Sulfonated Kraft Lignin Research Articles

A novel and efficient polymerization of lignosulfonates by horseradish peroxidase/H2O2 incubation

Lignosulfonates(LSs), by-products from chemical pulping processes, are low-value products with limited dispersion properties. The ability of commercially available horseradish peroxidase (HRP) to polymerize LS macromolecules and improve the dispersion properties of LSs was investigated. The polymerization of LSs proceeded efficiently under mild reaction conditions in an aqueous solution with HRP/H2O2. Gel permeation chromatography showed a significant increase in weight-average molecular weight (M w ) of sulfonated kraft lignin and sodium lignosulfonate (NaLS) by 8.5-fold and 4.7-fold, respectively. The mechanism of polymerization was investigated by elemental analysis, surface charge measurement, headspace gas chromatography, infrared spectroscopy (IR), and hydrogen nuclear magnetic resonance spectrometry ((1)H-NMR). The functional group measurements indicated that HRP incubation did not reduce the sulfonic group content. However, it decreased the phenolic and methoxyl group contents. As the phenolic group content decreased, M w increased as a power function. The polymerization was proposed to involve the random coupling of phenoxy radical intermediates. The radicals coupled with each other to form different inter-unit linkages, most of which were the β-O-4' type, as the (1)H-NMR spectra indicated. Moreover, the HRP/H2O2 incubation induced a significant improvement in the adsorption and dispersion properties of LSs. Therefore, the HRP/H2O2 incubation is a promising approach for industrial applications of LSs.

Lignosulfonate To Enhance Enzymatic Saccharification of Lignocelluloses: Role of Molecular Weight and Substrate Lignin

This study conducted an investigation of the effect of lignosulfonate (LS) on enzymatic saccharification of lignocelluloses. Two commercial LSs and one laboratory sulfonated kraft lignin were applied to Whatman paper, dilute acid and SPORL (sulfite pretreatment to overcome recalcitrance of lignocelluloses) pretreated aspen, and kraft alkaline and SPORL pretreated lodgepole pine. All three lignin samples inhibited cellulose saccharification of Whatman paper, but enhanced the saccharification of the four lignocellulosic substrates. The level of enhancement was related to the molecular weight and degree of sulfonation of the lignin as well as the substrate lignin structure. When different molecular weight (MW) fractions of one commercial LS (SXP), generated from sulfite pulping of hardwood, were applied to the Whatman paper, the large MW fraction (SXP1) with the lowest degree of sulfonation inhibited cellulose saccharification while the intermediate (SXP2) and smallest (SXP3) MW fractions enhanced saccharification. All MW fractions enhanced saccharification of the four lignocellulosic substrates with maximal enhancement by the smallest MW fraction, SXP3. The enhancement was most significant for the kraft lodgepole pine substrate and least significant for the SPORL pretreated lodgepole pine using all three LS and SXP fractions. The results suggest that LS acts as a surfactant to enhance pure cellullose saccharification. When LS is applied to lignocelluloses, it acts as a surfactant to block bound lignin from binding cellulase nonproductively leading to enhanced saccharification.

Evaluating the performance of sulfonated Kraft lignin agent as corrosion inhibitor for iron-based materials in water distribution systems

The effectiveness of sulfonated Kraft lignin (LS) as corrosion inhibition material of steel bar grade 60 (ASTM A615) in water distribution systems was studied using potentiodynamic polarization and electrochemical impedance methods. LS were evaluated primarily for iron-based materials in water distribution systems. The experiments were performed on different solutions which simulated internal conditions of water distribution pipelines without or with different corrosion inhibitors. Potentiodynamic polarization and electrochemical impedance were used to evaluate the iron-based material's corrosion resistance under these conditions, and linear polarization resistance (LPR) tests were used to compare the efficiency of the corrosion inhibitor. The potentiodynamic polarization studies showed a reduction in the pitting potential to more noble potential for protected corrosion cell. Consistently, the electrochemical impedance spectroscopy tests showed an increase in the corrosion resistance for iron-based material treated by sulfonated lignin. Based on the potentiodynamic polarization studies and electrochemical impedance spectroscopy tests, the LS optimal dosage was found to be 0.3–0.4mg/L. The conducted polarization resistance tests showed a decrease in corrosion rates of LS treated iron. This study showed that LS provided increased protection for iron-based materials in water distribution pipelines by inhibiting corrosion.

