Natural Rubber Latex Films Research Articles

Synergistic effects of chitosan and gamma irradiation on enhanced fungal growth inhibition and biodegradability of natural rubber latex film

Developing novel formulations and processes to improve the fungal growth inhibition and biodegradability of NR products has become a major challenge for the scientific community, given the health risks associated with fungi in natural rubber (NR) products and the environmental concerns regarding NR waste. Consequently, this study comprehensively investigated the synergistic effects of chitosan and gamma irradiation on enhancing fungal growth inhibition and biodegradability in natural rubber latex (NRL) films. The research involved incorporating varying chitosan contents (0, 3, 6, or 9 phr) into NRL composites and exposing them to different gamma doses (0, 5, 10, or 15 kGy). The results showed that increasing the chitosan content and the gamma dose improved the ability of the NRL samples to inhibit fungal growth on their surfaces. This was evidenced by the absence of fungal colonies after 7 days of incubation on potato dextrose agar (PDA) plates for NRL samples irradiated at 5–15 kGy with 9 phr of chitosan. This determination was based on isolating fungi from the film surfaces, followed by serial dilution and a viable plate count. The biodegradability tests also revealed that the NRL films irradiated at 15 kGy with 9 phr of chitosan had the highest weight loss, reaching as high as 10.42 ± 0.62 % after soil burial for 8 weeks. However, the results indicated that gamma irradiation on the pristine NRL and chitosan/NRL films did not substantially alter the thermal stabilities, density, morphology, and functional groups of the samples. Lastly, by comparing the tensile properties of all the NRL films to the ASTM D3578-01a standard for examination gloves, the optimum conditions for the NRL films were 5 kGy of gamma irradiation with 9 phr of chitosan. This combination resulted in gloves with sufficient tensile strength and complete fungal growth inhibition.

Natural Rubber Latex-Modified Concrete with Bottom Ash for Sustainable Rigid Pavements

This article investigates the viability of using natural rubber latex (NRL)-modified concrete with bottom ash (BA) as a partial replacement for river sand in sustainable rigid pavements. Concrete mixes with 10% and 20% BA replacement ratios and varying NRL dosages (0%, 1.0%, 1.5%, and 2.0% by weight of cement) were prepared and evaluated for their mechanical and microstructural characteristics. Results showed that BA substitution decreased the compressive strength of concrete. However, the addition of NRL at an optimal dosage of 1.0% significantly improved both the compressive and flexural strengths. The 10%BA+1.0%NRL and 20%BA+1.0%NRL mixes exhibited mechanical properties surpassing the control mix and meeting the minimum requirements for rigid pavement materials. However, excessive NRL content (1.5% and 2.0%) led to a reduction in mechanical strength. Scanning electron microscopy analysis exhibited a denser and more compact matrix in NRL-modified BA concrete, with NRL films enhancing the interfacial bonding and crack-bridging mechanism. Nonetheless, excessive NRL content resulted in the formation of abundant and thicker NRL films, which disrupted the continuity of the cement matrix and created weak zones. X-ray diffraction analysis confirmed the existence of crucial crystalline phases and their optimal balance in the 20%BA+1.0%NRL mix, contributing to its superior performance. Mixes with excessive NRL contents exhibited lower intensities of quartz, calcite, and portlandite peaks, indicating a disturbance in the proper formation and growth of essential crystalline phases. The findings demonstrated the potential of NRL-modified BA concrete as an eco-friendly and high-performance alternative for sustainable rigid pavements when using an optimal NRL dosage, promoting the employment of waste resources and reducing the environmental impact of the construction industry. Doi: 10.28991/CEJ-2024-010-08-05 Full Text: PDF

Synergistic Effect of Natural Rubber Latex Film Filled with Corn Starch

Synergistic Effect of Natural Rubber Latex Film Filled with Corn Starch

Effectiveness of Starch Nanocrystals on Mechanical and Shape Memory Behaviour of Smart Rubber

