José F. Colom

Enzymatic grafting of simple phenols on flax and sisal pulp fibres using laccases

Flax and sisal pulps were treated with two laccases (from Pycnoporus cinnabarinus, PcL and Trametes villosa, TvL, respectively), in the presence of different phenolic compounds (syringaldehyde, acetosyringone and p-coumaric acid in the case of flax pulp, and coniferaldehyde, sinapaldehyde, ferulic acid and sinapic acid in the case of sisal pulp). In most cases the enzymatic treatments resulted in increased kappa number of pulps suggesting the incorporation of the phenols into fibres. The covalent binding of these compounds to fibres was evidenced by the analysis of the treated pulps, after acetone extraction, by pyrolysis coupled with gas chromatography/mass spectrometry in the absence and/or in the presence of tetramethylammonium hydroxide (TMAH) as methylating agent. The highest extents of phenol incorporation were observed with the p-hydroxycinnamic acids, p-coumaric and ferulic acids. The present work shows for the first time the use of analytical pyrolysis as an effective approach to study fibre functionalization by laccase-induced grafting of phenols.

Optimization of a laccase-mediator stage for TCF bleaching of flax pulp

Summary Flax pulp obtained by anthraquinone-soda pulping, resulting in a kappa number of 11.1, a viscosity of 950 ml/g and 36.7% ISO brightness, was bleached in a totally chlorine-free sequence using the enzyme laccase from the fungus Pycnoporus cinnabarinus and 1-hydroxybenzotriazole (HBT) as redox mediator (stage L), followed by a hydrogen peroxide stage (P). The laccase treatment was optimized using a three-variable sequential statistical plan over the following ranges: 1–20 U/g o.d.p. (oven-dried pulp) laccase dose, 0.5–7.5% o.d.p. HBT dose and 1–24 h reaction time. The influence of these variables on several pulp properties after the P stage of the LP sequence was examined. The models defined from the results obtained predicted variations in ISO brightness, viscosity and kappa number of 57.6–74.8%,590–955 ml/g and 0–6.2, respectively. The variables most strongly influencing these pulp properties were found to be the reaction time and the enzyme dose. A compromise was adopted as regards the operating conditions in order to ensure optimum results. The study was completed by conducting a biobleaching assay in a pressurized reactor (590 kPa) to assess the effect of oxygen pressure. The high pressure level resulted in improved pulp properties by the laccase-mediator system.

Why Acid pH Increases the Selectivity of the Ozone Bleaching Processes

The influence of pH on pulp properties was studied by the kinetic analysis of ozone bleaching of Eucalyptus Kraft pulp. The crystallinity of the pulps was also evaluated by XRD. The rate constants of delignification and chromophore removal decreased with the increase in pH, while the rate constant of cellulose degradation increased. The selectivity of the process was 6 times higher at pH 2.5 than at pH 10. There was a portion of lignin inaccessible that cannot be removed by ozone, even at high doses, promoting a strong cellulose degradation. At high ozone doses and acid pH, the ozone reacted primarily with the crystalline portions of the cellulose, while at alkaline pH it reacted indiscriminately with amorphous and crystalline cellulose.

TCF BLEACHED PULPS FROM MISCANTHUS SINENSIS BY THE IMPREGNATION RAPID STEAM PULPING (IRSP) PROCESS

ABSTRACT The production of bleached cellulose pulps from elephant grass (Miscanthus sinensis) via a two-stage soda pulping process and a TCF bleaching sequence is evaluated in this work. The impregnation rapid steam pulping process (IRSP) involves impregnating of the lignocellulosic material with the pulping liquor, withdrawing the excess liquor and rapidly steaming the impregnated material at 180–200°C for a short time. In this paper the process variables and their effect on the kappa number, yield and viscosity of the unbleached pulps are discussed. Bleaching by an ozone-based TCF sequence was tested, and the papermaking properties of the bleached pulp were determined. A kappa number of 19 was obtained by impregnating at an alkali charge of 30 + 0.1% anthraquinone carboxylic acid (AQCA) and pulping at 180°C for only 15 min. Kappa was reduced to 16 by extending pulping time to 26 min. The alkali consumption during impregnation and pulping was 10.2 g NaOH/100 g of dry Miscanthus. Screened pulp yield, viscosity and brightness for this pulp were 54.6%, 913 mL/g and 37.3%, respectively. After bleaching, the pulp had an ISO brightness of 87.4% and a viscosity of 700 mL/g. Refining in a PFI mill provided optimal strength properties of the bleached pulp at 4500 revolutions (71°SR): breaking length 7.2 km, tensile index 72 N m/g, and burst index 4.3 kN/g. Tear index was 7.9 mN m2/g at this degree of refining.

The Role of Oxalic Acid in the Ozone Bleaching Kinetics of an Xo-Kraft Pulp

Abstract The effect of oxalic acid on the reaction kinetics of ozone with a Eucalyptus globulus kraft pulp was studied. Xylanase treatment (X) and oxygen delignification (O) were carried out on the pulp before the kinetic study. Ozone treatment was carried out in a special batch reactor at low consistency (0.5% o.d.p.). The main variables were ozone consumption and oxalic acid doses, and the measured responses were kappa number, viscosity and brightness. The positive effect of oxalic acid was shown. First order kinetics for both cellulose degradation and lignin removal were observed. For chromophore degradation, the kinetics were also first order. The addition of oxalic acid increased the rate of delignification and decreased that of cellulose degradation during ozone bleaching.