Protein-free natural rubber

Investigate the anaerobic degradation of high-acetone latex wastewater with magnetite supplement

This study evaluated the effects of acetone on the anaerobic degradation of synthetic latex wastewater, which was simulated from the wastewater of the deproteinized natural rubber production process, including latex, acetate, propionate, and acetone as the main carbon sources, at a batch scale in 5 cycles of a total of 60 days. Fe3O4 was applied to accelerate the treatment performance from cycle 3. Acetone was added in concentration ranges of 0%, 0.05%, 0.1%, 0.15%-included latex, and 0.15%-free latex (w/v). In the Fe3O4-free cycles, for latex-added vials, soluble chemical oxygen demand (sCOD) was removed at 43.20%, 43.20%, and 12.65%, corresponding to the input acetone concentrations varying from 0.05% to 0.15%, indicating the interference of acetone for COD reduction. After adding Fe3O4, all flasks reported a significant increase in COD removal efficiency, especially for acetone-only and latex-only vials, from 36.9% to 14.30%-42.95% and 83.20%, respectively. Other highlighted results of COD balance showed that Fe3O4 involvement improved the degradation process of acetate, propionate, acetone, and the other COD parts, including the intermediate products of latex reduction. Besides, during the whole batch process, the order of reduction priority of the carbon sources in the synthetic wastewater was acetate, propionate and acetone. We also found that the acetate concentration appeared to be strongly related to reducing other carbon sources in natural rubber wastewater. Microbial community analysis revealed that protein-degrading bacteria Bacteroidetes vadinHA17 and Proteinniphilum and methylotrophic methanogens might play key roles in treating simulated deproteinized-natural-rubber wastewater.

Effect of glycerol and dibutyl phthalate on modified natural rubber latex based drug delivery systems

The work highlights the impact of the incorporation of two pharmaceutical plasticizers viz.; glycerol (GLY; hydrophilic) and dibutyl phthalate (DBP; hydrophobic) on the controlled drug release features of a deproteinised natural rubber latex (DNRL) -based matrix. The effects of the plasticizers on the mechanical properties, glass transition temperature (T_g), water absorption behaviour and porosity of DNRL have been initially investigated. The plasticized membranes have been found to show a hemolysis percentage (HP) of <5 %; confirming its compatibility with human blood. The potential of the modified DNRL membranes to function as drug carriers have been examined with metformin hydrochloride (MET) as a model drug.

Recent development of biodegradable synthetic rubbers and bio-based rubbers using sustainable materials from biological sources

Rubber is an amorphous hyperelastic polymer which is widely used in this modern era. Natural rubber is considered the ultimate rubber in terms of mechanical performance, but over the years, some limitations and challenges in natural rubber cultivation that could result in serious shortages in the supply chain had been identified. Since then, the search for alternatives including new natural and synthetic rubbers has been rather intense. The initiative to explore new sources of natural rubber which started during the 1940s has been reignited recently due to the increasing demand for natural rubber. The commercialization of natural rubber from the Parthenium argentatum and Taraxacum kok-saghyz species, with the cooperation from rubber product manufacturing companies, has somewhat improved the sustainability of the natural rubber supply chain. Meanwhile, the high demand for synthetic rubber drastically increases the rate of depletion of fossil fuels and amplifies the adverse environmental effect of overexploitation of fossil fuels. Moreover, rubber and plastic products disposal have been a major issue for many decades, causing environmental pollution and the expansion of landfills. Sustainable synthetic rubber products could be realized through the incorporation of materials from biological sources. They are renewable, low cost, and most importantly, biodegradable in nature. In this review, brief introduction to natural and synthetic rubbers, challenges in the rubber industry, alternatives to conventional natural rubber, and recent advances in biodegradable and/or bio-based synthetic rubbers are discussed. The effect of incorporating various types of biologically sourced materials in the synthetic rubbers are also elaborated in detail.