Shape memory rubber (SMR) is a type of smart rubber that can undergo reversible changes when exposed to external stimuli such as temperature, solvent, pH, light, magnetic field and oxidation. Lightly crosslinked rubber demonstrated shape memory behaviour without any initial heat treatment. However, the strength of lightly crosslinked natural rubber latex (NRL) film cured by sulphur is relatively low. With the concept of sustainability in mind, the idea of fabricating green smart material for continuous development has motivated researchers to explore the realms of sustainable materials. This research aims to investigate the mechanical behaviour of starch nanocrystals (SNC) reinforced rubber composite films. To this end, the emphasis is laid on evaluating the effectiveness of SNC on shape memory effect (SME) of rubber nanocomposite films. In the current work, up to 8 wt% of SNC synthesized by acid hydrolysis was incorporated into NRL and the mixture was cast to form rubber nanocomposite films. SNC effectively increased the modulus and energy-storing potential of the rubber nanocomposite films. Moreover, the shape memory behaviour of the rubber nanocomposite films improved significantly with SNC content, leading to increased shape fixity (Sf) and full shape recovery (Sr).

Preparation and Characterization of Poly(Methyl Methacrylate) Grafted Natural Rubber Latex Films

Poly(methyl methacrylate) (PMMA) grafted natural rubber (NR) latex was successfully prepared and solely exploited even at high MMA concentration (1.5 mol/kg-rubber) to make coherent and uniform vulcanized films without blending with other polymer to achieve excellent physical properties. High ammonia natural rubber (HANR) latex was subjected to graft-copolymerization with methyl methacrylate (MMA) monomer in the presence of tert-butyl hydroperoxide (TBHP) and tetraethylenepentamine (TEPA). High conversion, i.e., 85.12 mol%, and grafting efficiency, i.e., 92.70 mol%, were obtained at 1.5 mol/kg-rubber MMA. The resulting gross PMMA grafted NR (1.5PMMA) latex was then compounded, dipped, and vulcanized to produce thin films. The tensile strength and modulus at 300 percent (M300) of vulcanized 1.5PMMA film were superior to vulcanized HANR film by 1-fold. While elongation at break (EB) was identical to each other due to the high gel content in both vulcanized films. Besides, the vulcanized 1.5PMMA film absorbed less oil compared to HANR film. The thermal stability of vulcanized 1.5PMMA film was found to be higher than that of vulcanized HANR film. Hence, it can be deduced that controlling the graft-copolymerization of PMMA in NR latex is the key to produce coherent thin films with improved properties at higher PMMA content.

The Interplay of Protein Hydrolysis and Ammonia in the Stability of Hevea Rubber Latex during Storage.

Natural rubber (NR) latex derived from Hevea brasiliensis is a complex colloid comprising mainly rubber hydrocarbons (latex particles) and a multitude of minor non-rubber constituents such as non-rubber particles, proteins, lipids, carbohydrates, and soluble organic and inorganic substances. NR latex is susceptible to enzymatic attack after it leaves the trees. It is usually preserved with ammonia and, to a lesser extent, with other preservatives to enhance its colloidal stability during storage. Despite numerous studies in the literature on the influence of rubber proteins on NR latex stability, issues regarding the effect of protein hydrolysis in the presence of ammonia on latex stability during storage are still far from resolved. The present work aims to elucidate the interplay between protein hydrolysis and ammoniation in NR latex stability. Both high- and low-ammonia (with a secondary preservative) NR latexes were used to monitor the changes in their protein compositions during storage. High-ammonia (FNR-A) latex preserved with 0.6% (v/v) ammonia, a low 0.1% ammonia/TMTD/ZnO (FNR-TZ) latex, and a deproteinized NR (PDNR) latex were labeled with fluorescence agents and observed using confocal laser scanning microscopy to determine their protein composition. Protein hydrolysis was confirmed via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results revealed that protein hydrolysis increased with the storage duration. The change in protein composition accompanying hydrolysis also allows the spatial distribution of allergenic proteins to be estimated in the latex. Concurrently, the latex stability increased with the storage duration, as measured by the latex's mechanical stability time (MST) and the zeta potential of the latex particles. As monitored by AFM, the surface roughness of the NR latex film increased markedly during extended storage compared with that of the DPNR latex, which remained smooth. These results underscore the pivotal role of ammonia in bolstering NR latex stability brought on by protein hydrolysis, which greatly impacts latex film's formation behavior. NR latex stability underpins the quality of latex-dipped goods during manufacturing, particularly those for medical gloves.

