Measurement of lipase activity in rubber (Hevea brasiliensis) seed

Lipase activity in para rubber (Hevea brasiliensis) seed was measured by monitoring the release of free fatty acid by lipolysis of the endogenous lipid in a crushed sample of seed incubated at 37.5°C for 30 min. Free fatty acid was determined colorimetrically by a modified copper soap method. Fresh seeds showed the highest lipase activity. Drying the seeds at 60°C inactivated the enzyme. Drying of the seed at this temperature may be useful as a pretreatment for extraction of oil from the seed.     

Evaluation of pyrolytic oil from used tires and natural rubber (Hevea brasiliensis)

The pyrolysis of used tires, UT, and natural rubber (Hevea brasiliensis), NR obtained from Nigerian NIG800 clonal rubber tree, was performed and the effects of process conditions on product yield were investigated. An optimum yield was attained at operating temperature of 600°C, a heating rate of 15°C?min^?1, for a feed size of 6?mm. The UT and NR gave maximum pyrolytic oil yield of 34.40 and 75.93?wt%, respectively. The pyrolytic oil was characterized using Fourier transform infrared, nuclear magnetic resonance, and gas chromatography–mass spectrometry (GC–MS). Results obtained reveal the pyrolytic oil to be a complex mixture, mainly of aliphatic and aromatic compounds, which can serve as feedstock for industrial application. Nevertheless, a comparative evaluation of the physical and chemical properties of the UT and NR pyrolytic oil showed that NR had hydrocarbon composition of 80% aliphatics, 12% aromatics (with less than 2% polycyclic aromatic hydrocarbon concentration). However, the UT pyrolytic oil had 42% aliphatic and 34% aromatic compounds (with polycyclic aromatic hydrocarbons concentrations of 18%). Also, NR pyrolytic oil had better physical properties such as density, viscosity, flash point, pour point, and higher heating value than that produced from UT in this study, and comparable with that of commercial diesel. Moreover, sulfur content, which is a limiting factor in the direct combustion of UT pyrolytic liquid, was absent in NR pyrolytic oil. Hence, it is technologically feasible for NR from H. brasiliensis to be a suitable source of pyrolytic oil than UT.     

Extensional rheology of raw natural rubber from new clones of Hevea brasiliensis

Natural rubber (NR) is a biopolymer whose properties depend on the molecular structure of the 1,4‐cis polyisoprene chains, nonrubber constituents, environmental conditions, etc. NR has been characterized by Mooney viscosity, Wallace plasticity, nitrogen content (%N). However, these cannot effectively account for clone's differences. The aim of this work is to use extensional rheology to characterize and differentiate NR samples as for clone type and the season of the year in comparison to the traditional characterizations. Three IAC 300 series and RRIM 600 clones of Hevea brasiliensis tapped between October 2006 (Oct_06) and August 2008 (Aug_08) were investigated. IAC 329 clones showed the least susceptibility to seasonal changes, whereas RRIM 600 was the most influenced. An opposite trend between extensional viscosity (η_E) and %N was established. The former was very sensitive to changes in the molecular structure of NR, being fundamental for monitoring purposes and strategic development of new rubber tree clones. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Ozonation of unstretched natural rubber film from Hevea brasiliensis studied by ozone consumption and 13C NMR

Unstretched films of natural rubber (NR) from Hevea brasiliensis were exposed to ozone flow of 15 ml min^?1 from 4 to 300 min. The efficiency of reaction was determined by ozone consumption of NR films. Plots of reacted ozone mass versus film thickness show that the ozone penetration and the ozone reaction progressed into deeper layers (170 µm) than described in the literature (～0.5 µm). The previous proposed model based on viscometry measurements was corroborated by ozone consumption results. The effect of thickness on the O₃/NR stoichiometric ratio indicated that the diffusion process that controls the ozonation in unstretched film does not consist of the boundary progression behind which all reactive sites have been saturated. Ozonation in unstretched rubber film, while being less efficient than ozonolysis in solution, does have a reaction efficiency of the same order of magnitude. NMR spectroscopy was used to characterise the products formed by ozonation. Copyright © 2004 Society of Chemical Industry     

Comparative study on the technological properties of latex and natural rubber from Hancornia speciosa Gomes and Hevea brasiliensis

