Research Articles

Conditions for obtaining microcrystalline cellulose (MCC) by the thermocatalytic method from hardwood (birch, aspen) and softwood (pine) bleached sulphate pulp have been developed. After thermocatalytic treatment, cellulose polymerization degree has decreased to the so-called levelling-off degree of polymerization (LODP), which, in the case of birch, aspen and pine wood pulp, made up 450, 370 and 250 units, respectively. After grinding the destructed pulp in a ball mill, MCC powder samples were obtained with particles, the major part of which had sizes of 2-20 mm. in terms of physico-chemical indices investigated in this work, the obtained samples conform to the pharmacopoeia requirements. Dispersing the destructed pulp in water medium, at a sufficiently high cellulose concentration (³ 8%), MCC gel samples were prepared, with rheological properties typical for liquid crystalline polymers. The indices of the obtained hardwood and softwood MCC were compared.

The conformations of a variety of crystalline lignin models representing different diastereomeric forms of structural elements in lignin of the arylglycerol b-guaiacyl ether type have been studied using X-ray crystallography. Based on X-ray crystallographic data, sequences of units attached to each other by b-guaiacyl ether linkages were constructed. The appearance of the resulting oligomers shows that stereoisomerism can be expected to influence the shape of the lignin molecules to a great extent. The constructed oligomers provide an idea about the contribution to the complexity of lignins by stereochemistry alone. It is proposed that structural differences, together with conformational variations, are the main reasons for the broadness of the signals in NMR spectra of lignins.

Manganese peroxidase (MnP) and lignin peroxidase (LiP) are two major peroxidases involved in lignin biodegradation. The cDNA mnp1 encoding a kind of MnPs, and cDNA clg5 encoding a kind of LiPs were fused to one cDNA mnp1- clg5 (rmc15) by over-lap PCR technology in this research. Then the recombinant cDNA rmc15 was cloned into a vector pTrcHisB to construct its efficient expression plasmid pTHmc15 in Escherichia coli. The E. coli transformed by pTHmc15 was induced by isopropyl-b-D-thiogalactoside. The expressed protein was analyzed by SDS-PAGE, and a new one was observed with a molecular weight of about 77KD. Enzyme activities of MnP and LiP could not be observed in the unfolded fused protein. However, the enzyme activity of MnP was detected in the recombinant protein after it was refolded and activated by Ca2+ and heme, while the activity of LiP was not detected. These results show that the enzyme activity of the protein at N-terminal was not affected, but at C-terminal it was affected in the fusion protein of ligninolytic enzymes. Therefore, it is unfeasible to construct the gene of bifunctional ligninolytic enzyme with the fusion of the cDNA mnp1 encoding MnP and cDNA clg5 encoding LiP.

It is well established that the glass transition temperature (Tg) is a sensitive measure of cure in neat thermosets. As cure advances, network mobility declines and the Tg rises in a systematic fashion. This study sought to determine if such a relationship exists for polymeric isocyanate adhesives (pMDI) cured in the presence of wood. Yellow-poplar (Liriodendron tulipifera) specimens were impregnated with neat pMDI and then isothermally cured for various periods in two different differential scanning calorimeters (DSCs). After this isothermal cure period, the Tg and residual heat of cure were determined. These thermal scans were performed using either constant (conventional) or modulated (MDSC) heating rates. For both methods, the degree of resin cure varied significantly under identical isothermal curing conditions; nevertheless a strong relationship was found between the degree of resin cure and the associated Tg. While the conventional DSC method yielded slightly improved sensitivity and reproducibility, results from both methods compared favorably.

Oxidative treatments, without and with assistance of a Laccase-Mediator System (LMS), were characterized in relation to their effects on the chemical composition and strength properties of the fibrous fraction of an unbleached recycled softwood kraft pulp. The LMS, composed of a Trametes hirsuta laccase extract and 1-hydroxybenzotriazole (HBT), was applied on the fibrous fraction of a recycled pulp at low consistency under continuous stirring and oxygen bubbling. Control treatments adding neither the enzyme nor the mediator were also considered. The LMS treatment caused a partial reversion of the detrimental effects of hornification. A considerable increase in the amount of carbonyl groups on the lignin structure was observed as a result of the enzyme treatment. The amount of extractives in ethanol:toluene also increased after the enzymatic treatment, and the dioxane-soluble kraft lignin underwent a noticeable decrease in its apparent molecular mass. This latter effect was readily attributed to the hydrolysis of aryl-ether bonds that survived the severity employed in the pulping process. These observations were useful to explain why LMS-recycled fibers produce handsheets with 9.4% better tensile strength than the control pulps.

