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Michel R Vignon - One of the best experts on this subject based on the ideXlab platform.
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topochemistry of carboxylated cellulose nanocrystals resulting from tempo mediated oxidation
Macromolecules, 2005Co-Authors: Suzelei Montanari, Mohamad Roumani, Laurent Heux, Michel R VignonAbstract:Surface carboxylated cellulose nanocrystals with different sizes and degrees of oxidation were prepared by TEMPO-mediated oxidation of cotton linters and microfibrils of parenchyma cell cellulose (PCC). The size of the oxidized crystals depended on (i) the starting material, (ii) an eventual acid prehydrolysis, and (iii) the oxidation conditions. The oxidized cellulose nanocrystals were characterized by transmission electron microscopy, Conductometric Titration, and solid-state NMR spectroscopy. During TEMPO oxidation, the main reaction corresponded to a selective oxidation of surface primary hydroxyl groups into carboxylic groups. At the same time, a decrease of the crystal size occurred, resulting from some degradation in the amorphous areas of the starting material. The introduction of negative charges at the interface of the crystalline domains induced a better individualization of the crystallites. The degrees of oxidation (DO) determined by Conductometric Titration were in agreement with those deduc...
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tempo mediated oxidation of cellulose iii
Biomacromolecules, 2003Co-Authors: Denilson Da Silva Perez, Suzelei Montanari, Michel R VignonAbstract:Various cellulose samples converted into cellulose III by two different ammonia treatments, either liquid or gaseous, were reacted with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite, and sodium bromide in water. A substantial increase in the reactivity of cellulose III samples was observed in comparison to those in cellulose I, and a relationship between oxidation conditions and cellulose primary hydroxyl groups accessibility was directly established. For the characterization, we have used several methods, mainly 13 C NMR, methylene blue adsorption, FTIR, and Conductometric Titration. In all samples, the primary alcohol groups were selectively oxidized into carboxyl groups, provided the sodium hypochlorite is added dropwise and the reaction is performed at constant pH 10.
M H W Sonnemans - One of the best experts on this subject based on the ideXlab platform.
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studies on the acidity of mordenite and zsm 5 1 determination of broensted acid site concentrations in mordenite and zsm 5 by Conductometric Titration
The Journal of Physical Chemistry, 1993Co-Authors: Mark Crocker, Ruud H M Herold, M H W Sonnemans, C A Emeis, A E Wilson, J N Van Der MoolenAbstract:The Broensted acidity of H-mordenite and H-ZSM-5 samples of varying proton concentration has been studied using aqueous Conductometric Titration, IR spectroscopy, and aqueous potentiometric Titration. Good agreement is observed between Broensted acid site concentrations determined by Conductometric Titration and IR measurements, while indirect potentiometric Titration affords acid site concentrations consistently lower than those measured using the Conductometric technique. This finding is rationalized on the basis that, in a Conductometric Titration, all the accessible Broensted acid sites are direct;y titrated, whereas in the potentiometric procedure utilized, only those protons which can be ion-exchanged out of the zeolite are titrated. After allowing for the presence of extraframework aluminum in the zeolites (determined by [sup 27]Al NMR), the measured acidity for H-mordenite is found to increase linearly with increasing Al content within the range 0-1.5 mmol Al/g but appears to reach a limiting value at higher Al concentrations. For H-ZSM-5, the experimentally determined number of Broensted acid sites is also found to be linearly dependent on the Al molar fraction within the range measured (0-1.20 mmol Al/g). For both series of zeolite samples, the measured acidity is generally found to be less than the theoretical maximum calculated on the basis of an H[supmore » +]/Al ratio of 1. 43 refs., 10 figs., 4 tabs.« less
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studies on the acidity of mordenite and zsm 5 2 loss of broensted acidity by dehydroxylation and dealumination
The Journal of Physical Chemistry, 1993Co-Authors: M H W Sonnemans, Den C Heijer, M CrockerAbstract:Quantitative determination of Broensted acid site concentrations in calcined H-mordenite and H-ZSM-5 by means of Conductometric Titration and infrared spectroscopy reveals that the concentration of Broensted acid sites present is lower than would be expected on the basis of the aluminum content. This discrepancy is attributed to dealumination and dehydroxylation processes occurring during calcination. A model is proposed according to which the degree of these processes strongly depends on the concentration of vicinal aluminum T sites in the zeolite: Broensted acid sites associated with these T sites are lost, and the remaining Broensted acidity is related to the concentration of the (remaining) isolated aluminum T sites. This model quantitatively correlates the experimentally determined concentration of Broensted acid sites with the concentration of isolated aluminum T sites. 33 refs., 4 figs., 2 tabs.
