Volume 2 Issue 4

The three main types of chemical components in wood are cellulose, hemicellulose, and lignin. These three components have rather different physical and chemical characteristics. In some respects, the three types of materials can be described as “incompatible.” However, most of the biomass existing on the planet depends on their successful interactions. It can be useful to think of wood as being a natural composite structure. Concepts related to composites also are useful as we envision possible new and improved uses of wood-derived materials.

Handsheets produced from corn stalks and wheat straw soda AQ pulps were recycled in the lab. Pulping of corn stalks resulted in a low pulp yield, low bonding strength, and low recyclability. Conversely, wheat straw fiber had a better yield, very good tensile properties, and showed a considerably better response to recycling. The tensile index of wheat straw fibers retained 67% of its original value after four cycles. It could be shown that recycling caused only small changes in chemical compo-sition, but that the crystallinity index increased considerably. To be able to understand the behavior of wheat straw fiber as part of a commercial papermaking furnish, a paper containing 20% wheat straw fiber was produced on a 24 inch pilot paper machine and was recycled using a handsheet mold with white water return. Chemical analysis of the control (no wheat fiber) and the wheat-containing paper demonstrated slightly higher xylan content for the wheat-containing material. Recyclability increased slightly with addition of wheat fibers to a commercial furnish.

High-value, large-volume utilization of forest thinning materials from U.S. National Forests is a potentially important contributor to sustainable forest health. This study demonstrated the utilization of wood chips produced from thinnings for the production of thermomechanical pulp (TMP). Both whole-log chips (primarily from small-diameter logs, tops, and reject logs) and sawmill “residue” chips from a HewsawTM system (Mäntyharju, Finland) were evaluated. The residue chips produced in this study were substituted for a TMP mill’s standard residue chips up to about 50%. The whole-log chips were substituted for the mill’s whole-log chips up to about 30%. The results show that substitution of chips produced from forest thinnings reduced refining energy in all trials. Pulp quality was maintained throughout all trials.

Sodium aluminosilicate has been precipitated in-situ as filler on hardwood bleached kraft pulp fibers using papermaker’s alum and sodium silicate. The filler was produced in two ways, first in the absence of the fibers and second in the presence of fibers, i.e. in-situ precipitation of filler. The filler produced in absence of fiber was then added to the pulp slurry. Various pulp and paper properties were compared for direct loading of market filler, fresh filler loading, and filler prepared in-situ with fibers. In-situ precipitation technology provided paper with significant improvements in various properties of paper as compared to fillers directly added to the stock. Bulk and stiffness of the handsheets prepared with in-situ precipitation were much higher as compared to those of sheets prepared with fillers directly added to the pulp. There was no appreciable increase in brightness and whiteness of paper with in-situ precipitation, as an appreciable proportion of filler was precipitated inside the fibers. In-situ filler loaded pulps showed a higher filler retention value as compared to directly filler loaded pulps, as a high dose of retention aid was needed with the fillers directly added to the stock.

The lignosulphonate/polymer complex, in which the macromolecules of both components are linked together by physico-chemical bonds, has been applied as a new effective lignin-based soil conditioner (LSC). lt has an adhesive affinity both for mineral soil particles and the organic surface of lignocellulosic mulch. The modification of the mulch particles with aqueous solutions of the developed conditioner by means of impreg-nation makes it possible not only to anchor mulch to sandy soil and, thereby, to diminish significantly the evaporation from the soil surface, but also, due to mulch biodegradation, to enrich soil with the main nutrient elements and to create favourable conditions for plant growth. The effect of the mulch modification is determined by the complex composition and depends on its content in the aqueous solution and the application rate.

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.