This work reports a systematic comparative study of the technological properties of natural lattices and rubbers extracted from Hancornia speciosa Gomes and Hevea brasiliensis [(Willd. ex Adr. de Juss.) Muell.‐Arg.] (clone RRIM 600) trees from 11 collections in Brazil throughout 2004. Natural rubber latex particle sizes and distributions were quite similar with an average diameter around 1 μm. Molecular weight, Wallace plasticity, and Mooney viscosity values were approximately the same for both rubbers. Fourier transform infrared spectroscopy peaks characteristic of natural rubber were observed for both Hancornia and Hevea. The measured differences in technological properties included lower values for Hancornia dry rubber content, % ash, % nitrogen, and plasticity retention index but higher value for acetone extract. Interestingly, nitrogen and protein content were much lower in Hancornia, suggesting that it may have important applications in nonallergic rubber uses. This represents the first report of lacticifer‐produced low‐protein natural rubber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

SEC‐MALS study of dynamic structuring of natural rubber: Comparative study of two Hevea brasiliensis genotypes

The dynamic structuring of natural rubber (NR) was studied selecting two specific Hevea brasiliensis genotypes (RRIM600 and PB235) to prepare model samples. The mesostructure (macromolecular structure + aggregates or gel) of NR samples was studied by SEC‐MALS. The NR samples were analyzed after (i) slow structuring (18 months' storage at room temperature) and (ii) fast structuring (stored for 24 h on P₂O₅ at 60°C). This study showed that the macromolecular structure, especially M_n, and the total gel rates were dramatically modified after fast structuring. For genotype RRIM600, the aggregates formed during fast structuring were essentially macroaggregates, whereas for genotype PB235 mostly microaggregates were formed. These results indicate that the dynamic structuring of NR is dependent on genotype. Depending on the genotype, for extreme conditions (fast structuring), it can be assumed there was percolation between elementary bricks, probably microaggregates, or no percolation. Although the mechanisms of dynamic structuring are quite complex and should be multifactors dependent, on the basis of our results, the degree of percolation seems to be partly dependent on the quantity of short polyisoprene chains initially present in the NR samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Properties of natural rubber vulcanizates containing mechanochemically devulcanized ground tire rubber

The devulcanization of ground tire rubber (GTR) was carried out with a self-designed pan-mill type mechanochemical reactor. Gel fraction and crosslink density measurements confirmed the occurrence of stress induced mechanochemical devulcanization of GTR. The partially devulcanized GTR (dGTR) was blended with virgin natural rubber (NR) at different ratios. The curing characteristics and mechanical properties of these composites were investigated and compared with those composites of raw ground tire rubber (rGTR) and NR. The results showed that the tensile properties of the dGTR/NR vulcanizates were much better than those of the rGTR/NR vulcanizates, which are comparable to or even better than the virgin vulcanizate, indicating the significant benefit of mechanochemical devulcanization. At the GTR content of 10%, the tensile strength of the dGTR/NR blends increased to 23.2 MPa from 13.7 MPa of the rGTR/NR blends, enhanced by 69% through partial devulcanization of GTR, and the elongation at break increased by 47%.     

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.     

Synthesis and properties of a novel epoxidised natural rubber-g-cassava starch polymer and its use as an impact strengthening agent

The polarity of epoxidised natural rubber (ENR) was improved by grafting it with cassava starch (CSt). A graft copolymer between ENR and CSt (ENR-g-CSt) was synthesised from CSt solution and ENR latex by using K₂S₂O₈ as an initiator. The highest percentage efficiency of grafting was obtained with 10 parts per hundred (phr) CSt. The swelling ratio of the ENR-g-CSt particles also decreased as a function of the CSt in the sample due to the polarity of the incorporated CSt. After synthesis, it was used as an impact strengthening agent for a polymer blend. Chemically modified NR polymers can form the basis of many value-added NR products that are environmentally friendly and cost effective for use as biopolymers in the future.     

Preparation and characterization of natural rubber dispersed in nano-matrix

Preparation of a model nano-matrix-dispersed polymer was investigated in terms of graft-copolymerization of deproteinized natural rubber latex with styrene, using tert-butyl hydroperoxide/tetraethylenepentamine as an initiator. The products were characterized by ¹H-NMR spectroscopy and size-exclusion-chromatography after ozonolysis. The grafting efficiency of styrene was found to be more than 90% under the best condition of the graft-copolymerization. The morphology of the film specimens, prepared from graft-copolymers, was observed by transmission electron microscopy after staining the films with OsO₄. Natural rubber particle of about 0.5 μm in diameter was dispersed in polystyrene matrix of about 15 nm in thickness.     