Isoconversional kinetic analysis of novolac-type lignophenolic resins cure

Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger–Akahira–Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.

Inhibition of Lysozyme Fibrillation by Natural and Synthetic Melanins

Amyloidogenesis, a multistep process in which protein mis‐folding results in the formation of aggregates with cross beta sheet structures, is associated with more than 20 diseases including diabetes, AL amyloidosis, Alzheimer's disease, and prion diseases. Hence, there is an ongoing interest in the development of drugs that inhibit amyloid formation or deposition. In this study, we tested the ability of natural and synthetic polyketides to inhibit lysozyme fibrillation in vitro. Solutions of lysozyme (Hen egg, 20 mg/mL) were incubated at 58°C in 20 mM glycine HCl buffer at 58°C for 8 days in the presence of one of the following compounds (concentration tested): 1. Kraft lignin (125 μg/mL), 2. sulfonated Kraft lignin (190 μg/mL), 3. allomelanin extracted from Echinacea purpurea (210 μg/mL), 4. ES‐EM (166 μg/mL), 5. ES‐CAM (190 μg/mL), 6. C11 (130 μg/mL), or 7. C12 (150 μg/mL). Compounds 4–7 are synthetic melanins obtained From BioActive Polymers.com, (La Grange Park, Illinois, 60526). The incubation mixtures were sampled repeatedly and the kinetics of lysozyme fibrillation were evaluated by Thioflavin T fluorescence, native PAGE, and fluorescence and dark field microscopy. Compounds 6, 4, 3, and 7 inhibited the development of THT fluorescence to levels that were 16%, 42%, 52%, and 61%, respectively of the untreated control mixtures. PAGE analysis of the time points taken during the incubation containing C11 showed that this compound decreased the generation of lysozyme oligomers during the first 48 hours of incubation and delayed the progression of the assembly of lysozyme monomers and oligomers into lysozyme fibers and aggregates. The data suggests that natural and synthetic melanins may be of therapeutic value as fibrillogenesis inhibitors.[Supported in part by a gift from the Charles and Lee Finkl Amyloidosis Foundation]

Lignins for phenol replacement in novolac‐type phenolic formulations. II. Flexural and compressive mechanical properties

AbstractSeveral hexamethylenetetraamine‐cured novolac‐type lignophenolic resins have been subjected to mechanical analysis to check the influence of the addition of different types of lignins (kraft pine lignin, soda/anthraquinone flax lignin, and sulfonated kraft lignin from mixed softwoods) and the influence of different phenol substitution levels. Both flexural and compression tests have been performed to evaluate the influence of the curing temperature and pressure. The results have been compared with those from a commercial novolac system. Flexural tests show that lignin incorporation leads to systems with increased rigidity, whereas up to 82% of the maximum strength can be retained with respect to a commercial phenolic (phenol–formaldehyde) at a 45 wt % substitution degree. Compression analyses show that modified prepolymers are not significantly affected by the presence of lignin at a medium curing pressure (150 bar), but their deformability results considerably increase at high curing pressures (400 or 600 bar). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Flocculation of papermaking fines by poly(ethylene oxide) and various cofactors: Effects of PEO entanglement, salt and fines properties

