J. Ariza

Hydrothermal and pulp processing of Eucalyptus.

Hydrothermal processing of Eucalyptus wood was performed at operation temperature of 181 degrees C, processing time or 37.5 min and solid water ratio of 1/6 to ensure a maximum loss of xylan recuperation with minimum cellulose fibre degradation. Under those conditions, the loss of xylan was 22% less than that achieved with the conditions 196 degrees C, 50.6 min and 1/8 (solid/water). IN In addition, an experimental design was used to study the influence of process variables: temperature (145-175 degrees C), pulping time (40-120 min) and ethanol concentration (40-70% weight concentration), on the properties of pulps (yield, kappa number, viscosity, cellulose, xylan, lignin acetyl groups contents and brightness) and paper sheets (stretch index, burst index and tear index) obtained from the solid fraction after hydrothermal treatment of Eucalyptus globulus. Pulps with acceptably high physical and chemical properties can be obtained operating at 175 degrees C for 90 min with 55% ethanol concentration.

Ethanol-acetone pulping of wheat straw. Influence of the cooking and the beating of the pulps on the properties of the resulting paper sheets

The influence of independent variables in the pulping of wheat straw by use of an ethanol-acetone-water mixture [processing temperature and time, ethanol/(ethanol + acetone) value and (ethanol + acetone)/(ethanol + acetone + water) value] and of the number of PFI beating revolutions to which the pulp was subjected, on the properties of the resulting pulp (yield and Shopper-Riegler index) and of the paper sheets obtained from it (breaking length, stretch, burst index and tear index) was examined. By using a central composite factor design and the BMDP software suite, equations that relate each dependent variable to the different independent variables were obtained that reproduced the experimental results for the dependent variables with errors less than 30% at temperatures, times, ethanol/(ethanol + acetone) value, (ethanol + acetone)/(ethanol + acetone + water) value and numbers of PFI beating revolutions in the ranges 140-180 degrees C, 60-120 min, 25-75%, 35-75% and 0-1750, respectively. Using values of the independent variables over the variation ranges considered provided the following optimum values of the dependent variables: 78.17% (yield), 15.21 degrees SR (Shopper-Riegler index), 5265 m (breaking length), 1.94% (stretch), 2.53 kN/g (burst index) and 4.26 mN m2/g (tear index). Obtaining reasonably good paper sheets (with properties that differed by less than 15% from their optimum values except for the burst index, which was 28% lower) entailed using a temperature of 180 degrees C, an ethanol/(ethanol + acetone) value of 50%, an (ethanol + acetone)/(ethanol + acetone + water) value of 75%, a processing time of 60 min and a number of PFI beating revolutions of 1750. The yield was 32% lower under these conditions, however. A comparison of the results provided by ethanol, acetone and ethanol-acetone pulping revealed that the second and third process-which provided an increased yield were the best choices. On the other hand, if the pulp is to be refined, ethanol pulping is the process of choice.

Use of formaldehyde for making wheat straw cellulose pulp

Abstract A central composite design was used to investigate the influence of the cooking conditions (time, temperature and formaldehyde concentration) for wheat straw with formaldehyde–water mixtures on the properties of the pulp obtained (yield and holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw. The equations derived predicted the yield, the holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents of the pulp, and the pH of the wastewater with multiple- R , R 2 , adjusted- R 2 and Snedecor F values of 0.99, 0.99, 0.99 and 321.33; 0.98, 0.95, 0.92 and 35.01; 0.92, 0.86, 0.78 and 10.68; 0.99, 0.97, 0.96 and 68.19; 0.91, 0.83, 0.80 and 29.68; and 0.97, 0.95, 0.93 and 46.10, respectively. While ensuring a high holocellulose content and low lignin and ethanol–benzene-extractive contents entails using high levels of the process variables involved, a compromise can be made in order to achieve both the previous objectives and a high α-cellulose content provided a long cooking time, a high temperature and a low formaldehyde concentration are used – alternatively, a long time, a high formaldehyde concentration and a low temperature can be equally effective and save energy. The yield, pH and holocellulose, α-cellulose, lignin and alcohol/benzene extractive contents are more sensitive to changes in the cooking time than they are to modifications of the formaldehyde concentration.

Optimization of hydrogen peroxide in totally chlorine free bleaching of cellulose pulp from olive tree residues.

The influence of the operating conditions used in the bleaching of olive wood trimmings pulp (viz. hydrogen peroxide concentration and time) on the yield, kappa index and viscosity of the resulting pulp and on strength-related properties of paper sheets was studied to determine the optimal bleaching conditions of this pulp. Hydrogen peroxide bleached pulps at different sequences (oxygen, ozone, chlorine dioxide and alkaline extractions) were compared. Hydrogen peroxide bleaching proved to be suitable for this pulp. Considerable improvements in viscosity were obtained with respect to other bleaching sequences such as oxygen, ozone and chlorine dioxide. Hydrogen peroxide bleaching decreased the kappa index 51.3% less than ozone bleaching, 25.0% less than chlorine dioxide (D) and 6.3% less combined chlorine dioxide-alkaline extraction (DE). To obtain kappa indices 50.9% and 37.9% lower than the index achieved by hydrogen peroxide, oxygen (LaO(p)) and ozone (LaO(LaZ)R) sequences respectively were needed. Lower-medium levels of hydrogen peroxide concentrations (1-3%) and high reaction times (210 min) proved to be suitable for bleaching of pulp olive trimming residues. This approach could be used on this residue to produce adequately bleached pulp.

