Maurice Kor Ndikontar

Effects of acacia gum and bentonite on the properties of composite bioplastics made of starch and acid hydrolyzed cellulose

Herman Assonfack Lekane, Arnaud Maxime Cheumani Yona, Fabien Lucioni Tsague, Tatiane Marina Abo, Martial Aimé Kuété, Derek Tantoh Ndinteh et 2 autre(s)

Discover Industrial Chemistry and Materials

Abstract This work focuses on the analysis of the effect of acacia gum and bentonite addition on the properties of the biocomposite cassava starch $$\:-$$ acid $$\:-$$ hydroxylyzed cellulose films. The acid $$\:-$$ hydroxylyzed cellulose (NCE) is obtained using cellulose from Ceiba pentandra . Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analyses (TGA) coupled to differential scanning calorimetry (DSC), mechanical stress-strain tests, soil burial biodegradation, and moisture absorption tests were used to characterize the films. FTIR and XRD analyses evidenced the presence of acacia gum and bentonite in the various formulations. Crystallinity indices, from XRD, was related to improved adhesion of polymers chains due to the acacia gum addition. DSC analysis shows a retardant effect to the melting of the starch-cellulose matrix when acacia gum and/or bentonite are added. This effect was associated to improve adhesion brought by the acacia gum and the barrier to heat diffusion due to the mineral phase. The moisture adsorption is reduced of 10% and 18% upon addition of acacia gum and combine bentonite-acacia gum respectively. The interactions between the polymers chains in the starch-NCE film with the additives seems improved with the addition of acacia gum. Biodegradation test evidenced that gum and bentonite addition, through moisture adsorption reduction, induce a slowing of the degradation of all the composites films. The Young modulus of the starch-NCE is improve from 39.9 MPa to 150.7 MPa and 133.3 MPa respectively with the addition of acacia gum and acacia gum $$\:-$$ bentonite. Overall, gum and gum-bentonite addition in starch-cellulose films induce biodegradation retardation through reduce water sensitivity.

• #nanocomposite films for food packaging
• #advanced cellulose research studies
• #polymer-based agricultural enhancements
• #gum acacia

Banana fibre reinforced geopolymer matrices: pore structure, mesoscale and insulating properties

Tatiane Marina Abo, Herman Lekane Assonfack, Joëlle Nadia Nouping Fekoua, Cyriaque Rodrigue Kaze, Rachel Yanou Nkwaju, Juvenal Giogetti Deutou Nemaleu et 3 autre(s)

Innovative Infrastructure Solutions

• #natural fiber reinforced composites
• #innovative concrete reinforcement materials
• #concrete and cement materials research
• #mesoscale meteorology

Isolation and Characterization of Lignin from Sapele (Entandrophragma cylindricum): Application in Flexible Polyurethane Foam Production

Hubert Justin Nnanga Guissele, Arnaud Maxime Cheumani Yona, Armel Edwige Mewoli, Désiré Yomeni Chimeni, L. Fomekong Tsague, Tatiane Marina Abo et 3 autre(s)

Polymers

Lignin used in this work was isolated from sapele (Entandrophragma cylindricum) wood through a hybrid pulping process using soda/ethanol as pulping liquor and denoted soda-oxyethylated lignin (SOL). SOL was mixed with a polyethylene glycol (PEG)–glycerol mixture (80/20 v/v) as liquefying solvent with 98% wt. sulfur acid as catalyst, and the mixture was taken to boil at 140 °C for 2, 2.5, and 3 h. Three bio-polyols LBP1, LBP2, and LBP3 were obtained, and each of them exhibited a high proportion of -OH groups. Lignin-based polyurethane foams (LBPUFs) were prepared using the bio-polyols obtained with a toluene diisocyanate (TDI) prepolymer by the one-shot method. Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) were used characterize lignin in order to determine viscosity, yield, and composition and to characterize their structure. The PEG-400–glycerol mixture was found to react with the lignin bio-polyols’ phenolic -OHs. The bio-polyols’ viscosity was found to increase as the liquefaction temperature increased, while simultaneously their molecular weights decreased. All the NCO groups were eliminated from the samples, which had high thermal stability as the liquefaction temperature increased, leading to a decrease in cell size, density, and crystallinity and an improvement in mechanical performance. Based on these properties, especially the presence of some aromatic rings in the bio-polyols, the foams produced can be useful in automotive applications and for floor carpets.

