Sulphur Prevulcanized Natural Rubber Research Articles

Effect of Latex Purification and Accelerator Types on Rubber Allergens Prevalent in Sulphur Prevulcanized Natural Rubber Latex: Potential Application for Allergy-Free Natural Rubber Gloves.

Natural rubber (NR) gloves manufactured from NR latex are widely utilized in various applications as a personal protective device due to their exceptional barrier characteristics in infection control. However, the use of NR gloves was associated with concerns on NR protein allergy. With comprehensive leaching procedures now a common practice in NR latex glove factories to eliminate latent rubber proteins and chemical allergens, occurrences and complaints of protein allergy from medical glove users have decreased drastically over the past two decades. The present work aims to eliminate further the residual rubber allergens in NR latex through effective purification of the NR latex and compounding the thus purified latex with an established formulation for allergy-free NR for glove applications. NR latex was purified by deproteinization and saponification, respectively. Several analytical techniques were used to verify rubber allergens eliminated in the purified latexes. Saponified NR (SPNR) latex was the purified NR latex of choice since it is devoid of allergenic proteins and poses the lowest risk of Type I allergy. The purified NR latex was compounded with zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), and zinc 2-mercaptobenzothiazole (ZMBT), respectively, for glove dipping. Among the investigated accelerators, only ZDBC was not detected in the artificial sweat that came into contact with the dipped articles. Thus, it is deduced that ZDBC poses the lowest risk of Type IV allergy to consumers. Additionally, the morphological and physical properties of dipped articles were assessed. It was revealed that the dipped film from the SPNR latex compounded with ZDBC provided thinner and less yellow products with a more uniform internal structure and a tensile strength comparable to those of commercial NR gloves.

Facile fabrication of high nanofiller-content natural rubber nanocomposites for reversible plasticity shape memory polymers

Reversible plasticity shape memory (RPSM) polymers that undergo a large deformation at room temperature and subsequently recover to their original shape upon heating is a new type of shape memory material just discovered in recent years. Herein, the RPSM polymers based on crosslinked natural rubber (NR) composites were fabricated by a simple ultrasonic mixing of zwitterionic chitin slurry, the precursor of chitin nanofibers (ChNFs), and sulfur-prevulcanized natural rubber latex (NRL) in aqueous media. The results showed that with the increase of the nanofiller content, the elastomer deformation of ChNFs/NR composites turned to plasticity deformation under uniaxially stretching. Meanwhile, the room-temperature plasticity deformation of ChNFs/NR composites with high nanofiller loading (>20 wt%) could be rapidly recovered in hot water (90 °C). Interestingly, it was also found that the stretch-induced crystallization of NR occurred at low strain (λ = 1) for the plasticity deformed ChNFs/NR composites, which is far lower than that of neat NR (λ > 4). Moreover, the stretch-induced crystals even persisted in the stretched high-content ChNFs/NR composites when the stress was unloaded. The significantly advanced stretch-induced crystallization of NR indicated the presence of strong interfacial interaction between ChNFs and NRL. To explain the RPSM behavior of as-prepared ChNFs/NR composites, the formation of ChNFs network and its water-induced softening mechanism were proposed to resist or give way to the recovery force of chemical crosslinking network in NR. This work provides a new insight into the fabrication of RPSM composites for promising applications.

Ecofriendly latex films from cassava starch-filled radiation pre-vulcanized natural rubber latex

ABSTRACTThe demands of the usage of hazardous ingredients for sulfur curing system in latex industries decrease with an increase in health-conscious and environmental awareness. This work demonstrates the incorporation of cassava starch (CS) as biodegradable fillers with natural rubber latex (NRL) through a sulfur-free crosslinking technique using radiation pre-vulcanization natural rubber latex (RVNRL) in comparison to sulfur pre-vulcanized natural rubber latex (PvNRL). The 20% CS dispersion was prepared, and 5–25 phr of dispersed CS content were compounded with NRL and formed into films by the coagulant dipping method. Microstructures and crystallinity of the films were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, and their mechanical properties of NRL/CS films were characterized by tensile and tear tests. The result revealed that the crystallinity of RVNRL films was lower than PvNRL films. The total bond of S−C from PvNRL contributes to high tensile strength compared to C−C intermolecular rubber bond from radiation vulcanization system. The trend of decrement of tensile properties from sulfur crosslinking was larger than radiation crosslinking, and both systems gave similar tensile behavior at 25 phr of CS content. This attributed to the better dispersion of CS in RVNRL as confirmed by SEM micrographs. It was found that the optimum tear strength of RVNRL/CS and PvNRL/CS films was obtained at 10 and 5 phr of filler content, respectively. The result presented in this study may facilitate a contribution to the current literature on the development of latex film by radiation pre-vulcanization for rubber industry in the future.

