Rubber Latex Particles Research Articles

In vitro Transient Expression System of Latex C‐serum was used for Analysis of Hevein Promoter in Response to Abscisic Acid in Hevea brasiliensis

Hevein has been found to be an essential element in coagulation of rubber particles in latex of rubber trees. In a previous study, we cloned a 1,241-bp fragment of a 5' upstream region of the hevein gene by genome walking. This fragment was analyzed by a 5' end nested deletion method in the present study, fused with a uidA (gus) gene to produce a series of tested constructs, which were transferred into C-serum of latex and the Gus activities were detected. Results showed that the fragment from -749 to -292 was sufficient for expression of gus gene in latex, and the fragment from -292 to -168 was crucial in response to abscisic acid inducement. In a transient transgenic test of rubber leaf with particle bombardment, construct Hev749 conferred gus-specific expression in veins, in which the latex tubes mainly distributed. This implies that the fragment from -749 to -292 was laticiferous-specific.

Molecular cloning and characterization of the rubber elongation factor gene and its promoter sequence from rubber tree (Hevea brasiliensis): A gene involved in rubber biosynthesis

Hevea rubber tree (Hevea brasiliensis) is the only plant species being cultivated for commercial production of rubber in the world. In order to meet ever increasing rubber demand, it is a prerequisite to identify and characterize a key gene involved in rubber biosynthesis and over-expression of rubber biosynthesis gene will eventually lead to enhance the latex (rubber) production in transgenic Hevea plants. Rubber elongation factor (REF) is a major protein located on the surface of large rubber particles in latex and is involved which is involved in rubber biosynthesis in H. brasiliensis. We report here cloning and characterization of REF gene as well as its 5′ promoter region from Hevea. REF gene (1367bp) has three exons interrupted by two introns and encoded a 138 amino acid peptide containing an open reading frame of 414bp with a calculated MW of 14,700Da. Nucleotide sequence analysis showed that 1.3kb genomic DNA showed 100% homology to REF cDNA from Hevea. Southern blot hybridization of genomic DNA with REF gene probe revealed that REF gene is encoded by a small gene family consisting of two members. RNA blot analysis indicated that REF transcript is highly expressed in high yielding clone than in low yielder. The cloned 5′ promoter region has a putative TATA element at −150 and CAAT box at −221 position. To identify the regulatory role of REF promoter, chimaeric fusion between REF promoter sequence and the β-glucuronidase (GUS) coding, uidA gene was constructed and used to transform tobacco and Arabidopsis. Expression of the uidA reporter gene was detected histochemically in the transformed tobacco plants where, GUS activity was detected in the leaf and petiole of transformed plants. The stable integration of REF:uidA fusion into the tobacco genome was further confirmed by PCR amplification and Southern blot analysis. A histochemical study of stable transformants demonstrated that the 5′ upstream region of REF can drive strong GUS gene expression specifically in the vascular tissues (xylem and phloem) of leaf, stem and midribs of transgenic Arabidopsis. GUS staining revealed that REF:GUS expression was also induced by wounding. The results suggested that the cloned REF promoter is capable of directing gene expression. Our ultimate goal is to produce transgenic Hevea plants with enhanced latex yield by over expression of REF protein.

Rubber–pristine clay nanocomposites prepared by co-coagulating rubber latex and clay aqueous suspension

