Recycling of natural rubber latex waste and its interaction in epoxidised natural rubber

On the possibility of using waste disposable gloves as recycled fibers in sustainable 3D concrete printing using different additives

Due to the Covid-19 pandemic, using large amounts of personal protective equipment (PPE) throughout the world has extensively increased in recent years. The lack of a practical method to dispose of these recycled materials is one of the main concerns of researchers. Hence, comprehensive experimental tests were conducted in the present study to investigate the feasibility of using disposable gloves in mortars to achieve a sustainable mixture. Accordingly, latex and vinyl gloves as recycled fibers were considered in the experimental program to improve the sustainability of 3D printing concrete. As using these recycled materials causes some deficiencies for printing layers, different mineral and chemical admixtures were used in the present study, including graphene oxide nanomaterials, polyvinyl alcohol, Cloisite 15A nanoclay, and micro silica fume. Also, the hybrid use of latex, vinyl, and polypropylene (PP) fiber was considered to improve the printability of concrete mixtures containing waste fibers. Moreover, the effect of internal reinforcement was also considered by using plain steel wire mesh to increase the composite behavior of printed layers in this simplified experimental program. Results indicate that the synergic influence of recycled fibers and admixtures meaningfully enhanced the 3D printing properties of mortar so that about 20%, 80%, 50%, and more than 100% improvements were obtained for workability, direct tensile strength, flexural strength, and buildability index respectively. However, an average percentage - 28.3% reduction was recorded for the concrete compressive strength. Sustainability analysis also showed that using waste disposable gloves considerably reduced CO₂ emissions.

Elastocaloric Waste/Natural Rubber Materials with Various Crosslink Densities

The characterization of the mechanical behavior of elastocaloric materials is essential to identify their viability in heating/cooling devices. Natural rubber (NR) is a promising elastocaloric (eC) polymer as it requires low external stress to induce a wide temperature span, ΔT. Nonetheless, solutions are needed to further improve DT, especially when targeting cooling applications. To this aim, we designed NR-based materials and optimized the specimen thickness, the density of their chemical crosslinks, and the quantity of ground tire rubber (GTR) used as reinforcing fillers. The eC properties under a single and cyclic loading conditions of the resulting vulcanized rubber composites were investigated via the measure of the heat exchange at the specimen surface using infrared thermography. The highest eC performance was found with the specimen geometry with the lowest thickness (0.6 mm) and a GTR content of 30 wt.%. The maximum temperature span under single interrupted cycle and multiple continuous cycles were equal to 12 °C and 4 °C, respectively. These results were assumed to be related to more homogeneous curing in these materials and to a higher crosslink density and GTR content which both act as nucleating elements for the strain-induced crystallization at the origin of the eC effect. This investigation would be of interest for the design of eC rubber-based composites in eco-friendly heating/cooling devices.

Biomedical waste plastic: bacteria, disinfection and recycling technologies-a comprehensive review

Plastic recycling reduces the wastage of potentially useful materials as well as the consumption of virgin materials, thereby lowering the energy consumption, air pollution by incineration, soil and water pollution by landfilling. Plastics used in the biomedical sector have played a significant role. Reducing the transmission of the virus while protecting the human life in particular the frontline workers. Enormous volumes of plastics in biomedical waste have been observed during the outbreak of the pandemic COVID-19. This has resulted from the extensive use of personal protective equipment such as masks, gloves, face shields, bottles, sanitizers, gowns, and other medical plastics which has created challenges to the existing waste management system in the developing countries. The current review focuses on the biomedical waste and its classification, disinfection, and recycling technology of different types of plastics waste generated in the sector and their corresponding approaches toward end-of-life option and value addition. This review provides a broader overview of the process to reduce the volume of plastics from biomedical waste directly entering the landfill while providing a knowledge step toward the conversion of "waste" to "wealth." An average of 25% of the recyclable plastics are present in biomedical waste. All the processes discussed in this article accounts for cleaner techniques and a sustainable approach to the treatment of biomedical waste.

