Sami Boufi

Modification of cellulosic fibres with functionalised silanes: development of surface properties

Abstract The surface modification of cellulosic fibres was carried out using organofunctional silane coupling agents in an ethanol/water medium. A heat treatment (curing) was applied after reaching the equilibrium adsorption of the prehydrolysed silanes onto the cellulosic substrate. The modified fibres were then characterised by diffuse reflectance infrared spectroscopy and contact angle measurements. The presence of Si–O–Cellulose and Si–O–Si bonds on the cellulose surface confirmed that the silane coupling agent was efficiently held on the fibres surface through both condensation with cellulose hydroxyl groups and self-condensation between silanol groups. The change of the surface properties after the modification was ascertained by contact angle measurements and inverse gas chromatographic analysis. It was shown that the silane functional groups appended to the fibre surface could participate in the chain growth of appropriate monomers to give a covalent continuity between the fibres and the ensuing polymer matrix.

Nanofibrillated cellulose: surface modification and potential applications

Interest in nanofibrillated cellulose has been increasing exponentially because of its relatively ease of preparation in high yield, high specific surface area, high strength and stiffness, low weight and biodegradability etc. This bio-based nanomaterial has been used mainly in nanocomposites due to its outstanding reinforcing potential. Solvent casting, melt mixing, in situ polymerization and electrospinning are important techniques for the fabrication of nanofibrillated cellulose-based nanocomposites. Due to hydrophilic character along with inherent tendency to form strong network held through hydrogen-bonding, nanofibrillated cellulose cannot uniformly be dispersed in most non-polar polymer matrices. Therefore, surface modification based on polymer grafting, coupling agents, acetylation and cationic modification was used in order to improve compatibility and homogeneous dispersion within polymer matrices. Nanofibrillated cellulose opens the way towards intense and promising research with expanding area of potential applications, including nanocomposite materials, paper and paperboard additive, biomedical applications and as adsorbent.

The application of the Diels-Alder reaction to polymers bearing furan moieties. 1. Reactions with maleimides

Two types of furan-containing polymers, namely polyurethanes and acrylic copolymers, were used as reactive substrates for Diels-Alder cycloadditions with mono- and bis-maleimides. The role of the specific position of the heterocycle in the macromolecular chains, as well as its frequency along them, was studied in order to assess the ease with which the coupling occurred. Both the simple adducts derived from the monofunctional dienophiles and the crosslinked products arising from the coupling of the furanic polymers with the bisdienophiles were fully characterized. Attempts to return to linear structures by heating the latter materials, via the retro Diels-Alder reaction, were not successful.

Starch nanoparticles formation via high power ultrasonication

Nano-sized starch particles (NSP) were prepared from starch granules using a purely physical method of high-intensity ultrasonication. Particle size distribution, Field Effect Scanning Electron Microscopy (FE-SEM), Raman spectroscopy, and Wide-Angle X-ray Diffraction (WAXD) were used to characterize the morphology and crystal structure of the ensuing nanoparticles. The results revealed that ultrasound treatment of the starch suspension in water and at low temperature for 75 min results in the formation of starch nanoparticles between 30 and 100 nm in size. An attempt to explain the generation of starch nanoparticles was made on the basis of WAXD, Raman analysis and FE-SEM observation. Compared to acid hydrolysis, which is the most commonly adopted process, the present approach has the advantage of being quite rapid, presenting a higher yield and not requiring any chemical treatment.

Physical immobilization of Rhizopus oryzae lipase onto cellulose substrate: Activity and stability studies

Rhizopus oryzae lipase (ROL) was immobilized by adsorption onto oxidized cellulose fibers and regenerated films. The maximum adsorption level increases with the raise in the amount of carboxylic groups on cellulose surface confirming that adsorption is being governed mainly by electrostatic interaction between the enzyme and the substrate. This hypothesis was further confirmed by zeta-potential measurements showing a decrease in the zeta-potential of the fibers after enzyme adsorption. XPS analysis showed an intensification of the N 1s peak attesting the presence of the enzyme on the surface. The effect of temperature, pH and solvent polarity on the immobilized enzyme activity and stability was investigated. The catalytic esterification of oleic acid with n-butanol has been carried on using hexane as an organic solvent. A high conversion yield was obtained (about 80%) at 37 degrees C with a molar ratio of oleic acid to butanol 1:1 and 150IU immobilized lipase. The adsorption achieved two successive cycles with the same efficiency, and started to lose its activity during the third cycle.

