Research Repository :: Browsing by Author "Mwaikambo, Leonard Y."

Browsing by Author "Mwaikambo, Leonard Y."

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Biopolymers
(2003) Tucker, Nick; Mwaikambo, Leonard Y.; Johnson, M.
Chemical Modification of Hemp, Sisal, Jute and Kapok Fibers by Alkalisation
(Wiley, 2002) Mwaikambo, Leonard Y.; Ansell, Martin P.
Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X-ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002
Cure Characteristics of Alkali Catalysed Cashew Nut Shell Liquid-Formaldehyde Resin
(Springer Link, 2001) Mwaikambo, Leonard Y.; Ansell, Martin P.
Cashew nut shell liquid (CNSL) is a naturally occurring chemical monomer consisting four alkyl substituted phenols. Its phenolic nature makes it suitable for polymerisation into resins by formaldehyde using sodium hydroxide (NaOH) as a catalyst and hexamethylenetetramine (HMTA) employed as a hardener. There is intense interest in understanding the cure characteristics and properties of CNSL-based resins. In this work the DSC technique has been applied to study the change in the glass transition temperature of the oven-cured resin with and without HMTA in order to monitor the extent of cure. The glass transition temperature was found to rise when the alkaline catalysed resin was subjected to higher curing temperatures regardless of the concentration of formaldehyde used. The mode of cure of the NaOH-catalysed CNSL-formaldehyde resin has been found to be more regular with HMTA hardener. FT-IR spectroscopy has been used to study the neat CNSL and polymerised CNSL-formaldehyde resin with and without HMTA. The use of the DSC and FT-IR techniques to elucidate the extent of cure of CNSL resins is a valuable step towards the production of commercially successful CNSL-natural fibre composites.
Current International Research into Cellulosic Fibres and Composites - Review. J Mater Sci
(2001) Eichhorn, Stephen J.; Baillie, Caroline A.; Zafeiropoulos, Nikolaos; Mwaikambo, Leonard Y.; Ansell, Martin P.; Dufresne, Alain; Entwistle, Kenneth M.; Franco, Pedro H.; Escamilla, G. C.; Groom, Leslie H.; Hughes, Mark; Hill, Callum A. S.; Rials, Timothy; Wild, Peter M.
The following paper summarises a number of international research projects being undertaken to understand the mechanical properties of natural cellulose fibres and composite materials. In particular the use of novel techniques, such as Raman spectroscopy, synchrotron x-ray and half-fringe photoelastic methods of measuring the physical and micromechanical properties of cellulose fibres is reported. Current single fibre testing procedures are also reviewed with emphasis on the end-use in papermaking. The techniques involved in chemically modifying fibres to improve interfacial adhesion in composites are also reviewed, and the use of novel fibre sources such as bacterial and animal cellulose. It is found that there is overlap in current international research into this area, and that there are complementary approaches and therefore further combining of these may make further progress possible. In particular a need to measure locally the adhesion properties and deformation processes of fibres in composites, with different chemical treatments, ought to be a focus of future research.
The Determination of Porosity and Cellulose Content of Plant Fibers by Density Methods
(2001) Mwaikambo, Leonard Y.; Ansell, Martin P.
A combination of the Archimedes method and the technique of helium pycnometry was used to perform accurate measurements of porosity and cellulose content. For this purpose, the densities of hemp, sisal, jute and kapok fibers were measured. An equation was developed using the bulk and absolute density of the fiber and the density of pure cellulose to determine the amount of cellulose a particular fiber contains. As a result, true plant fiber porosity and cellulose content were accurately determined.
The Effect of Chemical Treatment on the Properties of Hemp, Sisal, Jute and Kapok for Composite Reinforcement
(1999) Mwaikambo, Leonard Y.; Ansell, Martin P.
Two chemical treatments were applied to hemp, sisal, jute and kapok natural fibres to create better fibre to resin bonding in natural composite materials. The natural fibres have been treated with varying concentrations of caustic soda with the objective of removing surface impurities and developing fine structure modifications in the process of alkalisation. The same fibres were also acetylated with and without an acid catalyst to graft acetyl groups onto the cellulose structure, in order to reduce the hydrophilic tendency of the fibres and enhance weather resistance. Four characterisation techniques, namely XRD, DSC, FT-IR and SEM, were used to elucidate the effect of the chemical treatment on the fibres. After treatment the surface topography of hemp, sisal and jute fibres is clean and rough. The surface of kapok fibres is apparently not affected by the chemical treatments. X-ray diffraction shows a slight initial improvement in the crystallinity index of the fibres at low sodium hydroxide concentration. However, high caustic soda concentrations lower the fibre crystallinity index. Thermal analysis of the fibres also indicates reductions in crystallinity index with increased caustic soda concentrations and that grafting of the acetyl groups is optimised at elevated temperatures. Alkalisation and acetylation have successfully modified the structure of natural fibres and these modifications will most likely improved the performance of natural fibre composites by promoting better fibre to resin bonding.
