In this work, laccase-TEMPO (Lac-T) treatments were applied to bleached commercial dissolving pulp in order to introduce carbonyl and carboxyl groups, which were found to improve dry and wet strength-related properties. Also the solubility behavior towards xanthate reactions was assessed. The effect of a refining step (R) before the oxidative treatment, the absence or presence of oxygen pressure, TEMPO dose (2 or 8% oven dried pulp) and reaction time (8 or 20 h) were thoroughly examined. Treatments conducted in the presence of oxygen pressure exhibited greater amount of functional groups. Introducing a pre-refining treatment resulted in similar functional groups but higher wet strength was achieved. Specifically, a high W/D strength ratio was observed, indicating that wet strength-related property was satisfactorily developed. Besides the fact that all Lac-T treatments caused severe cellulose degradation, no fiber strength loss was detected. In fact, all oxidized samples presented higher Wet Zero-Span Tensile Strength, mainly in R+ Lac-T (O2) sample, which suggested the formation of hemiacetal linkages between the new introduced aldehyde groups and available free hydroxyl groups resulting from fibrillation
In this work, treatments with a xylanase (X) and carbohydrases mixture (Cx) were 19 applied on a TCF bleached sisal pulp in order to obtain high-cellulose content fibers 20 applicable on a wide range of uses. A limit of ˜12% w/w final content in hemicelluloses 21 was found regardless of the enzymatic treatment assessed. An extraction with 4% and 22 9% w/v NaOH was performed for further hemicelluloses removal. We found that NaOH dose could be strongly reduced if combined with Cx or Cx+X treatments. Also, if necessary, a stronger reduction could be obtained with 9% w/v NaOH, which was found to be boosted in a 14% if performed after a treatment with Cx. An end-product with a low content in xylans (˜2.9% w/w) and in HexA (5.8 µmol/odp) was obtained. Pulp Fock solubility was also increased (˜30%) by enzymatic treatments. HPLC analysis of effluents provided useful information of enzymatic catalytic mechanisms
Quintana, E.; Valls, C.; Barneto, A. G.; Vidal, T.; Ariza, J.; Roncero, M.B. Carbohydrate polymers Vol. 119, p. 53-61 DOI: 10.1016/j.carbpol.2014.11.019 Data de publicació: 2015-03-30 Article en revista
An enzymatic biobleaching sequence (LVAQPO) using a laccase from Trametes villosa in combination with violuric acid (VA) and then followed by a pressurized hydrogen peroxide treatment (PO) was developed and found to give high bleaching properties and meet dissolving pulp requirements: high brightness, low content of hemicellulose, satisfactory pulp reactivity, no significant cellulose degradation manifested by a-cellulose and HPLC, and brightness stability against moist heat ageing. The incorporation of a laccase–mediator system (LMS) to bleach sulphite pulps can be a good alternative to traditional bleaching processes since thermogravimetric analysis (TGA) showed that the laccase treatment prevented the adverse effect of hydrogen peroxide on fibre surface as observed during a conventional hydrogen peroxide bleaching treatment (PO). Although VA exhibited the best results in terms of bleaching properties, the performance of natural mediators, such as p-coumaric acid and syringaldehyde, was discussed in relation to changes in cellulose surface detected by TGA
Stoichiometric complexes of hyaluronic acid with alkyltrimethylammonium surfactants bearing octadecyl, eicosyl and docosyl groups were prepared by ionic coupling in aqueous solution. The complexes were non soluble in water but soluble in organic solvents. In the solid state they self-assembled in a biphasic layered structure with the alkyl side chains forming a separate phase that melted in the 50–60 °C range. They were stable to heating up to above 200 °C.
Various combinations of laccases, xylanase and cellulase were used to biobleach cellulose fibres from eucalyptus. The Trametes villosa and Myceliophthora thermophila laccases were used in combination with violuric acid (VATvL system) and methyl syringate (MeSMtL system), respectively, as mediator. A dissimilar mode of action of the two systems was found: the VATvL treatment released both hexenuronic acids and lignin, whereas the MeSMtL released lignin alone. Pulp properties were further improved by applying the mediator before the enzyme during treatment. Pulp properties comparable to those provided by industrial TCF sequences were obtained by inserting a xylanase pretreatment before VATvL, but no significant effect was observed after the cellulase pretreatment. As an added value, the resulting enzymatically bleached fibres possess a reduced hexenuronic acid content. The chemical oxygen demand of the effluents from each stage was also assessed
Rocasalbas, G.; Francesko, A.; Touriño, S.; Fernandez-Francos, X.; Gübitz, G. M,.; Tzanov, T. Carbohydrate polymers Vol. 92, num. 2, p. 989-996 DOI: 10.1016/j.carbpol.2012.10.045 Data de publicació: 2012-11-02 Article en revista
Laccase-assisted simultaneous cross-linking and functionalization of chitosan/gelatin blends with phenolic compounds from Hamamelis virginiana was investigated for the development of bioactive hydrogel dressings. The potential of these hydrogels for chronic wound treatment was evaluated in vitro, assessing their antibacterial and inhibitory effect on myeloperoxidase and collagenase. Rheological studies revealed that the mechanical properties of the hydrogels were a function of the enzymatic reaction time. Stable hydrogels and resistant to lysozyme degradation were achieved after 2 h laccase reaction. The inhibitory capacity of the hydrogel for myeloperoxidase and collagenase was 32% and 79% respectively after 24 h incubation. Collagenase activity was additionally suppressed by adsorption (20%) of the enzyme onto the hydrogel. Therefore, the bioactive properties of the hydrogels were due to the effect of both released phenolic compounds and the permanently functionalized platform itself. The hydrogels showed antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus.