• #lignin and wood chemistry
• #enzyme-mediated dye degradation
• #catalysis for biomass conversion
• #polyurethane

Extraction, characterization and concentration regimes of the natural gum from Triumfetta cordifolia stem bark

Michèle N. Fanwa, Arnaud Maxime Cheumani Yona, Bruno Gügi, Nicolas Hucher, Catherine Malhiac, Maurice Kor Ndikontar et 1 autre(s)

Food Hydrocolloids

Gum extracted from the Triumfetta. cordifolia plant is traditionally used for its impressive and versatile properties, but many of its intrinsic characteristics still remain poorly documented. This article presents the extraction, purification and physicochemical characterization of the gum present in the stem bark of the plant on the one hand, and the delineation of its concentration regimes in solution on the other. To this end, fresh stem bark was collected and cold extracted in distilled water, followed by ethanol precipitation. The gum was then characterized by elemental analysis, ICP-AES, FT-IR,TGA and GC-FID. Finally, the intrinsic viscosity was determined and concentration regimes delineated using both capillary viscometry and rheometry. Results revealed a monosaccharide composition rich in uronic acids, making T. cordifolia gum a polyelectrolyte, with a high mineral charge, and physicochemical properties similar to those of other polyelectrolyte gums. T. cordifolia gum solutions showed a relatively high intrinsic viscosity (24.3 ± 2.3 dL g−1) and exhibited three distinct concentration regimes (namely dilute, semi-dilute and concentrated) separated by two critical concentrations (C* = 0.3 g L−1 and C** = 1.4 g L−1). These properties open up new prospects for the use of T. cordifolia gum as a texturizing and structuring agent for a variety of mixtures and complex preparations such as emulsions.

• #polysaccharides composition and applications
• #polysaccharides and plant cell walls
• #proteins in food systems
• #chemistry

Eco-Friendly Blends of Recycled PET Copolymers with PLLA and Their Composites with Chopped Flax Fibres

Martial Aimé Kuété, Pascal Van Velthem, Wael Ballout, Nathan Klavzer, Bernard Nysten, Maurice Kor Ndikontar et 2 autre(s)

Polymers

The structure and properties of blends of a novel polyethylene terephthalate copolymer (COPET) obtained by chemical recycling of commercial PET with high-molar-mass poly-L-lactide (PLLA) are investigated and compared to corresponding composites with chopped flax fibres. The focus is on the morphology at nano- and micro-scales, on the thermal characteristics and on the mechanical behaviour. The blends are immiscible, as evidenced by virtually unchanged glass transition temperatures of the blend components compared to the neat polymers (49 °C for COPET and 63 °C for PLLA by DSC). At low PLLA content, the blends display a sea-island morphology with sub-micron to micron droplet sizes. As the composition approaches 50/50, the morphology transitions to a coarser co-continuous elongated structure. The blends and composites show strongly improved stiffness compared to COPET above its glass transition temperature, e.g., from melt behaviour at 60 °C for COPET alone to almost 600 MPa for the 50/50 blend and 500 MPa for the 20% flax composite of the 80/20 COPET/PLLA blend. The flax fibres increase the crystallisation rate of PLLA in blends with dispersed PLLA morphology. The evidence of cavitation on the fracture surfaces of blends shows that despite the immiscibility of the components, the interfacial adhesion between the phases is excellent. This is attributed to the presence of aliphatic ester spacers in COPET. The tensile strength of the 80/20 blend is around 50 MPa with a Young's modulus of 2250 MPa. The corresponding 20% flax composite has similar tensile strength but a high Young's modulus equal to 6400 MPa, which results from the individual dispersion and strong adhesion of the flax fibres and leads close to the maximum possible reinforcement of the composite, as demonstrated by tensile tests and nano-indentation. The Ashby approach to eco-selection relying on the embodied energy (EE) further clarifies the eco-friendliness of the blends and their composites, which are even better positioned than PLLA in a stiffness versus EE chart.

