Rubber Hevea Research Articles

Molecular species of triacylglycerols in the rubber particles of Parthenium argentatum and Hevea brasiliensis

Molecular species of acylglycerols (AG) in the lipid extracts of guayule (Parthenium argentatum) and Hevea (Hevea brasiliensis) rubber particles were compared using HPLC and MS. The contents of 54 molecular species of AG in the lipid extract of guayule rubber particles in decreasing order were as: LLnLn (4.6%), LLLn (3.6%), LLn-OH20:0 (2.4%), LnLnLn (1.9%), LLnP (1.3%), LLP (1.3%), LLn-OH20:1 (0.80%), LLL (0.62%), total of about 24%. The normal FA among the total FA was about 88%, hydroxy FA about 12% and odd carbon-numbered FA about 2.4%. The contents of 56 molecular species of AG in the lipid extract of Hevea rubber particle were as: 308-308-308 (21%), 308-308-O (4.9%), 308-308-324 (4.3%), 308-308-S (2.8%), 308-308-L (2.4%), 308-OL (1.5%) and LLL (1.3%), total of about 44%. 308 and 324 were the furan FA with the masses of 308 and 324. Furan FA with the mass 308 was 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid identified earlier. We proposed the structure of 324 as 10,13-epoxy-11-carboxyl-12-methyl-hexadeca-10,12-dienoic acid. Furan FA among the total FA was about 81%, normal FA about 17% and hydroxy FA about 1.6%. This is the first report of various intact molecular species of AG in rubber particles. It is also the first report of hydroxy FA in the neutral lipids in either species. The major FA in the total FA of guayule were L (38%), Ln (38%), in Hevea was 308 (76%). The molecular species of AG profiles of guayule and Hevea rubber particles may provide the necessary information to further improve guayule and Hevea natural rubbers.

Крым-сагыз: особенности растения, перспективы возделывания и селекции (обзор)

Taraxacum hybernum Steven, известный также под названием «крым-сагыз», является одним из потенциальных источников натурального каучука, однако он малоизвестен, в отличие от его «родственника» T. kok-saghyz L. E. Rodin. Обзор посвящен анализу советского опыта культивирования T. hybernum Steven в СССР и рассмотрению перспектив внедрения в современное производство этой культуры в России с учетом современных методов агротехники и биотехнологии. Приведено ботаническое описание растения. Оценено содержание и качество каучука T. hybernum Steven. Содержание каучука невысокое, но качество его превосходит даже гевейный каучук. Степень полимерности углеводорода каучука 2000 – 2970 и выше. Урожай сырых корней T. hybernum Steven двулетнего возраста достигает 100 ц/га, семян — 150 кг/га. Всходы T. hybernum Steven появляются через 8 – 15 дней после посева. Для хорошего прорастания семян требуется не только достаточное количество влаги, но и свободный доступ воздуха в почву. Эти условия наилучшим образом сочетаются при раннем посеве и заделке семян на глубину 1,5 – 2 см. На получение всходов от фактически высеянных семян за 14 дней после посева влияет глубина заделки: на 1 см — 63,6 %, на 2 см — 68,3 %, на 3 см — 47,1 %, на 4 см — 4,3 %. Вес 1000 семян примерно 1 г. Опыт выращивания этой культуры даже в небольших объемах важен для обеспечения ресурсной и стратегической безопасности нашей страны в будущем.

Finite Element Analysis of Simple Rectangular Microstrip Sensor for Determination Moisture Content of Hevea Rubber Latex

The Finite Element Method, FEM has been successfully used to model a simple rectangular microstrip sensor to determine the moisture content of Hevea rubber latex. The FEM simulation of sensor and samples was implemented by using COMSOL Multiphysics software. The simulation includes the calculation of magnitude and phase of reflection coefficient and was compared to analytical method. The results show a good agreement in finding the magnitude and phase of reflection coefficient when compared with analytical results. Field distributions of both the unloaded sensor as well as the sensor loaded with different percentages of moisture content were visualized using FEM in conjunction with COMSOL software. The higher the amount of moisture content in the sample the more the electric loops were observed.