PMMA particles coated with chitosan-silver nanoparticles as a dual antibacterial modifier for natural rubber latex films

The antibacterial activity in sulphur prevulcanized natural rubber (SPNR) latex film was effectively improved by deposition of poly(methyl methacrylate) (PMMA) particles encircled with chitosan-coated silver nanoparticles (AgNPs-CS). With the focus on a green process, CS was selected as a safe reducing and stabilizing agent for the one-step synthesis of AgNPs-CS (38 nm, +40.4 mV) in an autoclave. The adsorption of small-sized AgNPs-CS directly onto rubber film did not provide an inhibitory effect on S. aureus. It also had a low antibacterial effect on E. coli. This is because of the particles becoming completely/partially submerged into the soft rubber matrix upon drying. Hence, the AgNPs-CS were fabricated as a shell surrounding a rigid PMMA core (496 nm, -30.9 mV). This was done using a heterocoagulation technique prior to coating on SPNR film. The presence of PMMA/AgNPs-CS on the surface of SPNR film effectively increased the surface roughness from ca. 44 to 150 nm. This substantially promoted the antibacterial activity against E. coli and S. aureus by way of contact killing and repelling mechanisms. The cytotoxicity on L-929 fibroblasts was also suppressed. This study would be, therefore, applicable to the development of antibacterial SPNR film with high surface roughness, low cytotoxicity. It could also be applied for other soft substrates.

Enhanced antibacterial activity of NR latex gloves with raspberry-like PMMA-N,N,N-trimethyl chitosan particles

Raspberry-like poly(methyl methacrylate) (PMMA) latex particles stabilized with silica nanoparticles (SiNPs) were prepared via the Pickering emulsion polymerization for use as substrate of N,N,N-trimethyl chitosan (TMC) adsorption. With the aims to simultaneously reduce the surface friction and improve the antibacterial activity of rubber gloves, the synthesized PMMA-SiNPs(TMC) particles were electrostatically deposited onto a sulphur prevulcanized natural rubber (SPNR) latex film. From SEM and AFM analyses, the results showed the highest surface coverage of PMMA-SiNPs(TMC) particles on the surface of SPNR film of 41% and the surface roughness of 69nm. The coated SPNR film exhibited effective antibacterial activity especially against S. aureus. Therefore, this investigation would be useful for fabrication of special gloves with antibacterial properties.

Preparation and Properties of Acidified Prevulcanized Natural Rubber Latex

After a maturation of three days at ambient temperature, the sulfur-prevulcanized natural rubber latex (SNRL) was stabilized by 20wt% Peregal O, and then acidified with the 36wt% acetic acid by a ratio of 5, 15, 25, 35 and 45 g of 36wt% acetic acid to 100g SNRL, to obtain acidified prevulcanized NR latex (ASNRL) with different acidity, respectively. The viscosity of ASNRL increased, while the nitrogen content decreased, with the increment of acetic acid content and the decrease in pH; for unaged samples, the tensile strength, elongation at break, 300% and 500% moduli of the ASNRL films were only slightly lower than those of SNRL film; however the hot-air aging resistance decreased with the increment of acetic acid content.

PMMA-N,N,N-trimethyl chitosan nanoparticles for fabrication of antibacterial natural rubber latex gloves

This paper presents one-pot synthesis of N,N,N-trimethyl chitosan (TMC) stabilized poly(methyl methacrylate) (PMMA) latex particles via the miniemulsion polymerization technique. From 1H NMR, synthesized TMC contains 52% degree of quaternization. Compared to native biopolymer chitosan, TMC possesses permanently positive charges as well as provides greater antibacterial activity. Combining properties of PMMA and TMC, PMMA–TMC latex nanoparticles (hydrodynamic size ≈282nm) could be used in place of inorganic lubricating powder in fabrication of latex gloves at pH ≥7. After immersing sulphur prevulcanized natural rubber (SPNR) film into 3wt% of PMMA–TMC latex at pH 7, significant amount of nanoparticles uniformly deposited onto SPNR film was observed under SEM. A number of nanoparticles present on film surface would increase surface roughness of the rubber film and potentially inhibit the bacterial (Escherichia coli and Staphylococcus aureus) growth, which would be useful for fabrication of special gloves with antibacterial property.