• #biodegradable polymer synthesis and properties
• #natural fiber reinforced composites
• #microplastics and plastic pollution
• #materials science

Concentration regimes of solutions of a natural polysaccharide from Triumfetta cordifolia (Malvaceae) stem barks

Michèle Fanwa Nzokou, Arnaud Maxime Cheumani Yona, Catherine Malhiac, Nicolas Hucher, Maurice Kor Ndikontar, Michel Grisel

HAL (Le Centre pour la Communication Scientifique Directe)

• #polysaccharides composition and applications
• #malvaceae
• #polysaccharide
• #traditional medicine

Integrated Approach to Eco-Friendly Thermoplastic Composites Based on Chemically Recycled PET Co-Polymers Reinforced with Treated Banana Fibres

Martial Aimé Kuété, Pascal Van Velthem, Wael Ballout, Bernard Nysten, Jacques Devaux, Maurice Kor Ndikontar et 2 autre(s)

Polymers

A major societal issue of disposal and environmental pollution is raised by the enormous and fast-growing production of single-use polyethylene terephthalate (PET) bottles, especially in developing countries. To contribute to the problem solution, an original route to recycle PET in the form of value-added environmentally friendly thermoplastic composites with banana fibres (Musa acuminata) has been developed at the laboratory scale. Banana fibres are a so far undervalued by-product of banana crops with great potential as polymer reinforcement. The melt-processing constraints of commercial PET, including used bottles, being incompatible with the thermal stability limits use of natural fibres; PET has been modified with bio-sourced reactants to produce co-polymers with moderate processing temperatures below 200 °C. First, commercial PET were partially glycolyzed with 1.3-propanediol to produce co-oligomers of about 20 repeating units, which were next chain extended with succinic anhydride and post-treated in a very unusual “soft solid state” process at temperatures in the vicinity of the melting point to generate co-polymers with excellent ductility. The molar mass build-up reaction is dominated by esterification of the chain ends and benefits from the addition of succinic anhydride to rebalance the acid-to-hydroxyl end-group ratio. Infra-red spectroscopy and intrinsic viscosity were extensively used to quantify the concentration of chain ends and the average molar mass of the co-polymers at all stages of the process. The best co-polymers are crystallisable, though at slow kinetics, with a Tg of 48 °C and a melting point strongly dependent upon thermal history. The composites show high stiffness (4.8 GPa at 20% fibres), consistent with the excellent dispersion of the fibres and a very high interfacial cohesion. The strong adhesion can be tentatively explained by covalent bonding involving unreacted succinic anhydride in excess during solid stating. A first approach to quantify the sustainable benefits of this PET recycling route, based on a rational eco-selection method, gives promising results since the composites come close to low-end wood materials in terms of the stiffness/embodied energy balance. Moreover, this approach can easily be extended to many other natural fibres. The present study is limited to a proof of concept at the laboratory scale but is encouraging enough to warrant a follow-up study toward scale-up and application development.