BIOBLEACHING OF CELLULOSE PULP FROM WHEAT STRAW WITH ENZYMES AND HYDROGEN PEROXIDE

The influence of the operating conditions (temperature, time, enzyme concentration, pH and pulp consistency) used in the enzymic step of an XP (Cartazyme–hydrogen peroxide) sequence for bleaching soda pulp from wheat straw on various properties of the resulting pulp (yield, brightness, viscosity and kappa number) and of the paper sheets obtained from it (brightness, breaking length, stretch, burst index and tear index) was studied. A 2m−1 central composite rotatable design was used for this purpose. The results of the 27 experiments performed were processed using the BMDP software suite, which provided equations that reproduced the values of the dependent variables with errors less than 10%. Application of the steepest ascent method to the equations thus derived allowed the identification of the most suitable conditions for optimizing the values of the dependent variables. Based on these results, using an enzyme concentration of 0.04% by dry pulp weight, a temperature of 35°C, a pH of 4.7 and a consistency of 12% for 2 h in the enzymic step provided paper sheets of acceptable quality. The XP bleaching sequence decreases pulp yield by 28.3% (19.2% in step X and 9.1% in step P), and the kappa number and viscosity of the pulp by 37.2 and 6.4%, respectively; on the other hand, it increases the brightness, breaking length, stretch, burst index and tear index of the paper sheets obtained from the pulp by 42.7, 32.4, 21.9, 49.7 and 7.7%, respectively.

Pulping and bleaching of pulp from olive tree residues

The influence of operating conditions (active alkali concentration, temperature and time) used in the kraft pulping of wood from olive trimming residues on the yield and kappa index of the pulp and the stretch index, burst index and tear index of paper sheets obtained from it, as well as that of the chlorine dioxide concentration used to bleach the pulp according to the D1ED2 sequence (chlorine dioxide-alkaline extraction-chlorine dioxide) on the yield, kappa index, brightness and viscosity of the bleached pulp, were studied. A 2n central composite factor design was used to derive equations that relate the dependent variables to the operating variables considered in the pulping and bleaching processes. The equations reproduce the experimental results with errors less than 10%. Based on the pulping results, obtaining readily bleached pulp of acceptable strength-related properties entails using an active alkali concentration of 25%, a temperature of 175°C and a time of 93 min. Based on the bleaching results, using chlorine dioxide concentrations of 7.5 and 1% in steps D1 and D2, respectively, ensures the obtainment of acceptably bright (>88%) pulp with little loss of yield (<2%) and viscosity (<3%).

Use of thermogravimetric analysis to monitor the effects of natural laccase mediators on flax pulp

The effects of 1-hydroxybenzotriazole (HBT) and the natural laccase mediators gallic acid, caffeic acid and p-hydroxybenzoic acid, on the enzymatic bleaching of flax pulp were compared. The treatment was performed under atmospheric air and oxygen pressure, and, for the first time, monitored by thermogravimetric analysis (TGA) for comparison with chemical analysis, FTIR and X-ray diffraction (XRD) spectroscopies. Thermogravimetric data were simulated by applying a nucleation kinetic equation to a combustion model based on four pseudo-components (hemicellulose, amorphous and crystalline cellulose, and lignin). The results thus obtained show that the effects of the natural mediators are similar to those of HBT and lead to increased order in cellulose microfibril surfaces. An increase in pulp crystallinity was additionally exposed by the XRD and FTIR techniques, and a reduction in microfibril equatorial size by the XRD patterns. Simulated DTG curves were used to determine the kinetic parameters for thermal degradation.

Organosolv pulping of olive tree trimmings by use of ethylene glycol/soda/water mixtures

Abstract This paper reports on the influence of independent variables in the ethylene glycol/soda pulping of olive wood trimmings (165–195°C, 30–90 min, ethylene glycol concentration 5–15%, soda concentration 2.5–7.5% and liquid/solid ratio 4–6), on the yield and Kappa index of the pulps and the strength properties (breaking length, burst index and tear index) of paper sheets. By using a central composite factorial design, equations that relate each dependent variable to the different independent variables were obtained which reproduced the experimental results for the dependent variables with errors less than 12%. Using a temperature of 184°C, ethylene glycol and soda concentrations of 15% and 7%, respectively, a liquid/solid ratio of 5:1 and a cooking time of 30 min results in yield, Kappa index, breaking length, burst index and tear index values that depart by 14.3%, 8.2%, 17.1%, 17.0% and 2.3%, respectively, from their optimum levels. These conditions result in substantial savings in power consumption and immobilised capital investments as they involve a lower temperature, a lower liquid/solid ratio, and a shorter time than the maximum values tested.

Studying the effects of laccase treatment in a softwood dissolving pulp: cellulose reactivity and crystallinity.

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 α-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.

Comparative study of paper sheets from olive tree wood pulp obtained by soda, sulphite or kraft pulping

Abstract Paper sheets from olive tree wood pulp obtained by soda, sulphite or kraft pulping were studied to examine the influence of pulp beating on properties of the paper sheets. Paper sheets from kraft and sulphite pulps exhibited the highest resistance, and sulphite pulp the highest brightness. Soda pulp required more intensive beating than did kraft or sulphite pulps; in fact, the PFI beater had be operated at a 40–50% higher number of beating revolutions to obtain soda pulp with 70–80° SR. The breaking length, stretch, burst index and tear index of paper sheets obtained from kraft pulp, beaten to a Shopper–Riegler index of 70–80° SR were 20–30%, 30–50%, 50–60% and 15–35% higher, respectively, than those of sheets obtained from soda pulp.