Pre-vulcanized Natural Rubber Research Articles

Optimized titanium dioxide loading for properties of natural rubber latex and acrylic emulsion blends

Blends of prevulcanized natural rubber (PVNR) and acrylic emulsion (AC) were prepared at the fixed PVNR/AC ratio of 30/70. Effects of titanium dioxide (TiO2) addition were optimized across the contents 0, 10, 20 and 30 parts per hundred parts of polymer (php) with respect to various properties. Morphological analysis revealed a two-phase system in which the PVNR particles were dispersed in the AC matrix. Incorporation of TiO2 induced a finer blend morphology in which a part of the TiO2 was located at the interfaces of blend components. The tensile strength increased with initial TiO2 loading and reached its maximum at 10 php loading, with an improvement by about 127% over the blend without filler. However, further increase in filler loading reduced the tensile strength, and the filler tended to agglomerate at those higher loadings. Thermal stability and storage modulus in rubbery region of the blends containing TiO2 were also improved over the unfilled blend, due to the improved morphology and the hydrogen bonds between TiO2 filler and polymer matrix. TiO2 improved water wettability and adhesion of the blend. The maximum peel strengths on wood and metal substrates were about 120% and 26% larger than for the reference unfilled blend. Such drastic improvements suggest that the filled blends may find applications as coating materials.

Preparation and Characterization of Easy Wrap Film Prepared from Domestically Polymeric Materials

Easy wrap film has been widely used a single use film for dust free storage and COVID 19 prevention during the global pandemic. In the study, natural rubber (NR) latex was chosen as the domestic raw material for a coating application. Sulfur pre-vulcanized NR (PVNR) latex was prepared and purposely planned to be mixed with PVAc-co-PVA (Polyvinyl acetate-co-polyvinyl alcohol) or copolymer as the coating product for the proposed easy wrap film. Role of ratio between polymeric materials in physical, mechanical, thermal and weather resistant properties of the prepared films was elucidated. Ability of spark resistance of the easy wrap film prepared from the polymer mixtures prepared was tested.

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.

Compositing prevulcanized natural rubber with multiwalled carbon nanotubes to make antistatic films

AbstractNatural rubber was prevulcanized using ultraviolet (UV) light and the resulting prevulcanized natural rubber (PVNR) was composited with multiwalled carbon nanotubes (MWCNT) as a conductive filler, to make films suitable for antistatic gloves. These films were characterized in terms of mechanical properties and electrical resistivity. Effects of type of UV radiation and other specifics of the production process, on mechanical properties of neat PVNR were first investigated. This was followed by an investigation of the effects of surfactant type on the dispersion of MWCNT in water and the PVNR matrix. Four surfactants with different headgroups were used in preparing MWCNT dispersions that were then mixed with the PVNR latex to form the different films. As a consequence of its milk‐like turbidity, the natural rubber latex was found to require deeply penetrating UVA light for satisfactory prevulcanization. Sodium dodecyl sulfate (SDS) was the best surfactant for dispersing MWCNT both in water and in PVNR matrix. SDS resulted in MWCNT–PVNR composite films with the least electrical resistivity and good mechanical properties for making antistatic gloves. SDS did not interfere with stress transfer at NR–MWCNT interface. SDS was superior to the other surfactants because its head group had a charge opposite to that on the NR surface and lacked a benzene ring that would have interacted strongly with the hydrophobic surface of MWCNT.

Study of the Effect of Ion implanation in Pre-vulcanized Natural rubber Latex

Study of the Effect of Ion implanation in Pre-vulcanized Natural rubber Latex

Effect of the Elastomer Matrix on Thermoplastic Elastomer-Based Strain Sensor Fiber Composites.

