[Show abstract][Hide abstract] ABSTRACT: The effects of bleaching treatment of oxygen-delignified softwood kraft pulp with hydrogen peroxide under acidic and alkaline conditions were studied using standard technological techniques and spectroscopic analytical methods: near-infrared (NIR), Fourier-transform infrared (FTIR) and Fourier-Transform (FT) Raman spectroscopies. Among the three tested spectroscopic techniques, NIR analysis appeared to be the most appropriate in terms of possible technological applications. The use of NIR spectroscopy combined with multivariate data analysis allowed to create models for pulp bleaching monitoring based on CIE L*a*b* measurements. Near-infrared and FTIR spectroscopic studies allowed differentiating between the effects of the acidic and alkaline peroxide bleaching stages, but failed in relation to the delignification process. The most representative bands in the FTIR and FT-Raman spectra in terms of delignification and chromophore removal exhibited no correlation with standard technological measurement results.
Full-text · Article · Mar 2014 · Vibrational Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: To study luminescence, reflectance, and color stability of dental composites and ceramics.
IPS e.max, IPS Classic, Gradia, and Sinfony materials were tested, both unpolished (as-cast) and polished specimens. Coffee, tea, red wine, and distilled water (control) were used as staining drinks. Disk-shaped specimens were soaked in the staining drinks for up to 5 days. Color was measured by a colorimeter. Fluorescence was recorded using a spectrofluorometer, in the front-face geometry. Time-resolved fluorescence spectra were recorded using a laser nanosecond spectrofluorometer.
The exposure of the examined dental materials to staining drinks caused changes in color of the composites and ceramics, with the polished specimens exhibiting significantly lower color changes as compared to unpolished specimens. Composites exhibited lower color stability as compared to ceramic materials. Water also caused perceptible color changes in most materials. The materials tested demonstrated significantly different initial luminescence intensities. Upon exposure to staining drinks, luminescence became weaker by up to 40%, dependent on the drink and the material. Time-resolved luminescence spectra exhibited some red shift of the emission band at longer times, with the lifetimes in the range of tens of nanoseconds.
Unpolished specimens with a more developed surface have lower color stability. Specimens stored in water develop some changes in their visual appearance. The presently proposed methods are effective in evaluating the luminescence of dental materials. Luminescence needs to be tested in addition to color, as the two characteristics are uncorrelated. It is important to further improve the color and luminescence stability of dental materials.
Full-text · Article · Feb 2012 · Journal of Prosthodontics
[Show abstract][Hide abstract] ABSTRACT: The effects of bleaching of high-yield mechanical pulps (TMP, CTMP) with hydrogen peroxide under acidic and alkaline conditions were studied using different spectroscopic analytical methods. Diffuse reflectance laser flash photolysis (DRLFP) showed the differences in photochemical behavior reflecting transformation of chromophores upon treatment with acidic hydrogen peroxide. FT IR spectroscopic studies allowed to differentiate between the effects of the alkaline peroxide treatment with various stabilizing agents. FT-Raman technique provided additional information on localization of chemical changes after treatment under acidic and alkaline conditions, especially concerning the removal of coniferaldehyde-type groups.
Full-text · Article · Sep 2010 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: The work was motivated by the necessity to evaluate the emission changes of dental composites, as the emission under UV light is one of the important optical parameters of the hard tooth tissue.
Fulfill extra, Artemis and Durafill VS materials in A3.5 shade were tested. Coffee, tea, red wine and distilled water (blank) were used as staining drinks. The samples were soaked for 7 days. Total luminescence matrices were collected with an interval of 1 nm in emission and 10nm in excitation, in the front-face geometry.
The exposure of dental composites to staining drinks caused a reduction in luminescence intensity by up to 40%, the magnitude of the reduction depending on the drink and on the composite material. In the special case of the intrinsically weak fluorescent Durafill VS, the exposure to coffee apparently caused an increase in luminescence intensity due to coffee components adsorbed on the sample surface.
It is important to improve the emission stability of dental composites. The presently proposed methods are effective in evaluating the emission of dental composites. Emission needs to be tested in addition to color, as the two parameters are uncorrelated.
No preview · Article · May 2008 · Dental Materials
[Show abstract][Hide abstract] ABSTRACT: The effects of thermomechanical pulp (TMP) bleaching with hydrogen peroxide under acidic and alkaline conditions were studied using different spectroscopic analytical methods. The results of hydroxyl radical determination in bleaching solutions, analyses of carbonyl and carboxyl groups contents in the pulp, and the cellulose fiber surface analysis by X-ray photoelectron spectroscopy (XPS) elucidate the chemistry of the hydrogen peroxide treatment. Diffuse reflectance laser flash photolysis (DRLFP) method showed the differences in the photochemical behavior that reflect the changes of the chromophoric system after the preliminary peroxide bleaching stage under acidic conditions. Fourier transform infrared (FTIR) spectroscopy confirmed the non-delignifying character of the bleaching process. Suppression of carbonyl and formation of carboxyl groups in the case of the two-stage peroxide bleaching performed in the presence of catalysts and stabilizers was also confirmed. FT-Raman studies showed the removal of coniferaldehyde groups after treatment under acidic and alkaline conditions.