Fillat, A.; Gallardo, Ó.; Vidal, T.; Pastor Blasco, Francisco Ignacio Javier; Diaz Lucea, M. Pilar; Roncero, M.B. Carbohydrate polymers Vol. 87, num. 1, p. 146-152 DOI: 10.1016/j.carbpol.2011.07.030 Data de publicació: 2012-01-04 Article en revista
Unbleached flax fibres for paper production were treated with laccase from Pycnoporus cinnabarinus and low molecular weight phenols (syringaldehyde – SA, acetosyringone – AS and p-coumaric acid – PCA) to evaluate the potential of this treatment to biomodify high cellulose content fibres. After the enzymatic treatment with the phenols, an increase in kappa number was found, probably due to a covalent binding of the phenoxy radicals on fibres. Grafting was more evident in pulps treated with PCA (an increase of 4 kappa number points with respect to the laccase control was achieved). Paper handsheets from treated pulps showed antimicrobial activity against the bacteria tested: Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae. An important reduction on microbial count was obtained after incubation of liquid cultures of the bacteria with grafted handsheets. AS and PCA grafted fibres showed a high antibacterial activity on K. pneumoniae, getting a nearly total growth inhibition. AS fibres also caused a high reduction in bacterial population of P. aeruginosa (97% reduction). Optical properties of handsheets from treated pulps were also determined, showing a brightness decrease and increase in coloration, evaluated by CIE L*a*b* system, caused by the laccase induced grafting of the phenols. The results suggest that these low molecular weight phenols, covalently bound to the flax fibres by the laccase treatment, can act as antimicrobial agents and produce handsheets with antimicrobial activity
Ionic coupling of both polygalacturonic and alginic acids with alkyltrimethyl ammonium surfactants containing 18, 20 and 22 carbon atoms in the alkyl side chain was conducted in water solution to prepare non-soluble comb-like complexes. These amphiphilic complexes are arranged in a biphasic layered structure with the paraffinic phase made of alkyl side chains alternating with the hydrophilic phase made of polyuronic chains. The complexes displayed the thermal behaviour typical of comb-like systems carrying long polymethylene groups, which melt at temperatures between 40 and 80 ◦C without significant disruption of the layered arrangement. Melting temperature, crystallinity and thermal stability were
slightly higher for the polygalacturonic complexes and all they increased almost steadily with the length of the alkyl chain within each series. The melting-crystallization process was followed by combined WAXS/SAXS and 13C CP-MAS NMR, which revealed that the transition involves an expansion-contraction of the structure that may attain up to 20% of the original dimension. The transition takes place without
large conformational changes and is not fully reversible.
This work was conceived to investigate for the first time the effectiveness of the combined use of xylanase
and laccase for the removal of hexenuronic acids (HexA) and lignin from sisal pulp fibres. To this end,
xylanase (X) and laccase (L) treatments were used in an XLQPo sequence (where Q denotes a chelating
stage and Po an oxygen-reinforced peroxide multi-step treatment) that was applied to pulp in order
to obtain sisal fibres with a high cellulose content. The results of the XLQPo sequence were compared
with those of an LQPo sequence. The L stage of both sequences was performed in the presence of either
the natural compound sinapyl aldehyde (SLD) or the synthetic compound violuric acid (VA), employed
as mediators, in order to compare their efficiency in aiding pulp bleaching and HexA removal. Changes
in HexA content and the contributions of lignin and HexA to kappa number during each sequence were
examined. The xylanase treatment was found to remove 47% of lignin, 15% of xylan and 27% of HexA from
the initial pulp, whereas the laccase–VA system removed 28% of HexA and exhibited higher efficiency
than the laccase–SLD system in reducing kappa number and increasing brightness. In any case, when
the X treatment was applied, the sequence including laccase–SLD treatment resulted in the strongest
delignification effect. The effluents from each stage of the bleaching sequences were analysed for COD,
colour and toxicity, which peaked after the L stage and were significantly higher with SLD than with VA
Gallardo, Ó.; Valls, C.; Vidal, T.; Diaz Lucea, M. Pilar; Pastor Blasco, Francisco Ignacio Javier; Roncero, M.B. Carbohydrate polymers Vol. 80, num. 1, p. 154-160 DOI: 10.1016/j.carbpol.2009.11.006 Data de publicació: 2010-03-25 Article en revista
Four new bacterial xylanases from different glycosyl hydrolase families (11, 10 and 5) were evaluated for hexenuronic acid (HexA) removal capacity and bleach boosting ability of a eucalypt kraft pulp. The family 11 xylanase was the most effective in enhancing HexA removal and also in increasing delignification and brightness. A very innovative point was that a xylanase from family 5 was applied in pulp bleaching for the first time, showing a notable contribution to pulp bleachability. On the contrary, the family 10 xylanases did not modify kappa number or brightness. A remarkable effect was that the tested xylanases reduced pulp HexA content. The effects produced by the different xylanases in pulp properties were closely related with the effects observed in the effluent properties. The effluents from enzymatic treatments showed the dissolved xylans and xylooligosaccharides branched with HexA, as well as lignin. In addition, a simple tool to assess the boost bleaching ability of a xylanase treatment was also used.
The changes produced in cellulosic fibres when they are subjected to successive drying and rewetting
cycles could have an important impact on the resistance and durability of cement mortar composites
based on these fibres. In this paper, unbleached, oxygen delignificated, semi-bleached, and fully bleached
softwood pulps have been subjected to drying and rewetting cycles and the corresponding dried pulps
characterized. The morphological structures and thermal stabilities were investigated with X-ray diffraction
and thermogravimetric analysis. While the water retention values decrease significantly with drying
and rewetting cycles, an overall increase in the crystallinity index and in the thermal stability was found
in the hornificated pulps. Natural fibres from cotton linters were also studied and the results compared
with the fibres from these softwood pulps.