• #natural fiber reinforced composites
• #biodegradable polymer synthesis and properties
• #additive manufacturing and 3d printing technologies
• #molar mass

Thermal performance of polyurethane nanocomposite from phosphorus and nitrogen-containing monomer, polyethylene glycol and polydimethylsiloxane for thermal energy storage applications

Stanley Olivier Kanemoto, Siddan Gouthaman, M. Venkatesh, Arnaud Maxime Yona Cheumani, Maurice Kor Ndikontar, Madurai Suguna Lakshmi

Journal of Thermal Analysis and Calorimetry

• #polymer composites and self-healing
• #flame retardant materials and properties
• #polymer nanocomposites and properties
• #polyurethane

Water–soluble extracts from banana pseudo–stem as functional additives for polylactic acid: Thermal and mechanical investigations

Thomas Sango, Grégory Stoclet, Nicolas Joly, Adeline Marin, Arnaud Maxime Cheumani Yona, Lucie Duchatel et 2 autre(s)

European Polymer Journal

• #biodegradable polymer synthesis and properties
• #natural fiber reinforced composites
• #nanocomposite films for food packaging
• #materials science

Chemical Modification of Cassava Starch by Transesterification Using Vegetable Oil/Aluminum Chloride

A.G Gouater Issola, Alexis Ngueteu Kamlo, Arnaud Maxime Cheumani Yona, Maurice Kor Ndikontar

JOURNAL OF RENEWABLE MATERIALS

Chemical modification of cassava starch by transesterification of a vegetable oil (palm kernel oil) using aluminum chloride as a Lewis acid catalyst was achieved under relatively mild conditions (temperature 60–110 °C; atmospheric pressure). The reaction was carried out without any additional solvent. The modified starch was characterized by degree of substitution (DS), FTIR, X-ray diffraction and thermal analysis. DS of 0.09 to 0.53 were obtained. The cassava starch presented an X-ray diffraction pattern of a type A starch. X-ray analyses showed that the reaction did not significantly affect the crystallinity of starch. The modified starch films (MStF) adsorbed less water than the reference native starch film (NStF) at all the relative humidities investigated. The MStF were also less soluble in water. The tensile tests showed an increase of the strength and a decrease of the flexibility of MStF compared to the reference NStF. The results showed that this chemical route could be used to increase the water resistance of starch-based materials.

• #cassava research and cyanide
• #starch
• #crystallinity
• #transesterification

Inhibition of fungi with wood extractives and natural durability of five Cameroonian wood species

Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar, André Désiré Fouda Belinga, Steeve Mounguengui, Jacques Michel Njankouo, Stéphane Durmaçay et 1 autre(s)

Industrial Crops and Products

• #african botany and ecology studies
• #wood treatment and properties
• #fungicide
• #extraction (chemistry)

Chemical composition of some plantation wood species (Eucalyptus saligna, Cupressus lusitanica and Eucalyptus paniculata) and assessment of compatibility with plaster

David Vernon Chokouadeu Youmssi, Yves Didier Modtegue Bampel, Jacques Michel Njankouo, Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar

Journal of the Indian Academy of Wood Science

• #wood treatment and properties
• #natural fiber reinforced composites
• #lignin and wood chemistry
• #compatibility (geochemistry)

Investigations on the durability of several Congo basin wood species

Steeve Mounguengui, Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar, Stéphane Dumarçay, Christiane Attéké, Dominique Perrin et 1 autre(s)

HAL (Le Centre pour la Communication Scientifique Directe)

International audience

• #wood treatment and properties
• #wood and agarwood research
• #african botany and ecology studies
• #gallic acid

Total phenolic and lignin contents, phytochemical screening, antioxidant and fungal inhibition properties of the heartwood extractives of ten Congo Basin tree species

Steeve Mounguengui, Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar, Stéphane Dumarçay, Christiane Attéké, Dominique Perrin et 2 autre(s)

Annals of Forest Science

• #lignin and wood chemistry
• #phytochemicals and antioxidant activities
• #enzyme-mediated dye degradation
• #phytochemical

Discoloration and biodegradation of two dyes by white-rot fungi Perreniporia tephropora MUCL 47500 isolated in Gabon

Steeve Mounguengui, Christiane Attéké, Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar, Stéphane Dumarçay, Philippe Gérardin

