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Standard nutrient values are needed for the assessment of optimum nutrient concentrations for improved and sustained yields. The aim of this study was to establish optimum soil and plant nutrient values for Hevea brasiliensis in the humid... more
Standard nutrient values are needed for the assessment of optimum nutrient concentrations for improved and sustained yields. The aim of this study was to establish optimum soil and plant nutrient values for Hevea brasiliensis in the humid forest region of Cameroon. A nutrient survey was carried out during August 2010 and August 2011 in some rubber growing zones of Cameroon. Both soil and leaf samples were collected for the determination of their macronutrient contents. Using the macronutrient concentrations and yield data, boundary lines were calculated. These boundary lines were described by second degree polynomials. Equating the first derivative of the second degree polynomial equations to zero, the following optimum nutrient values 3.5%, 0.31%, 1.53%, 0.28% and 0.83% were obtained for N, P, K, Mg and Ca, respectively, for Hevea leaves. On the other hand, the optimum soil nutrient levels were 3.1% for organic carbon, 0.18% for N, 5.9 mg/kg for P, 262. mg/kg for K, 432 mg/kg for C...
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La gestion de la fertilite des sols est devenue cruciale dans les exploitations paysannes plurispecifiques ou certains processus influencant leur durabilite sont ignores. Une etude a ete menee dans certaines parcelles a base de cultures... more
La gestion de la fertilite des sols est devenue cruciale dans les exploitations paysannes plurispecifiques ou certains processus influencant leur durabilite sont ignores. Une etude a ete menee dans certaines parcelles a base de cultures perennes implantees dans la foret humide du sud ouest Cameroun afin de mieux comprendre la gestion de cette fertilite et identifier les facteurs qui contribuent a l'epuisement des macros elements. Les donnees collectees ont ete modelisees avec l'outil NUTMON. Les resultats ont montres que les systemes de cultures influencent les strategies globales d'exploitation. Tandis que le flux des elements nutritifs dans les parcelles est confirme, les mouvements en N, P et K etaient differents selon la culture perenne principale. Le bilan complet en element nutritif moyen de chaque parcelle a ete negatif largement pour l'azote et positif pour potassium et phosphore. Le bilan partiel, ignorant les flux biophysiques (fixation d'azote, lessiva...
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Research Interests: Food Science and Roasting
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Ce travail a ete realise pour mieux comprendre les phenomenes lies a la variabilite du caoutchouc naturel lors de sa mise en oeuvre. L'etude des lipides dans les echantillons de caoutchouc naturel etudies (coagula) n'a pas permis... more
Ce travail a ete realise pour mieux comprendre les phenomenes lies a la variabilite du caoutchouc naturel lors de sa mise en oeuvre. L'etude des lipides dans les echantillons de caoutchouc naturel etudies (coagula) n'a pas permis de conclure quant a leur implication dans la mesostructure (macrogel et microget). Les profits lipidiques obtenus montraient une hydrolyse importante de l'ensemble des lipides. Apres methanolyse du caoutchouc naturel, le macrogel disparait bien mais environ 25% de microgel persiste. La methanolyse du macrogel seul genere essentiellement du microgel. Ces observations, associees aux donnees de la litterature sur la biosynthese du caoutchouc naturel, nous ont permis de proposer une representation schematique de la structure du caoutchouc naturel. La degradation du caoutchouc naturel par mastication a temperatures elevees (> 115°C) est conditionnee par la teneur en gel total et la quantite relative de courtes chaines de polyisoprene, ce dernier parametre apparaissant comme un facteur limitant. Le macrogel se degrade tres rapidement donnant essentiellement du microgel. Les resultats obtenus semblent montrer que des echantillons de meme macrostructure (viscosite Mooney ou VR et PRI), mais de microstructure et mesostructure differentes, vont conserver ces differences de microstructure et mesostructure apres mastication. L'evolution du couple lors du cisaillement dans le viscosimetre Mooney et sa relaxation a l'arret du cisaillement caracterisent la viscoelasticite du caoutchouc. La relaxation Mooney est parfaitement modelisee avec l'equation de Maxwell et l'equation empirique de Wu-Abbott. Certains des parametres obtenus sont correlees a la Mw (microstructure) et a la quantite de gel total (mesostructure). (Resume d'auteur)