Starch Nanocrystal Stabilized Pickering Emulsion Polymerization for Nanocomposites with Improved Performance

Latex/starch nanocrystal (SNC) nanocomposite dispersions were successfully synthesized via a one-step surfactant-free Pickering emulsion polymerization route using SNC as the sole stabilizer. The effect of the SNC content, initiator type and comonomer on the particle size, colloidal stability, and film properties were investigated. Both HCl and H2SO4-hydrolysed starch nanocrystals, each bearing different surface charges, were used as Pickering emulsion stabilizing nanoparticles. SNCs from HCl hydrolysis were found to provide a better stabilization effect, giving rise to a polymer dispersion with a lower average particle size. The mechanistic aspects of the Pickering emulsion polymerization were also discussed. Nanocomposites formed by film-casting the polymer Pickering emulsions showed better mechanical properties and optical transparency than those obtained by blending the polymer emulsion with a nanocrystal dispersion, showing the one-pot route to nanocomposite precursors to be doubly advantageous. Therefore, this in situ polymerization technique not only facilitates the use of SNC nanoparticles, it also provides a valuable nanocomposite with enhanced mechanical properties and high transparency level.

Poly(methacylic acid-co-maleic acid) grafted nanofibrillated cellulose as a reusable novel heavy metal ions adsorbent

A poly(methacrylic acid-co-maleic acid) grafted nanofibrillated cellulose (NFC-MAA-MA) aerogel was prepared via radical polymerization in an aqueous solution using Fentons reagent. The ensuing aerogel, in the form of a rigid porous material, was characterized by FTIR and NMR and used as an adsorbent for the removal of heavy metals from aqueous solutions. It showed an efficient adsorption, exceeding 95% toward Pb(2+), Cd(2+), Zn(2+) and Ni(2+) when their concentration was lower than 10 ppm and ranged from 90% to 60% for a metal concentration higher than 10 ppm. Over 98% of the adsorbed metal ion was recovered using EDTA as a desorbing solution, and the subsequent washing allowed the aerogel to be reused repeatedly without noticeable loss of adsorption capacity. It was concluded that the (NFC-MAA-MA) aerogel may be used as a high capacity and reusable sorbent material in heavy-metal removing processes.

Dispersion of Al2O3 suspension with acrylic copolymers bearing carboxylic groups

Abstract The interaction between acrylic copolymers carrying carboxylic groups and the surface of an alumina powder in water has been studied. The trends of the adsorption isotherms suggest the formation of a monolayer according to the Langmuir model. The quantity absorbed on the plateau increases when the fraction of carboxylic groups on the polymer decreases. The electrokinetic properties of the alumina suspensions were also analysed. Results indicate that the copolymer adsorption leads to a shift in the IEP towards acidic pH. Moreover, the density of charge of the surface of alumina particle at pH 8–9 was found to depend on the quantity of adsorbed carboxylic groups and on the configuration of the adsorbed polymer. The stability of dispersions was investigated through particle size distribution and rheological properties after addition of various amounts of copolymers. The ability of the acrylic copolymer to stabilise alumina suspensions was found to be greatly affected by the content of carboxylic groups contained in the macromolecular chain.

Alumina interaction with AMPS–MPEG random copolymers: I. Adsorption and electrokinetic behavior

Adsorption of brush copolymers, bearing sulfonate groups and polyethylene glycol segments, on to alumina particles in suspension in water has been investigated. Study of the adsorption isotherms revealed that the copolymers displayed a strong affinity for the surface of the alumina regardless of the fraction of ionic groups on the polymer. For poly(ethylene glycol) content greater than 50%, the adsorption isotherms revealed an initial adsorption plateau followed by a second one. The shape of the adsorption isotherms was interpreted in terms of the polymer configuration at the solid-to-liquid interface. The effects of the pH and the ionic force on adsorption were studied and connected to the effects of interaction between chain segments at the surface of the alumina particles. Changes in the electrokinetic properties of the alumina particles after addition of the copolymers were investigated by following the zeta potential of particles as a function of pH. In the presence of the copolymer continuous shift of the isoelectric point IEP to a more acidic values was observed. Beyond a certain concentration the zeta potential remained negative regardless of the pH.

Effect of the combination of biobeating and NFC on the physico-mechanical properties of paper

The combined effect of enzymatic treatment (biobeating) and NFC addition on the mechanical and physical properties of a papermaking pulp suspension was investigated. The influence of pH, consistency of pulp and reaction time of the enzyme on the pulp strength was evaluated by measuring the breaking length of paper sheets made thereof. The results showed that the enzymatic treatment improved mechanical properties of fibres without modifying drainability. After biobeating, NFC was added to the enzyme-treated pulps. Mechanical properties were enhanced, obtaining length at break values similar to those observed in commercial printing/writing paper. Opacity remained constant, whereas porosity was gradually reduced as more amount of NFC was added. The presence of NFC also reduced drainability, although it remained at suitable levels for the papermaking industry. The results suggest that the combination of biobeating and NFC addition can be considered as an alternative to mechanical beating.