Changes in chromophoric composition of high-yield mechanical pulps due to hydrogen peroxide bleaching under acidic and alkaline conditions (original) (raw)
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The Journal of Physical Chemistry A, 2007
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 fibre surface analysis by XPS elucidate the chemistry of the hydrogen peroxide treatment. Diffuse Reflectance Laser Flash Photolysis (DRLFP) method showed the differences in the photochemical behaviour that reflect the changes of the chromophoric system after the preliminary peroxide bleaching stage under acidic conditions. FTIR spectroscopy confirmed non-delignifying character of the bleaching process. Suppression of carbonyl and formation of carboxyl groups in the case of the twostage 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.
Nordic Pulp and Paper Research Journal, 2014
To evaluate the causes behind the formation of colour in mill systems, the effect of different process waters on the optical properties of hydrogenperoxide bleached Norway spruce mechanical pulp during storage was studied. The influence of process water type, temperature, time, pulp consistency and pH was evaluated over the visible range of wavelengths. The darkening was more pronounced when pulp was stored in process waters compared to in distilled water. Increased temperature and prolonged storage times increased the darkening as expected, whereas a higher storage consistency gave less darkening than a lower storage consistency (15% compared to 5%). The pH value that gave the lowest brightness reduction and a minimum in Δk460 was found to be 5.5-6.0. Storage of pulp in white water from the paper machine resulted in a broad shoulder in the k spectra indicating colour formation related to the particles in this water. Part of this shoulder in absorption spectra was related to added d...
Nordic Pulp and Paper Research Journal, 2014
The discolouration of hydrogen-peroxide bleached Norway spruce mechanical pulp during storage in mill systems was studied and the contributions of process water, iron and dyes were evaluated over the visible spectrum. Washing of the pulp made it less sensitive to storage, possibly due to the removal of extractives, lignin-like substances, iron and pulp fines. Storage in white water gave extensive discolouration with a shoulder in the absorption spectrum at around 550- 650 nm. Most of the colour was associated with pulp fines or filler but some colour was also found in smaller fractions and in the water phase. The addition of ferric ions increased the light absorption coefficient during storage, initially at short wavelengths and then over the whole spectrum, but could not explain the increased absorption at 550-650 nm and could not be the only cause of the darkening in the mill system. A cationic basic violet dye gave a shoulder in the absorption spectrum similar to that in the mill...
Nordic Pulp and Paper Research Journal, 2006
The influence on the brightness stability of various oxidizable structures viz.: lignin, hexenuronic acid and other "non-lignin" structures in kraft pulps was studied. Samples of pulp of different wood species (spruce, birch, eucalyptus) taken from TCF and ECF bleaching sequences were chemically characterised by kappa number fractionation and subjected to accelerated ageing. It was shown that the selective removal of all oxidizable structures of carbohydrate origin present in the pulp significantly improved the brightness stability. The thermal yellowing of the pulps was found to be proportional to the content of hexenuronic acid groups regardless of the pulp origin or bleaching history. Quantitative determination of the changes during ageing showed that 2-furancarboxylic acid and 5-formyl-2-furancarboxylic acid are formed in the course of decomposition of hexenuronic acid. The difference between the original amount of hexenuronic acid groups in a pulp sample and the sum of the remaining hexenuronic acid together with the 2-furancarboxylic acid and 5-formyl-2-furancarboxylic acid suggests that the latter are involved in further reactions leading to the formation of chromophoric structures. It was also found that 2,3-dihydroxy-2-cyclopenten-1-one (reductic acid) is formed during the ageing.
BioResources, 2021
The thermal yellowing of hornbeam chemi-mechanical pulps (CMP) after bleaching with hydrogen peroxide and sodium dithionite was investigated. The hornbeam chips were randomly chosen from Mazandaran wood and paper industries. The CMP pulps prepared with 85% yield were separately bleached with diethylenetriamine pentaacetic acid (DTPA), without DTPA, and hydrogen peroxide. Some pulps were bleached with sodium dithionite. The optical properties of prepared hand-sheets of 60 g/m2 after spraying with 0.5% DTPA were measured using TAPPI standard methods. All prepared papers were thermally aged separately in an oven at 105 °C for 0, 10, 20, 30, and 40 h. The optical properties, such as brightness, yellowness, coefficient of absorption, k/s ratio, post color (PC) number, and a* factor, before and after thermal aging were measured. The results showed that from 0 to 40 h, the optical properties of paper increased except brightness and greenness. This increase was more extensive u...
Conference: 2002 TAPPI Fall Technical Conference (San Diego, CA USA), 2002
Oxidation of cellulose, caused by metal-catalyzed hydrogen peroxide decomposition, is one of the main potential reactions that can occur during the alkaline peroxide bleaching of pulp. This oxidation decreases the individual fiber strength and consequently the sheet strength. The bleaching reaction should be controlled to limit degradation. The goal of this project was to characterize the fiber surface metal topography using TOF-SIMS (Time-of-Flight Secondary-Ion-Mass-Spectroscopy) on laboratory generated hydrogen peroxide bleached pulps. TOF-SIMS is a powerful spectroscopic technique combining the chemical identification ability of mass spectroscopy with the spatial resolution available from highly resolved microscopic techniques. The study also examined the application of a relatively new chelating agent, phytic acid, for its ability to bind deleterious metals and improve the efficiency of peroxide bleaching. This study represents one of the first of its kind for the pulp and pape...