Research Articles

The effect of hemicellulose extraction of pine wood chips by water prehydrolysis on subsequent kraft cooking and paper properties was studied. Prehydrolysis reduced the required cooking time by approximately 40% and increased kappa number reduction in oxygen delignification. Prehydrolysis decreased the overall brownstock pulp yield on wood by 7.2 percentage units. Consequently, valuable products would need to be produced from the prehydrolyzate to compensate for the resulting increase in wood consumption. In DED-bleaching, lower bleaching chemical dosages were needed with prehydrolyzed than with unhydrolyzed pulps to obtain similar final brightness. As expected, removal of hemicelluloses led to a decrease in the tensile index and increase in the tear index. At a given density, the strength potential of prehydrolyzed pulps was higher than that of unhydrolyzed pulps. There was an up to more than fivefold increase in beating revolutions in a PFI-mill needed to obtain comparable tensile indices. This significant reduction in beating response might pose problems in the commercialization of prehydrolyzed pulps. In general, differences between the paper properties of prehydrolyzed pulps and unhydrolyzed pulps are attributed to decreased inter-fiber bonding in prehydrolyzed pulps.

Current deinking processes use potentially environmentally damaging chemicals in large quantities. The use of enzymes could be an attractive alternative to certain other chemicals used in deinking. In this research, the effects of different HLB (hydrophile-lipophile balance) values and enzymatic treatments on the deinking of old newspaper pulp (ONP) was studied, and optical properties and mechanical strengths of deinked pulps (DIP) were determined. Enzymatic treatments of old newspaper pulps were performed at two temperatures, 20°C and 50°C. Nonionic surfactants with different HLB values were used as the flotation agent. The flotation was conducted for pulps with and without enzymatic treatment. The results showed that brightness values for the floated pulp without enzyme treatment were slightly greater than for the enzyme-treated deinked pulp. Also, dirt count for treated pulps with commercial cellulase and floated with ethoxylated fatty alcohol of HLB 12 at 50°C was lower than that of other pulps. The mechanical strengths of the enzymatically deinked pulps, in terms of burst, tensile, folding endurance, E-MOD, and elongation, were increased, but tear strength for the floated pulps with ethoxylated fatty alcohol of HLB 12 was increased at 50°C without enzymatic treatment. Also, the deinking efficiency of handsheets made from treated pulps with commercial cellulase and ethoxylated fatty alcohol of HLB 12 was highest. The treated pulps with enzyme only, with a combination of commercial cellulase and lipase at 50°C, showed the lowest freeness value in comparison with other pulps.

Worldwide cultivation of corn is expanding, due in part to the increasing production of bioethanol. In consequence, huge amounts of corn stalks residues are been produced. Instead of incineration, we transformed the corn stalks into a semichemical pulp and successfully applied it as reinforcement in polypropylene composites. PP composites reinforced with 40% wt corn stalk single fibers were prepared, and their mechanical properties were evaluated. Through mechanical properties modeling of the composites, the intrinsic tensile strength of the cellulosic fibers that constitute the corn stalk have been determined.

In order to develop novel polymeric supports based on cellulosics, cellulose extracted from pine needles, a perennial resource material available in huge quantities as waste, was graft copolymerized with vinyl monomers. Cellulose, cellulose derivatives, and their graft copolymers with highest percent grafting (Pg) were used as supports for immobilization of an industrially important protease enzyme and the protein bovine serum albumin (BSA) by a specific sorption method. The Manachini method was used to determine activity of the immobilized enzyme. Sorption of protein was characterized by activity of protein concentration by the Lowry method. Cellulose itself was found to be effective as a polymeric support to retain a good amount of protease and BSA, whereas cellulose derivatives were effective to adsorb BSA only. Among cellulose graft copolymers, those based on methyl methacrylate proved to be better sorbents.

Cellulose nanofibers were isolated from kenaf core fibers by employing chemo-mechanical treatments. The morphologies and sizes of the fibers were explored with environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). The results of chemical analysis showed that the cellulose contents of the bleached pulp fibers and nanofibers increased from 46% to 92% and to 94%, respectively. Most of the produced nanofibers had diameters in the range of 20 to 25 nm, whereas kenaf nanofibers ranged in diameter diameters from 10 to 75 nm. Fourier transform infrared spectroscopy (FTIR) analysis revealed the removal of lignin and the majority of the hemicelluloses from the kenaf core fibers. The thermogravimetric analysis (TGA), which was carried out to evaluate the thermal properties of the fibers, demonstrated that the thermal stabilities of these fibers were increased by the chemo-mechanical treatments. The results of X-ray analysis confirmed that chemical and mechanical treatments can improve the crystallinity of fibers.