A numerical investigation of damping in fuzzy oscillators with poroelastic coating attached to a host structure

This paper analyzes efficacy of fuzzy oscillators combined with poroelastic coatings to reduce low frequency vibrations. The authors had previously shown that the poroelastic interactions across contact interfaces are tunable for broadband rate-independent damping. As a follow-up to that work, dynamic analyses are conducted on a host structure interacting with multiple fuzzy oscillators through contact interfaces across poro/viscoelastic coatings. Contact interactions are modeled by Fractional Zener Models. As viscoelastic coating material, hevea rubber is chosen because of its exceptionally high damping characteristics (i.e., highest loss tangent). For the poroelastic coating, relaxed and unrelaxed compliances as well as maximum damping capacity are assumed as identical to the viscoelastic rubber coating. In the first step, the dominant vibration mode of a host structure is modeled as a single degree-of-freedom system. The modal frequency of the host structure is first assumed to match peak relaxation frequency of the viscoelastic coating (220 kHz). Then, the modal frequency is reduced to lower frequencies (20,100 and 200 Hz). In the next step of the analysis, the investigation is extended to a host structure modeled as a two degree of freedom system. Results show that, if relaxation frequencies of the viscoelastic and poroelastic materials are close to the modal frequency of the host structure, the vibration suppression performances of both coatings are similar. However, poroelastic coating outperforms the viscoelastic coating at lower modal frequencies due to its tunable dynamic relaxation properties. Viscoelastic coating, in contrast, responds as a spring, and loses its damping capacity away from its peak relaxation frequency. To explore the best possible performance of the poroelastic coatings for low frequency damping, an optimization routine is adopted, and optimal number of fuzzy oscillators with optimally distributed mass and frequency properties is found. Results promise up to ∼35 dB vibration reduction around the structural modes for the single degree of freedom systems. For two degree of freedom system, vibration reduction level is predicted up to ∼27 dB reduction for the first mode and ∼15 dB for the second mode.

Correlation between DNA methylation status and rubber yield and related characteristics in Hevea brasiliensis tapped at different heights

The natural yield of cis-1,4-polyisoprene rubber from Hevea brasiliensis is complex and is affected by the tapping-cut height, i.e., the height at which the laticifer site is severed. From rubber biosynthesis to latex exploitation, genetic modifications have been used to improve yield levels. In this study, we determined the correlation between DNA methylation and the fluctuation in rubber yield and its related characteristics during latex regeneration, and cloned and sequenced methylated sites detected by methylation-sensitive amplified polymorphisms. Latex yield and absolute and relative dry yields were lower from high tapping-cut than low tapping-cut plants; latex DNA methylation levels were greater in high tapping-cut than in low tapping-cut plants. There were significant positive correlations between tapping-cut height and latex yield, absolute and relative dry rubber yields, and the hemi-, full, and total methylation ratios in latex. There were significant negative correlations between tapping-cut height and full and total methylation ratios in leaves. Latex yield and absolute and relative dry rubber yields were negatively correlated with full and total methylation ratios in latex, and positively correlated with hemi- and total methylation ratios in leaves. A homology analysis of the methylated genes revealed that the functions of their homologous sequences were mainly associated with transcription, protein biosynthesis, signal transduction, energy, transport, and plant defense. Thus, the accumulation of polyisoprene in the laticiferous production system of Hevea might be regulated by DNA methylation. This is the first report on latex and leaf global DNA methylation analyses during rubber production in self-rooting clones, and thus it provides novel insights into increasing the production of Hevea rubber.

Subcellular localization and interactions among rubber particle proteins from Hevea brasiliensis.

Natural rubber (polyisoprene) from the rubber tree Hevea brasiliensis is synthesized by specialized cells called laticifers. It is not clear how rubber particles arise, although one hypothesis is that they derive from the endoplasmic reticulum (ER) membrane. Here we cloned the genes encoding four key proteins found in association with rubber particles and studied their intracellular localization by transient expression in Nicotiana benthamiana leaves. We show that, while the cis-prenyltransferase (CPT), responsible for the synthesis of long polyisoprene chains, is a soluble, cytosolic protein, other rubber particle proteins such as rubber elongation factor (REF), small rubber particle protein (SRPP) and Hevea rubber transferase 1-REF bridging protein (HRBP) are associated with the endoplasmic reticulum (ER). We also show that SRPP can recruit CPT to the ER and that interaction of CPT with HRBP leads to both proteins relocating to the plasma membrane. We discuss these results in the context of the biogenesis of rubber particles.