Surface Modification of Natural Rubber Film with PMMA Nanoparticles Stabilized by Chitosan or its Derivative

Poly(methyl methacrylate) (PMMA) latex particles stabilized by chitosan (CS) or N,N,N-trimethylated chitosan (TMC) (50% degree of quaternization) were prepared via the miniemulsion polymerization. The spherical PMMA-CS nanoparticles (342 nm) were then deposited onto sulphur-prevulcanized natural rubber (SPNR) film via the Layer-by-Layer (LbL) technique. The aims were to reduce the surface friction of rubber film and to avoid the direct contact between SPNR and human skin which might cause the allergic problem for some hypersensitive users. Results confirmed the presence of PMMA-CS particles which caused an increase in the surface roughness of SPNR from 46 to 57. However, the PMMA-CS did not exhibit the antimicrobial activity. Therefore, the antimicrobial activity against E.coli and S.aureus of the SPNR film coated with PMMA-TMC particles is investigated.

Reduction of cytotoxicity of natural rubber latex film by coating with PMMA-chitosan nanoparticles

Poly(methyl methacrylate) (PMMA) latex stabilized by chitosan (CS) oligomer was synthesized via the miniemulsion polymerization. By using 1% CS solution (in 0.1M acetic acid), the spherical PMMA-CS particles with an average size of 380nm were obtained. The positive zeta potentials at pH 2–7 confirmed the presence of CS as the outermost layer of the latex particles. Therefore, these particles directly interacted with the indigenous non-rubbers at the surface of sulphur prevulcanized natural rubber (SPNR) film. The deposition of PMMA-CS particles caused an increase in surface roughness of the coated SPNR film as a function of latex concentration and immersion time. The simple coating of the rubber substrate with PMMA-CS particles effectively reduced the in vitro cytotoxicity on L-929 cells. This study would be, therefore, helpful for development of latex gloves designed for hypersensitive users.

Green preparation and physical properties of maleated sulfur-prevulcanized natural rubber

The maleated sulfur-prevulcanized natural rubber (M-SPNR) was prepared from grafting maleic anhydride (MA) onto SPNR latex particle by using benzoyl peroxide as an initiator. Natural rubber latex particle was vulcanized first, and then it was maleated to M-SPNR. The average particle size of M-SPNR was greater than that of SPNR possibly due to the formation of aggregate after addition of MA. The symmetric (strong) and asymmetric (weak) carbonyl stretching vibrations of succinic anhydride rings were confirmed by ATR–FTIR at 1,780–1,784 and 1,854 cm−1, respectively. The swelling ratios of M-SPNR latex film decreased with increasing MA contents. The tensile strength, modulus, hardness, and elongation at break of SPNR latex film dramatically increased after grafting with MA. Due to the reduction of double bond, the thermal stability of M-SPNR film was better than that of SPNR. The environmental friendly M-SPNR would be further applied as a compatibilizer between NR and biopolymer.

Preparation and Properties of Interpenetrating Polymer Network Films from Prevulcanized Natural Rubber Latex/Chitosan Blends

The acidfied sulfur-prevulcanized natural rubber (NR) latex was mixed with 1～20 parts per hundred rubber (phr) of a 2wt% solution of chitosan (CS) in 1wt% acetic acid, then cast to preapare a series of NR/CS semi-interpenetrating polymer network (semi-IPN) films; the NR/CS semi-IPN films were further treated with 0.5wt% glutaraldehyde（GA）solution for respectively 1, 3 and 6h to obtain NR/CS IPN films. The mechanical properties and swelling behavours in various media of water, toluene and reference olis of IRM901 and IRM 903 of these films were studied and compared with those pure sulfur-prevulcanized natural rubber latex (SNRL) film. Results showed that, NR/CS IPN films with better mechanical properties could be obained by treating the 24h-leached NR/CS semi-IPN films than by treating directly the unleached ones with 0.5wt% GA solution; the tear strength, 300% modulus, Shore A hardness, hydrophilicity and resistance to non-polar solvents and oil of the SNRL films increased with the incorporation of CS, while the NR/CS IPN films exhibited better than the NR/CS semi-IPN films, especially in tear strength enhancement; the tensile strength and elongation at break of NR/CS semi-IPN and IPN films gradually decreased with the increase in CS content. However, most of the elasticity of pure NR vulcanizate could be reserved, when the CS content was not greater than 15 phr.