Hemp Fibre Reinforced Cashew Nut Shell Liquid Composites
(Elsevier, 2003) Mwaikambo, Leonard Y.; Ansell, Martin P.
Abstract Hemp fibre bundles were alkalised at concentrations between 0.8 and 8% NaOH and the change in surface morphology was elucidated using scanning electron microscopy. Fibres were tested in tension and the 4 and 6% NaOH treatment resulted in the highest Young's modulus and tensile strength of 65 GPa and 1064 MPa respectively. The Young's modulus and tensile strength of untreated fibres were 38 GPa and 591 MPa respectively. The treated fibres with the highest strength were used as reinforcement for cashew nut shell liquid matrix. Nonwoven fibre mats and unidirectional fibre composites were manufactured by hand lay-up compression moulding. Tensile properties, porosity and fracture surface topography of the composites were analysed. The unidirectional fibre composites exhibited the best mechanical properties and composites with lowest porosity offered the highest mechanical properties. Increase in the moulding pressure resulted in a decrease in the mechanical properties except for untreated nonwoven hemp composites in which the presence of inherent binders in the fibres contributed to an enhanced fibre-matrix interface. The contribution of naturally occurring lignin-containing fibres with natural monomers containing similar phenolic compounds provides a compatible interaction on polymerisation hence improved mechanical properties.
Kapok/cotton Fabric–Polypropylene Composites
(Elsevier, 2000) Mwaikambo, Leonard Y.; Martuscelli, Ezio; Avella, Maurizio
Kapok/cotton fabric has been used as reinforcement for conventional polypropylene and maleic anhydride grafted polypropylene resins. Treating the reinforcement with acetic anhydride and sodium hydroxide has modified the fabric (fibres). Thermal and mechanical properties of the composites were investigated. Results show that fibre modification gives a significant improvement to the thermal properties of the plant fibres, whereas tests on the mechanical properties of the composites showed poor tensile strength. Mercerisation and weathering were found to impart toughness to the materials, with acetylation showing slightly less rigidity compared to other treatments on either the fibre or composites. The modified polypropylene improved the tensile modulus and had the least toughness of the kapok/cotton reinforced composites. MAiPP reinforced with the plant fibres gave better flexural strength and the same flexural modulus at lower fibre content compared with glass fibre reinforced MAiPP.
Low Environmental Impact Polymers
(2004) Ansell, Martin P.; Avella, Maurizio; Barber, J.; Bhamra, Tracy; vanErven, R.; Gayet, J. C.; Hughes, Mark; Johnson, M.; Lofthouse, V.; Malinconico, Mario; Masaro, L.; Miller, M.; Mwaikambo, Leonard Y.; O'Brien, M.; Orlando, Pierangelo; Price, D.; Sanadi, A. R.; Tucker, Nick; Whitehouse, R.
Mechanical Properties of Alkali Treated Plant Fibres and Their Potential as Reinforcement Materials II. Sisal Fibres
(Springer Link, 2006) Mwaikambo, Leonard Y.; Ansell, Martin P.
The tensile strength and Young’s modulus of sisal fibre bundles were determined following alkalisation. The results were then analysed with respect to the diameter and internal structure such as cellulose content, crystallinity index and micro-fibril angle. The tensile strength and stiffness were found to vary with varying concentration of caustic soda, which also had a varying effect on the cell wall morphological structure such as the primary wall and secondary wall. The optimum tensile strength and Young’s modulus were obtained at 0.16% NaOH by weight. The stiffness of the sisal fibre bundles obtained using the cellulose content also referred to as the micro-fibril content was compared with the stiffness determined using the crystallinity index. The stiffness obtained using the crystallinity index was found to be higher than that obtained using the cellulose content however, the difference was insignificant. Alkalisation was found to change the internal structure of sisal fibres that exhibited specific stiffness that was approximately the same as that of steel. These results indicates that the structure of sisal fibre can be chemically modified to attain properties that will make the fibre useful as a replacement for synthetic fibres where high stiffness requirement is not a pre-requisite and that it can be used as a reinforcement for the manufacture of composite materials.
Mechanical Properties of Alkali Treated Plant Fibres and their Potential as Reinforcement Materials. I. Hemp Fibres
(2006) Mwaikambo, Leonard Y.; Ansell, Martin P.