The structure of several rubber–clay nanocomposites, including styrene butadiene rubber (SBR)–clay, natural rubber (NR)–clay, nitrile butadiene rubber (NBR)–clay, carboxylated acrylonitrile butadiene rubber (CNBR)–clay nanocomposites, prepared by directly co-coagulating the rubber latex and clay aqueous suspension, were investigated. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) micrographs showed that these nanocomposites possessed a unique structure, in which the rubber molecules “separated” the clay particles into either individual layers or just silicate layer aggregates of nanometer thickness without the intercalation of rubber molecules into clay galleries, different from intercalated and exfoliated clay nanocomposites. Such a structure resulted from the competition between separation of rubber latex particles and re-aggregation of single silicate layers during the co-coagulating process. The content of bound rubber of SBR–clay nanocompound is more than that of the corresponding rubber filled with micrometer clay or silica because of the increased networking of silicate layers with the nano-meter dispersion and the high aspect ratio. The glass transition temperature of SBR–clay nanocomposites increased as compared with that of the pure SBR. The tensile strength of SBR–clay nanocomposite loading 20 phr clay was 6.0 times higher than that of the conventional SBR–clay composite. The gas permeability of separated rubber–clay nanocomposites containing 20 phr decreased 50% as compared with the corresponding gum vulcanizates.

Composite natural rubber based latex particles: a novel approach

The oil resistance of natural rubber (NR) film could be effectively improved by using the heterocoagulation of large NR particle with small polychloroprene (CR) particles. In the preparation of NR/CR composite particle with a core-shell structure, a nonionic surfactant whose molecule bears poly(ethylene oxide) (PEO) was adsorbed on CR particles and allowed to form complexes between PEO and indigenous surfactant (protein–lipid) on the NR particle surface. Composite latex particle obtained was characterised by particle size, zeta potential and glass transition temperature measurements and the data indicated the presence of CR on the outer layer of composite particle. Better oil resistance of film casted from heterocoagulated latex when compared to that of NR film confirmed the NR/CR core-shell structure. The epoxidised natural rubber (ENR), crosslinked ENR and/or skim latex particles were investigated in order to replace the use of CR in the heterocoagulation process.

Cryo‐sectioning and chemical‐fixing ultramicrotomy techniques for imaging rubber latex particle morphology

Two methods adapted from biological microscopy are described for a new application in imaging the morphology of rubbery latex particles. In the first method, a drop of latex is frozen in liquid nitrogen, sectioned with a diamond knife and vapour-stained with osmium tetroxide, then viewed by transmission electron microscopy. When applied to latexes made by emulsion polymerization of methyl methacrylate in a natural rubber latex seed, inclusions are clearly visible. A chemical fixation method is then described for imaging the morphology of such rubbery latex particles. Glutaraldehyde is added to the latex, followed by osmium tetroxide. The sample is then dehydrated in ethanol, epoxy resin added, and the sample cured, ultramicrotomed, and imaged with transmission electron microscopy. An inclusion morphology is again clearly seen.

Morphology of peroxide-prevulcanised natural rubber latex: effect of reaction time and deproteinisation

A non-uniform mesh structure, i.e. a dense network near the surface of peroxide-prevulcanised natural rubber latex particles, was observed under transmission electron microscopy. In the initial period of prevulcanisation, the swelling ratio of the latex sheet decreased with longer reaction time while an increase in crosslink density of rubber particles containing polystyrene, prepared using the phase transfer/bulk polymerisation process, was noticed. The modulus of the rubber sheet increased up to maximum crosslinking and thereafter decreased. After removal of proteins from the latex membrane layer, derived from protein-lipid originally existing at the rubber particle surface, could not be detected. The absence of proteins, which act as free radical scavengers, resulted in a rapid diffusion of alkoxy radicals into the rubber phase of deproteinised latex and, therefore, a uniform crosslink distribution inside each particle was obtained.

Morphology of natural rubber latex particles prevulcanised by sulphur and peroxide systems

Transmission electron microscopy provided direct evidence of the morphology of sulphur- and peroxide-prevulcanised natural rubber latex particles. A mesh structure of all cross-linked rubber particles containing polystyrene, prepared using the phase-transfer/bulk polymerisation process, was found. Each peroxide-prevulcanised particle had a nonuniform network structure, whereas the rubber network in sulphur-prevulcanised particles was homogeneous, irrespective of size. The effects of maturation and sodium dodecyl sulphate on the swelling ratio of the sulphur-prevulcanised latex film were investigated.