HAL (Le Centre pour la Communication Scientifique Directe)

International audience

• #microbial metabolism and applications
• #enzyme-mediated dye degradation
• #dye analysis and toxicity
• #white rot

Study of the feasibility of a natural dye on cellulosic textile supports by red padouk (Pterocarpus soyauxii) and yellow movingui (Distemonanthus benthamianus) extracts

Jean‐Bosco Saha Tchinda, Anélie Pétrissans, Stéphane Molina, Maurice Kor Ndikontar, Steeve Mounguengui, Stéphane Dumarçay et 1 autre(s)

Industrial Crops and Products

• #dyeing and modifying textile fibers
• #biological stains and phytochemicals
• #bamboo properties and applications
• #viscose

Discoloration of dyes by Hexagonia apiara fungus isolated in Gabon and screening of enzymes on solid culture medium

Steeve Mounguengui, Christiane Attéké, Jean‐Bosco Saha Tchinda, Maurice Kor Ndikontar, Stéphane Dumarçay, Philippe Gérardin

HAL (Le Centre pour la Communication Scientifique Directe)

The white-rot fungus Hexagonia apiaria isolated in wood parks in Gabon showed a high capacity to degrade synthetic dyes used in the textile industry. The results of this study show that this fungus has an optimum growth temperature between 30°C and 40°C. Optimum physicochemical parameters of discoloration on solid culture media are 35°C and 0.3g/L. On solid culture medium, the fungus produces different enzymes (cellulase, laccase, phenoloxidase, and peroxidases) in the presence of different substrates. At the concentration of 0.3g/L after 6 day 0.76 and 0.78 (cm/day) respectively for Orange G, Reactive blue 4 and Congo red. The study reveals the opportunity of using this yet poorly known fungus for discoloration of synthetic dyes.

• #microbial metabolism and applications
• #enzyme-mediated dye degradation
• #dye analysis and toxicity
• #fungus

Nature and Performance of Tropical Wood Natural Fiber Cementitious Composites

Mizi Fan, Maurice Kor Ndikontar

Journal of Materials in Civil Engineering

Twelve commercially available tropical wood natural fiber species and their cementitious composites were thoroughly studied for possible production of natural fiber cementitious composites (NFCCs) through (1) the determination of chemical constituents of the fiber species, (2) determination of compatibility of natural fiber cement and correlation of the compatibility with chemical constituents, and (3) examination of the mechanical property of NFCC and its correlation with the compatibility and chemical constituents of wood natural fibers. The results showed that (1) the chemical constituents of the 12 tropical wood fibrous materials varied considerably from one another, with cellulose content ranging between 40 and 57%, lignin ranging between 21 and 34%, and solubility ranging between 2.40 and 29.06% depending on the type of solutions, (2) pH values were below 7 for all natural fibers tested (pH of 3.36–6.22), and the acid-to-base ratio (ABR) values were no greater than 1, indicating that the base buffering capacity (BBC) values were higher than the acid buffering capacity (ABC) values, (3) the compatibility reduced as the wood natural fiber content increased and was polynomially correlated to the solubility of the wood natural fiber species, (4) mechanical properties of NFCC decreased as the fiber content increased, with the highest bending strength (7.21 MPa) and compressive strength (33.18 MPa) for movingui NFCC corresponding to the lowest hot water and Ca(OH)2 solubility; the lowest bending and compressive strengths (0 MPa) were for both moabi and doussie NFCCs corresponding to their high solubility contents, and (5) the five best natural fiber species studied for NFCCs were movingui, nkanang, eyong, tali, and padauk, whereas the least suitable two were moabi and doussie. The results provided a fundamental and essential database and technologies for better understanding tropical wood natural fiber species to use them as value-added commercial products in the construction industry and further academic research.

