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My research consist in developing novel plant fibre-reinforced matrix composites that could compete with synthetic fibre-based homologues in structural or semi-structural applications. It deals mainly with fibre/matrix interfacial adhesion issues, implying the development of novel compatibilisation systems and other chemical modification of the fibre surface. Thermoset-based composites prepared with a Resin Tranfer Moulding technique (RTM) were particularly investigated.

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A significant number of wood properties, such as dimensional instability, biodegradability, weathering, poor wettability for some adhesives or coatings� are closely related to the hydrophilic character of its main constituents (e.g. cellulose, hemicellulose and lignin). It is reasoned that the chemical grafting of highly hydrophobic components to wood could drastically change its hygroscopicity and decrease many of its water-related drawbacks.

Therefore, wood, paper and other natural products were hydrophobized by chemical reaction with silicone, an extremely hydrophobic material. Distinct methods for the introduction of varied silicones at the surface of natural products are then developed.

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Chemical modification is a very effective means of improving wood properties such as dimensional stability or biological resistance. The processes involved rely essentially upon forming covalent bonding between the hydroxyl groups of wood and some chemical reagent; leading to a modification of the basic chemistry of the cell walls. Many studies in this area have been focused on either etherification or esterification reactions, with a particular attention on acetylation with acetic anhydride.

With this work, the effect of grafted (hydrophobic) organosilicon groups on the dimensional stability of wood is specifically studied. For instance, Maritime pine sapwood (Pinus pinaster) was esterified using three synthesised organosilicon models bearing trimethylsilyl groups. The grafting was confirmed by infrared spectroscopy as well as ¹³C and ²⁹Si NMR CP MAS analysis. The mechanism of dimensional stabilisation, whether it arose purely from a bulking effect or substrate hydrophobicity, was particularly discussed.

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The manufacture of paper requires the intermittent use of various additive formulations to improve or impart certain qualities to the paper product. Fillers such as titanium dioxide (TiO₂) are used to provide brightness and opacity to paper and must be retained on the sheet to be effective. Titanium dioxide pigments are finely divided, chemically inert white powders that possess a high refractive index. They are commercially available in two distinct crystal forms, anatase and rutile.

The objective of this study is to chemically modify the pulp in order to improve the retention of TiO₂ (rutile form) during sheet formation. This was achieved by an enzymatic treatment of the pulp, using 2-ethoxyethanol and b-glucosidase:

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In the last few years, there has been growing interest in using cellulose and its derivatives in the biomedical field. The biocompatibility of cellulose is well documented and there have already been some successful attempts to use cellulosic materials as implants in cardiovascular and orthopaedic surgery.

In the present work, the phosphorylation of cellulose is envisaged with the view to stimulate bone induction. Once implanted, phosphorylated cellulose could promote the formation of calcium phosphates, having therefore closer resemblance to bone functionality. Satisfactory bonding at the interface between hard tissue and the biomaterial could also be expected.

For instance, the reactivity of cellulose with regard to phosphorylation was investigated, using the phosphorus oxychloride method (POCl₃):

The degree of substitution of cellulose hydroxyl groups was evaluated by potentiometric titration.

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Hemp fibre-reinforced polyester composites were prepared using a Resin Transfer Moulding (RTM) technique and the flexural and impact behaviour investigated. Flexural stress at break and flexural modulus showed an increasing trend with fibre content. Impact strength was found to decrease at low fibre content, then gradually increase with further addition of fibres

A strong interfacial adhesion between hemp and polyester was obtained using chemically modified hemp. This modification consisted in introducing reactive vinylic groups at the surface of the fibres, via esterification of hemp hydroxyl groups, using methacrylic anhydride. Increased bonding between fibres and matrix did not affect the flexural stress at break of the composite but was detrimental to toughness. This behaviour was ascribed to a change in the mode of failure, from fibre pull-out to fibre fracture, resulting in a marked reduction in the energy involved in the failure of the composite, leading to a more brittle material.

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Half fringe photoelasticity was used to evaluate the two dimensional state of stress in epoxy matrix micro-tensile specimens. The experimental technique is described in detail and demonstrated by the measurement of the stress distribution around a circular hole in a thin epoxy film subject to uniaxial tension. The results obtained using this photoelastic technique compare well with theoretical solutions. This system has enabled the mapping of stresses in the matrix of single (hemp) filament composites, strained parallel to the fiber axis, to be undertaken. Concentrations of stress were observed in the interphase region, adjacent to kink bands (micro-compressive defects) and stress concentration factors of ~ 1.4 were recorded. The role that these stress concentrations play in the failure of hemp fiber reinforced composites is discussed.

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The dimensional stabilisation imparted to Maritime pine sapwood by chemical modification with hydrophobic organosilicon compounds was investigated. The modification was performed via esterification, using different chemically synthesised models bearing trimethylsilyl groups: 3-trimethylsilylpropanoic anhydride (I), 2-trimethylsilylmethylglutaric anhydride (II) and trimethylsilylethenone (III). The grafting was confirmed by infrared spectroscopy as well as ¹³C and ²⁹Si NMR CP MAS analysis and was located into the wood cell walls. The dimensional stabilisation induced by (I) and (II) appeared to be stable during the three oven-dry/water-soak cycles and, for a given number of hydroxyl blocked, to be much better than with acetic anhydride. On the other hand, the graft from (III) was found to hydrolyse progressively into an acetyl group via a metallotropic rearrangement. Further investigation on hygroscopicity and swelling behaviour of modified wood from (I) and (II) indicated that dimensional stabilisation was attributable to a bulking effect rather than a change in substrate hygrocopicity. The bulky grafts from (I) and (II) were, in particular, thought to over-swell locally the wood cell wall, revealing areas with new water-accessible hydroxyl groups.

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The hydrophilicity of Maritime Pine wood surfaces was modified by silicone, an extremely hydrophobic material. A generic method for the introduction of varied silicones at the surface of pre-treated wood was developed. The initial treatment of wood with maleic anhydride and allyl glycidyl ether gave oligoesterified wood bearing terminal alkenes. The hydrosilylation of these groups, performed with hydride-terminated silicones, led to very hydrophobic surfaces, even after soxhlet extraction. The presence of silicon only at the surface of hydrosilylated wood was confirmed by ESCA. The silicones appear to be attached to the wood by covalent bonds.

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A simple single-step method for the introduction of varied silicones at the surface of wood, paper and other hydropolymers has been developed and is currently being patented.

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Last update: December 21, 1999