Research Articles

From experimental simulation of the process of high consistency pulp moving in a bleaching tower, the aerated bulk density and packed bulk density were measured and studied by using a self-made experimental system. The scattered experimental data – pressure p, and bulk density difference, which was between packed bulk density and aerated bulk density (ρ-ρ0) – were fitted by using Matlab software, and some good-fitting regression curves and equations were obtained. The results showed there was a break point W in the regression curves; within the range 0 £ p £ W the relationship between (ρ-ρ0) and p was a linear function, while for W £ p £ 70000 the relationship was a power function. To effectively meet with the bleaching response for the different kinds and different consistencies of pulp in the tower, by using the fitting regression equations combined with the expressions of average bulk density and pressure in the tower caused by gravity-driven pulp, two equations for average packed density ρa were deduced with the aim of deciding the maximum volume value of the tower, in agreement with the sizes of the towers presently used by major companies.

To further clarify reasons for formation of condensed residues during the last stage of wood liquefaction in the medium of polyhydric alcohols and sulfuric acid catalyst, the weight loss behaviors and thermal reaction kinetics of condensed residues were studied by thermogravimetric analysis (TGA). Simultaneously, chemical methods were used to analyze the contents of lignin, cellulose, and holocellulose in the condensed residues. For all the unliquefied wood residues, the contents of cellulose decreased, and the residual ratios after TGA pyrolysis and the contents of lignin increased as a function of liquefaction time. Moreover, the highest weight loss rate went gradually to the higher temperature region after the liquefaction time and heating rate were extended. The values for apparent activation energy were lower at 150 minutes and 180 minutes and higher at 25 minutes. Liquefaction time had a smaller effect on the pyrolysis mechanism, as revealed by TGA. In conclusion, the thermal stabilities of condensed residues were higher than those of decomposed residues and wood. The condensation reaction occurred mainly during wood liquefaction, and condensed residues resulted possibly from mutual reaction among small molecules from decomposed lignin.

An investigation was conducted on the adsorption of oxymatrine (OMT) on a spherical cellulose adsorbent embedded with wattle bark tannin. The results showed that the adsorption of the OMT on the adsorbent was solution pH dependent and the adsorption process followed the Freundlich adsorption isotherm. The adsorption kinetics of the OMT on the adsorbent could be well described by the pseudo-second-order rate model. And, the adsorption capacity calculated by the pseudo-second-order rate model was close to the experimental data. Desorption and regeneration experiments showed that the OMT adsorbed on the adsorbent could be easily recovered by 50% methanol solution.

The correlation between the fibre flexibility and cross-sectional area moment of inertia of thermomechanical pulp fibres was investigated. The main effects of refining were found to be internal fibrillation, external fibrillation, and fibre shortening. Internal fibrillation increases fibre flexibility and fibre collapsibility, improving fibre-to-fibre contact in a paper sheet. The raw materials used were pulps produced from six different Norway spruce logs and six different Scots pine logs, chosen in a manner that allowed variation of fibre wall thickness and fibril angle independently. Each wood sample was refined in four stages using a pressurized 12″ Sprout Waldron single disc refiner. Fibre flexibility was assessed by FiberMaster bendability measurements. Fibre bendability was measured on the +48 Bauer McNett fractions of the twelve 2nd, 3rd, and 4th stage thermomechanical pulps (TMP). The fibre cross-sectional samples were imaged using scanning electron microscopy (SEM). An image analysis method to calculate the area moment of inertia of each fibre using numerical integration was developed. Fiber bendability increased with specific energy consumption for both wood species (spruce and pine) from the 2nd refining stage to the fourth refining stage. Spruce had a higher rate of bendability increase than pine upon refining. It was expected that fibres with a low area moment of inertia would result in higher bendability, but no such correlation was found for either spruce or pine. Fibre bendability increased with internal fibrillation, as assessed from Simons staining. These results imply that local damage of the fibre wall such as delaminations, kinks, and compressions was the main effect in increasing the flexibility through refining of TMP.

Response surface methodology was used with four factors to screen for the best starch and optimize the use of chemicals in order to maximize precipitated calcium carbonate (PCC) filler retention in a peroxide-bleached TMP suspension. Three commercial starches were used in conjunction with colloidal silica and flocculant. The PCC loading level and the interactions between PCC level, starch, flocculant, and silica were investigated, and empirical models were constructed. The empirical process models were then employed to predict the retention and drainage. It was found that medium-charged cationic starch (S858) gave the highest total and filler retention, whereas high-charged cationic starch (S880) resulted in the best drainage. The ash content of the handsheet can be pushed up to 40% using the retention system with medium (S858) and high (S880) charged cationic starch. The high-charged cationic starch (S880) gave stronger paper, probably because of its higher affinity with the fiber and fines.

