Gérard Mortha

Control of size and viscoelastic properties of nanofibrillated cellulose from palm tree by varying the TEMPO-mediated oxidation time.

The main objective of the present study was to control and optimize the preparation of nanofibrillated cellulose (NFC) from the date palm tree by monitoring the oxidation time (degree of oxidation) of the pristine cellulose and the number of cycles through the homogenizer. The oxidation was monitored by TEMPO (1-oxo-2,2,6,6-tétraméthylpipyridine 1-oxyle) mediated oxidation. Evidence of the successful isolation of NFC was given by FE-SEM observation revealing fibrils with a width in the range 20-30nm, depending of the oxidation time. The evolution of the transparency of the aqueous NFC suspension and carboxylic content according to the degree of oxidation and number of cycles were also analyzed by UV-vis transmittance, Fourier-transform infrared spectroscopy (FT-IR), conductimetry, and X-ray diffraction analysis. A significant NFC length reduction occurred during the TEMPO-mediated oxidation. The rheological properties of NFC suspensions were characterized as function of the oxidation time. Dynamic rheology showed that the aqueous suspension behavior changed from liquid to gel depending on the concentration. The highest concentration studied was 1wt% and the modulus reached 1MPa which was higher than for non-oxidized NFC. An explanation of the gel structure evolution with the oxidation time applied to the NFC (NFC length) was proposed. The gel structure evolves from an entanglement-governed gel structure to an immobilized water molecule-governed one.

Flow electrification in power transformers: study of a potential remedy

Understanding the exact nature of the phenomena at the origin of the electrical charging tendency of transformer pressboards submitted to oil circulation in high power transformers is still a challenging problem. Former studies demonstrated that flow electrification depends in a large part on the chemical functional groups of the pressboard surface, and especially carboxyl groups. In this study, the action of several additives has been tested. Three experimental devices (conductivity cell, flow loop and electrostatic charging tendency tester) have been used to investigate the effect of the additives on the charge generation, accumulation and leakage currents. Moreover, experiments with demineralised pulps treated by carboxyl complexing agents such as methylene blue have confirmed the important role of ionisable groups in paper. Some additives were found to reduce the electrification phenomenon. A comparison between these results and some aspects of ionic chromatography could be done, and the related theory can be attempted to explain the chemical process which takes place between the oil and the pressboard

Comparative Studies of Chlorine Dioxide Reactions with Muconic Acid Derivatives and Lignin Model Compounds

Abstract The reaction of chlorine dioxide with different types of lignin model compounds was investigated in order to compare the kinetics and to evaluate the amount of oxidant consumed by the different substrates. Complete reaction of lignin model compounds was observed at ClO2‐to‐substrate molar ratios of 0.9–1.2, which corresponds to an electron transfer varying between 5–6 equivalents per mole of substrate. Muconic acid derivatives also fully reacted, at a ClO2‐to‐substrate molar ratio of 1.2, with the oxidant consumption being about 4 equivalents per mole of substrate. The reaction of mixtures of phenolic, non‐phenolic, and muconic acid type substrates showed that the reaction rates of non‐phenolic and muconic acid type substrates were rather similar. This study suggests that further reaction between ClO2 and the primary lignin oxidation products, such as muconic acid type structures could be the cause of overconsumption of oxidant in a D stage.

Influence of pressboard physico-chemical composition on static electrification in power transformers

As part of a research program in the field of flow electrification in power transformers, some fundamental studies have been engaged on the physical chemistry of this phenomenon. The two main constituents involved in the process of charge generation are the oil and the pressboard. As oil composition is difficult to deal with, the choice has been made to understand the overall chemistry through the role played by the pressboard whose composition is better mastered. In order to identify the chemical species in the pressboard responsible for the charge generation, in view of perfecting additives to neutralize the phenomenon, the EFPG laboratory carried out modifications on commercial pressboards, and manufactured some others. Charge accumulation, measured from capacitive currents on insulated electrodes facing the pressboard ducts, has been observed for modified and manufactured pressboards with regard to oil flow rate and temperature. All the experiments have led to various behaviors in terms of kinetics and magnitude of the charge accumulation. The obtained results tend to prove that chemical composition of pressboards, with regard to their content in chemical functional groups (hydroxyl or carboxyl groups) or radical nature (lignin), as well as board manufacturing parameters (pulp refining, layer composition), or surface properties seem to be at the origin of the electrification phenomenon.

Structural investigation of cellulose nanocrystals extracted from chili leftover and their reinforcement in cariflex-IR rubber latex

The morphology and chemical composition of chili fibres were investigated. Unusual low lignin content was found when compared to other annual plants. High aspect ratio cellulose nanocrystals (CNCs) were prepared from these fibres by an acid hydrolysis treatment. CNCs extracted from chili leftover were characterized using FT-IR, AFM, TGA and XRD to access their functional, structural, thermal and crystallinity properties, respectively. The length and diameter of the chili leftover CNC were 90-180 nm and 4-6 nm, respectively, resulting in an average aspect ratio of 26. This high aspect ratio ensures percolation at low filler content which in turn results in high thermal and mechanical properties of the nanocomposites. These CNCs were used to prepare nanocomposite films using the highly marketing commercial latex called Cariflex-Isoprene (IR) by casting/evaporation in order to investigate their reinforcing effect. The mechanical properties of nanocomposite films were investigated in both the linear and nonlinear range by DMA and tensile test, respectively, and their morphology was studied using scanning electron microscopy.