Physico‐mechanical properties of natural rubber sheets coated by polyethyleneimine‐functionalized poly(methyl methacrylate) nanoparticles

AbstractThe surface modification of sulfur‐prevulcanized natural rubber (SPNR) sheets by the polyethyleneimine‐functionalized‐poly(methyl methacrylate) (PMMA/PEI) nanoparticles was successfully performed via a simple dipping method. The percentage of surface coverage (Cs) of the nanoparticles on SPNR sheets was found to be affected by a variation of nanoparticle latex concentrations and immersion times. The adsorption isotherm of PMMA/PEI nanoparticles on SPNR sheets was analyzed and found to fit well to the Freundlich model. After coating, it can be observed that the presence of PMMA/PEI nanoparticles on SPNR surface had no effects over the SPNR mechanical properties e.g., tensile strength, elongation at break, and hardness. On the other hand, the coated SPNR sheets showed a reduction of surface friction coefficients and interfacial adhesion up to 45 and 59%, respectively. Furthermore, PMMA/PEI nanoparticles adsorbed on the SPNR surface was subjected to stretching and wearing conditions, and found to be stable for at least seven stretching and wearing cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In vitro cytotoxicity evaluation of natural rubber latex film surface coated with PMMA nanoparticles

In order to increase surface roughness of the sulphur-prevulcanized natural rubber (SPNR) film and, hence, decrease the direct contact between the rubber and skin, the poly(methyl methacrylate) (PMMA) latex particles were deposited onto the SPNR film grafted with polyacrylamide (SPNR-g–PAAm). The surface coverage of PMMA particles on the SPNR-g–PAAm increased with increasing latex immersion time, particle size and concentration. Prior to the in vitro cytotoxicity evaluation on L-929 fibroblasts, the SPNR and SPNR-g–PAAm coated with PMMA particles were extracted by using the culture medium. Results showed that the cytotoxicity effect could be significantly reduced by coating PMMA particles onto the rubber film. At the extract concentrations of ≤12.5% for 24 h at 37 °C, no toxicity potential was detected. The study will be helpful for development of gloves designed for the hypersensitive person.

Reduction of surface friction of natural rubber film coated with PMMA particle: Effect of particle size

The friction coefficient of the sulphur-prevulcanized natural rubber (SPNR) film could be effectively reduced by deposition of poly(methyl methacrylate) (PMMA) particles. The nanoscale surface roughness of rubber, determined by atomic force microscope, was directly proportional to the particle size of PMMA particle at 12% surface coverage (Cs). The %Cs and surface roughness of the modified SPNR increased, while the friction coefficient decreased, with increasing PMMA latex concentration and immersion time. By using a mixture of latexes having both large and small sizes, the increase in the amount of small particles resulted in the better distribution of large particles deposited on the rubber surface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Polyethyleneimine-functionalized poly(methyl methacrylate) colloidal nanoparticles for directly coating natural rubber sheet

This work illustrated a convenient surface modification of sulphur-prevulcanized natural rubber (SPNR) sheet with poly(methyl methacrylate) (PMMA) colloidal nanoparticles without pre-treatment of the rubber. The SPNR sheet was simply immersed into the latex of PMMA core that was functionalized with polyethyleneimine (PEI) shell (PMMA/PEI) via a soap-free emulsion polymerization. The presence of PMMA/PEI nanoparticles on the SPNR sheet was revealed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). It was also traced by the changes of surface roughness, adhesion force, and relative surface stiffness obtained from atomic force microscopy (AFM) analysis. The surface coverage ( C s) values depended on the variation of immersion time and particle concentration. Water contact angles on the PMMA/PEI-coated SPNR sheet decreased with increasing C s values.

Surface modification of sulphur prevulcanized natural rubber latex sheet via layer-by-layer assembled PMMA particles

Poly(methyl methacrylate) (PMMA) particles were deposited onto the sulphur prevulcanized natural rubber (SPNR) latex film by using the layer-by-layer (LbL) technique in order to increase the roughness and, hence, decrease the friction on the rubber surface. Prior adsorption of PMMA particles, the SPNR sheet was pretreated with argon plasma followed by UV-induced graft copolymerization of polyacrylamide (PAAm). The percent coverage of PMMA particles on the surface of substrate (Cs), determined under scanning electron microscope (SEM), was directly proportional to the latex concentration and immersion time. Apply the contraction–extension forces (at 300% strain) from 0 to 7 cycles on the modified SPNR sheet, SEM micrographs showed the slight decrease of Cs from 23 to 19%. The bulk properties, i.e., tensile strength and elongation at break, of the modified SPNR sheet not only insignificantly changed but also were in the range indicated in the standard glove's test (ASTM D 3577).