Development of a new procedure for lipid extraction from Hevea brasiliensis natural rubber

Non‐isoprene components and especially lipids have been reported to be involved in some key properties of natural rubber. Unfortunately, these results are hardly comparable due to different extraction methods. This work aimed to optimize lipid extraction from natural rubber either in the liquid state (latex) or in the dry state (unsmoked sheets). Extraction of unsmoked sheets from the RRIM 600 clone was carried out with different combinations of organic solvents (chloroform/methanol and hexane/isopropanol mixes). Chloroform/methanol (2 : 1 vol/vol) was found to be the most suitable for lipid extraction from unsmoked sheet rubber. The lipid extraction yield was improved by increasing the exchange surfaces by grinding rubber under liquid nitrogen and extracting the ground rubber for 6 h at room temperature, leading to 1.82% lipid extraction yield (versus dry rubber). Concerning latex extraction, the problem of lipid entrapment in the coagulum from immediate coagulation of latex in the solvent was solved by preliminary two times dilution of latex, giving a 3.24% extract (versus dry rubber) containing a minimum quantity of contaminating polyisoprene. Concerning the nature of lipids, dilution increased mainly neutral lipid extraction, which may suggest that neutral lipids were those entrapped by coagulation.     

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.     

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     

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     

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.     

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     

DSC valuation of PRI of raw natural rubber

Thermal oxidation of raw natural rubber from Hevea brasiliensis was analyzed by differential scanning calorimetry (DSC) in dynamic mode. The results obtained revealed a linear relation between the PRI and onset temperature obtained by DSC (r² = 0.91), for PRI values <70. On the other hand, when the natural rubber PRI was over 70, DSC was unable to assess that criterion accurately. This was probably because the two techniques were not equivalent regarding the phenomenon measured. Oxidation primarily results in chain scissions during PRI measurement. In DSC, the transition seen during thermal oxidation was associated with crosslinking. In fact, thermo‐oxidation is in the initial phase when PRI is measured, but in the terminal phase at the onset of transition in DSC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2354–2359, 2001     

Yield response of rubber (Hevea brasiliensis) to fertilizers on an Ultisol in Nigeria

The effect of various combinations of N, P, K and Mg fertilizer on yield of rubber over a 3 year period is discussed.N, K and Mg increased yield consistently over the period. The average annual increase in yield over control as a result of application of N, K and Mg were 11%, 3% and 9% respectively; where the effect of P was positive it was negligible.Combined applications of N, K and Mg produced increases that were higher than when they were applied individually. The N₁ K₂ combination produced a mean annual increase of 18% over N₀ K₀, while N₁ Mg₁ increased yield by an average of 26% annually over N₀ Mg₀.N, K and Mg are thus considered as generally required by the rubber trees.     

Study on effective storage time of raw natural rubber

The effective storage time (i.e., storage life) of raw natural rubber (NR) was investigated with heat‐accelerated storage aging combined with thermogravimetry (TG) and differential thermal analysis (DTA) method, as well as the heat aging life equation. The test results show that the effective storage time of raw NR can be estimated more conveniently in relatively shorter time by this method. It is found that the effective storage time of raw NR is associated with rubber processing technology and with ambient temperature during storage, but it has little relation with P₀ and PRI. At ambient temperature, the effective storage time of the natural‐coagulated and biological‐coagulated NR is obviously higher than the acetic acid‐coagulated NR; the lower the ambient temperature, the longer the effective storage time. The effective storage time of the acetic acid‐coagulated NR is 12.2–13.4 years at ambient temperature of 30°C, 23.8–25 years at 25°C, and 47.4–47.9 years at 20°C. The effective storage time of the natural‐ and biological‐coagulated NR is 13.7–15.2 years at 30°C, 29.6–30.4 years at 25°C, and about 62.5–65.8 years at 20°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4114–4119, 2006     

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.     

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     

Evaluation of chemical and nutritional characteristics of the seed of the rubber tree (Hevea brasiliensis)

Some chemical and nutritional characteristics of the rubber seed Hevea brasiliensis were studied. The protein content, its amino acid composition as well as the iron, calcium, phosphorus and cyanide (free and bound) concentrations, were determined in the dehulled seed. The effect of soaking, cooking, soaking-cooking and cooking-fat extraction procedure of the seed on the cyanide content and its in vivo protein utilization, was also evaluated. The protein quality was biologically assessed using the protein efficiency ratio (PER). The protein content of the seed was 18%, and the most limiting amino acid was threonine, with a chemical score of 71.6. The iron, calcium and phosphorus contents were 6.2, 109 and 429 mg/100 g, respectively. Its fat content was 48% with a total energy value of 702 kcal/100 g (2,948 Kj/100 g). The total cyanide content in the fresh seed was 130-230 mg/100 g; 6% was in the free form and 94% as bound cyanide. The most effective treatment for reducing the cyanide content was found to be 20 hours of soaking in water, combined with one hour of cooking. The raw seed had a low nutritive value and produced weight loss and death when fed to rats. The protein value, however, improved upon the seed treatment, reaching PER values close to those found in traditional cereals such as corn. It is therefore concluded that the seed of Hevea brasiliensis is a good source of energy, calcium, valine, isoleucine, phenylalanine and tyrosine. In contrast, it is a poor source of threonine, leucine and lysine. Its cyanide content is high, but when removed by treatment, such as soaking in water, cooking or fat extraction, the protein utilization can be improved.     