In this study, a thermoplastic elastomer sensor fiber was embedded in an elastomer matrix. The effect of the matrix material on the sensor properties and the piezoresistive behavior of the single fiber-matrix composite system was investigated. For all composites, cycling test (dynamic test) and the relaxation behavior at different strains (quasi-static test) were investigated. In all cases, dynamic properties and quasi-static significantly changed after embedding, compared to the pure fiber. The composite with the silicone elastomer PDMS (Polydimethylsiloxane) as matrix material exhibited deviation from linear response of the resistivity at low strains and proved an unsuitable choice compared to natural rubber. The addition of a spring construct in the embedded sensor fiber natural rubber composite improved the linearity at low strains but increased the mechanical and electrical hysteresis of the soft matter sensor composite. Using pre-vulcanized natural rubber improved linearity at low strains and reduced significantly the stress and relative resistance relaxation as well as the resistance hysteresis, especially if the resistance remained low. In both cases of the pre-vulcanized rubber and the spring structure, the piezoresistive behavior was improved, and at the same time, the stiffness of the system was increased indicating that using a stiffer matrix can be a strategy for improving the sensor properties.

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.

Prevulcanized natural rubber and carbon black: High-deformation piezoresistive composites

This work aimed at developing materials with the potential to be employed as high-deformation piezoresistive sensors based on conductive polymer composites, from prevulcanized natural rubber (PNR) and carbon black (CB). Materials were obtained by casting in different volumetric ratios of PNR/CB. The composite of PNR with a 7% inclusion of CB showed great potential for use as an electromechanical sensor: a linear behavior of the electric resistance with the mechanical deformation in repeated cycles with an appreciable gauge factor.

Surface treatment with microwave plasma improving PEDOT:PSS adhesion on natural rubber

Hydrophobic surface of pre-vulcanized natural rubber can be modified to a hydrophilic surface under plasma treatment. This is useful to make flexible and composite substrate from natural rubber in many applications. A low-cost microwave plasma cleaner was built using argon gas as a source for generating plasma. The plasma treatment conditions on rubber were investigated under two parameters: treatment time and treatment cycles. We found that the water contact angle was decreased when the pre-vulcanized natural rubber was treated more time or more cycles. To create the conductivity of natural rubber, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in water was spin on the treated rubber surface. The electrical measurement shows conductivity on the rubber surface with a uniform current-voltage relationship. Without plasma treatment, PEDOT:PSS hardly attached on surface yielding no conductivity appeared on natural rubber.

Removal of Surfactant from Nanocomposites Films Based on Thermally Reduced Graphene Oxide and Natural Rubber

Electrically conducting elastomer composites based on natural rubber and reduced graphene oxide (rGO) is reported. These composites were prepared by a latex method and an easy washing process. The latex method consists of the mixing of an aqueous suspension of rGO, stabilized by sodium dodecyl sulfate and pre-vulcanized natural rubber, followed by solvent casting. The percolation threshold of composites was estimated at 1.54 wt.% of rGO. The washing process allowed elimination of the surfactant completely from nanocomposites. The absence of surfactant in nanocomposites was demonstrated by Raman spectroscopy and dynamo-mechanical analysis. The surfactant-free nanocomposites showed improved mechanical and electrical properties.

Biodegradable IPN Hydrogels Based on Pre-vulcanized Natural Rubber and Cassava Starch as Coating Membrane for Environment-Friendly Slow-Release Urea Fertilizer

Biodegradable interpenetrating polymer network (IPN) hydrogels based on pre-vulcanized natural rubber (NR) and cassava starch (St) using sulphur (S) and glutaraldehyde (GA) as crosslinkers were developed in a solution form as a coating membrane for slow-release nitrogen fertilizer. The NR/St ratios affecting water swelling, water permeability and biodegradation were investigated. Results revealed that water swelling, water permeability and biodegradation of IPN NR/St hydrogels decreased with increasing NR content. The wax was used as outer coating shell to further improve the release characteristic of the coated urea. The urea bead (UB) coated with IPN NR/St and wax layers (W-IPN-CUB) exhibited exceptional release behavior up to 24 days in soil compared to native UB (3 days). The release mechanisms of W-IPN-CUB in both water and soil environments were a non-Fickian diffusion with n = 0.88 and 0.85, respectively, relating to the diffusion through porous membrane. Also, the W-IPN-CUB was able to slow the leaching of urea fertilizer and significantly improve the performances of corn and basil height compared to native UB (P < 0.05). Thus, the W-IPN-CUB material proved to be a good candidate material for slow release fertilizer which could be widely used in agricultural and horticultural applications.