Two industrial elemental chlorine free (ECF) bleaching sequences, D0(EOP)D1(EP)D2 and OQ(PO)DP, are compared with respect to the bulk content of lignin, carboxyl, hexeneuronic acids (HexA), and reducing groups after each bleaching stage. HexA groups contribute significantly to the total content of carboxyl groups, and their degradation during chlorine dioxide bleaching is reflected by a decrease of the carboxyl content. The higher degradation using an enhanced use of oxygen-based bleaching chemicals is associated with a higher fiber charge reduction, mainly due to xylan depletion. Additionally, the effect of process variables of a laboratory final hydrogen peroxide stage on the chemical composition of the fully bleached pulp (D0(EOP)D1P and OQ(PO)DP) is studied. The ability of final peroxide bleaching to raise the content of carboxyl groups is dependent on the operating conditions and pulp bleaching history. A balance between carbohydrate oxidation and dissolution of oxidized groups determines the effect on fiber charge. The effect of hydrogen peroxide stabilizers added into the final stage on the content of carboxyl groups is also reported.

Urea-formaldehyde prepolymer and hot-press drying were used to improve the properties of poplar wood. The wood was impregnated with the prepolymer using a pulse-dipping machine. The impregnated timbers were compressed and dried by a multilayer hot-press drying kiln. The drying rate was more rapid during the chemical modification and hot-press drying than conventional kiln-drying. In addition, the properties of timber were also enhanced obviously. When the compression rate was 28.6%, the basic density, oven dry density and air-dried density of modified wood improved 22%, 71%, and 70%, respectively. The bending strength and compressive strength parallel to grain increased 60% and 40%. The water uptake of treated wood was significantly decreased compared with the untreated wood. The FTIR analysis successfully showed that the intensity of hydroxyl and carbonyl absorption peaks decreased significantly, which was attributed to a reaction of the NHCH2OH of urea-formaldehyde prepolymer with the wood carboxyl (C=O) and hydroxyl (-OH) groups. The XRD results indicated that the degree of crystallinity increased from 35.09% to 36.91%. The morphologic models of chemical within wood were discovered by SEM.

Broom (Cytisus scoparius) samples were processed in media containing formic acid and hydrogen peroxide (MILOX process) to obtain cellulose-enriched solids. The chemical processing of broom samples was assessed by means of a centered, second order factorial design of experiments. Empirical models derived from the experimental data gave a close interpretation of the experimental patterns, and enabled the selection of operational conditions for achieving extensive delignification and hemicellulose removal, while minimizing the dissolution of cellulose. Broom samples processed under the selected conditions were employed to reinforce PLA composites, which were characterized mechanically and by DSC, SEM, and water absorption experiments.

Mercerized wood species were impregnated with N, N-dimethylacetamid. The FT-IR showed enhanced absorption at 1419 cm-1(-C-/CH3), and the 1267 cm-1 (-N-/ CH3) stretching band confirmed the polymerization reaction. Differential scanning calorimetric analysis indicated that the decomposition temperature of WPC gives a higher thermal stability compared to the raw material. WPC yielded higher MOE and MOR compared to the untreated wood. The Young’s modulus of Xylopia Spp Artocarpus Rigidus and Eugenia Spp were significantly different between raw wood and WPC. The increase in the stiffness and the thermal stability of the composites increased due to the crystallinity of WPC as indicated by XRD analysis.

The effect of hardwood admixture (15-25% birch or aspen) in kraft cooking on the strength properties of the fully bleached pulp was investigated. Results obtained from both lab- and mill-processed ECF bleached pulps showed that adding 15-25% birch or aspen to the production of fully bleached softwood kraft pulp had a minor effect on the strength properties. No significant effect was observed for the hardwood admixture on the apparent density over a wide range of breaking length. Under the conditions studied, the results showed that pulping of mixed softwood/hardwood chips (chip blending) resulted in overall better strength properties than the pulp blending at a given freeness. It was hypothesized that the softwood fibers would be cooked to a higher kappa number in the cooking of mixed softwood/hardwood chips for the same target kappa number, thus having higher fiber strength due to higher pulp viscosity and preservation of the hemicellulose. This was supported by the results from zero-span tensile strength of the long fiber fraction of the samples from chip blending and pulp blending. The implication is that some softwood kraft pulp mills can add up to 25% of hardwood chips to the kraft cooking of softwood chips without significantly affecting the overall pulp strength properties.