• #natural fiber reinforced composites
• #wood treatment and properties
• #bamboo properties and applications
• #solubility

Antioxidant activities, total phenolic contents and chemical compositions of extracts from four Cameroonian woods: Padouk (Pterocarpus soyauxii Taubb), tali (Erythrophleum suaveolens), moabi (Baillonella toxisperma), and movingui (Distemonanthus benthamianus)

Jean‐Bosco Saha Tchinda, Daouda Abia, Stéphane Dumarçay, Maurice Kor Ndikontar, Philippe Gérardin, Joseph Ngamveng Noah et 1 autre(s)

Industrial Crops and Products

• #biological stains and phytochemicals
• #plant-derived bioactive compounds
• #plant biochemistry and biosynthesis
• #gallic acid

Cement-bonded composites made from tropical woods: Compatibility of wood and cement

Mizi Fan, Maurice Kor Ndikontar, Xiangming Zhou, J. Noah Ngamveng

Construction and Building Materials

• #wood treatment and properties
• #bamboo properties and applications
• #natural fiber reinforced composites
• #compatibility (geochemistry)

GRAFT COPOLYMERISATION OF ACRYLAMIDE ON CARBOXYMETHYL CELLULOSE (CMC)

Abel Tame, Maurice Kor Ndikontar, J. Noah Ngamveng, Richard Mpon, Emmanuel Njungab

Graft copolymers of acrylamide (AA) on unmodified holocellulose and holocellulose containing carboxy methyl moieties (of degree of substitution (DS): 0.215; 0.120 and 0.057) were prepared using Ce 4+ initiator in aqueous medium at 29°C. The results indicate that carboxymethylation enhances the graftability of the cellulose substrate. The graft levels and molecular weights of grafted polyacrylamide chains on CMC were higher than those obtained on cellulose. Increases in graft levels of up to 70% and 50% for graft copolymer involving CMC with DS 0.215 and 0.120 respectively were observed. The grafting frequencies of polyacrylamide were less on CMC (DS 0.215) than on CMC (DS 0.120) and on cellulose. This study provides information on the grafting characteristics of AA on CMC, a substrate of particular interest because of its wide range of applications. The influence of ceric ion concentration, degree of substitution of substrate, monomer concentration, time of reaction on the extent and rate of graft copolymerisation of AA unto modified and unmodified cellulose were examined.

• #advanced cellulose research studies
• #electrospun nanofibers in biomedical applications
• #carboxymethyl cellulose
• #acrylamide

Mechanical Properties and Life-Cycle Sustainability Aspects of Natural Fibre

Sharon Kao‐Walter, Etienne Mfoumou, Maurice Kor Ndikontar

Advanced materials research

In order to understand the basic definition of the natural material, references of recently published articles were studied. From these articles, the definition of different terms like renewable material, recyclable material, biodegradable material, sustainable material and finally natural material were collected. Furthermore, a classification of natural fibre was drawn. One of these natural fibres - the coconut was chosen for a more detail analysis in mechanical point of view. An integrated method to analyse the sustainability of the coconut fibre as one of the blend components in building construction will be suggested. Finally, several uses of the fibre are reviewed.

• #natural fiber reinforced composites
• #sustainability
• #natural materials
• #natural (archaeology)

Probing of wood–cement interactions during hydration of wood–cement composites by proton low-field NMR relaxometry

Y. A. M. Cheumani, Maurice Kor Ndikontar, B. DE JESO, Gilles Sèbe

Journal of Materials Science

• #wood treatment and properties
• #masonry and concrete structural analysis
• #concrete and cement materials research
• #cement