Many natural dyes, for example carminic acid, are soluble in water. We present a simple strategy to naturalize synthetic azadyes through their linkage with lactose to induce their water solubility. The dyeing process of textile fibres then becomes possible in water without additives such as surfactants and mordants, which result in products that are difficult to eliminate. Glyco-azadyes (GADs) we are presenting here are obtained through a diether linker to bond the azadye and the sugar. Tinctorial tests were carried out with fabrics containing wool, polyester, cotton, nylon, and acetate. GADs were found to be multipurpose and capable of dyeing many fabrics efficiently under mild conditions.

Pectins are important structural elements in spruce fibres. Alkaline peroxide bleaching of spruce thermomechanical pulp (TMP) causes degradation and demethylation of pectins, yielding high-charge-density pectic acids. The pectic acids in fibres contribute strongly to the negative fibre charge, and the dissolved pectic acids increase the cationic demand of bleached TMP water. In this study, a method to isolate pectic acids from peroxide-bleached TMP pulp water is presented. The pectic acids were isolated and purified in good yield using a polyacrylate resin to remove lignin, a cellulose filter to remove galactoglucomannans (GGM), and an anion exchange resin to separate pectic acids from neutral carbohydrates. Salts and residual low-molar-mass carbohydrates were further removed from the isolated pectic acids by dialysis. The isolated pectic acids (>80% purity) had a low molar mass and a wide polydispersity (5.9 kDa, MW/MN 3.3). The aggregation and precipitation of the isolated pectic acids, as well as citrus fruit pectic acids with well-defined molar masses, by Ca2+-ions were studied. The molar mass of pectic acids was a key factor determining the precipitation of Ca2+-pectates. Pectic acids below 6 kDa were not precipitated by Ca2+, while higher molar masses led first to partial and then to complete precipitation. The precipitated Ca2+-pectates may impair paper machine runnability and paper quality.

In this paper multifactor non-linear dependencies of cutting forces from several machining parameters for low density wood of Liriodendron tulipifera Linn., known as Yellow Poplar, and Cordia alliodora Ruiz. & Pav., known as laurel blanco wood or capa prieto, were evaluated from experimental matrices. In the analyzed relations there was evidence for several strong interactions, which have been graphically illustrated and discussed.

Model surfaces of alkyl ketene dimer (AKD) and alkenyl succinic anhyd-ride (ASA) were prepared by casting and spin-coating methods. The surface chemical composition and surface topography were investigated by XPS, ellipsometry, AFM and contact angle studies. Spin-coating resulted in layered structure of AKD and ASA surfaces; the molecular layer thickness of both AKD and ASA was found to be ca. 2.5 nm. To achieve a covering surface layer, an average thickness of ca. 35 nm was required. The rms roughness of the created surfaces was 1 - 6 nm. Colloidal probe adhesion measurements were performed to verify that the roughness was in a range suitable for these measurements. The high reactivity of ASA with water generated stability problems with the ASA layers and it has to be recognized that surface force measurements with ASA in aqueous environment are very difficult, if not impossible. How-ever, surfaces created in this way were found to be useful in providing explanations of earlier ASA adhesion studies. The contact angle measurements on ASA layers also indicated that it might be possible to asses the hydrolysis rate issues through a set of similar measurements.

Modification of chemithermomechanical pulp (CTMP) by fungal treatment was investigated. Eucalyptus CTMP was treated with three different types of white-rot fungi, namely, Phanerochaete chrysosporium (P.c-1767), Trametes hirsute 19-6 (T.h-19-6), and Trametes hirsute19-6w (T.h-19-6w), under a stationary culture condition. Pulp total weight loss, lignin loss, and cellulose loss were determined to compare the different enzymes secreted by the three fungal strains. Pulp physical strengths, optical properties, and bleachability after the fungal treatment were investigated to compare the effect of fungal treatment on the pulp quality improvement. The results show that lignin reduction by both T.h-19-6 and T.h-19-6 (w) was about twice as much as that by P.c-1767. However, the selectivity of T.h-19-6 (w) towards lignin over cellulose was only 0.82, while that of T.h-19-6 was as high as 4.43. After T.h-19-6 treatment, pulp tensile, tear, and internal bonding strength increased by about 27%, 38%, and 40%, respectively.