Preparation and characterization of natural rubber latex films containing red propolis and copper for biomedical applications

Preparation and characterization of natural rubber latex films containing red propolis and copper for biomedical applications

Wetting-drying durability performance of cement-stabilized recycled materials and lateritic soil using natural rubber latex

This research was conducted to assess the role of natural rubber latex (NRL) in improving the durability of cement stabilized lateritic soil and recycled materials blends against wetting–drying (w-d) cycles. 70% and 50% by weight of recycled materials, including steel slag (SS) and recycled concrete aggregate (RCA) were replaced for Lateritic soil (LS) and 5% cement by weight of dry aggregate was used in this research. The dry NRL to cement (r/c) ratios of 0%, 3%, 5%, and 10% were the influence factor that were investigated. The unconfined compressive strength (UCS), physical and weight loss, water absorption, and microstructural analysis were performed to evaluate the influence of NRL on the durability of cement-NRL stabilized SS:LS and RCA:LS by comparison with those of control cement-stabilized mixtures (without NRL). The results indicated that the UCS development of all mixtures was found to be similar in that the UCS value increased up to the third w-d cycle and gradually decreased thereafter. The microstructural analysis result indicated that the increase of UCS during the w-d cycles can be attributed to the high temperature, which promotes the moisture diffusivity of cementitious materials and thus increases chemical reaction and strength development. However, with further increase of w-d cycles, the strength reduction was attributed to the Ca2+ leaching from the cement-stabilized materials during the soaking stages and the dissolution of cementitious products. In addition, the crack propagation and extension gradually caused the crumbling of samples and microcracks, resulting in the deterioration and strength loss of samples. It was evident that the formation of the NRL films filled up the pore spaces and microcrack, acting as NRL film crack-bridging mechanism, resulting in the enhanced interparticle bonding strength and durability.

Biodegradation of natural rubber latex films by highlighting the crosslinked bond

Natural rubber latex (NRL) films are used to manufacture single-use items such as condoms, blood transfusion tubes, and gloves. Natural rubber is a biopolymer, but the vulcanization process that imparts resilience and elasticity makes it difficult to degrade, resulting in an amount of waste that takes too long to biodegrade in the environment. This study evaluated the effect of crosslink bonds on the biodegradation of NRL films containing two accelerators, zinc diethyldithiocarbamate (ZDEC) and tetramethylthiuram disulfide (TMTD), in various sulfur-based curing systems. The NRL films were buried for up to 180 days and their physical, chemical, and mechanical properties were examined to determine biodegradability. Microorganism colonies were visible using scanning electron microscopy (SEM), and functional group alterations detected using Fourier transform-infrared spectroscopy (FTIR) indicated chain scission. The sample 0.6/0, followed by 1.2/0, showed a more pronounced Tonset decrease at 60 and 90 days of soil burial. At 180 days, there is no difference among the samples since all of them showed decreases in Tonset and Tmax of about 70 °C and 10 °C, respectively. Tensile strength of all samples decreased over time, but only the 0.6/0 NRL film had a decrease higher than 50% at 30 days. Additionally, lower mono- and disulfide bond concentrations result in greater tensile strength loss. Results indicated that NRL latex films with lower crosslink density and higher polysulfide bond content exhibited significant reductions in mechanical properties, indicating that these factors contribute to biodegradability.