Characterization of the aging behavior of raw epoxidized natural rubber with a rubber processing analyzer

Tests of the strain sweep, frequency sweep, and stress relaxation for raw epoxidized natural rubber were carried out with a rubber processing analyzer. The results showed that the complex viscosity, η*, decreased with the prolongation of the aging time in the region of Newtonian flow, but in the region of non‐Newtonian flow, the decrement of η* with a rising shear rate decreased with the prolongation of the aging time. The torque (S′) response from the strain sweep indicated that aging brought about an obvious decrease in the increment of S′ with rising strain in the linear viscoelastic region and a small increase in the slope of the plateau on the curve of the S′ response in the nonlinear viscoelastic region. The stress relaxation rate constants k and b, calculated according to the equations S_t = S₀e^?kt and S_t = S₁t^?b (where S_t, S₀, and S₁ are the stresses at relaxation time t, t = 0, and t = 1, respectively), increased, and the stress relaxation time obtained directly from the rubber processing analyzer shortened with the prolongation of the aging time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1277–1281, 2006     

Thermal degradations of chlorinated natural rubber from latex and chlorinated natural rubber from solution

The thermal degradations of chlorinated natural rubbers from latex (CNR‐L) and from solution (CNR‐S) under nitrogen atmosphere were studied with thermogravimetric analysis (TGA). The thermal degradations of CNR‐L and CNR‐S are one‐step reaction. The shapes of the thermogravimetric and derivative thermogravimetric curves are similar. The degradation temperatures of CNR‐L and CNR‐S increase linearly with the increment of heating rates. The heating rate hardly affects the thermal degradation rates of CNR‐L and CNR‐S at the various degradation stages. The thermal degradations of CNR‐S and CNR‐L are dehydrochlonation reactions. The reaction activation energy (E) of CNR, at the first stage, is around 100 kJ/mol. After that, E remains relatively steady (80–140 kJ/mol). At the last stage, E rises rapidly (130–270 kJ/mol). The variation tendency of frequency factor (A) is similar to that of E. As the initial degradation temperature T₀ of CNR‐L is 10.9°C lower than that of CNR‐S, the thermal stability of CNR‐S is better than that of CNR‐L, which may be caused by the difference of molecular structure between CNR‐L and CNR‐S, as FTIR results indicate that there are more ? OH, ? C?O and ? COO? groups in the CNR‐L molecular chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Oxidative reactions of the pentose pathway and the origin of reducing equivalents for the biosynthesis of rubber in Hevea brasiliensis latex

The presence of the oxidative reactions of the pentose phosphate pathway in hevea latex and their interaction with the biosynthesis of rubber are demonstrated using radioisotopes. During the second oxidation–reduction reaction of the pentose phosphate pathway the tritium in C₃ of glucose‐6‐phosphate is transported as tritiated nicotinamide adenine dinucleotide phosphate and serves to reduce [3‐¹⁴C] 3‐hydroxy‐3‐methylglutaryl coenzyme A to mevalonate. Reduced nicotinamide adenine dinucleotide phosphate is the inter‐connection between these two metabolic routes present in hevea latex, thus the hydrogens of glucose end up in rubber. © 2000 Society of Chemical Industry     

Effect of natural coagula maturation on the processability,cure, and mechanical properties of unfilled vulcanizates of Hevea natural rubber

Fresh latex from different Hevea brasiliensis clones was naturally coagulated, subjected to different durations of maturation, processed into solid rubber, and compounded into pure gum stocks and vulcanized. Coagula maturation had clone‐specific effects on the processability of the raw rubber: reduced for some clones, while others was less sensitive. The cure and mechanical behaviors of the compounded stocks and vulcanizates, respectively, were not sensitive to the clonal origin of coagula and their duration of maturation. Although coagula maturation could be associated with leaching, deactivation of inherent antioxidants in Hevea latex, as well as crosslinking and/or oxidation of polyisoprene chains, these results show that compounding with a standard pure gum recipe compensates for the Hevea latex constituents affected by maturation. Hence, extended maturation of Hevea coagula, for economic or other reasons, would influence much more the bulk behavior of raw rubber and have insignificant effects on the compounded stocks and vulcanizates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2359–2363, 2007