Gilles Sèbe

Acetylation of Cellulose Nanowhiskers with Vinyl Acetate under Moderate Conditions

A novel and straightforward method for the surface acetylation of cellulose nanowhiskers by transesterification of vinyl acetate is proposed. The reaction of vinyl acetate with the hydroxyl groups of cellulose nanowhiskers obtained from cotton linters was examined with potassium carbonate as catalyst. Results indicate that during the first stage of the reaction, only the surface of the nanowhiskers was modified, while their dimensions and crystallinity remained unchanged. With increasing reaction time, diffusion mechanisms controlled the rate, leading to nanowhiskers with higher levels of acetylation, smaller dimensions, and lower crystallinity. In THF, a solvent of low polarity, the suspensions from modified nanowhiskers showed improved stability with increased acetylation.

Supramolecular structure characterization of cellulose II nanowhiskers produced by acid hydrolysis of cellulose I substrates.

Cellulose II nanowhiskers (CNW-II) were produced by treatment of microcrystalline cellulose with sulfuric acid by both controlling the amount of H(2)SO(4) introduced and the time of addition during the hydrolysis process. The crystalline structure was confirmed by both XRD and (13)C CP-MAS NMR spectroscopy. When observed between crossed polarizers, the cellulose II suspension displayed flow birefringence and was stable for several months. The CNW-II nanowhiskers were significantly smaller than the cellulose I nanowhiskers (CNW-I) and had a rounded shape at the tip. The CNW-II average length and height were estimated by AFM to be 153 ± 66 and 4.2 ± 1.5 nm, respectively. An average width of 6.3 ± 1.7 nm was found by TEM, suggesting a ribbon-shape morphology for these whiskers. The average dimensions of the CNW-II elementary crystallites were estimated from the XRD data, using Scherrers equation. A tentative cross-sectional geometry consistent with both XRD and NMR data was then proposed and compared with the geometry of the CNW-I nanowhiskers.

Hydrophobization of wood surfaces: covalent grafting of silicone polymers

Abstract The hydrophilicity of Maritime pine wood surfaces was modified by silicone, an extremely hydrophobic material. A generic method for the introduction of a variety of silicones at the surface of pre-treated wood was developed. The initial treatment of wood with maleic anhydride and allyl glycidyl ether resulted in oligoesterified wood bearing terminal alkenes. The hydro- osilylation of these groups, performed with hydride-terminated silicones, led to very hydrophobic surfaces, even after extensive soxhlet extraction with good solvents for silicones. Thze 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.

Penetration of amino-silicone micro- and macro-emulsions into Scots pine sapwood and the effect on water-related properties

Abstract An amino-silicone in the form of a micro- and a macro-emulsion (average particle size 40 and 120 nm, respectively) was tested in impregnation of solid wood. During vacuum-pressure impregnation, the uptake of 5% emulsions was only slightly reduced compared to water up-take. At 15% concentration, a significant reduction in emulsion uptake was observed, particularly in the radial and tangential directions of the wood. The penetration of silicone into the cell wall was dependent on the particle size of the emulsion. Applied as a macro-emulsion, a maximum of only 14% of the total silicone penetrated the cell wall, whereas 25–35% of the silicone was found in the cell wall when applied as a micro-emulsion. The degree of cell wall penetration of silicone for the micro-emulsion was confirmed by X-ray micro-analysis (SEM-EDX). The penetrated silicone caused bulking and dimensional stability. 1H NMR relaxometry T 2 distributions were determined for dried and moisture-conditioned wood samples. The silicone-treated specimens displayed spin-spin interactions of protons from water and silicones (or their emulsifiers). Conditioning of samples at 25°C and 65% relative humidity appeared to cause a decrease in the mobility of the non-water protons of the silicone and/or emulsifier. Freezing to -5°C caused separation of protons from bound water and from the silicone at low relaxation times. It is assumed that treatment with the micro-emulsion reduced water sorption due to micro-pore blocking in the cell wall. The formation of a sandwich complex is postulated, which comprises cell wall polymers, water molecules and a layer of silicone.

A novel simple route to wood acetylation by transesterification with vinyl acetate

Abstract A novel method for the acetylation of wood was investigated and compared with the classical method based on acetic anhydride. The transesterification reaction between vinyl acetate (VA) and hydroxyl groups of maritime pine sapwood (Pinus pinaster Soland) was performed in the presence of potassium carbonate as a catalyst and led to acetylated wood in high yield. The transesterification reaction was confirmed by FTIR and 13C CP-MAS NMR spectroscopy. The efficiency of the VA transesterification increased with increasing temperature, reaction time, and catalyst amount, but a significant weight percentage gain (WPG) was obtained after only 3 h at 90°C.