Morphology and aggregation process of natural rubber particles

Natural rubber particles (NRPs) are the main place of natural rubber biosynthesis and storage which exist as the organelle in the latex tube cells of rubber trees. Here, we observed the aggregation process from the morphology of rubber particles and correlated the aggregate structure with the mechanical properties. The rubber particle sizes were first examined by optical microscopy, and the distribution showed a Gaussian curve with an average diameter of 1200 nm. Scanning electron microscopy (SEM) was then used to photograph the smaller particles, which supported a Gaussian distribution for NRPs smaller than 200 nm in diameter. They collectively indicated a bimodal distribution of NRP size, consistent with the results of the laser particle size analyzer. The percentage of the small rubber particles was measured to be 68.3 % and 31.7 % for the large rubber particles. The aggregation process of NRPs was observed as membrane fusion, superimposed aggregation, followed by the concavity of the inner core from the outside, and finally the formation of aggregated state rubber. Subsequently, the natural rubber latex films were obtained by spreading the latex at room temperature. The green strength was tested in its naturally dried stacked aggregated state, reaching a notable strength of 8 MPa. This was about 7 times higher than that of the ribbed smoked sheet (RSS). In contrast, when the naturally dried rubber film was processed by high-temperature molding and low-temperature setting, its green strength dropped to the level of the RSS. It thus supports that the processing methods, such as high temperature and shearing, could significantly impact the structure and performance of natural rubber (NR). Consequently, excellent performance of elastomeric materials might be reached under low-temperature drying and normal-temperature vulcanization processing methods.

Potential Bio-filler Cellulose Derived from Cucumber Pomace Filled Natural Rubber Latex Films

Potential Bio-filler Cellulose Derived from Cucumber Pomace Filled Natural Rubber Latex Films

Effect of wetting and drying cycles on mechanical strength of cement-natural rubber latex stabilized recycled concrete aggregate

In this study, natural rubber latex (NRL) was used as a polymer additive to modify the durability against wetting and drying (w-d) cycles of the cement-stabilized recycled concrete aggregate (RCA) when used as a pavement base/subbase material. This research investigated the performance of cement-stabilized RCA and cement-NRL stabilized RCA at various dry rubber-to-cement (r/c) ratios against w-d cycles. The weight loss, unconfined compressive strength (UCS), rate of deterioration, modulus of elasticity, and microstructural analysis of the studied samples before and after being subjected to w-d cycles were performed. The r/c ratio of 10% was found to be the optimum r/c ratio for cement-NRL stabilized RCA, which provided the best performance for all test results. The weight loss was found to increase, while the UCS value subsequently decreased with an increase of w-d cycles for all studied samples. At the optimum r/c ratio, the UCS results of cement-NRL stabilized after 12 w-d cycles were still higher than the minimum requirement (UCS > 2.413 MPa) for a high-volume traffic road. In addition, its modulus of elasticity was higher than that of cement-stabilized RCA samples. This indicated that the NRL additive could enhance the ductility of cement-stabilized RCA. The microstructural analysis illustrated that the formation of a stable cross-linked matrix between the cement hydration products and NRL films could improve the durability against the w-d cycles of cement-stabilized RCA as a pavement base material.

Excellent hydrophobic, superior ozone and UV resistant, and high thermal stable films from bio‐based natural rubber latex via fluorinating under mild conditions

AbstractAs a renewable and widely applied bio‐based material, the relatively weak resistance of natural rubber (NR) resulting from the inherent unsaturated structure to the harsh environments limits their further applications in some special areas. Thus, the fluorinated natural rubber (FNR) latex was prepared with fluorinated acrylate as the monomer in aqueous emulsion system at ambient temperature. The fluorinating reaction, the structure and morphology of NR latex were examined. It was demonstrated that as the intrinsic surface layer of NR latex particles, the non‐rubber component hindered the penetrating of fluorinated monomer or initiator radicals into the inner NR Latex particles and reduce the grafting reactivity. The fluorination renders the resultant FNR latex film strong hydrophobicity and superior environmental resistance to UV, ozone, and heat. The defective time of the FNR latex film improved 65 times as long as the net NR latex film via ozone aging. The thermal decomposition temperature increased by 37.0°C compared with net NR latex film. This work provides a facile way for preparation of FNR with excellent stability under extreme environments such as high ozone concentration, high UV intensity and high temperature.