In this study a thorough analysis of physical and fine structure of hemp fibre bundles, namely surface topography, diameter, cellulose content and crystallinity index, have been presented. The fibre bundles have been alkalised and physical and mechanical properties analysed. Alkalisation was found to change the surface topography of fibre bundles and the diameter decreased with increased concentration of caustic soda. Cellulose content increase slightly at lower NaOH concentrations and decrease at higher NaOH concentrations. The crystallinity index decrease with increase in caustic soda concentration up to 0.24% NaOH beyond which, it decreases with increase in NaOH concentration. It was also found that the tensile strength and stiffness increases with increase in the concentration of NaOH up to a limit. Tensile strength and Young’s modulus increase with decrease in cellulose content, while crystalline cellulose decreases slightly but with improved crystalline packing order resulting in increased mechanical properties. Similar observations are elucidated by the crystallinity index. Alkalised hemp fibre bundles were found to exhibit a similar specific stiffness to steel, E-glass and Kevlar 29 fibres. The results also show that crystallinity index obtained following alkalisation has a reverse correlation to the mechanical properties. Stiffer alkalised hemp fibre bundles are suitable candidates as reinforcements to replace synthetic fibres. The improvement in mechanical properties of alkali treated hemp fibre bundles confirms their use as reinforcement materials.
Mechanical Properties of Hemp Fibre Reinforced Euphorbia Composites
(Wiley, 2007) Mwaikambo, Leonard Y.; Tucker, Nick; Clark, Andrew J.
A composite material consisting of hydroxide-modified hemp fibres and euphorbia resin was produced. The composites were tested in tension, short-beam interlaminar shear stress and in impact. There was an increase in the tensile strength and modulus for resins with high-hydroxyl-group based composites. Similar results were obtained for interlaminar shear stress while low-hydroxyl group euphorbia resin based composites exhibited high impact strength. The euphorbia resin with high hydroxyl content yielded composites with high stiffness. The use of euphorbia-based resins in composite manufacture increases the value of the euphorbia oil as well as creating a new route of composite manufacturing.
Performance of Cotton-Kapok Fabric-Polyester Composites
(Elsevier, 1999) Mwaikambo, Leonard Y.; Bisanda, Elias T. N.
Cotton–kapok fabric, at a ratio of 2:3, has been incorporated with unsaturated polyester resin in various fibre volume fractions. The fabric was also treated with 5% sodium hydroxide with the aim of improving fibre–matrix adhesion. A simple manual lay up technique was used in fabricating the composites. A hand operated hydraulic electrically heated press was used and the composites were cured at 100°C for 60 min and post cured overnight in the oven at 80°C. Mechanical properties such as tensile strength, tensile modulus, impact strength, and flexural properties of composites not subjected to weathering conditions and weathered composites have been evaluated. Composites with untreated fibres had higher fibre volume fractions than composites prepared using treated fibres. The tensile strength of composites with untreated fibres was higher than that of composites prepared using treated fibres but had, on average, higher tensile modulus than composites manufactured using untreated fibres. The impact strength decreased with increase in fibre volume fractions for both composites, with or without alkali treated fibres. Reductions in flexural strength and moduli were observed with weathered composites. The specific strength of the composites was comparable to that of other vegetable fibre reinforced resins.
The Structure of Cotton and Other Plant Fibers
(2009) Ansell, Martin P.; Mwaikambo, Leonard Y.
The structure and properties of plant fibres are reviewed with emphasis on the deposition of cellulose microfibrils in the plant cell wall and the effect of microfibril angle on mechanical properties such as strength and stiffness. The worldwide production of cotton fibres for textile applications far exceeds that of other plant fibres, hence the structure of cotton is reviewed in detail. Plant fibre bundles such as sisal, hemp, jute and kenaf are finding new uses in structural applications in the automotive and construction industries and a significant proportion of the chapter is devoted to these industrial fibres. New developments in understanding structure-property relationships are continuously appearing in the literature and natural fibres have a strong part to play in a sustainable future.
Tensile Properties of Alkalised Jute Fibres
(2009) Mwaikambo, Leonard Y.
The structure of jute fibre has been modified using caustic soda up to a limit in order to improve its performance. The SEM micrographs of untreated jute fibres show a smooth surface, while alkalised jute fibres show rough and void regions between individual fibre cells. The study showed that the tensile strength and Young’s modulus of jute fibre bundles depends on the physical characteristics of its internal structure such as the cellulose content, changes in the crystalline region content expressed in terms of crystallinity index, and micro-fibril angle. Results also showed tensile properties optimised at 0.24% NaOH (w/w). Overall, alkalised fibres exhibit brittle fracture. The study demonstrated the dependence of tensile properties on the changes in fibre structure following alkalisation.

Browsing by Author "Mwaikambo, Leonard Y."

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