Effect of Clonal Rootstocks on the Growth and Yield of Hevea Rubber

In Hevea brasiliensis (Willd. ex A. Juss.) Mull. Arg., the genetic diversity of seedling rootstocks is considered as the major factor responsibles for intra-clonal variation in the latex yield. Genetically uniform clonal rootstock is used to reduce this variation. In this study, the effect of four rootstocks including three clonal rootstocks namely, CATAS 8813, Haiken 2, Dafeng 99 and a seedling rootstock were investigated after grafted to PR 107 with respect to growth, rubber yield, biochemical parameters of latex and intra-clonal variation. Rootstocks significantly affected the sucrose, inorganic phosphorus and thiol contents. The clone CATAS 8813 and seedling rootstocks showed higher sucrose, inorganic phosphorus and thiol contents than the trees of Haiken 2 and Dafeng 99. Dry rubber yield was found to be highest in CATAS 8813 followed by Dafeng 99 and Haiken 2. The three clonal rootstocks reduced intra-clonal variation in latex yield, exhibiting lower range of latex yield and lower coefficient of variation, compared to the seedling rootstocks. The effect of the four rootstocks on the girth growth was not significantly different. The present study suggested that the clonal rootstock CATAS 8813 might be a potential source for improving rubber yield of scion PR 107.

Processing and mechanical properties of natural rubber/waste-derived nano filler composites compared to macro and micro filler composites

Abstract Nano-sized fillers produced from renewable materials can generate high performance natural rubber (NR) composites while reducing dependency on petroleum. We made NR composites, with both hevea and guayule NR, containing nano-scale waste-derived fillers as complete and partial replacements of carbon black. The effect of nano-filler type and loading on composite mechanical properties was analyzed and compared to previous results with micro and macro fillers. Also, processability of the compounds was investigated. Reinforcement of both NRs was achieved by nano-sized waste-derived fillers, even with complete replacement of carbon black. Increases of up to 2.4 and 1.8 times higher tensile and tear strength, respectively, were achieved in some of the composites compared to the unfilled compound. Better relative reinforcement was obtained in guayule than in hevea rubber due to different rubber macromolecular structure and the strength of the rubber-waste filler interactions. Composites containing waste-derived fillers as co-fillers with carbon black displayed uncommon combinations of properties not achieved with single conventional reinforcing fillers. Furthermore, significant reductions in power consumption during mixing, up to 10% in hevea and 19% in guayule composites, were obtained even by replacement of a small portion of carbon black in the composites. Despite increased interest in nano-sized particles, micro-sized fillers are effective reinforcing fillers when used as partial replacements of carbon black, and can be produced at a much lower cost than nano-sized particles.

Guayule as an alternative source of natural rubber: A comparative life cycle assessment with Hevea and synthetic rubber

A comparative cradle-to-gate life cycle assessment (LCA) including raw material acquisitions, rubber production and transportation of synthetic rubber (SBR) and two natural rubbers, namely imported Hevea and US-grown guayule, was conducted to quantify environmental impacts and to identify area(s) of environmental improvement. The use of co-products from the two natural rubbers as a source of energy was explored for their impacts and energy offset potential. Three environmental impact categories-ozone depletion (ODP), global warming (GWP), and acidification potential (AP)-and net energy were evaluated.Results indicated that guayule rubber had a lower ODP impact compared to SBR, and lower GWP and AP impacts compared to Hevea rubber. The Hevea rubber production with biodiesel co-product from seed oil scenario had the highest GWP and AP impacts, whereas guayule rubber production with bio-oil co-product from bagasse had the highest ODP impact. Only the scenario of Hevea rubber production with biodiesel production indicated an overall energy production of 3.25 MJ/kg rubber, whereas all other scenarios indicated a net energy consumption. However, co-products contributed to reduction in total energy consumed in every scenario that was investigated. The most promising guayule rubber scenario among the six examined was that with electricity production from bagasse, as it contributed the least to all three impact categories and yielded the most net energy. Sensitivity analysis on this most promising guayule scenario indicated rubber yield, water use and electricity for water pumping in guayule irrigation as the key parameters that have significant impacts on results.