Heterocoagulation of polychloroprene on natural rubber latex particles for use in the preparation of toughened polystyrene

AbstractThe toughness of high‐impact polystyrene based on γ‐radiation‐vulcanized natural rubber (NR) was effectively enhanced by the addition of a block copolymer at the NR/polystyrene interface. An NR/polychloroprene (CR) composite latex particle was produced by the heterocoagulation technique for its use as a model in a compatibilization study. A nonionic surfactant (Tween 80), whose molecule bore poly(ethylene oxide) (PEO), was adsorbed onto the CR particle and allowed to form a complex between PEO and an indigenous surfactant (protein–lipid) on the NR particle surface. The presence of CR–Tween on the outer layer of the obtained composite polymer particle was characterized by the particle size, ζ potential, and glass‐transition temperature. That the film cast from the heterocoagulated latex showed better oil resistance than the NR film confirmed the NR/CR core–shell structure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 9–13, 2003

Polypyrrole-coated natural rubber latex by admicellar polymerization

Admicellar polymerization has been used for the preparation of an electrically conductive polypyrrole coating on latex particles. An anionic surfactant, sodium dodecyl sulfate (SDS), was adsorbed onto natural rubber (NR) latex particles to form the surfactant bilayers after adjusting the pH below the point of zero charge of the latex surface. Adsorption of SDS and pyrrole adsolubilization were determined as a function of pyrrole and sodium chloride concentrations. Pyrrole caused a decrease in SDS adsorption at equilibrium. Sodium chloride increased the surfactant adsorption and the pyrrole adsolubilization. Thermogravimetric results showed the presence of polypyrrole. The conductivity of the polypyrrole-coated NR latex film prepared by admicellar polymerization without salt was the lowest; however, with salt addition, the conductivity of the film improved significantly. The oxidative polymerization technique resulted in a relatively higher conductivity than oxidative admicellar polymerization.

Applications of phase transfer technique to the study and development of natural rubber

The phase transfer technique was used for surface characterization of natural rubber latex and for preparation of toughened polystyrene based on γ-radiation vulcanized natural rubber. This process was extended to embed deproteinized natural rubber latex particles, crosslinked by γ-ray, in polystyrene for morphologically study. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1505–1509, 2000

New evidence of the surface morphology of deproteinized natural rubber particles

A new evidence of the morphology of deproteinized natural rubber (DPNR) latex particles, i.e., γ-radiation vulcanized-deproteinized NR (RV-DPNR) and deproteinized-γ-radiation vulcanized NR (DP-RVNR), was obtained by transmission electron microscopy (TEM). Micrographs of the rubber particles embedding in polystyrene, prepared by using a phase transfer/ bulk polymerization process, revealed the destruction of membrane layer surrounded the DPNR particles crosslinked by γ-ray (DP-RVNR).

The Role of the Morphology of Natural Rubber and Polybutylacrylate-based Composite Latex Particles on the Toughness of Polycarbonate\Brittle Polymer Blends

The dependence of the toughness of polycarbonate (PC)/poly(styrene-co-acrylonitrile) (PSAN) and PC/polystyrene (PS) blends on the architectural structure of incorporated natural rubber (NR) or poly(n-butylacrylate) (PBuA)-based latex particles is presented. By means of a twin screw extruder PC was melt blended with PSAN or PS blends containing different composite latex particles. Those materials that consisted of 70% PC could be effectively toughened by only 6–8% of the prepared toughening particles. Fractographic analysis by scanning electron microscopy has been used to analyze the failure mechanisms of the reinforced ternary PC blends. The principal feature of fracture surfaces of PC/PSAN blends containing pure NR particles was multiple rubber particle cavitation. A hard polymethylmethacrylate shell deteriorated the effectiveness of NR-based latex particles. Rigid PS subinclusions considerably increased the performance of the NR-based core—shell particles. They shifted the failure mechanism at impact from a brittle mode to a ductile tearing mode and much more energy could be absorbed. Good impact properties were also achieved in PC/PS blends reinforced by NR-based core—shell particles containing rigid subinclusions. The morphological structure of smaller-sized PBuA-based latex particles was less crucial.

