investigated. Based on results of morphology and mechanical properties, the dual fillers phase nanocomposites (hybrid nanocomposite) perform better in comparison with single filler phase nanocomposites. The reinforcing capability of nano-CaCO3 and organoclay in NR was characterized by means of cure rheometry, morphology, and mechanical properties. NR/single filler phase and two filler phase nanocomposites were prepared by simple melt mixing method. Concentration of nano-CaCO3 and organoclay in NR was 10 and 5 parts per one hundred parts of rubber by weight, respectively. The microstructure and homogeneity of the compounds was confirmed by studying the dispersion of nanoparticles in NR via X-ray diffraction and field emission scanning electron microscopy. A more pronounced effect was achieved by using dual filler based nanocomposites as compared with single filler phase nanocomposites. The obtained results reveal that hybrid nanocomposites have more adequate morphology, rheometery, and mechanical behaviors as well as swelling resistance. The effect of mixing sequence of fillers has been studied in detail. Simultaneous addition of the two nanofillers to the NR compound would lead to better nanocomposite properties compared with other mixing sequences. Also, the results show that the mixing sequence of these nanofillers in NR has little effect on the performance of the nanocomposite.

NATURAL RUBBER HYBRID NANOCOMPOSITES REINFORCED WITH SWELLED ORGANOCLAY AND NANO-CALCIUM CARBONATE

Two natural rubber (NR) nanocomposites have been prepared with organoclay(MMT) and swelled organoclay (SMMT) using melt intercalation method. The effect of these two MMTss on the morphology, rheometery, and mechanical behaviors of NR has been evaluated. Scorch times for the MMT-filled compounds were very short compared to unfilled compounds. A more pronounced effect was achieved by using SMMT as reinforcing agent. The obtained results reveal that nanocomposites reinforced by SMMT have more adequate morphology, rheometery, and mechanical behaviors as well as swelling resistance. The microstructure of the NR/MMT systems was studied by x-ray diffraction and field emission scanning electron microscopy. Following, the effect of different content of nano-calcium carbonate on dispersion of MMT layers in NR/SMMT nanocomposites was investigated. The results show that the optimized value of filler in dual fillers-based nanocomposite systems was equal to 10 phr nano-calcium carbonate. NR based hybrid nanocomposites containing SMMT and nano-calcium carbonate was showed 445% increase in tensile strength, 144% stress improvement at 100% strain, and only 3% increase in elongation at break compared to pure NR.