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Investigations on the nutritional status of Hevea brasiliensis plantations in the humid forest zone of Cameroon Part 2: Establishment of macro nutrient norms Untersuchungen zum Nährstoffstatus von Hevea brasiliensis- Plantagen in der Feuchtwald-Zone von Kamerun Teil 2: Ableitung von Makronährstof...more
Investigations on the nutritional status of Hevea brasiliensis plantations in the humid forest zone of Cameroon Part 1: Micronutrient status and distribution in soils Untersuchungen zum Nährstoffstatus von Hevea brasiliensis- Plantagen in der Feuchtwald-Zone von Kamerun Teil 1: Mikronährstoffstat...more
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Wide variations have been observed in dirt content values from identical raw natural rubber samples in different laboratories using similar test procedures. Factors investigated in this study ranged from the physical nature and... more
Wide variations have been observed in dirt content values from identical raw natural rubber samples in different laboratories using similar test procedures. Factors investigated in this study ranged from the physical nature and concentration of the peptiser employed to heat transfer during dissolution of raw natural rubber in the solvent. Rubbers of latex grade, as against those of cuplump, required longer heating before the formation of clear homogeneous solutions. After a critical duration of dissolution, prolonged heating led to the formation of a macrogel that remained insoluble in most nonpolar hydrocarbon solvents. This macrogel seemed to have been in part responsible for the poor repeatability of dirt values. The duration of swelling in white spirit, before heating, affected the formation of insoluble fractions, though this seemed to vary with the time of introduction of the rubber into the mixture. (Resume d'auteur)
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La viscosite Mooney normalisee (ISO 289), utilisee pour predire le comportement viscoelastique des elastomeres bruts, presente souvent un faible pouvoir discriminatoire, ne pouvant pas distinguer les composantes elastiques et visqueuses... more
La viscosite Mooney normalisee (ISO 289), utilisee pour predire le comportement viscoelastique des elastomeres bruts, presente souvent un faible pouvoir discriminatoire, ne pouvant pas distinguer les composantes elastiques et visqueuses de la mesure. Les donnees sur la relaxation de cette viscosite pour le caoutchouc naturel (grades TSR 3CV et TSR 10) ont ete donc modelisees avec des equations derivees du modele constitutif de Maxwell et autres equations empiriques, afin de generer des coefficients qui pourront mieux caracteriser cette viscoelasticite. Ces coefficients ont donc ete correles aux attributs de la macrostructure (viscosite en masse), la microstructure (masses molaires moyennes, l'indice de polymolecularite, etc.) et la mesostructure (microgel, macrogel, teneur en gel total). Parmi ces coefficients, ceux des modeles de Maxwell et de Wu-Abbott ont ete fortement correles a la structure macromoleculaire du caoutchouc, permettant egalement une meilleure discrimination entre echantillons de meme viscosite Mooney. Les coefficients de la relaxation modelisee sont apparus plus pertinents que la viscosite Mooney pour caracteriser la viscoelasticite du caoutchouc naturel brut. (Texte integral)
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Several exploitation systems are being used today to sustainably improve dry rubber production by the rubber tree (Hevea brasiliensis). These involve different combinations of tapping frequencies, cut lengths, stimulation frequencies, and... more
Several exploitation systems are being used today to sustainably improve dry rubber production by the rubber tree (Hevea brasiliensis). These involve different combinations of tapping frequencies, cut lengths, stimulation frequencies, and stimulant concentrations. Such combinations are much easier to ascertain for confirmed clones as opposed to new introductions, for which extensive testing is required. A study was therefore conducted in the South West region of Cameroon characterized by a monomodal rainfall regime (one dry and one rainy season) to evaluate yield response to Ethephon stimulation (conc. 2.5%) of some newly introduced rubber clones (IRCA 18, IRCA 19, RRIC 100, and RRIC 110) for large-scale planting in Cameroon. Generally, annual yields and tree productivity ranged between the referenced clones tested: some closer to the intermediate yielding GT 1 (IRCA 18 and IRCA 19) and others to the high yielding PB clones (RRIC 100 and RRIC 110) indicating thereby the possible con...