Improving Deproteinization in Colombian Latex from Hevea brasiliensis: A Bibliometric Approximation

Natural Rubber Field Latex (NRFL) allergens restrict its use in some markets due to health-threatening allergic reactions. These molecules are proteins that are related to asymptomatic sensitization and hypersensitivity mediated by immunoglobulin E (IgE). Although NRFL allergens have been investigated since the 1980s, there are still gaps in knowledge regarding the development of deproteinized natural rubber (DPNR). Therefore, in this study, the deproteinization of NRFL from the lower basin of the Cauca River, Antioquia-Colombia was evaluated using eight systems. The highest removal value was 84.4% and was obtained from the treatment containing SDS (Sodium dodecyl sulfate), Urea, and Ethanol. It was also possible to determine that at high concentrations of SDS, removal percentages higher than 70% are reached. On the other hand, all deproteinizing systems decreased NRFL Zeta potentials without self-coagulation, suggesting enhanced colloidal stability in DPNR latex. On the other hand, the bibliometric analysis presented technological advances in DPRN through different parameters and bibliometric networks. The analysis presented makes an important contribution from the bibliometric approach that could be positive for the development of research on DPNR.

The role of natural rubber endogenous proteins in promoting the formation of vulcanization networks

Non-rubber components are critical in the formation of the natural rubber (NR) vulcanization network, which leads to outstanding mechanical properties of NR. This study reports the effect of NR endogenous proteins (C-serum protein/lutoid protein [CSP/LP]) on the formation of vulcanization networks at the molecular level. Results indicate that CSP/LP has a positive effect on vulcanization. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses demonstrate that the decrease in vulcanization time of CSP/LP is ascribed to coordination interaction between Zn2+ and amide bond. The interaction increases the availability of ZnO in the matrix, thereby promoting the formation of the vulcanized network. CSP/LP also participates in the construction of the vulcanization network as a new crosslinking point, thus increasing crosslinking density and improving the mechanical properties of the NR. This study provides new research ideas for studying the relationship among component–structure–property of NR materials and developing high-strength and high-toughness elastomer materials.

Identification and transcriptional analysis of poly(cis-1,4-isoprene) degradation gene in Rhodococcus sp. strain RDE2

The microbial degradation of synthetic and natural poly(cis-1,4-isoprene) rubber is expected to become an alternative treatment technique for waste from poly(cis-1,4-isoprene) products, such as scrap tires. A gram-positive rubber-degrading bacterium, Rhodococcus sp. strain RDE2, was isolated from the waste of a rubber-processing factory in Vietnam. This strain grew on natural rubber as a sole source of carbon and energy and produced oligo-isoprenoid metabolites containing aldehyde groups from poly(cis-1,4-isoprene). To identify the genes responsible for poly(cis-1,4-isoprene) degradation, the complete genome sequence of this strain was determined. The complete genome sequence consists of a 5,715,406 bp chromosome and 6 plasmids (GenBank accession numbers AP025186.1 to AP025192.1) with an average GC content of 67.9%. The genome contains 5358 protein-coding sequences and 12 and 68 copies of rRNA and tRNA genes, respectively. Based on genome sequence analysis, the lcp gene (RDE2_08,770), responsible for the initial step of poly(cis-1,4-isoprene) degradation, was identified. The gene product obtained from Escherichia coli depolymerizes poly(cis-1,4-isoprene) to low-molecular-weight oligo-isoprenoids. The transcription of this gene is activated during the utilization of poly(cis-1,4-isoprene) in strain RDE2. The lcpR gene (RDE2_08,760), which encodes a putative transcriptional regulator, is located upstream of lcp. The lcpR gene product recognizes the promoter region of lcp. When the lcpR gene is deleted, the constitutive transcription of lcp is observed. Thus, it is inferred that the LcpR negatively regulates lcp transcription. These results strongly suggest that the lcp and lcpR genes are involved in poly(cis-1,4-isoprene) utilization in strain RDE2.