19F NMR spectroscopy for the quantitative analysis of carbonyl groups in lignins

Summary The amount of carbonyl groups in an organosolv lignin was determined by 19F NMR spectroscopy after different derivatizations: derivatization with trifluoromethylphenylhydrazine, fluorobenzoylation of alcohol groups formed after NaBH4 reduction of lignin, fluorobenzoylation of phenolic hydroxyl groups after catalytic hydrogenation of lignin. Oximation was also used for comparison. Carbonyl group contents determined by 19F NMR after trifluoromethylphenylhydrazine derivatization were in good correlation with results from other methods. Trifluoromethylphenylhydrazine derivatization is a fast and easy technique, which provides a distinct quantification of aldehyde, ketone and quinone groups. Some round robin lignins (Milne et al. 1992), using trifluoromethylphenylhydrazine derivatization and modified oximation (Zakis 1994) provided significantly higher carbonyl group contents than the round robin test data, which had been measured either by classical oximation or by reduction-UV methods. Other recently reported carbonyl group estimations on round robin lignins (Faix et al. 1998; Ahvazi et al. 1999) were either in agreement or in disagreement with the herein-presented results. This indicates that carbonyl group analysis in lignins is difficult and that care must be taken when selecting an appropriate method.

Carrier-free co-immobilization of xylanase, cellulase and β-1,3-glucanase as combined cross-linked enzyme aggregates (combi-CLEAs) for one-pot saccharification of sugarcane bagasse

Combined cross-linked enzyme aggregates (combi-CLEAs) are an innovative prospect and a lucrative technology. The present study addresses the preparation, characterization and application of combi-CLEAs with xylanase, cellulase and β-1,3-glucanase to achieve one-pot bioconversion of lignocellulosic biomass to fermentable sugars. A three-phase partitioning (TPP) method was used to aggregate the enzymes. Glutaraldehyde (100 mM) was employed as a cross-linker with the cross-linking time of 7.5 h. Scanning electron microscopy of the tri-enzyme biocatalyst has a coarse-grained appearance. Combi-CLEAs were more thermally stable, retaining about 70% of their initial activity at 70 °C compared to 30% for the free enzyme. The storage stability of combi-CLEAs was more than 97% of their activity after incubation for 11 weeks at 4 °C, whereas the free enzymes retained about 65% of initial activity. The residual activity of combi-CLEAs remained constant at 90% until the sixth cycle. Contrary to free enzymes that remain in the hydrolysate, which prevents their recovery, reuse of combi-CLEAs was possible. Free enzymes hydrolyze the ammonia cooked sugarcane bagasse at about 73%, whereas the combi-CLEAs resulted in maximum hydrolysis of about 83.5% in 48 h.

Strengthening of degraded cellulosic material using a diamine alkylalkoxysilane

The physicochemical modifications in papers upon introducing AEAPMDMS (3 N-(2-aminoethyl)-3-aminopropylmethyl-dimethoxysilane) as a dry strength and deacidification agent were explored. The double amine functionality was shown to favor penetration in the cellulose fibers, with large uptakes being achieved at low concentration. In situ polymerization in the paper was demonstrated using 29Si CP-MAS and 1H NMR. The distribution of the compound inside and on the fibers surface was evidenced with SEM-EDS and XPS. The deacidification efficacy was established. The strengthening effect was shown to arise from the interaction of AEAPMDMS with the fibers, and depended on the fiber composition (lignin content) and oxidation state, with a higher efficiency for the less degraded and less lignified fibers. In the most degraded papers, the occurrence of yellowing was interpreted as due to the formation of Schiff bases, where the amine functional group reacts with the carbonyl groups on the oxidized cellulose.

A new method for the titration of free phenolic groups in pulps

Abstract A fast and semi-quantitative wet chemical method was developed for the titration of free phenolic groups in residual lignins of pulps. The method is based on selective chlorine dioxide reaction with phenolic units of lignin at 0°C. A known amount of ClO2 is reacted for up to 30 min with various substrates and ClO2 consumption is measured. Experiments with monomeric lignin-like model compounds, a dioxane/HCl lignin (isolated from kraft pulp), kraft pulp, and one thermomechanical pulp (TMP) were performed. The ideal stoichiometric consumption of 1 mol of ClO2 per Ar-OH was approximated in a few cases. More model compound experiments are necessary to establish the possibilities and limitations of the method, but the results of these preliminary experiments are promising. First studies on pulps and comparison of the data with those obtained by 13C NMR analysis on dioxane/HCl lignins showed some deviations in the first instance, which were attributed to reaction of the intermediates HClO and Cl2 involved in the overall mechanism. However, using DMSO as HClO trapping agent improved the ClO2/Ar-OH stoichiometric ratio close to the theoretical value of 2, which essentially yielded better results. This improved stoichiometry was verified for three model compounds, one kraft pulp and one TMP, yielding results were similar to those obtained by 13C NMR analysis.

Ultrasonic assisted production of starch nanoparticles: Structural characterization and mechanism of disintegration

In this paper, the disintegration of starch (waxy and standard starch) granules into nanosized particles under the sole effect of high power ultrasonication treatment in water/isopropanol is investigated, by using wide methods of analysis. The present work aims at a fully characterization of the starch nanoparticles produced by ultrasonication, in terms of size, morphology and structural properties, and the proposition of a possible mechanism explaining the top-down generation of starch nanoparticles (SNPs) via high intensity ultrasonication. Dynamic light scattering measurements have indicated a leveling of the particle size to about 40nm after 75min of ultrasonication. The WAXD, DSC and Raman have revealed the amorphous character of the SNPs. FE-SEM. AFM observations have confirmed the size measured by DLS and suggested that SNPs exhibited 2D morphology of platelet-like shapes. This morphology is further supported by SAXS. On the basis of data collected from the different characterization techniques, a possible mechanism explaining the disintegration process of starch granules into NPs is proposed.