QUANTIFICATION OF THE CONTRIBUTION OF FILLER CHARACTERISTICS TO NATURAL RUBBER REINFORCEMENT USING PRINCIPAL COMPONENT ANALYSIS

ABSTRACTPractical statistical models were developed to quantify individual contributions from characteristics of conventional and non-conventional fillers and predict resulting mechanical properties of both hevea and guayule natural rubber composites. Carbon black N330 and four different agro-industrial residues, namely, eggshells, carbon fly ash, processing tomato peels, and guayule bagasse, were used in this study. Filler characteristics were used as explanatory variables in multiple linear regression analyses. Principal component analysis was used to evaluate correlations among explanatory variables based on their correlation matrices and to transform them into a new set of independent variables, which were then used to generate reliable regression models. Surface area, dispersive component of surface energy, carbon black, and waste-derived filler loading were found to have almost equal importance in the prediction of composite properties. However, models developed for ultimate elongation poorly explained variability, indicating the dependence of this property on other variables. Agro-industrial residues could potentially serve as more sustainable fillers for polymer composites than conventional fillers. This new modeling approach for polymer composites allows the performance of a wide range of different waste-derived fillers to be predicted with minimum laboratory work, facilitating the optimization of compound recipes to address specific product requirements.

Refinements to Hevea rubber breeding

Hevea brasiliensis (Willd. Ex. A. de. Juss. Muell-Arg.) is the prime source of natural rubber. Domestication of rubber began since 1876 with Wickham collecting 70,000 seeds from Upper Amazon and transported them to Kew Botanic Gardens. Somehow, rubber trees covering millions of hectares are believed to be derived from “22 seedlings” of Wickham’s original stock. Improving dry rubber yield is the exclusive and ultimate objective of Hevea breeding with consistent yield of 70 to 80 g/tree/tapping. Ultimately, in a small holding, a planter must gain an average yield of around 2200 to 2400 kg/ha from his stand (under optimal conditions), after accommodating tree-to-tree variations due to stock-scion interactions and soil heterogeneity. This is arduous, but achievable. Initial production of high-yielding clones gave 1600 kg/ha against 496 kg/ha of unselected seedlings. Adaptation and yielding potential of clones to specific environments are optimized through localized experimentation. Studies on adaptation of clones to new environments, especially to sub-optimal or marginal areas, are gaining momentum. As this extension happens, demand for new clones is on the rise. Possibilities of using rubber trees for reforestation, carbon sequestration and application of genomics in deriving climate resilient clones may come up in future, which breeders may have to take up with required priority. Five major methodologies followed are (a) primary clones and seed gardens, (b) derivation of recombinants and clone selection, (c) genetic analysis and variability management (d) early selection and estimation of genetic value and (e) application of genomics. Primary clones have immensely contributed in exploiting heterosis and production of new clones. For evaluation of recombinants, families are to be raised in closer spacing (2 or 3 m) and allowed to attain tappable girth for evaluation. While a normal breeding cycle takes 35 to 40 years, through skipping SSCTs and LSCTs, the scheme proposed can derive a clone in 17 years. Recent advances like transcriptome sequencing of bark and EST sequences generated from suppression subtractive hybridization-cDNA libraries could facilitate marker-assisted selection that could very well be used for selecting high-yielding genotypes at juvenile stage. Paternity identification can be done through breeding without breeding (BwB) in half-sibs and poly-cross (open pollinated) seedlings. Transcriptome studies have to come a long way to yield meaningful results to tag vivid genes responsible for QTLs, resistance and other quality traits, especially markers for cold/drought stress. It is opined that instead of subjecting plants for artificial cold/drought conditions, plants continuously exposed to such stress conditions must be used for analyses that can give a comprehensive indication of stress tolerance. The application of genotyping-by-sequencing (GBS) technique to simultaneously discover and delineate single nucleotide polymorphism (SNP) markers is a robust and cost-effective approach for generating a common set of genome-wide SNP data suitable for constructing integrated linkage maps from multiple populations. Studies on mitochondrial and chloroplast DNAs are welcome steps towards understanding ATP efficiency of accessions that need to be augmented further, so that clones with higher ATP efficiency can be used for breeding. Such innovative techniques shall govern breeding Hevea rubber in the future, only when breeders and genomic specialists are working in tandem.