ESSAIS DE STABILISATION DE LA LATERITE AVEC LES FIBRES CELLULOSIQUES

AB Bakam, Maurice Kor Ndikontar, I Konfor Njilah

African Journal of Science and Technology

RÉSUMÉ:- Afin de valoriser les matières premières locales, des blocs de latérite comprimée ont été stabilisés par des fibres cellulosiques provenant du Cyperus papyrus (cyperus), fibres longues et du Manihot esculenta (manioc), fibres courtes. Ainsi, la plus grande valeur de la résistance à la flexion statique à sec, 2,5 MPa, a été obtenue avec des blocs de latérite comprimée stabilisés à 5% de fibres longues. A cette même teneur, les blocs de latérite contenant les fibres courtes donnent une résistance inférieure, soit 1,69 MPa. De façon inattendue, à 10% de fibres courtes, la résistance à la flexion à sec des briques (2,47 MPa) est supérieure à celle des briques à fibres longues à teneur égale (2,08 MPa). La résistance à la flexion humide de tous ces blocs apparaît nulle avec, cependant une conservation du réseau des blocs de latérite contenant les fibres cellulosiques du cyperus et du manioc à des teneurs supérieures ou égales à 5%. Les briques absorbent l'eau de remontée capillaire en fonction de leur teneur en fibres cellulosiques et de la nature de ces dernières. Pour les briques non stabilisées, le pourcentage d'eau absorbée est de 9,5%. A 7,5% de fibres longues, il n'est plus que 6,0%, alors qu'à 10% de fibres longues, il monte à 15,3% pendant que celui des fibres courtes atteint la valeur de 16,2% au bout d'une période de 22 heures. Mot clés: latérite, briques stabilisées, fibres cellulosiques, résistance à la flexion, absorption par capillarité. ABSTRACT:- In order to give added value to local raw materials, compressed laterite bricks have been stabilised with cellulose fibres of Cyperus papyrus (cyperus), long fibres and Manihot esculenta (cassava), short fibres. The highest value of the dry flexural resistance, 2.53 MPa, was obtained with blocks stabilised at 5% long fibres content. At the same content the blocks of laterite containing short fibres gave a dry flexural resistance of 2.47 MPa which is higher than the value of 2.08 MPa for long fibres. The wet flexural resistance of all blocks is zero. But it can be noted that bricks containing cellulose fibres of cyperus and cassava at percentages higher or equal to 5% conserve their shape during complete immersion. The bricks absorbed water by capillarity depending on the nature and the percentage content of cellulose fibres. After a period of 22 hours, bricks containing 7.5% long fibres absorbed 6.0% water, less than 9.5% for unstabilised bricks; while at 10% of long fibres, absorption increased to 15.3%. In the same period, with 10% short fibres, the percentage water absorbed rose to 16.2%, indicating the better performance of the longer fibres. Key words: laterite, stabilised bricks, cellulose fibres, flexural resistance, absorption by capillarity. African Journal of Science and Technology Vol.5(1) 2004: 22-28

• #aeolian processes and effects
• #water management and technologies
• #soil erosion and sediment transport
• #humanities

<b>Physicochemecal studies of some hexamethylenetetramine metal(II) complexes</b>

Moise Ondoh Agwara, Peter T. Ndifon, Maurice Kor Ndikontar

Bulletin of the Chemical Society of Ethiopia

Divalent metal (Mn, Co, Ni) complexes of the ligand hexamethylenetetramine (HMTA, C6H12N4) with sulfate, nitrate and fluoroborate as counter ions have been synthesized in ethanolic media. Whereas the complexes with BF4- and NO3- as counter ions have two molecules of hexamethylenetetramine, those with SO42- as counter ion contain just one molecule of hexamethylenetetramine. The complexes have been characterized by elemental analyses, infrared and visible spectroscopy and room temperature magnetic susceptibility measurements. The results suggest octahedral coordination in which the central metal ion is bonded to hexamethylenetetramine and water molecules. KEY WORDS: Divalent metal (Mn, Co, Ni) complexes, Hexamethylenetetramine, Sulfate as counter ion, Nitrate as counter ion, Fluoroborate as counter ion Bull. Chem. Soc. Ethiop. 2004, 18(2), 143-148.

• #inorganic and organometallic chemistry
• #various chemistry research topics
• #hexamethylenetetramine
• #chemistry