Co-compatibilising effect of carbon nanotubes and liquid isoprene rubber on carbon black filled natural rubber/polybutadiene rubber blend

Abstract

Bis-(triethoxysilylpropyl)-tetrasulfane functionalised carbon nanotubes (t-CNTs) were used as compatibiliser along with liquid isoprene rubber (LIR) in the natural rubber (NR)/polybutadiene rubber (BR) blend. Their reinforcing and compatibilising effects were evaluated by mechanical, fatigue crack growth resistance properties and blend homogeneity. Scanning electron microscope and transmission electron microscope showed enhanced interfacial adhesion between the binary rubber phases and improved dispersion of the minor phase in the rubber blend respectively with the co-existence of LIR and carbon nanotubes. The tensile strength of the carbon black (CB) filled NR/BR blend reached its optimum when 3 phr CB was replaced with an equal amount of t-CNTs in the presence of 7 phr LIR, while the fatigue crack growth resistance property achieved its maximum in the presence of 3 phr LIR. This interesting co-compatibilisation behaviour of t-CNTs and LIR suggests that t-CNTs have a better effect than CB with the assistance of LIR, which is an effective plasticiser in the NR/BR blend.     

轮胎专用复合天然橡胶的发展趋势

轮胎专用复合天然橡胶是专门用于轮胎生产加工的天然橡胶的特殊称呼,这类橡胶产品的工艺技术是对传统的天然橡胶初加技工艺术的革新和改造。该类产品从工艺流程、产品质量、市场竞争力都比以往的天然橡胶标准产品更受下游厂家的认可,有更大的竞争优势。但它的发展也面临着重重困难,包括从原料控制、工艺监督、成品销售等方面还需要等待实践的检验、产业的规划发展等多重因素的影响。对轮胎专用复合天然橡胶的发展进行中长期发展规划,让它的发展能在市场上占有一席之地,这是对现有橡胶初加工企业的一种升级改造,也不断促进天然橡胶产业经济可持续发展。     

Organo-montmorillonite as substitute of carbon black in natural rubber compounds

The use of octadecylamine modified montmorillonite as substitute of carbon black in natural rubber (NR) compounds is studied. Rubber with 10 parts per hundred resin (phr) of pristine (clay) and octadecylamine modified montmorillonite (organoclay) were compared with 10 and 40 phr carbon black as filler. The modified silicate is analysed by X-ray, FTIR and thermogravimetric analysis. Vulcametric curves show that the organoclay and carbon black accelerate the vulcanization reaction and, furthermore, give rise to a marked increase in the torque, indicating a higher degree of crosslinking as was also confirmed by swelling measurements and DSC. The vulcanisation rate and torque value of the organoclay compound are sensibly higher than the carbon black compound even at high contents (40 phr). Mechanical characterization shows the strong reinforcing effect of both fillers up to 350% in the strength in relation to NR. The mechanical properties of NR with 10 phr organoclay are comparable to the compound with 40 phr carbon black. Moreover, the organoclay improves the strength of the NR without hardly any reduction in the elasticity of the material.     

Chemically modified starch reinforced natural rubber composites

Chemically modified starch paste (MST) with polybutylacrylate (PBA) graft chains is investigated as a reinforcing filler of rubber through mixing and co-coagulating with natural rubber (NR) latex. The PBA graft chains are designed to prevent hydrogen bonding and crystallization of starch and to improve compatibility between starch and rubber. Through the comparison of mechanical properties and phase morphology, MST is proved to be much superior to unmodified starch paste. Unmodified starch paste acts as essentially inert filler causing a decrease of tensile strength, tear strength and elongation at break. In contrast, optimum MST shows obvious reinforcement effect on NR matrix by increasing tensile strength, elongation at break and tear strength besides modulus and hardness. Moreover, fine starch dispersion and strong interfacial interaction are achieved in NR/MST composites. The observed reinforcement effect is interpreted based on the results of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscope (SEM) analyses of grafted starch in comparison with natural starch and gelatinized starch.     

