Jana Kolar

Evaluation of size-exclusion chromatography and viscometry for the determination of molecular masses of oxidised cellulose

The molecular masses of oxidised cellulose samples from two different sources were determined by size-exclusion chromatography (SEC) and viscometry. SEC was performed at room temperature using a cross-linked polystyrene-divinylbenzene column and 1% LiCl (w/v) in N,N-dimethylacetamide (DMAc) as the eluent. Cellulose samples were oxidised using aqueous solutions of H2O2, NaClO or KlO(4), and dissolved in the LiCl-DMAc solvent system using activation with water and a solvent exchange procedure. Viscometry in the cupriethylenediamine (CED) solvent system was performed following the standard technique. Oxidised cellulose samples are prone to degradation by alkalis, While the dissolution in LiCl-DMAc was shown not to have a degrading effect, the oxidised cellulose samples are unstable in the highly alkaline CED solvent, thus introducing a systematic error to the viscometric measurements. A stabilising reduction procedure usually recommended for such samples was tested, and shown to be advantageous, although degradation cannot be completely avoided

Size exclusion chromatography of cellulose in LiCl/N, N-dimethylacetamide

Size exclusion of cellulose in LiCl/N,N-dimethylacetamide has been used for the past 15 years, yet much of the current research is still devoted to fundamental studies, as many issues regarding column calibration, separation mechanisms and solution behavior have not been resolved yet. The paper reviews practical aspects of sample preparation and it is demonstrated that sample heating and several techniques to aid solvent exchange call for reevaluation. It is further shown that the use of internal standard may introduce minor improvements in repeatability. The commonly used column calibration procedures, chromatographic conditions and applications are also reviewed. Further research is needed to understand the mechanisms of separation, to optimize column calibration and to facilitate and optimize sample preparation.

Chemiluminescence from paper I. Kinetic analysis of thermal oxidation of cellulose

Abstract Kinetic analysis of chemiluminescence intensity—time and chemiluminescence intensity—temperature runs for oxidation of cellulose at elevated temperatures is presented showing a good coincidence of the first-order rate constants from non-isothermal chemiluminescence experiments with those obtained from polymerisation degree determinations and from the literature. Rate constants from isothermal runs are lower than those from non-isothermal runs, however, when repeating non-isothermal runs several times in so-called temperature cycling experiments, the non-isothermal rate constants approach isothermal ones. A method enabling the differentiation of faster and slower processes in oxidation of cellulose based on non-isothermal chemiluminescence runs is demonstrated.

Near-UV and visible pulsed laser interaction with paper

The applicability of excimer laser at 308 nm and Nd:YAG laser at 532 nm with fluences below 0.86 J/cm2 for cleaning of cellulose and paper materials was evaluated. The extent of degradation of purified cotton cellulose and Fabriano paper after laser treatment as well as after a period of accelerated humid oven ageing was determined by following the changes in the degree of polymerization. While irradiation of paper with the excimer laser at 308 nm results in depolymerization of cellulose accompanied by a decrease in ISO brightness, no detrimental effects of Nd:YAG laser treatments were observed.

Chemiluminescence during thermal and thermo-oxidative degradation of cellulose

The chemiluminescent phenomena during thermal and thermo-oxidative degradation of cellulosic material and model substances were found to originate in at least three relatively independent processes. The low-temperature chemiluminescent phenomenon typical of samples previously irradiated with an incandescent light source and dependent on both temperature and composition of the surrounding atmosphere during irradiation is attributed to the decay of charge-transfer complexes between oxygen and hydroxyl and/or ether groups in cellulose. A peak in chemiluminescence during dynamic experiments at 135°C typical of pre-oxidised samples can be associated with decomposition of peroxide groups present in the sample. An intense chemiluminescence at temperatures approaching 200°C was found to correlate with polymer chain scissions, resulting in the decrease in the degree of polymerisation determined by viscometry. The results show that the chemiluminescence approach may shed new light on the radical degradation mechanisms of cellulose and related polyhydroxylated polymers.

Enthalpic interactions in size exclusion chromatography of pullulan and cellulose in LiCl–N,N-dimethylacetamide

Enthalpic phenomena were shown to contribute to the size exclusion separation mechanisms during chromatographic analysis of solutions of pullulan and cellulose in LiCl-N,N-dimethylacetamide (LiCl-DMAc) solvent and eluent. The effect of LiCl concentration in the sample solutions and the effect of temperature were of the same order of magnitude for both pullulan and cellulose samples. This led to systematic errors in the determination of mean molecular mass in the range of tens of percent, depending on the chromatographic conditions and on the molecular mass of the analyte. The systematic error is much higher than the random errors; the typical values of the latter being up to a few percent (RSD). Low column temperature and a higher content of LiCl in the sample solution led to lower determined mean molecular mass values. This can be explained by a decrease in the interactions between dissolved macromolecules, although polymer-stationary phase interactions should also be taken into account. Furthermore, the cellulose stability in solution was determined: the zero order random degradation constant being k = 6.9 x 10(-8) mol mol-1 monomer day-1.