Effect of Non-Rubber Constituents on Guayule and Hevea Rubber Intrinsic Properties

To meet the increasing demand for natural rubber (NR), currently sourced from the tropical rubber tree Hevea brasiliensis, and address price volatility and steadily increasing labor costs, alternate rubber-producing species are in commercial development. One of these, guayule (Parthenium argentatum), has emerged on the market as a commercial source of high quality rubber. Non-rubber constituents play an important role in the physical properties of NR products. The intrinsic composition of the two NR materials differs and these differences may be a principal cause of the performance differences between them. We have compared the effect of non-rubber constituents, such as protein, lipids, resin and rubber particle membranes. Firstly, a film casting method was developed to obtain rubber films with a uniform thickness. Secondly, the glass transition temperature of different rubbers was determined by dynamic mechanical analysis, and tensile properties were tested for uncompounded materials. Guayule natural rubber (GNR), from which most of the membranes were removed while in latex form (MRGNR) was found to have higher intrinsic strength than GNR or gel-free NR (FNR). An acetone extraction was performed to quantify the resin and free lipids in the rubber samples.

Guayule (Parthenium argentatum) pyrolysis biorefining: Fuels and chemicals contributed from guayule leaves via tail gas reactive pyrolysis

Guayule (Parthenium argentatum), a woody desert shrub cultivated in the southwestern United States, is a source of natural rubber and organic resins that promises to revolutionize the tire and rubber industry. Some 20,000kgha−1yr−1 is reported to be harvested worldwide and expected to grow due to renewed interest in guayule to replace imported Hevea rubber. We have recently reported the use of guayule bagasse, the residual biomass after latex extraction, as feedstock in a pyrolysis process that employs a reactive gas environment to formulate a special intermediate bio-oil product that is easily distillable and readily synthesized to hydrocarbon (drop-in) fuels (Boateng et al., 2015). This submission reports on the use of the same pyrolysis process for the leaves of the guayule plant and the array of fuels and chemicals that the leaves can contribute to a co-located guayule biorefinery at a latex plant that could utilize the entire biomass residue value chain. The composition of the guayule leaves is different from the bagasse, with the main differences being lower resin content along with higher ash (>16wt%) and higher nitrogen (2.6wt%, dry ash free, daf) contents resulting from the higher concentration of the plant proteins (16.4wt% (daf)). Since the former two components have exhibited a drastic influence on pyrolysis product distribution in the past, it was incumbent upon us to explore whether the resin content would provide additional synergistic effects and influence product selectivity pathways to bio-based chemicals. We found that the combined effect of the tail gas reactive pyrolysis process, the proteinaceous nature of the guayule leaf and resin combine to create a complex mechanism that results in an interesting bio-oil intermediate product from which a slew of fuel and commodity chemical compounds can be synthesized upon mild upgrading.

Hevea leaf boundary identification based on morphological transformation and edge detection

Hevea (Rubber tree) leaf characteristics have not been utilized yet for automation systems to classify different clones. However rubber tree leaves have some features that can be used to differentiate the clones. The rubber tree leaf is in the class of palmate leaves which means three leaflets are joined at one mutual base. This unique feature gives different positions of the leaflets whether the leaves are overlapping or separated that it can distinguish a particular clone from all other clones. This paper focuses on the position of leaflets in order to identify leaf boundaries. The proposed framework is producing satisfactory results to identify the rubber tree leaf boundaries.

STUDY OF AMINO ACID MODIFIERS IN GUAYULE NATURAL RUBBER

ABSTRACT Guayule, a desert shrub indigenous to the United States, is under development as a source of natural rubber that can be used in place of petroleum-based rubber or Hevea rubber. In natural rubbers, physical and chemical properties can be strongly affected by nonrubber constituents, typically proteins and lipids, present in the material, depending on the plant species and postharvest processing. Hevea natural rubber typically contains high levels of nonrubber constituents that contribute to thermal-oxidative stability, cure acceleration, and especially strain-induced crystallization. The latter has been attributed to compound properties that render Hevea natural rubber uniquely suited for the most demanding rubber applications (e.g., aircraft tires). Hevea proteins are susceptible to hydrolysis, releasing free amino acids into the latex, which can affect rubber and compound properties. Here, low-protein guayule latex was blended with a series of amino acids varying in chemical structure. Bulk viscosity was reduced, thermal-oxidative stability was improved, and cure rate was influenced by the addition of amino acids. Generally, gel formation, green strength, and tensile strength were not affected. The results introduce a new perspective for amino acids as biobased rubber compound additives and provide insights into naturally occurring nonrubber constituents' interaction with natural rubber polymers.

Protein influences on guayule and Hevea natural rubber sol and gel

ABSTRACTGuayule (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.