Natural rubber latex films with effective growth inhibition against S. aureus via surface conjugated gentamicin

Hospital-associated infections and related complications are of extreme concern in the healthcare sector since biofilms generated over material surfaces not only create turbulence in the healthcare practices followed but also ruin the device performance, and increased medication, leading to significant chances of drug resistance. Natural rubber latex (NRL) being the first choice for the manufacture of several conventional biomedical devices, it is essential to ensure the surfaces of the same are inherently inactive against most microorganisms. This study presents NRL film surface conjugated with a well-known antibiotic, gentamicin through an amide linkage to generate antibacterial activity to the surface with a significant growth inhibition rate, especially against Staphylococcus aureus. The NRL films were surface-oxidized under controlled acidic conditions to generate carboxyl groups exploring the unsaturation of the base monomer unit. The carboxyl group reacts with the amine groups of gentamicin facilitating its surface conjugation. The surface anchoring was authenticated by FTIR-ATR complimented further by contact angle measurement as a function of hydrophilicity and elemental analysis by EDX spectroscopy. The antibacterial efficacy of modified NRL films was evaluated using antibacterial drop test and the results indicated a substantial growth inhibition rate (>60%) against Pseudomonas aeruginosa and Staphylococcus aureus. The study could be further optimized and proposed as a viable route for the conjugation of active molecules over inert polymer molecules.

Microwave-assisted silver-doped zinc oxide towards antibacterial and mechanical performances of natural rubber latex film

Microwave-assisted silver-doped zinc oxide towards antibacterial and mechanical performances of natural rubber latex film

Improved fatigue properties of cement-stabilized recycled materials – Lateritic soil using natural rubber latex for sustainable pavement applications

This research project investigates the role of a new recycled pavement material and natural rubber latex (NRL), in improving the resilient and fatigue performances of cement-stabilized recycled materials and lateritic soil (LS) blends under traffic loads. Two types of recycled materials, being steel slag (SS) and recycled concrete aggregate (RCA) and 5% cement content by weight were studied in this research. The dry rubber content in NRL to cement (r/c) ratios of 0%, 3%, 5%, 10%, and 15% were designed as the influence factor. The results indicated that mechanical strength properties namely unconfined compressive strength (UCS) and indirect tensile test (ITS), as well as fatigue properties namely indirect tensile resilient modulus (IT Mr) and indirect tensile fatigue (ITF) were enhanced with the NRL additive. Beyond the optimum r/c ratio, the excessive amount of NRL generated thick NRL films and retarded the cement hydration products, resulting in low strength and performance improvement. The r/c ratios of 3% and 5% were found to be the optimum r/c ratios for cement-NRL stabilized SS:LS and RCA:LS blends, respectively. The brittleness and permanent deformation of cement-stabilized SS/RCA:LS blends were significantly improved by the NRL additive. The superior mechanical and physical properties of SS and RCA were also attributed to the enhancement of fatigue characteristics of the cement-NRL stabilized blends. Finally, the mechanistic and fatigue models of cement- and cement-NRL stabilized soil with recycled material replacements were proposed, which are important for pavement designers and engineers when using a mechanistic-empirical pavement design approach.

Antioxidating and reinforcing effect of polydopamine functionalized silica on natural rubber latex films

AbstractSince the outbreak of COVID‐19, the demand for natural latex products with increased mechanical properties and aging resistance has surged. Based on the excellent adhesion and antioxidant properties of polydopamine (PDA), we employed a one‐pot method to modify the surface of silica substrates using PDA containing a polyphenol structure, to prepare a reinforced silica‐PDA composite latex material with antioxidant properties. As expected, the silica‐PDA composite achieved both uniform dispersion and good interfacial interactions with natural rubber latex (NRL). In addition, compared with common NRL/silica films, the mechanical properties of the NRL/silica‐PDA film were significantly improved; specifically, silica‐PDA can highly‐enhanced the mechanical property of NRL film from 24.94 to 32.18 MPa of tensile strength. Further, the antioxidant activity of the silica‐PDA film exceeded that of commercially available antioxidant D. Considering the notable performance boost of silica‐PDA composites on NRL films, we believe that the treatment of silica with natural polyphenols offers a convenient and facile new route for the preparation of environmentally friendly multifunctional silica additives.