Suzelei Montanari - One of the best experts on this subject based on the ideXlab platform.
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topochemistry of carboxylated cellulose nanocrystals resulting from tempo mediated oxidation
Macromolecules, 2005Co-Authors: Suzelei Montanari, Mohamad Roumani, Laurent Heux, Michel R VignonAbstract:Surface carboxylated cellulose nanocrystals with different sizes and degrees of oxidation were prepared by TEMPO-mediated oxidation of cotton linters and microfibrils of parenchyma cell cellulose (PCC). The size of the oxidized crystals depended on (i) the starting material, (ii) an eventual acid prehydrolysis, and (iii) the oxidation conditions. The oxidized cellulose nanocrystals were characterized by transmission electron microscopy, Conductometric Titration, and solid-state NMR spectroscopy. During TEMPO oxidation, the main reaction corresponded to a selective oxidation of surface primary hydroxyl groups into carboxylic groups. At the same time, a decrease of the crystal size occurred, resulting from some degradation in the amorphous areas of the starting material. The introduction of negative charges at the interface of the crystalline domains induced a better individualization of the crystallites. The degrees of oxidation (DO) determined by Conductometric Titration were in agreement with those deduc...
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tempo mediated oxidation of cellulose iii
Biomacromolecules, 2003Co-Authors: Denilson Da Silva Perez, Suzelei Montanari, Michel R VignonAbstract:Various cellulose samples converted into cellulose III by two different ammonia treatments, either liquid or gaseous, were reacted with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite, and sodium bromide in water. A substantial increase in the reactivity of cellulose III samples was observed in comparison to those in cellulose I, and a relationship between oxidation conditions and cellulose primary hydroxyl groups accessibility was directly established. For the characterization, we have used several methods, mainly 13 C NMR, methylene blue adsorption, FTIR, and Conductometric Titration. In all samples, the primary alcohol groups were selectively oxidized into carboxyl groups, provided the sodium hypochlorite is added dropwise and the reaction is performed at constant pH 10.
Derek G Gray - One of the best experts on this subject based on the ideXlab platform.
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estimation of the surface sulfur content of cellulose nanocrystals prepared by sulfuric acid hydrolysis
Cellulose, 2013Co-Authors: Tiffany Abitbol, Elisabeth Kloser, Derek G GrayAbstract:The conditions required for the accurate measurement of the sulfur content of cellulose nanocrystals (CNCs) by Conductometric Titration are discussed. CNCs from sulfuric acid hydrolysis are electrostatically stabilized in aqueous suspension due to the introduction of charged sulfate ester groups onto the surface of the crystallites during reaction. The sulfur content thus largely reflects the surface charge of the crystals, and is crucial to the characterization and understanding of material properties. Conductometric Titration is commonly used to quantify the sulfur content of CNCs, however, the exhaustive removal of free acid by dialysis and the necessity, type, quantity and duration of ion-exchange resin treatments are not always consistent. Here we explore the standard conditions of dialysis, ion-exchange, and the reproducibility of Titration results. Extensive dialysis is found to be effective in the removal of free acid, but similar results are also achieved in shorter times and with less water using membrane ultrafiltration. It is also shown that the conditions of ion-exchange most commonly employed in the literature can lead to inaccurate sulfur contents. Finally, good agreement is obtained between the sulfur contents of different CNC batches prepared using the same hydrolysis conditions, and from Titration and elemental analysis when thoroughly purified, well-dispersed samples, and appropriate resin conditions are used.
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cationic surface functionalization of cellulose nanocrystals
Soft Matter, 2008Co-Authors: Merima Hasani, Emily D Cranston, Gunnar Westman, Derek G GrayAbstract:The surface of cellulose nanocrystals, prepared by sulfuric acid hydrolysis of cotton, was rendered cationic through a reaction with epoxypropyltrimethylammonium chloride. The resultant nanocrystal suspensions were characterized by ζ-potential, Conductometric Titration and polarized light microscopy. Atomic force microscopy (AFM) showed no change in the size or shape of the nanocrystals, but the functionalization process reversed the surface charge and led to a reduction of the total surface charge density. These modifications led to stable aqueous suspensions of nanocrystalline cellulose with unexpected gelling and rheological properties. Shear birefringence was observed, but no liquid crystalline chiral nematic phase separation was detected.