Novel Chloroplast Microsatellite (cpSSR) Markers for Genetic Diversity Assessment of Cultivated and Wild Hevea Rubber

Understanding the genetic diversity and population structure of Hevea is of great importance for managing its conservation and for utilization of rubber genetic resources. In this study, we investigated the genetic diversity and population structure of eight populations of Hevea rubber genotypes from Malaysia (MY), India (IN), Sri Lanka (LK), Indonesia (ID), France (FR), Thailand (TH), Brazil (BR), and China (CN), in addition to individual primary clones, using 10 nuclear and 11 polymorphic novel chloroplast microsatellite markers (nSSRs and cpSSRs, respectively). The BR population exhibited the greatest genetic diversity (He) for both nSSR (0.841) and haploid genetic diversity (cpSSR; 0.207) markers. Bayesian analysis was applied to infer genetic structure based on nSSR data using STRUCTURE software, and a neighbor-joining tree was used to construct an unrooted phylogram based on Nei’s genetic distance that clustered these Hevea genotypes into three groups. Six polymorphic cpSSR markers produced 13 alleles and eight chlorotypes. Seven chlorotypes, A, B, C, D, E, F, and H were detected among Brazilian populations from Acre (AC), Rondonia (RO), and Mato Grosso (MT) locations. The G and H chlorotypes were found in Asiatic genotypes or Wickham clones and only one genotype, 15 AC-F-7 38-62 from AC location. These results provide valuable data for in situ or ex situ conservation and utilization of germplasm collections for breeding programs.

Treatment of natural rubber latex serum waste by co-digestion with macroalgae, Chaetomorpha sp. and Ulva intestinalis, for sustainable production of biogas

AbstractBiogas production is proposed as an alternative approach to using natural rubber Hevea brasiliensis latex serum, a major waste product from the production of concentrated latex. To make the most efficient use of the reactor size, the addition of macroalgal biomass as a co-substrate to the fermentation system was investigated. The biogas yield of latex serum as a single substrate was (398 ± 14) L per kg of volatile solids added (VSA). For the co-digestion system, algae mixed with serum were investigated at wet mass ratios of Chaetomorpha sp. to Ulva intestinalis to serum at 3 : 0 : 1, 2 : 0 : 2, 1 : 0 : 3, 0 : 1 : 3, 0 : 2 : 2 and 0 : 3 : 1. The co-digestion system with latex serum at 2 to 3 out of 4 parts produced the highest biogas yields within the range of 422-460 L kg

Novel endophytic lineages of Tolypocladium provide new insights into the ecology and evolution of Cordyceps-like fungi

The objective of this study was to identify a group of unknown endophytic fungal isolates from the living sapwood of wild and planted Hevea (rubber tree) populations. Three novel lineages of Tolypocladium are described based on molecular and morphological data. Findings from this study open a window for novel hypotheses regarding the ecology and role of endophytes within plant communities as well as trait evolution and potential forces driving diversification of Cordyceps-like fungi. This study stresses the importance of integrating asexual and sexual fungal states for a more complete understanding of the natural history of this diverse group. In addition, it highlights the study of fungi in the sapwood of tropical trees as habitat for the discovery of novel fungal lineages and substrate associations.

Permittivity models for determination of moisture content in Hevea Rubber Latex.

The commercial open-ended coaxial probe (Agilent 85070E) is the most commonly used sensor to determine the permittivity of wet materials. This paper extends the usability and applicability of the sensor to the estimation of moisture content in Hevea Rubber Latex. The dielectric constant and loss factor were measured using the commercial probe whilst the moisture contents were obtained using the standard oven drying method. Comparison results were obtained between the different dielectric models to predict moisture content in latex. Both the dielectric constant and the loss factor of rubber latex linearly increased with moisture content at all selected frequencies. Calibration equations were established to relate both the dielectric constant and the loss factor with moisture content. These equations were used to predict moisture content in Hevea latex from measured values of the dielectric constant and the loss factor. The lowest mean relative error between actual and predicted moisture contents was 0.02 at 1 GHz when using the Cole-Cole dielectric constant calibration equation. Keywords: open-ended coaxial probe, permittivity models, Hevea Rubber Latex, moisture rubber content DOI: 10.3965/j.ijabe.20140705.005 Citation: Yahaya N Z, Abbas Z, Ibrahim N M, Hafizi M H M, Yahaya M Z. Permittivity models for determination of moisture content in Hevea Rubber Latex. Int J Agric & Biol Eng, 2014; 7(5): 48－54.