Study of Aquilaria crassna Wood as an Antifungal Additive to Improve the Properties of Natural Rubber as Air-Dried Sheets

Fungal growth on rubber sheets confers inferior properties and an unpleasant odor to raw natural rubber (NR) and products made from it, and it causes environmental concerns. The purpose of the present work was to investigate the effects of Aquilaria crassna wood (ACW) on the antifungal, physical and mechanical properties of NR as air-dried sheets (ADS) and ADS filled with ACW. The results show that the ACW-filled ADS had an increased Mooney viscosity, initial plasticity (P_O), and high thermo-oxidation plasticity (i.e., high plasticity retention index PRI). Additionally, superior green strength was observed for the ACW-filled ADS over the ADS without additive because of chemical interactions between lignin and proteins in NR molecules eliciting greater gel formation. A significant inhibition of fungal growth on the NR products during storage over a long period (5 months) was observed for ACW-filled ADS. Thus, it can be concluded that ACW could be applied as an antifungal additive that reduces fungal growth. This is a practically important aspect for the rubber industry, as fungal growth tends to spoil and cause the loss of NR sheets during storage. Moreover, the ACW is active as an incense agent, reducing negative impacts from odors that fungi, on rubber surfaces, release. Therefore, these filled intermediate NR products provide added value through, an environmentally friendly approach, this is pleasant to customers.

PROTEIN INFLUENCE ON THE MECHANICAL PROPERTIES OF NR

Effect of protein on vulcanization of NR, obtained from Hevea brasiliensis, was investigated by analyzing the crosslinking structure of the resulting vulcanizates prepared from untreated NR, deproteinized natural rubber (DPNR), and protein-free natural rubber (PFNR) by swelling methods and rubber-state NMR spectroscopy. The proteins present in NR were removed by three methods: deproteinization with enzyme, urea, or urea–acetone in the presence of sodium dodecyl sulfate. The amount of proteins present in NR, approximately 0.238 w/w%, was reduced to 0.000 w/w% by urea–acetone deproteinization, whereas it was reduced to approximately 0.003 and 0.019 w/w% by enzyme and urea deproteinizations, respectively. Hardness, swelling degree, and crosslinking structure depended on the amount of proteins. Changes in mechanical properties for the vulcanizates prepared from not only non-filler compounds but also carbon black–filled and silica-filled compounds were attributed to the amount of proteins.

Effect of protein on the thermogenesis performance of natural rubber matrix

Under high-speed strain, the thermogenesis performance of natural rubber products is unstable, leading to aging and early failure of the material. The quality of rubber latex and eventually that of the final products depends among others on the protein content. We found that when the protein is almost removed, the heat generated by the vulcanized rubber increases rapidly. After adding soy protein isolate to the secondary purification rubber, the heat generation of the vulcanized rubber is reduced, and the heat generation is the lowest when the added amount is 2.5–3.0 phr, which on account of protein promotes the construction of a vulcanization network and increases the rigidity of the rubber chain, resulting in a decrease in the potential frictional behavior of the rubber chain during the curl up-extension process.

Characterization of the genes responsible for rubber degradation in Actinoplanes sp. strain OR16

A Gram-positive rubber-degrading bacterium, Actinoplanes sp. strain OR16 (strain NBRC 114529), is able to grow on agar plates containing natural and synthetic rubber as the sole sources of carbon and energy. When this strain was grown on natural rubber latex overlay agar plates, translucent halos around the cells were observed. To identify the natural rubber degradation genes and other features of its metabolism, its complete genome sequence was determined. The genome of OR16 consists of 9,293,892 bp and comprises one circular chromosome (GenBank accession number AP019371.1) with a G + C content of 70.3%. The genome contains 8238 protein-coding and 18 rRNA genes. A homology search of the genome sequence revealed that three genes (lcp1, lcp2, and lcp3) are homologous to an extracellular latex-clearing protein (Lcp) of Streptomyces sp. K30. RT-PCR analysis revealed that lcp1 and lcp2 seem to constitute an operon. Purified lcp gene products have oxygen consumption activity toward natural rubber latex, suggesting that all these genes encode rubber-degrading enzymes in OR16. Quantitative reverse transcription-PCR analysis indicated that the transcription of these genes is induced during the growth of OR16 on natural rubber. The genes located adjacent to lcp1 and lcp3, which code for a TetR/AcrR-type transcriptional regulator, can bind to the promoter regions of these lcp genes. It is suggested that the putative regulators play a role in regulating the transcription of the lcp genes. These results strongly suggested that three lcp genes are required for the utilization of natural rubber in strain OR16. Key Points • The complete genome sequence of Actinoplanes sp. strain OR16 was determined. • Three lcp genes which are involved in the natural rubber degradation in OR16 were identified. • Transcription of these lcp genes is induced during utilization of rubber in OR16. • Two regulators, which bind to the promoter regions of lcp, were determined.