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Effect of Single-Walled Carbon Nanotubes on the Cross-Linking Process in Natural Rubber Vulcanization

In this study, the effect of single-walled carbon nanotubes (SWCNTs) on the cross-linking of natural rubber (NR) using organic peroxides was investigated. NR-SWCNTs nanocomposites were prepared in an open two-roller mill followed by vulcanization with the compression molding process. Three different organic peroxides, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (T29), dicumyl peroxide (DCP), and 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne (T145), were used as vulcanizing agents. SWCNTs promote a remarkable reduction in the vulcanization time and increase the degree of cross-linking of vulcanized rubber when compared with neat or natural rubber-carbon-black composites; the same tendency was obtained in the NR-SWCNTs vulcanized with sulfur. Additionally, the mechanical performance of the NR-SWCNTs composites was significantly improved up to 75, 83, 27, and 10% for tensile strength, moduli, tear strength, and hardness. Raman spectroscopy studies evidence the occurrence of reaction between nanotube walls and free radicals generated from using organic peroxides during the vulcanization process. These results demonstrate that the incorporation of SWCNTs in combination with the use of organic peroxides for the NR vulcanization represents a potential alternative for the improvement of the physicochemical properties of NR composites.

Cellulose nanocrystals as nucleating agents for the strain induced crystallization in natural rubber

Vulcanized natural rubber (NR)/cellulose nanocrystals (CNC) composites with a CNC content of up to 5 wt% using physical blending and dicumyl peroxide crosslinking were prepared. The tensile properties were investigated at slow and high strain rates. The slow strain rate tests revealed an increase of the elastic modulus concomitant with a decrease of strain at the crystallization onset while increasing the CNC fraction. The high strain rate tests performed near adiabatic conditions demonstrated the ability of the CNC to improve the elastocaloric properties of the NR matrix, with an increase of 30% and 15% of heating and cooling capacities, respectively, in the presence of 3 wt% CNC. Such results were ascribed to (i) a higher thermoelastic effect, due to strain amplification in the NR matrix in the presence of CNC and (ii) a nucleating effect of the CNC on strain induced crystallization. This series of materials can be proposed as a promising eco-friendly alternative to conventional carbon black filled rubber as potential green elastocaloric materials (heating pump, cooling machines).

Effect of latex reclaim on physico-mechanical and thermal properties of carbon black filled natural rubber/butadiene rubber composite

As a material having high rubber content, latex reclaim (white reclaim) has been used in the production of premium grade rubber products like tyres, retreading materials, etc. Introduction of latex reclaim (LR) is also an ideal method to reduce the cost of rubber products. In the present work, natural rubber (NR), butadiene rubber (BR), and latex reclaim (LR) combinations were prepared to develop cost efficient tread materials. LR was mixed with NR/BR at various proportions to produce tread materials which will comply with national specifications. The blends were prepared and the cure and mechanical properties were investigated. Results have indicated that the scorch time and cure time had decreased with the increase of reclaim loading. The mechanical properties like tensile strength, tear strength, abrasion resistance decrease with the increase in the LR content. It was found that 70–80% of the mechanical properties were retained even after addition of 30 phr of LR. The thermal behaviour and activation energy of NR/BR/LR system was investigated using thermogravimetry TGA analysis and increased activation energy showed that the thermal stability has increased when the amount of LR is high. SEM studies had indicated the morphology change due to the viscosity mismatch between NR and BR especially in the presence of LR.

Recycling of waste tire rubber: Microwave devulcanization and incorporation in a thermoset resin

This study focused on the possibility of recycling Waste Tire Rubber (WTR) to be used as polymer modifier. Thus, WTR was grinded into powder, at ambient temperature, with a disc mill PQ500 and microwave electromagnetic energy was used to devulcanize this powder with the final aim of producing a new composite by its incorporation in a thermoset resin. The influence of the treatment microwave energy on the devulcanization ratio was investigated. FTIR analysis revealed that rupture of Sulfur-Sulfur (SS) and Carbon-Sulfur (CS) bonds have occurred during the treatment. Swelling analysis showed that the microwave treatment can lead to a very significant degree of devulcanization. The Ground Tire Rubber (GTR) and the Devulcanized Ground Tire Rubber (DGTR) were then separately used to prepare epoxy based composites. It appeared that epoxy composites filled with DGTR have better mechanical properties than those filled with untreated GTR. This result agrees with scanning electron microscopy observations which highlighted a better interface coherence between DGTR and epoxy. A complementary analysis pointed out a linear relationship between the rubber modulus and the number of crosslink per chain.