Surface Structure of Natural Rubber Latex Particles from Electrophoretic Mobility Data

Fresh natural rubber latex particles are stabilized by adsorbed proteins and phospholipids while those for high-ammonia latex concentrate are stabilized mainly by adsorbed long-chain fatty acid soaps, the hydrolysis products of phospholipids. The structure of this surface layer surrounding the latex particles is analyzed using the electrophoresis model of Ohshima and Kondo. Good agreement between theoretical and observed electrophoretic mobility was found, except at very low ionic strength. The results were consistent with a model of an uncharged bared polyisoprene latex particle coated by a charged mixed layer of long-chain fatty acid soaps, proteins, and polypeptides of finite thickness in matured latex concentrate. This surface layer is ion-penetrable and its resistance to liquid flow changes with time on prolonged hydrolysis.

Atomic-force microscopy of a fractured rubber-toughened epoxy

Atomic force microscopy (AFM) is a powerful scanning probe technique, which is capable of imaging polymer surfaces. This technique is complementary to the scanning electron microscope (SEM) but because of the AFM's sensitivity in the z direction surfaces that are too smooth to image by SEM can easily be imaged by AFM. This study utilizes transmission electron microscopy(TEM) to image the morphology of the latex rubber particles; SEM and AFM are used to study the degree of dispensability of the latex particles in the epoxy, and the fatigue-fracture surface of the rubber modified epoxy.Core-shell latex particles were prepared with a core of poly(butadiene-styreiie) |P(B-S)| and a shell Poly(methyl methacrylate)(PMMA). In order to study the interaction between the core/shell particles and the epoxy matrix, the shell is systematically varied in terms of chemical bonding, physical interaction and the extent of these interactions by incorporating acrylonitrile(AN). glycidyl-methacrylate(GMA). and crosslinking agent divinylbenzene(DVB) of varying concentrations in the shell.

The effect of electrolytes, pH and surfactant on the adsorption of natural rubber latex on tin tailings slimes

The interaction of a stable clay dispersion from tin tailing slimes from an ex-mining pond with natural rubber latex particles in a mixed colloidal system was investigated as a function of the concentration of sodium chloride, the cation types, the non-ionic surfactant concentration and the pH. In all cases, the amount of latex adsorbed increased linearly with the latex concentration. The slope of the straight line increased with increasing concentration of NaCl but decreased as the pH of the dispersion was increased. An increase in the slope was taken to indicate an increase in affinity of the latex particles towards the clay surface. The slope was found to increase with an increase in the valency of the cations used but the reverse effect was found for the non-ionic surfactant concentration. A heterocoagulation mechanism between the two dissimilar types of particles is proposed to explain the observations.

Modification of natural rubber latex. III. Natural rubber–polystyrene composite latexes synthesized using azobisisobutyronitrile as initiator

AbstractMaterials which may be classified as interpenetrating polymer networks have been prepared by the in situ polymerization of styrene in natural rubber latex using azobisisobutyronitrile (AIBN) as the initiator. The resulting materials have been characterized by electron microscopy, Soxhlet extraction coupled with proton nuclear magnetic resonance spectroscopy, dynamic mechanical analysis, and stress‐strain analysis. The styrene polymerizes within the natural rubber latex particles to give a relatively fine phase‐separated morphology with some evidence for a limited degree of segmental mixing. Moreover, it is clear that AIBN, despite what is stated in the literature, does lead to some grafting of polystyrene, and, in addition, causes significant degradation of the natural rubber molecules when the styrene content is low.