Enhancement of the Antibacterial Activity of Natural Rubber Latex Foam by Blending It with Chitin

To enhance the antibacterial activity of natural rubber latex foam (NRLF), chitin was added during the foaming process in amounts of 1-5 phr (per hundred rubber) to prepare an environmentally friendly antibacterial NRLF composite. In this research, NRLF was synthesized by the Dunlop method. The swelling, density, hardness, tensile strength, elongation at break, compressive strength and antibacterial activity of the NRLFs were characterized. FTIR and microscopy were used to evaluate the chemical composition and microstructure of the NRLFs. The mechanical properties and antibacterial activity of the NRLF composites were tested and compared with those of pure NRLF. The antibacterial activity was observed by the inhibition zone against E. coli. NRLF composite samples were embedded in a medium before solidification. The experimental results of the inhibition zone indicated that with increasing chitin content, the antibacterial activity of the NRLF composites increased. When the chitin content reached 5 phr, the NRLF composite formed a large and clear inhibition zone in the culture dish. Moreover, the NRLF-5 phr chitin composite improved the antibacterial activity to 281.3% of that of pure NRLF against E. coli.

Development and Characterization of Bacterial Cellulose Reinforced with Natural Rubber

Films of bacterial cellulose (BC) reinforced by natural rubber (NR) with remarkably high mechanical strength were developed by combining the prominent mechanical properties of multilayer BC nanofibrous structural networks and the high elastic hydrocarbon polymer of NR. BC pellicle was immersed in a diluted NR latex (NRL) suspension in the presence of ethanol aqueous solution. Effects of NRL concentrations (0.5%–10% dry rubber content, DRC) and immersion temperatures (30–70 °C) on the film characteristics were studied. It was revealed that the combination of nanocellulose fibrous networks and NR polymer provided a synergistic effect on the mechanical properties of NR–BC films. In comparison with BC films, the tensile strength and elongation at break of the NR–BC films were considerably improved ~4-fold. The NR–BC films also exhibited improved water resistance over that of BC films and possessed a high resistance to non-polar solvents such as toluene. NR–BC films were biodegradable and could be degraded completely within 5–6 weeks in soil.

Complete genome sequence of natural rubber-degrading, gram-negative bacterium, Rhizobacter gummiphilus strain NS21T

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The genome sequence of rubber-degrading Rhizobacter gummiphilus NS21^T was determined.

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An alternative rubber-degrading gene (latA2) was identified.

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β-oxidation pathway genes which is involved in the rubber degradation were predicted.

Gram-negative natural rubber-degrader, Rhizobacter gummiphilus NS21^T, which was isolated from soil in the botanical garden in Japan, is a newly proposed species of genus of Rhizobacter. It has been reported that the latA1 gene is involved in the natural rubber degradation in this strain. To gain novel insights into natural rubber degradation pathway, the complete genome sequence of this strain was determined. The genome of strain NS21^T consists of 6,398,096 bp of circular chromosome (GenBank accession number CP015118.1) with G + C content of 69.72%. The genome contains 5687 protein-coding and 68 RNA genes. Among the predicted genes, 4810 genes were categorized as functional COGs. Homology search revealed that existence of latA1 homologous gene (latA2) in this genome. Quantitative reverse-transcription-PCR and deletion analyses indicated that natural rubber degradation of this strain requires latA2 as well as latA1.

Novel membranes from physico-chemically modified deproteinized natural rubber latex: development, characterisation and drug permeation

Novel blend membranes from physico-chemically modified deproteinized natural rubber latex for drug release applications.