Full-text · Article · Nov 2007 · The Journal of Physical Chemistry A
[Show abstract][Hide abstract] ABSTRACT: This paper presents time resolved laser induced luminescence (LIL) and diffuse reflectance laser flash-photolysis (DRLFP) studies of solid powdered samples of xanthione (XT) and 4H-1-benzopyran-4-thione (BPT). These thioketones form inclusion complexes with ptert-butylcalixarene (CLX) and p-tert-butylcalixarene (CLX). Room temperature air equilibrated LIL studies for XT/CLX inclusion complex have shown the existence of both fluorescence and delayed fluorescence emission S-2 -> S-0 emissions in the nanosecond and microsecond time ranges, respectively) peaking at ca. 460 nm while phosphorescence peaks at about 670 nm with a half life of about 4 mu s. For the BPT/CLX inclusion complex, the emissions now peak at ca. 450 and 630 nm, respectively. When these two thioketones are included into the CLX nanocavities similar luminescence spectra were detected. The phosphorescence spectra in all cases present a clear vibrational structure characteristic of non-polar environments, in accordance with the non-polar character of the calixarene's cavities. Diffuse reflectance transient absorption spectra revealed in all cases the presence of the triplet state of the thioketones and also of longer lived species. The use of chromatographic methods (GC-MS) allowed us to identify the formation of xanthone, chromone and hydroxy-thio ketones following laser irradiation at 355 or 337 nm. (c) 2006 Elsevier B.V. All rights reserved.
No preview · Article · Feb 2007 · Journal of Molecular Structure
[Show abstract][Hide abstract] ABSTRACT: We characterized spruce thermomechanical high-yield pulps subject to a variety of non-delignifying hydrogen peroxide treatments. Apart from standard technological analysis, spectral and photophysical properties of the sample pulps were evaluated using steady-state diffuse reflectance spectroscopy and time-resolved emission and diffuse reflectance spectroscopy with sub-microsecond time resolution. The steady-state diffuse reflectance spectra allow to obtain a more complete information as compared to standard brightness measurements, as they include the data from the UV-A zone, crucially determining the yellowing rates of the respective paper products. Time-resolved emission and diffuse reflectance results provide additional information on the amount and reactivity of photoactive groups present in the pulp, which also affect the yellowing rates of the paper products. The best characteristics were registered for the pulp sample prepared using a two-stage hydrogen peroxide brightening, with the preliminary acidic and the final alkaline treatment, which can be recommended for industrial implementation.
Full-text · Article · Nov 2006 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: Quantum chemical density functional theory (DFT) calculations and spectral data were employed to investigate the possibility of the excited-state double proton transfer (ESDPT) in lumichrome crystals. The calculations in a lumichrome dimer predict a transfer of a proton in the first excited state, leading to a cation-anion pair. The presently reported X-ray structure of 1,3-dimethyllumichrome and its complex solid-state luminescence indicate that also in this molecule intermolecular hydrogen bonds might be involved in the photophysics. The long-wavelength emission in lumichrome crystals peaked at 530 nm is attributed to excited-state proton transfer, whereas a wider emission band in methylated lumichrome derivatives peaked at 560 nm is attributed to ions formed upon photoexcitation of the crystals.
Full-text · Article · May 2006 · The Journal of Physical Chemistry A
[Show abstract][Hide abstract] ABSTRACT: Experimental time-resolved spectral and photon counting kinetic results confirm formation of an isoalloxazinic excited state via excited-state double proton transfer (ESDPT) catalyzed by a carboxylic acid molecule that forms a hydrogen-bond complex with the parent alloxazine molecule. This isoalloxazinic tautomer manifests itself as a distinct long-lived emissive species formed only in such alloxazine derivatives that were not substituted at the N1 nitrogen atom, being a product of the excited-state reaction occurring from the alloxazinic excited state. Theoretical calculations support the idea that the ESDPT occurs by the concerted mechanism. The calculated activation barrier in the excited state is much lower than the same barrier in the ground state and even disappears for the HOMO-1 to LUMO excitation, which explains the fact that the reaction takes place in the excited-state only. The reaction rate estimated from the emission kinetics is ca. 1.4 x 10(8) dm3 mol(-1) s(-1) in ethanolic solutions of lumichrome with added acetic acid.
Full-text · Article · Jan 2006 · The Journal of Physical Chemistry A
[Show abstract][Hide abstract] ABSTRACT: The fluorescence decay of alloxazines adsorbed into microcrystalline cellulose shows a complex kinetics suggesting at least three emitting species. The exponential series method and the Albery model were used to calculate the underlying distributions, providing results about the decay rate constants or lifetime distributions.
No preview · Article · Sep 2005 · Journal of Molecular Structure