François Brouillette

Advances in cellulose chemistry - Microwave-assisted synthesis of propargylcellulose in aqueous medium

A fast and simple reaction activated by microwave irradiation permits the “green synthesis” of propargylcellulose in an aqueous alkaline medium. The influence of several reaction parameters such as amount of propargyl bromide, reaction time or microwave activation on the reaction efficiency are reported herein. The propargylcellulose samples obtained, with degrees of substitution (DS) from 0.35 to 1.88, were characterised by means of FTIR and NMR spectroscopy.

Phosphorylation of Kraft fibers with phosphate esters.

Phosphate esters, derived from two different long-chain aliphatic alcohols, were used as phosphorylating reagents for Kraft pulp fibers. High phosphorus contents and almost non-degraded fibers were obtained by following this pathway. The phosphorylation efficiency was influenced by the alkyl chain length of PEs since the phosphorus content in modified fibers was higher for the shorter chain reagent. Due to the heterogeneous reaction environment, the amount of grafted phosphorus was found to be almost three times higher at the surface than in the bulk of the fibers. Analyses also indicated that the phosphorus was bonded to fibers as a phosphate-like structure. Furthermore, the situation seemed to be different for the fiber surface where significant amounts of phosphorus were present in more complex structures like pyrophosphate or even oligo-phosphate.

Tosylcellulose synthesis in aqueous medium

p-Toluenesulfonyl cellulose was prepared by reacting cellulose in aqueous medium, instead of via traditional routes, which involve the use of DMAc/LiCl, or more recently, ionic liquids. The influence of several parameters on the reaction efficiency has been studied; amount of tosylchloride, presence of triethylamine, reaction time and use of sodium hydroxide or sodium chloride. The resulting p-toluenesulfonyl cellulose samples were characterized by means of FTIR and NMR spectroscopy. The effects of solvent on the crystalline change during tosylation were investigated by X-ray diffraction (XRD). The degree of substitution (DS) was determined by 1H NMR and confirmed by X-ray photoelectron spectroscopy (XPS). Tosylcelluloses with DS from 0.1 to 1.7 have been prepared.

Synthesis and photobactericidal properties of a neutral porphyrin grafted onto lignocellulosic fibers.

Photodynamic antimicrobial chemotherapy (PACT), as one of the promising alternative antimicrobial treatment, has received great attention in recent years. In this work, a new antimicrobial material has been elaborated by grafting a neutral porphyrin, the metallated 5-(4-azidophenyl)-10,15,20-triphenylporphyrin, onto lignocellulosic fibers by using the Copper (I)-Catalyzed Alkyne-Azide 1,3-dipolar Cycloaddition (CuAAC) reaction. The cross-linked porphyrin-Kraft pulp material was characterized by infrared and by XPS spectroscopy analyses, which proved the covalent linkage between the porphyrin and propargylated Kraft pulp fibers. The antimicrobial activity of this material was tested under visible light irradiation with a low light dose (9.5 J/cm(2)) against Staphylococcus aureus and Pseudomonas aeruginosa. The two bacterial strains deposited on the resulting photosensitizing Kraft pulp are efficiently killed after illumination. Such materials could find applications in industrial, household and medical environments as an alternative to overcome the widespread microbial multiresistance to classical treatments.

Hydrophobization of phosphorylated cellulosic fibers

Due to their flame retardant behavior, phosphorylated cellulosic fibers could be interesting candidates for use in the composite material field. However, because of the phosphate groups, the fiber network is highly charged and hydrophilic reducing its compatibility towards synthetic resins. An effective hydrophobization method for phosphorylated cellulosic fibers was therefore developed in order to enhance their hydrophobic behavior. The best results were obtained with a straightforward addition of tosylated fatty alcohols. The influence of the carbon chain length on the reaction efficiency, the thermal degradation and the hydrophobic behavior are reported. The success of the alkylation reaction was confirmed by FTIR analyses and the degree of substitution by elemental analysis. Contact angle with water of more than 100° were obtained after alkylation. The cellulosic samples were furthermore characterized by means of SEM, fiber length distribution, NMR spectroscopy and thermo gravimetric analysis.

Effet de l’acétylation en masse sur la mouillabilité et la stabilité thermique des fibres lignocellulosiques

RÉSUMÉ. L’acétylation est l’un des traitements chimiques les plus répandus qui visent l’amélioration de l’affinité des fibres lignocellulosiques avec les matrices polymériques dans les matériaux composites. Dans cette étude, des fibres de lin et des pâtes de bois (pâte kraft blanchie et pâte thermomécanique) ont été acétylées dans des conditions respectueuses de l’environnement et convenables pour un usage industriel. Ces fibres ont fait l’objet d’une étude concernant leur stabilité thermique. Le passage de l’hydrophilie à l’hydrophobie des fibres a été étudié par la mesure de l’angle de contact que forme une goutte d’eau avec la surface des fibres. La mouillabilité des fibres à la résine époxy a été également évaluée pour confirmer l’amélioration de l’affinité des fibres acétylées envers la matrice époxy. Les résultats ont montré que l’hydrophilie des fibres diminue avec la durée de la réaction et cette évolution devient de plus en plus faible à des taux d’acétylation élevés. Il en ressort que les fibres acétylées peuvent concurrencer les renforts d’origine fossile dans les matériaux composites.

Dielectric Properties of Paper Made from Pulps Loaded with Ferroelectric Particles

Due to its physical properties and its ease of manufacture, paper is widely used in various engineering applications such as electrical insulation materials for components in high voltage technology. In this study, paper loaded with ferroelectric nanoparticles (BaTiO3 and SrTiO3) was made with fibers obtained from plants growing on the Moroccan soil [Halfa (Stipa tenacissima), Agave (Agave americana), Pennisetum (Pennisetum alopecuroides), Typha (Typha latifolia), and Junc (Juncus effusus)] and two commercial pulps (bleached softwood Kraft and newsprint grade thermomechanical pulps). A retention aid, cation polyacrylamide (Percol 292), was necessary to retain ferroelectric particles in the fibrous network and improve the dispersion of strontium titanate particles. The different pulp and handsheets used were characterized according to standard methods (Pulp and Paper Technical Association of Canada, PAPTAC). It is well known that annual and perennial plants contain high percentages of fines (length < 0.2 mm) and short fibers. The results show that there is a strong interdependence between the dielectric properties of the loaded paper and surface finish, porosity, dispersion level of ceramic particles, fines content, shape, conformability, and sheet formation. The single dielectric relaxation detected towards low frequencies is attributed to hydroxyl groups present on fiber surfaces, in ceramic particles and adsorbed water.