Post-irradiation degradation of radio-oxidized natural rubber latex films induced by 60Co gamma rays

The present work involves the post-irradiation aging of radio-oxidized natural rubber latex (NRL) films irradiated by 60Co gamma rays. The NRL films underwent the two consecutive processes: irradiation oxidation in air with a dose of 0.1 kGy h−1 (pre-irradiation phase) and radiolysis in argon with a dose of 10 kGy h−1 (post-irradiation phase). The changes of oxygen-containing groups in radio-oxidized NRL films were subsequently analyzed by FTIR (ATR method), XPS, and Raman spectroscopy. Analysis of the EPR spectra of free radicals and macroscope properties (including mechanical and thermodynamic properties) were also carried out. Pre-irradiation of NRL films in air resulted in the rapid formation of various carbonyl and unsaturated carbonyl products related to aliphatic esters, ketones, and carboxylic acids. These were followed by the decomposition of the oxygen-containing functional groups in the post-irradiation phase. In particular, the formation of an enol tautomer of a β-diketone functionality was observed. The increase and decrease of free radicals by EPR analysis were closely related to the crosslinking and degradation of the NRL network structures induced by irradiation. Further analysis indicated that the variations in macroscopic properties of NRL films were attributed to the secondary reactions of free radicals. Mechanistic routes for these irradiation aging processes are proposed and discussed.

Natural fluorescent red colorants produced by Talaromyces amestolkiae as promising coloring agents for custom-made latex gloves

Synthetic-based colorants have been extensively used in several industries, viz., cosmeceutical, feed, pharmaceuticals, food and textile. However, the growing awareness of potential teratogenicity, carcinogenicity and environmental concerns of certain synthetic colorants have expressed several limitations regarding their use in some products. These limitations, justifies the motivation to look for eco-friendly alternatives (cf., natural colorants) to be used as coloring agents for industrial applications. The filamentous fungi Talaromyces amestolkiae appeared as a promising source of natural fluorescent red colorant (NFRC) for the development of custom-made latex gloves. In this study, some basic colorant properties, including 3D-fluorescence and CIELAB color characteristics were first investigated systematically before their incorporation in natural rubber latex (NRL) films. The NFRC-NRL films properties were evaluated by physicochemical tests and toxicity through cell viability using 3T3 fibroblasts, wherein eluate of NFRC-NRL films (2.28 AU) revealed viability >70 % (exposing the biocompatibility). Regardless of the strategy proposed, it is shown as a proof-of-concept the potential application of NFRC in the NRL matrix as a biocompatible alternative to produce sustainable commercial colored custom-made latex gloves.

Carboxymethyl chitosan capped copper oxide nanomaterials as antibacterial and antibiofilm coating for vulcanized natural rubber film

The constant menace of infections caused by many microorganisms is one of the significant concerns to humankind. Also, implant-associated biofilms are prevalent in the healthcare sector, which opens up the need for various protective armories against diseases, including antibacterial coatings. In the current context, developing an appropriate antibacterial coating for the materials utilized in the health sector has significance. Synthesis of copper oxide (CuO) nanoparticles (NPs) by the chemical precipitation method and capping of CuO with carboxymethyl chitosan (CMC) provides outstanding antibacterial action. Natural rubber is widely used for various biomedical purposes, regardless its dormancy against most pathogens. An economical and practical method has been developed to transform the Natural Rubber Latex (NRL) film surface to be sufficiently antibacterial by CuO/CMC lamination. This paper discusses the antibiofilm activity of the rubber films against Escherichia coli (MTCC No. 729) and Staphylococcus aureus (MTCC No. 902), and the non-cytotoxicity of the NRL films after CuO/CMC lamination. Hence this surface modification over the NRL film provides excellent prospects for antibacterial polymer materials.