Adsorption of Sodium Dodecyl Sulfate on Natural Rubber Latex Particles and Determination of Specific Surface Area of the Particles

Abstract Soap titration of polymer latex is a widely used method for the determination of the specific surface area and particle size in synthetic latices. The method involves the titration of a latex of known polymer and soap content with a standard soap solution until the critical micelle concentration (CMC) is reached. At this concentration, saturation adsorption of the soap to form a monolayer on the particle surface occurs. From a knowledge of the amount and kind of soap adsorbed and the effective molecular area of the soap on the surface, the specific surface area and average diameter of the particles can be calculated. The effective molecular area of soap at saturation adsorption on polymer particle surface has been determined by comparing adsorption data with particle size data obtained by electron microscopy. Little information is available on the adsorption of sodium dodecyl sulfate (SDS) on NR latex particles. In ammoniated latex, these particles are covered by a complex mixture of proteins, fatty acid soaps, and lipids, the composition and concentration of which are not known accurately. Cockbain modified the soap titration method of determining particle sizes in synthetic latices and claimed that it was applicable to NR latices. In this method SDS was titrated to the latex adjusted to pH 6 ± 0.2. It was assumed that at this pH the interfacial activity of SDS was high while that of the proteins and fatty acid soaps initially present on the latex particles was comparatively low. Under these conditions the SDS would displace almost all the proteins and fatty acid soaps on the particles when sufficient SDS has been added to form micelles in the aqueous phase. The specific surface area was calculated from the SDS adsorption after assuming the molecular adsorption area of SDS to be 60 A˚. No account was taken of the effect of the poly(vinyl alcohol) creaming agent on adsorption. Sekhar found that Cockbain's method of soap titration was temperature dependent. Van den Tempel has shown that electron microscopy cannot yield accurate specific surface area of NR latex particles because of the heterogeneous particle size distribution inherent in unconcentrated latex.

The effect of rubber latex particles on the mechanical properties of highly crosslinked epoxy polymers

Taking as a model system a highly crosslinked epoxy polymer with elastic inclusions, a study has been made of the effect of the content, composition and properties of elastic inclusions on the stability of the materials towards the propagation of cracks (the surface fracture energy or the critical rate of elastic energy release in the propagation of cracks), as well as on the rigidity, static and impact strengths and dielectric relaxation of the polymers. It is shown that the introduction of rubber latex particles into a highly crosslinked epoxy polymer does not alter the pseudo brittle character of fracture, while there is a marked increase in the parameters of stability towards the propagation of cracks. An increase in the content of latex particles in a cured epoxy polymer is accompanied by a marked increase in the parameters of stability towards crack propagation, along with maintenance of rigidity and of thermal stability, but appreciable reductions in the static and impact strengths are observed.

Electrochemical Aspects of Rubber Latex, Compounding Ingredients, and Their Mixtures

Abstract The electrophoretic speeds of rubber latex particles as well as of colloidally dispersed compounding agents, e.g., zinc oxide, sulfur, china clay, and mixtures of them as are generally employed in baths for electrodeposition, have been measured in a microcataphoresis cell of the Northrup-Kunitz type. The ζ-potential of latex, calculated from the electrophoretic speeds, is considerably influenced by the presence of the compounding agents. Sulfur sol having the lowest ζ-potential tends to reduce that of latex as well as of others in a mixture, whereas zinc oxide and china clay, which have higher ζ potentials, tend to increase the value for latex. A mixture of zinc oxide and china clay shows the highest (60 mV) ζ-potential compared to latex itself (ζ=28.8mV). The isoelectric point of rubber latex was measured by calculating the ζ-potential from the electrophoretic speed at different pH values, which were maintained by means of Na2CO3⋅NaHCO3 buffers at the higher range and acetate buffers at the lower range. The I.P. was 4.2 and was lowered in the presence of zinc oxide and china clay sols to 3.0 and 3.8, respectively, but increased to 5.1 in the presence of sulfur sol.

641. Kinetics and mechanism of hydrochlorination of the surface of rubber latex particles

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