Additive manufacturing of traditional ceramic powder via selective laser sintering with cold isostatic pressing

For improving the final density of traditional ceramic products via selective laser sintering (SLS), cold isostatic pressing (CIP) technologies were introduced into the process. The proposed approach in the work combined spray drying with mechanical mixing by which we prepared a kind of compound powder consisting of epoxy resin E06 (10 wt %) and kaolin so as to get a good fluidity for SLS. At the first step, SLS products reached the highest density of about 0.76 g/cm3 when the laser energy density was 0.3575 J/mm2, which facilitated the next operation and improvement of final density. Then, a soft polymer canning was prepared for CIP around the surface of SLS kaolin ceramic products using pre-vulcanized natural rubber latex RTV-2, gelation, and film. Following that, SLS green bodies were pressed with a holding pressure of 50 MPa. Based on thermal gravity curve of epoxy resin E06, green bodies were debinded and furnace-sintered. We experimented on different laser energy densities which had similar effects on densification of kaolin products in CIP, debinding, and sintering. Finally, the density of kaolin products reached 2.65 g/cm3 after high-temperature sintering process. Field emission scanning electron microscopy was used to analyze the densification evolvement in each stage of process and the fracture mechanism. The study showed a positive and practical approach to fabricate traditional ceramic products with complex shape by an additive manufacturing method of SLS.

Sulfur-Free Prevulcanization of Natural Rubber Latex by Ultraviolet Irradiation

The possibility of prevulcanizing natural rubber latex via ultraviolet (UV) irradiation was investigated using 2-hydroxy-2-methyl-1-phenylpropanone as the photoinitiator and 1,9-bis(acryloyloxy)nonane as the coagent. Effects of the following process variables were assessed on the tensile strength and the cross-link density of thin films prepared from the prevulcanized natural rubber (PVNR) latex: the duration of UV irradiation, the distance between the light source and the latex being irradiated, the mixing time of the latex with the coagent and the phtoinitiator, the depth of the latex pool, and the mass ratio of the photoinitiator to the coagent used. The PVNR films produced under optimal conditions had nearly 4-fold the tensile strength of the film produced without UV irradiation. Fourier transform infrared spectroscopy and 13C nuclear magnetic resonance spectroscopy were used to assess the UV reactions, and a mechanism was proposed for UV-induced prevulcanization with the above identified photoinitiat...

Effect of Micro and Nano Zinc Oxide on the Properties of Pre-Vulcanized Natural Rubber Latex Films

Zinc oxide (ZnO) nanoparticles were synthesized through a solution free mechano-chemical route and their effects on pre-vulcanized natural rubber latex properties were investigated. Effect of nano ZnO loading on swelling, antimicrobial, mechanical and ageing properties of pre-vulcanized latex vulcanizates were examined and compared with conventional micro ZnO filled vulcanizates. In comparison with micro filled system, nano filled system exhibits better performance in all respects. The ageing resistance of nano ZnO incorporated latex films was found to be high.

Reinforcing Natural Rubber with Cellulose Nanofibrils Extracted from Bleached Eucalyptus Kraft Pulp

Reinforced natural rubber (NR) nanocomposites were prepared by solution mixing. casting. and evaporation of pre-vulcanized natural rubber latex and an aqueous suspension of cellulose nanofibrils (CNFs) extracted from bleached eucalyptus kraft pulp. Scanning electron microscopy (SEM) images showed that there were no micro-scaled aggregates observed in the nanocomposites. The addition of CNFs changed the mechanical behavior of the nanocomposites as observed in tensile tests. The tensile strength was significantly enhanced with CNFs, but the material became brittle at higher CNFs loading levels. Dynamic mechanical analysis (DMA) proved the strong reinforcing tendency of CNFs in the NR matrix as the storage modulus of the nanocomposites increased with CNFs content across the entire temperature range. Thermal gravimetric analysis (TGA) showed that CNFs had a slightly negative impact on the thermal stability of NR nanocomposites. There was no change in the glass transition temperature of the rubber matrix with the addition of cellulose nanofibrils, which was characterized by differential scanning calorimetry (DSC) measurements.