Protein influences on guayule and Hevea natural rubber sol and gel

Guayule (Parthenium argentatum) is under cultivation in the southwestern United States as an alternative source of natural rubber free from proteins that cause Type I latex allergies. However, since guayule lacks the protein‐polymer interactions present in Hevea latex, its physical and chemical properties may differ. The solvent‐soluble (Sol) and insoluble (Gel) fractions from guayule and Hevea natural rubbers were isolated through a solubilization/centrifugation deproteinization process. Protein could be reduced or removed by centrifugation, or concentrated in the gel fraction for both Hevea and guayule rubber. Separation of the sol fraction of Hevea rubber reduced the overall protein level, in some cases to below detection limits, without impacting rubber thermo‐oxidative stability. Notably, no detectable cross reactions took place between guayule protein antibodies and Hevea‐based materials, nor vice‐versa. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42051.     

Poly(dimethylaminoethyl methacrylate) grafted natural rubber from seeded emulsion polymerization

The grafting efficiency of dimethylaminoethylmethacrylate (DMAEMA) on to natural rubber (NR) has been studied. Grafting was by ‘topology-controlled’ emulsion polymerization, whereby polymerization is initiated by a redox couple where one component (tetraethylene pentamine) is hydrophilic and the other (cumene hydroperoxide) is hydrophobic. This should promote grafting at the interface between hydrophobic natural rubber particles and the hydrophilic DMAEMA. The effects of different amounts of monomer were examined, with NMR to obtain the percent branching, transmission electron microscopy to obtain information on morphology, gel fraction measurement and dynamic mechanical analysis to obtain information on mechanical properties. Although there will be significant amounts of ungrafted polyDMAEMA present, there is good evidence for the formation of graft copolymers of NR with core-shell morphology, and significant amounts of grafting, at high concentrations of monomer.     

Seasonal and clonal variations in technological and thermal properties of raw Hevea natural rubber

This study was undertaken over a 10‐month period under environmental conditions within the state of Mato Grosso, Brazil, to evaluate the causes of variation in the technological and thermal properties of raw natural rubber (NR) from different clones of Hevea brasiliensis (GT 1, PR 255, FX 3864, and RRIM 600). These clones were chosen to represent good clones available in Brazil. The technological properties of raw NR were evaluated in terms of their dry rubber content (DRC), Wallace plasticity, plasticity retention index (PRI), and Mooney viscosity. The thermal performance was evaluated with the thermogravimetry (TG)/differential thermogravimetry (DTG) technique. There were significant variations (p < 0.01 and p < 0.05) between clones and tappings for all technological properties, except for the percentage DRC among the clones. Of the clones studied, clone PR 255 presented the highest sensitivity to thermooxidation, as measured by its PRI value. The clone type and period of the year did not significantly influence the thermal behavior (TG/DTG under a nitrogen atmosphere) among the four clones evaluated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fatigue crack growth dynamics in filled natural rubber

Abstract

We present fatigue experiments performed on filled natural rubber and study the correlations between crack growth dynamics and fracture morphologies imprinted by an irregular crack path. Slow crack growth dynamics is obtained by cyclic fatigue in a pure shear test. We will show that an unstable crack growth regime exists for high loads. We will also discuss the appearance of sawtooth striations which follow a scenario that significantly differs from previous results reported in the literature.     

Effect of microorganisms during the initial coagulum maturation of Hevea natural rubber

The involvement of microorganisms in the initial stage of maturation of natural rubber coagula was assessed with five latex treatments that varied in the initial quantity of microorganisms; the treatments ranged from latex added with an antimicrobial agent (3.4 × 10⁴ CFU/mL) to strongly inoculated latex (2.4 × 10⁷ CFU/mL). After 0–6 days of maturation, the obtained rubber was characterized with respect to its physical and structural properties. The Wallace plasticity (P₀) and plasticity retention index (PRI) remained constant during maturation with the antibiotic‐added treatment. PRI decreased with the maturation time, and the rate was proportional to the initial microorganism concentration. P₀ of all inoculated rubber increased for the first 2 days of maturation and decreased after 6 days of maturation. With respect to structural parameters, a higher initial microorganism content corresponded to a higher gel content and a lower weight‐average molar mass after maturation, drying, and storage. The inoculated rubber showed a stable value for the number‐average molar mass (M_n), in contrast to the noninoculated samples, for which an increase in M_n during maturation was observed. The quantity of microorganisms significantly affected the physical properties and structure of the processed dry rubber. The mechanisms occurring during the initial stage of maturation are complex, and microorganisms are involved not only in the increase in sensitivity to thermooxidation but also in the crosslinking phenomenon between isoprene chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010