Use of genetic algorithms with multivariate regression for determination of gelatine in historic papers based on FT-IR and NIR spectral data.

Quantitative non-destructive analysis of individual constituents of historic rag paper is crucial for its effective preservation. In this work, we examine the potentials of mid- and near-infrared spectroscopy, however, in order to fully utilise the selectivity inherent to spectroscopic multivariate measurements, genetic algorithms were used to select spectral data derived from information-rich FT-IR or UV-vis-NIR measurements to build multivariate calibration models based on partial least squares regression, relating spectra to gelatine content in paper. A selective but laborious chromatographic method for the quantification of hydroxyproline (HYP) has been developed to provide the reference data on gelatine content. We used 9-fluorenylmethyl chloroformate (FMOC) to derivatise HYP, which was subsequently determined using reverse-phase liquid chromatographic separation and fluorimetric detection. In this process, the sample is consumed, which is why the method can only be used as a reference method. The sampling flexibility afforded by small-size field-portable spectroscopic instrumentation combined with chemometric data analysis, represents an attractive addition to existing analytical techniques for cultural heritage materials.

Initial degradation processes of cellulose at elevated temperatures revisited - chemiluminescence evidence

The initial processes governing degradation of cellulose at elevated temperatures are re-examined. The influences of moisture, alkali-earth metal carbonates, and atmosphere at 180 degreesC, were studied. The various effects were studied both conventionally, by determining the changes in the degree of polymerisation by viscometry, and by chemiluminescence measurements. The moisture initially contained in the sample was shown to have no effect on degradation in dry nitrogen although the chemiluminescence of moist samples is initially considerably higher. It was associated with production of singlet oxygen. On the other hand, presence of moisture in oxygen atmosphere enhances oxidation. Some initial degradation occurs during rapid heating and was attributed to mechanical degradation, though no chemiluminescent phenomenon could be associated with it. The degradation rates during the more advanced phases were shown to be related to the presence of earth-alkali metal cations. It is suggested that complex formation between a metal cation and glycosidic oxygen might play an important role in the degradation mechanism

New colourimetric method for determination of hydroxyl radicals during ageing of cellulose

Abstract It is believed that oxidative degradation involving free radicals leads to the deterioration of alkaline paper during ageing. However, due to the high detection limit of conventional methods, e.g. ESR, the presence of radical species during ageing of pure cellulose at close to ambient conditions has not yet been established. In the present work, N,N′-(5-nitro,1,3-phenylene)bisglutaramide is used as a colour indicator of hydroxyl radical production in cellulosic materials. Quantitative determinations of its hydroxylated products can be performed using colourimetry. The measurements are rapid, non-destructive and demand a small amount of sample, which makes the new method attractive for use in industrial laboratories for a variety of materials. Several sources of systematic errors are identified and evaluated. Hydroxyl radicals are shown to be important intermediates in the oxidative processes during ageing of alkaline cellulose (pH>7). Furthermore, the importance of alkalinity on oxidative degradation of bleached chemical pulps is demonstrated.

Degradation of pullulans of narrow molecular weight distribution—the role of aldehydes in the oxidation of polysaccharides

Degradation of pullulan samples of narrow molecular weight distribution was studied in O2 and N2 atmosphere at 180 °C and in air at 80 °C, 65% RH. At higher temperatures, size exclusion chromatographic analyses provided evidence for non-random degradation and formation of cross-links, a phenomenon depending on the concentration of carbonyl groups. Initial degradation rates in oxidative and inert environments were comparable, while at longer reaction times extensive cross-linking was typical of degradation in oxygen. At 80 °C, in a moderately alkaline environment, the degradation remains random, as demonstrated by the mono-modal distributions of molecular weights. Furthermore, there was no evidence of cross-linking. Correlations between the concentration of aldehyde end-groups in the pullulan samples, rates of degradation and the content of peroxides after a pre-oxidation treatment, as determined by the use of chemiluminometry, were demonstrated. This leads to the conclusion that aldehyde groups, via the peroxide intermediates, have the decisive influence on the rates of oxidative degradation of polysaccharides.