Stephanie Beck - One of the best experts on this subject based on the ideXlab platform.
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determination of sulfur and sulfate half ester content in cellulose nanocrystals an interlaboratory comparison
Metrologia, 2018Co-Authors: Linda J Johnston, Stephanie Beck, Zygmunt J Jakubek, Jun Araki, Emily D Cranston, Christophe Danumah, Douglas M Fox, Jun Wang, Zoltan Mester, Audrey MooresAbstract:Charged functional groups on the surface of cellulose nanocrystals (CNCs) are important for controlling the colloidal stability of suspensions and the interaction of the material with its environment. Quantification of surface groups is therefore an important metric for reproducible production of this nanomaterial. Here we report the results of an interlaboratory comparison (ILC) with twelve participants piloted by National Research Council Canada (NRC) that evaluated two methods for determining the sulfur content for an NRC reference material (CNCD-1) produced from CNCs extracted by sulfuric acid hydrolysis of wood pulp. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was used to measure the total sulfur content of CNCs after microwave assisted digestion in strong acid. Conductometric Titration quantified the negatively charged sulfate half-ester groups on the CNC surface after dialysis and protonation using ion exchange resin. The data was analyzed with an ASTM method that employs h and k statistics to identify data sets for which the laboratory mean or standard deviation show excessive variation from the overall mean or standard deviation and the NIST consensus builder (NICOB) engine using the DerSimonian–Laird meta-analysis to determine a consensus estimate of the mean and its associated measurement uncertainty. The consensus estimates ± uncertainty for total sulfur and sulfate half ester content were (8771 ± 94) mg kg−1 and (252.0 ± 8.2) mmol kg−1, respectively. Neither approach identified any outliers in the data sets and the consensus estimates were in agreement with values obtained during certification of the reference material. The results confirmed that the difference between the sulfur content measured by Conductometric Titration and ICP-OES is larger than the combined 95% expanded uncertainties. The higher sulfur content measured by ICP-OES may reflect the presence of sulfur impurities that are not detected by Titration. Overall the ILC provides validation for the protocols for the two methods and indicates that both are reasonably tolerant of small variations from the protocol. A more reliable method of assessing the Titration endpoint and a quality control (QC) sample were identified as potential improvements to reduce variability for the Conductometric Titration.
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general procedure for determining cellulose nanocrystal sulfate half ester content by Conductometric Titration
Cellulose, 2015Co-Authors: Stephanie Beck, Myriam Methot, Jean BouchardAbstract:Charged groups on the surface of cellulose nanocrystals (CNCs) control the colloidal stability and electrostatic and rheological properties of aqueous CNC suspensions, as well as their ability to self-assemble into liquid crystalline structures with unique optical properties. CNCs extracted from wood pulp by sulfuric acid hydrolysis typically contain 200–300 mmol/kg of anionic sulfate half-esters introduced at some of the hydroxyl sites. Two analysis methods to determine CNC surface charge are presented in the published literature: total sulfur content determination by elemental analysis and protonated sulfate half-ester group determination by Conductometric Titration with sodium hydroxide. The main drawbacks to elemental analysis are the expensive and complicated instrumentation and sample preparation procedures it requires. Conductometric Titration is a much simpler method, but requires complete protonation of the CNC samples in order to obtain an accurate value. Unfortunately, significant discrepancies between the sulfate half-ester contents measured with the two techniques are often observed in the literature, particularly with neutralized Na-CNCs. There are specific assumptions and pitfalls inherent to both analysis methods which must be taken into account and reconciled if comparable results are to be achieved by Titration and elemental analysis. In particular, sample preparation is crucial to obtaining accurate determinations of sulfate half-ester content by Conductometric Titration; however, methods differ widely among laboratories and are often not specified in detail, rendering published results meaningless. We have developed a rapid sample preparation protocol which allows quantitative and accurate determination of the sulfate half-ester content of CNCs from various cellulosic feedstocks (for H- and Na-CNCs, in both never-dried and redispersed dried forms) by Conductometric Titration, yielding results in good agreement with the total sulfur content determined by elemental analysis.