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Traditional leafy vegetables form a major part of the diets and incomes of rural and urban households in Cameroon. However, despite their relative importance, information on their management is scanty. This study was undertaken to... more
Traditional leafy vegetables form a major part of the diets and incomes of rural and urban households in Cameroon. However, despite their relative importance, information on their management is scanty. This study was undertaken to evaluate the influence of different harvesting techniques used at first harvest on the subsequent fresh and dry shoot yields of Solanum scabrum. Two accessions of S. scabrum were used as main plot treatments with four harvesting techniques as subplot treatments in a split-plot arrangement. A linear relationship was observed between the cumulative fresh and dry shoot weights. Irrespective of the harvesting technique adopted, the two accessions gave similar cumulative fresh and dry shoot weights. However, harvesting the plants while leaving one or no lateral shoot gave significantly higher subsequent cumulative shoot yields than with the standard practice of plucking the shots at random. Key words: Huckleberry, Solanum scabrum , cumulative fresh shoot yields, shoot dry yields
ABSTRACT Natural rubber must be technically specified for various uses. Variability in technological properties of raw nat-ural rubber leads to problems of grading. A study was conducted to establish relationships between physio-logical... more
ABSTRACT Natural rubber must be technically specified for various uses. Variability in technological properties of raw nat-ural rubber leads to problems of grading. A study was conducted to establish relationships between physio-logical parameters of latex and technological properties of the raw rubber. The latex samples were analysed by micro-latex diagnosis technique and the relevant technological properties of the processed rubber estimated usi-ng International Standard organization (ISO) procedures. Correlations were found between physiological para-meters and technological properties of processed crumbs; specifically, between the plasticity retention index, Mooney viscosity, Initial Wallace plasticity and inorganic phosphorus, total solid content and sucrose content. The relationships varied with the clones. The best empirical equations fit describing the relationship between physiological parameters of latex and technological properties of the raw rubber were polynomials, while the master equation was a power function with coefficient of determination of 0.84. The values of technological properties of raw rubber could be predicted from the values of some physiological parameters of the latex, and such empirical relationships would assist farmers to forecast values of the technological properties, and modify the properties as required prior to processing.
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... 1): The vil-lages of Bombe, Banga Bakundu, Etam II and Mukonje, respectively in Muyuka, Mbonge, Tombel and Kumba ... Ländliche Entwicklungsprogramme 2007 bis 2013 in Deutschland im Vergleich–Finanzen, Schwerpunkte, Maßnahmen 12, 00€... more
... 1): The vil-lages of Bombe, Banga Bakundu, Etam II and Mukonje, respectively in Muyuka, Mbonge, Tombel and Kumba ... Ländliche Entwicklungsprogramme 2007 bis 2013 in Deutschland im Vergleich–Finanzen, Schwerpunkte, Maßnahmen 12, 00€ 316 Michaela Schaller und ...
Research Interests: Environmental Science, Soil Science, Analytical Chemistry, Forestry, Biogeochemistry, and 15 moreChemometrics, Organic Geochemistry, Ecology, Soil Chemistry, Quantitative analysis, Biological Sciences, Environmental Sciences, Soils, Loss on Ignition, Sol, Relation, Organic carbon, Quantitative Analysis, Earth Science, and Regression equation
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ABSTRACT Drying of natural rubber (NR) crumb (grade TSR10) requires high temperatures (100–120 °C). In order to determine the changes in bulk viscosity during the drying process, ageing kinetics at 120 °C were studied on model NR samples.... more
ABSTRACT Drying of natural rubber (NR) crumb (grade TSR10) requires high temperatures (100–120 °C). In order to determine the changes in bulk viscosity during the drying process, ageing kinetics at 120 °C were studied on model NR samples. During the process, changes in Mooney viscosity and weight-average molar mass (MW) were monitored. Rubber from clones GT 1 and PR 107, with a bimodal inherent molar mass distribution (MMD0), was degraded in a two-phase process. During the first phase, Mooney viscosity and MW increased, undoubtedly owing to a predominance of storage hardening over chain scissions [0 < t (min) <120]. During the second phase, chain scissions predominated (t > 120 min) and Mooney viscosity and MW decreased. For rubber samples from clone PB 217, with a unimodal MMD0, no or reduced storage hardening was observed throughout the ageing process. These results showed that the key parameter involved in storage hardening seems to be the quantity of short polyisoprene chains and probably the nature of the chain ends. Copyright © 2003 Society of Chemical Industry
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ABSTRACT Raw natural rubber samples of different Mooney viscosity values and inherent molar mass distributions (MMD) were used to characterize changes occurring during high-temperature mastication and to identify the structural components... more
ABSTRACT Raw natural rubber samples of different Mooney viscosity values and inherent molar mass distributions (MMD) were used to characterize changes occurring during high-temperature mastication and to identify the structural components conditioning mastication-induced degradation. The macrogel degraded rapidly to essentially microgel, the latter of which was also continuously degraded, and at times completely. Mastication provoked decreases in the average molar mass of polyisoprene chains and changes in their MMD. The MMDs evolved differently as mastication progressed, differences that could be linked to the inherent MMD of each rubber. The non-viscosity stabilized grade rubber (TSR 10) of monomodal MMD was progressively degraded by mastication, whereas rubber of the same grade but with a bimodal MMD was degraded much slowly and even stagnated on prolonged mastication. The stage at which stagnation occurred was characterized by an offset of the balance between long and short polyisoprene chains due to increases in the quantity of short chains, which facilitate the sliding of the longer ones. POLYM. ENG. SCI., 46:222–227, 2006. © 2005 Society of Plastics Engineers
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Biochemical studies of lipids bound to rubber particles have been complicated due to the solubility of polyisoprene chains in most extracting solvents and the rather delicate nature of polar lipids that are often denatured when... more
Biochemical studies of lipids bound to rubber particles have been complicated due to the solubility of polyisoprene chains in most extracting solvents and the rather delicate nature of polar lipids that are often denatured when traditional solvent extraction techniques are employed. In this paper, we describe a traditional technique and accompanying solvents that permit optimal extraction of rubber particle bound lipids. The technique, which is validated after characterizing the lipid extracts by elemental analysis, silica column adsorption and thin layer chromatography, appeared more suitable for extracting total lipids with optimal glycolipid and phospholipid contents. This technique is proposed as an alternative to traditional extraction methods used for solid natural rubber as it offers advantages with respect to ease of application, extract quality, extraction yields and reproducibility.