Densification of alumina components via indirect selective laser sintering combined with isostatic pressing

To improve the final density of ceramic parts via indirect selective laser sintering (SLS), cold/hot isostatic pressing (CIP/HIP) technologies were introduced into the process. The proposed approach in the present study combined spray drying with mechanical mixing by which we prepared a kind of compound powder consisting of polyvinyl alcohol (PVA, 1.5 wt%), epoxy resin E06 (8 wt%), and alumina so as to get a good fluidity for SLS. At the first step, SLS parts reached the highest relative density of about 32 % when the laser energy density was 0.094 J/mm2, which facilitated the next operation and improvement of final density. Then, a soft polymer canning was prepared for CIP around the surface of SLS alumina ceramic parts using pre-vulcanized natural rubber latex RTV-2, gelation and film. Following that, we experimented on different CIP maximum pressure which had different effects on densification of SLS alumina parts, the whole process in CIP was divided into three stages of I, II, and III. Based on thermal gravity curve of epoxy resin E06, ignoring the impacts of the only 1.5 wt% PVA on degreasing, green bodies were degreased and furnace-sintered. Finally, the relative density of alumina parts reached 95.94 % after HIP process. Field emission scanning electron microscopy was used to analyze the densification evolvement in each stage of process and the fracture mechanism. The study showed a positive and practical approach to manufacture ceramic matrix and ceramic components with complex shape by indirect SLS technology.

Effects of different additions of sago starch filler on physical and biodegradation properties of pre-vulcanized NR latex composites

This paper presents results on the physical and biodegradation properties of pre-vulcanized natural rubber (NR) latex composites with sago starch as protein enhancer. Sago starch fillers are added into NR latex via Methods A (prior pre-vulcanization) and B (after pre-vulcanization) at 80°C. For the biodegradation process, composites are buried in soil and brought out on a weekly basis to investigate their mechanical and morphological properties. Results show that optimum filler loading are achieved at 10phr with optimum tensile properties. As the biodegradation periods elapse, the mechanical properties for both composites decrease, which indicates the occurrence of biodegradation process. Based on scanning electron microscope images, Method A shows better filler–rubber interaction system from the severed sago starch granular structure, whereas Method B gives better mechanical properties as evaluated from tensile properties.

Properties and recyclability of thermoplastic elastomer prepared from natural rubber powder (NRP) and high density polyethylene (HDPE)

Preparation of thermoplastic natural rubber (TPNR) was carried out by blending high density polyethylene (HDPE) with natural rubber powder (NRP) obtained from spray drying of pre-vulcanized natural rubber latex. The blend ratio of NRP/HDPE was varied and the properties and recyclability of the TPNRs were investigated. The results reveal that, due to flow restriction of the crosslinked NRP, viscosity of the TPNR increases continuously with increasing NRP content. As expected, when NRP content is increased, properties of the TPNR are more rubber-like, as clearly observed from the stress–strain curve characteristics, the reductions in modulus and hardness and, most importantly, the significant improvement of permanent set. Although phase size of the dispersed NRP is relatively large, the tensile strength tends to increase gradually with increasing NRP content. The phenomenon of strain-induced crystallization is proposed to explain the results. It is also found that recycling has a noticeably detrimental influence on most properties of the TPNRs such as tensile strength, tear strength, hardness and tension set. This is thought to be a consequence of thermal degradation of the NRP during the recycling process.

The Modification of Asphalt Emulsion Using Pre-Vulcanized Natural Rubber Latex for Highway Application

Asphalt emulsion is manufactured by emulsification of asphalt, and it is an energy-saving, ecologically safe material because it does not need any heating processes which can emit gas and fire hazard in its use. The purpose of this study is to elucidate the feasibility on using pre-vulcanized natural rubber latex as an admixture for asphalt emulsion in order to improve thermal stability and useful mechanical properties of the asphalt emulsion. The crosslink density was determined by swell ratio. The effect of vulcanizing agent on residue properties of modified asphalt emulsions was studied. The morphology properties of the modified asphalt were also investigated by using an optical microscope. The results showed that asphalt emulsion which was modified using pre-vulcanized NR latex could provide a standard asphalt emulsion and applicable for highway construction application. The mechanical and physical properties of the dried asphalt emulsion were also very well modified by the vulcanized rubber phase. The residue properties of modified asphalt with natural rubber and pre-vulcanized natural rubber latex, including softening point and penetration was improved. The increase in vulcanizing agent could also increase softening point. At low polymer contents, the samples reveal the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase was observed.