Dispersibility and Emulsion-Stabilizing Effect of Cellulose Nanowhiskers Esterified by Vinyl Acetate and Vinyl Cinnamate

The surface of cotton cellulose nanowhiskers (CNWs) was esterified by vinyl acetate (VAc) and vinyl cinnamate (VCin), in the presence of potassium carbonate as catalyst. Reactions were performed under microwave activation and monitored by Fourier transform infrared (FT-IR) spectroscopy. The supramolecular structure of CNWs before and after modification was characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Distinctively from the acetylation treatment, an increase in particles dimensions was noted after esterification with VCin, which was assigned to π-π stacking interactions that may exist between cinnamoyl moieties. The dispersibility and emulsion stabilizing effect of acylated CNWs was examined in ethyl acetate, toluene, and cyclohexane, three organic solvents of medium to low polarity. The acylated nanoparticles could never be dispersed in toluene nor cyclohexane, but they formed stable dispersions in ethyl acetate while remaining dispersible in water. Stable ethyl acetate-in-water, toluene-in-water, and cyclohexane-in-water emulsions were successfully prepared with CNWs grafted with acetyl moieties, whereas the VCin-treated particles could stabilize only the cyclohexane-in-water emulsions. The impact of esterification treatment on emulsion stability and droplets size was particularly discussed.

Chemical reaction of maritime pine sapwood (Pinus pinaster Soland) with alkoxysilane molecules: A study of chemical pathways

Abstract The chemical modification of maritime pine sapwood (Pinus pinaster) with alkoxysilanes was studied according to three different pathways: carbamoylation with 3-isocyanatopropyltriethoxysilane, etherification with 3-glycidoxypropyltrimethoxysilane and alcoholysis of n-propyltrimethoxysilane. Grafting was confirmed by weight percent gain calculations (WPG), infrared spectroscopy (FTIR) as well as 13C and 29Si NMR CP MAS analysis. Signals of the grafted groups in the different spectra were assigned and the reactivity of the trialkoxysilane moieties towards wood was discussed. Experiments with model wood blocks showed that the reactions investigated occurred within the wood cell walls. Grafted chemicals were found to be relatively stable with regard to water leaching but only slight dimensional stabilisation was noted after treatment.

Chemical reaction of alkoxysilane molecules in wood modified with silanol groups

Abstract Chemical reaction between silanol-modified wood and methyltrimethoxysilane (MTMS) was carried out using two different approaches with dibutyltin dilaurate (DBTDL) or ethylamine (EtNH2) as catalysts. Modifications were characterised by Fourier-transform infrared (FTIR) spectroscopy, as well as solid-state 13C and 29Si cross-polarisation with magic-angle spinning nuclear magnetic resonance (CP-MAS NMR) spectroscopy and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis. Silanol-modified wood was obtained by carbamoylation reaction with 3-isocyanatopropyltriethoxysilane (IPTES) and subsequent hydrolysis of the triethoxysilane end groups. 29Si CP-MAS NMR spectroscopy indicated that SiOH groups existed mostly in the form of mono- and di-condensed structures in wood, whatever the level of modification (low or high). The attachment of methyltrimethoxysilane (MTMS) molecules to silanol sites was apparently achieved when ethylamine was used as a catalyst. The reacted MTMS remaining in wood was found to exist mostly in the form of polysiloxane polymers (or oligomers), as shown by 29Si CP-MAS NMR results. Reactions performed with unmodified wood were much less effective, thereby demonstrating the importance of the IPTES pre-treatment.

Modification of Fagus sylvatica L. with 1,3-dimethylol-4,5-dihydroxy ethylene urea (DMDHEU). Part 2: Pore size distribution determined by differential scanning calorimetry

Abstract The enthalpy of melting and the freezing point depression of European beech (Fagus sylvatica L.) wood modified with 0.8, 1.3, and 2.3 M 1,3-dimethylol-4,5-dihydroxy ethylene urea (DMDHEU) were determined at different levels of moisture content above the fibre saturation point by differential scanning calorimetry. The results permitted estimations of the amount of water bound to the cell wall, non-freezing water (NFW), and pore size distribution. The NFW of wood modified with DMDHEU, calculated on a dry wood basis, was not significantly lower than that of the control. The ratio of bound to total water present in the sample was higher in unmodified than in DMDHEU-modified samples. The proportion of pores with a diameter ≤30 nm was 70% of the total cell wall voids for wood modified with 2.3 M DMDHEU and 18% for unmodified wood. These results indicate that DMDHEU reduced the pore size of the samples by occupying the void space present in the cell wall.

The dimensional stabilisation of Maritime pine sapwood (Pinus pinaster) by chemical reaction with organosilicon compounds

Summary The dimensional stabilisation imparted to Maritime pine sapwood by chemical modification with hydrophobic organosilicon compounds was investigated. Modification was performed via esterification, using different chemically synthesised models bearing trimethylsilyl groups: 3-trimethylsilylpropanoic anhydride (I), 2-trimethylsilylmethylglutaric anhydride (II) and trimethylsilylethenone (III). 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 three oven-dry/water-soak cycles and, for a given number of hydroxyl blocked, to be superior to that imparted by acetylation. The graft from III, however, was found to hydrolyse progressively into an acetyl group via a metallotropic rearrangement. Further investigation on the 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 hygroscopicity. The bulky grafts from I and II were, in particular, thought to locally over-swell the wood cell wall, revealing regions with new water-accessible hydroxyl groups.