Research Interests: Phospholipids, Biological Sciences, Immersion, Lipids, LaTeX, and 15 moreIntact polar lipids, Solvent Extraction, Methanol, Temperature, Hevea brasiliensis, CHEMICAL SCIENCES, Phytochemical Analysis, Glycolipids, Hevea, Caoutchouc, Quntitative Thin Layer Chromatography, Acetone, Solvents, Chloroform, and Medical and Health Sciences
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ABSTRACT 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... more
ABSTRACT 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
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Intrinsic viscosity [η] characterizes flow, polymerization, or degradation of dilute polymer solutions. Unlike other high polymers, natural rubber hardly completely dissolves in most organic solvents, and eliminating the insoluble phase... more
Intrinsic viscosity [η] characterizes flow, polymerization, or degradation of dilute polymer solutions. Unlike other high polymers, natural rubber hardly completely dissolves in most organic solvents, and eliminating the insoluble phase undermines the quality of the measurement and its interpretation. On using some natural and synthetic polyisoprene samples, the Huggins and Schulz-Blaschke best-fits were most suitable for estimating [η] for very
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Different natural rubber-based masterbatches compounded using an efficient sulphur, conventional sulphur, peroxide, and diurethane vulcanisation systems were characterised in terms of cure behaviour, vulcanised to different levels of... more
Different natural rubber-based masterbatches compounded using an efficient sulphur, conventional sulphur, peroxide, and diurethane vulcanisation systems were characterised in terms of cure behaviour, vulcanised to different levels of cure, and then tested for set in ...
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Research Interests: Geography, Agroforestry, Performance Assessment, Performance indicators, Sustainability Assessment, and 13 moreÉvaluation, Management Practice, Economic performance, Aide à La Décision, Production Function, FARMING SYSTEM, Durabilité, Food Products, Performance Indicator, Agroforestry Systems, Agroforestry System, South West, and Agroforesterie
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Research Interests: Engineering, Principal Component Analysis, Statistical Analysis, Natural rubber, Applied, and 10 moreMeasurement Error, Dissolution, CHEMICAL SCIENCES, Repeatability, Standard Error, Precision, Caoutchouc, Metrologie Et Controle De Qualité, Journal of Applied Polymer Science, and measurement accuracy
ABSTRACT Better assessment of natural rubber (NR) quality and processability, through the identification of new attributes, is still a major challenge. With this scope, 12 model samples of natural polyisoprene and two of synthetic... more
ABSTRACT Better assessment of natural rubber (NR) quality and processability, through the identification of new attributes, is still a major challenge. With this scope, 12 model samples of natural polyisoprene and two of synthetic polyisoprene were characterized in terms of Mooney torque relaxation, using the standardized ISO289 method (ML(1+4)100, explained later in the Section 1). The main purpose of this study was to identify a model that gave a better fit for the experimental decay of Mooney torque over time (ML(t)=f(t)) than the usual power law model used before (Y=at−b, [G.M. Bristow, A.G. Sears, The use of novel parameters in the assessment of natural rubber processability, NR Technol. 18 (1987); H.G. Burhin, W. Spreutels, J.M. Campbell, MV2000 Mooney viscometer: Mooney relaxation measurements on raw polymers and compounded rubber stocks, Kautsch. Gummi Kunstst. 43 (1990) 431]). The results showed that a generalized Maxwell model, and the Wu–Abbott empirical model [T. Wu, J.A. Abbott, Firmness and force relaxation characteristics of tomatoes stored intact or as slices, Postharvest Biol. Technol. 24 (2002) 59–68], recently used for describing stress relaxation of tomato flesh, allowed a better description of the relaxation curve for the samples studied than the power law or stretched exponential traditionally used.Moreover, the total relaxation time (τm) given by the generalized Maxwell model showed good correlation with the total gel content of the samples studied.