A study was made of the classification of pulp, paper, and peat particles by size with a device called a tube flow fractionator. An accurate and simple experimental model was formulated in order to estimate the time required for fractionation, yielding an excellent correlation between the observed and predicted fractionation times. The results showed that the fractionation time of a certain size of pulp, paper, and peat particles in the tube flow device can be accurately estimated from the length, width, and thickness of the particle. The results can be used to facilitate the selection of specific fractions of pulp and paper samples.

Levulinic acid (LA), 4-oxo-pentanoic acid, is a new platform chemical with various potential uses. In this paper, catalytic hydrogenation and oxidation of levulinic acid were studied. It was shown from experiments that levulinic acid can be hydrogenated to γ-valerolactone (GVL) over transition metal catalysts and oxidative-decarboxylated to 2-butanone (methyl-ethyl-ketone, MEK) and methyl-vinyl-ketone (MVK) by cupric oxide (CuO), cupric oxide/cerium oxide (CuO/CeO2), cupric oxide/ alumina (CuO/ Al2O3), and silver(I)/ peroxydisulfate (Ag(I)/S2O82-).

In this work tannin was isolated from the outer bark of the eucalyptus tree, then treated with Ba(OH)2 to synthesize barium tannate (Ba-tan). The derivative was evaluated as a thermal stabilizer for polyvinyl chloride (PVC). PVC was mixed with Ba-tan thermally at four percentages (0.5, 1.0, 2.0, and 2.5)% w/w. The samples were pressed thermally to films having thickness ranging between 0.25 and 0.30 mm. The effect of Ba-tan was studied by monitoring the weight of samples under iso-thermal conditions at 250 oC. Thermal stability of PVC increased with increasing Ba-tan percent. Samples weight curves also indicated that the additive had been suitably active to increase the resistance of PVC against thermal degradation, where the degradation rates decreased from about 0.21 % wt/min. at 0.5% of Ba-tan on PVC to reach to 0.05% wt/min. for the 2.5% treated sample. The ability of Ba-tan to react with and remove HCl from the system of polymer during thermal conditioning of samples and during the measurement led to this effect. Therefore the present results demonstrate the performance of this derivative as a thermal stabilizer.

Three switchgrass cultivars (‘Performer’, ‘BoMaster’, and ‘Colony’ switchgrass) were delignified using NaOH at varying concentrations and residence times at 121 oC for improved sugar production in enzymatic hydrolysis. Because of its greater carbohydrate/lignin ratio and the more substantial lignin reduction upon alkaline attack, ‘Performer’ switchgrass gave greater sugar productions under all the pretreatment conditions investigated. Maximum sugar production from ‘Performer’ was 425 mg/g raw biomass, which was achieved at 1% NaOH and 0.5 h. Sugar production increased with the improvement of delignification until the lignin reduction reached 30%. The more severe pretreatment conditions, which led to greater lignin reductions, did not favor the increase of sugar production because of greater solid losses. Linear models were proven effective in correlating a modified severity parameter log(Mo) to lignin reduction and sugar production of ‘Performer’ switchgrass.

The adsorption of xylan on pulp fibers improves the strength properties of paper. However, the optical properties are decreased significantly. The objective of our research was to bleach hardwood kraft pulp with adsorbed birch xylan by hydrogen peroxide and study the effect of bleaching parameters on paper properties. The bleaching parameters studied included bleaching temperature, time, initial pH as well as MgSO4 dosage. The optical properties (whiteness, brightness, opacity) and physical properties (tensile index, tearing index, bulk) of handsheets made from the pulp bleached with different process variables were measured. The results showed that better optical properties were obtained with higher bleaching temperature, longer bleaching time, and more MgSO4 dosage. Bleaching from an initial pH of 11 provided the highest brightness value. On the other hand, strength properties were improved with decreasing of the bleaching temperature, and increasing the initial pH and MgSO4 dosage. The relationship between strength properties and bleaching time varied depending on bleaching temperature. According to the results, both good mechanical properties and optical properties could be achieved when the operating parameters were controlled properly. Therefore hydrogen peroxide bleaching was proved to be a suitable method for bleaching hardwood kraft pulp with adsorption of birch xylan.