Deproteinised natural rubber latex grafted poly(dimethylaminoethyl methacrylate) - poly(vinyl alcohol) blend membranes: Synthesis, properties and application

Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical modifications to make high functional membranes for drug delivery applications. Initially, DNRL was prepared by incubating with urea, sodiumdodecylsulphate and acetone followed by centrifugation. The deproteinisation was confirmed by CHN analysis. The DNRL was then chemically modified by grafting (dimethylaminoethyl methacrylate) onto NR particles by using a redox initiator system viz; cumene hydroperoxide/tetraethylenepentamine, followed by dialysis for purification. The grafting was confirmed by dynamic light scattering, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The grafted system was blended with a hydrophilic adhesive polymer PVA and casted into membranes. The membranes after blending showed enhanced mechanical properties with a threshold concentration of PVA. The moisture uptake, swelling and water contact angle experiments indicated an increased hydrophilicity with an increased PVA content in the blend membranes. The grafted DNRL possessed significant antibacterial property which has been found to be retained in the blended form. A notable decrease in cytotoxicity was observed for the modified DNRL membranes than the bare DNRL membranes. The in-vitro drug release studies using rhodamine B as a model drug, confirmed the utility of the prepared membranes to function as a drug delivery matrix.

Identification of natural rubber degradation gene in Rhizobacter gummiphilus NS21

A Gram-negative rubber-degrading bacterium, Rhizobacter gummiphilus NS21 grew and produced aldehyde metabolites on a deproteinized natural rubber (DPNR)-overlay agar medium forming a clearing zone. A transposon-insertion mutant, which had lost the ability to degrade DPNR, was isolated to identify the rubber degradation genes. Sequencing analysis indicated that the transposon was inserted into a putative oxygenase gene, latA. The deduced amino acid sequence of latA has 36% identity with that of roxA, which encodes a rubber oxygenase of Xanthomonas sp. strain 35Y. Phylogenetic analysis revealed that LatA constitutes a distinct group from RoxA. Heterologous expression in a Methylibium host and deletion analysis of latA indicated that the latA product is responsible for the depolymerization of DPNR. The quantitative reverse transcription-PCR analysis indicated that the transcription of latA is induced during the growth on DPNR. These results strongly suggest that latA is directly involved in the degradation of rubber in NS21.

New Elastomeric Materials Based on Natural Rubber Obtained by Electron Beam Irradiation for Food and Pharmaceutical Use

The efficiency of polyfunctional monomers as cross-linking co-agents on the chemical properties of natural rubber vulcanized by electron beam irradiation was studied. The following polyfunctional monomers were used: trimethylolpropane-trimethacrylate, zinc-diacrylate, ethylene glycol dimethacrylate, triallylcyanurate and triallylisocyanurate. The electron beam treatment was done using irradiation doses in the range of 75 kGy-300 kGy. The gel fraction, crosslink density and effects of different aqueous solutions, by absorption tests, have been investigated as a function of polyfunctional monomers type and absorbed dose. The samples gel fraction and crosslink density were determined on the basis of equilibrium solvent-swelling measurements by applying the modified Flory-Rehner equation for tetra functional networks. The absorption tests were done in accordance with the SR ISI 1817:2015 using distilled water, acetic acid (10%), sodium hydroxide (1%), ethylic alcohol (96%), physiological serum (sodium chloride 0.9%) and glucose (glucose monohydrate 10%). The samples structure and morphology were investigated by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy techniques.

New green polymeric composites based on hemp and natural rubber processed by electron beam irradiation

A new polymeric composite based on natural rubber reinforced with hemp has been processed by electron beam irradiation and characterized by several methods. The mechanical characteristics: gel fraction, crosslink density, water uptake, swelling parameters, and FTIR of natural rubber/hemp fiber composites have been investigated as a function of the hemp content and absorbed dose. Physical and mechanical properties present a significant improvement as a result of adding hemp fibres in blends. Our experiments showed that the hemp fibers have a reinforcing effect on natural rubber similar to mineral fillers (chalk, carbon black, silica). The crosslinking rates of samples, measured using the Flory-Rehner equation, increase as a result of the amount of hemp in blends and the electron beam irradiation dose increasing. The swelling parameters of samples significantly depend on the amount of hemp in blends, because the latter have hydrophilic characteristics.