Papermaking fines are small pulp fiber fragments, which improve paper properties, such as paper strength and optical properties. They can be retained in a sheet of paper as fines aggregates or by deposition on fibers. Here we report on the flocculation of fines by a dual component flocculation system, consisting of poly(ethylene oxide) (PEO) and a cofactor. Previous studies showed that PEO is more effective when freshly dissolved than when well dissolved. This was ascribed to PEO entanglements present in freshly dissolved PEO, which disappear with time, shear or dilution. In this study the efficiencies of flocculation of thermomechanical pulp fines by entangled and disentangled PEO have been compared in the presence of different cofactors: a carboxylated phenolic resin (CPR), tannic acid (TA) and a sulfonated kraft lignin (SKL). The results support previous studies, showing that the state of entanglement of PEO has a significant effect on fines flocculation. In addition, we found that different cofactors affect disentangled PEO differently in response to salt addition and fines properties. When PEO was entangled, these cofactors caused the same high flocculation rate and the effect of the particle properties was negligible. When PEO was disentangled, the fines flocculation efficiency decreased to different levels for various cofactors, showing that CPR was superior to TA and SKL. The fibrillar fines and chunky fines were also flocculated at different rates by disentangled PEO/CPR, indicating the influence of particle properties. Adding salt prior to the cofactor and disentangled PEO improved the flocculation rate to the same level as entangled PEO at a given dosage when CPR was used as a cofactor.

Coacervate complex formation between cationic polyacrylamide and anionic sulfonated kraft lignin

Polyelectrolyte complex formation (PEC) is a common phenomenon occurring when positively charged polymers react with anionic polyelectrolytes and other anionic substances. Our interest is in papermaking, where cationic polyelectrolytes are used as retention aids (flocculants) added to papermaking suspensions, which contain various dissolved anionic substances. In general, there are three types of polyelectrolyte complexes: soluble, colloidal and coacervate complexes, of which the latter two phase-separate. The formation of each individual type of complex depends on the chemical and physical properties of the two oppositely charged polyelectrolytes. The focus of this study is on the formation of the coacervate complex between various cationic polyacrylamides (cPAM) and anionic sulfonated kraft lignin (SKL). The reaction between cPAM and SKL was found to be nearly stoichiometric. The amount of insoluble PEC (i.e. colloidal and coacervate complex) was found to be constant for a given cPAM charge; however, the ratio between colloidal and coacervate complex varied depending on the molecular weight of cPAM used. The formation of the coacervate complex increased with increasing molecular weight of cPAM while low molecular weight cPAM formed predominantly colloidal complexes with SKL.

Stability of ground and precipitated CaCO 3 suspensions in the presence of polyethylene oxide and kraft lignin

The behavior of two commercial types of ground and precipitated CaCO 3 pigments differ because of different surface characteristics. Ground CaCO 3 is treated with a dispersant and, in the absence of salt, it forms a stable suspension because of electrical double layer repulsion. Its stability and surface charge are not affected by polyethylene oxide or sulfonated kraft lignin, added separately or in combination. Destabilization takes place in the presence of a sufficient amount of salt owing to the compression of double layers. However in a narrow region of salt concentration the polyethylene oxide improves stability by an electrosterical effect. In contrast, precipitated CaCO 3 aggregates at fast rates, even in the absence of salt, because of insufficient double layer repulsion. Its behavior is not affected by polyethylene oxide addition, but the presence of kraft lignin results in stabilizing the suspension by adsorbing on CaCO 3 particles, thus increasing the negative surface charge and, consequently, the electrostatic repulsion.

Effect of a cofactor on the polymer bridging of latex particles to glass by polyethylene oxide

Polymer bridging by high molecular weight polyethylene oxide (PEO) is enhanced by a cofactor, usually a low molecular weight phenolic compound. PEO-cofactor systems are widely used in papermaking as a so-called retention aid. In this study the effects of one particular cofactor, sulfonated kraft lignin (SKL), on polymer bridging by PEO, was investigated. The deposition of latex spheres on a glass surface coated by PEO was observed with the impinging jet technique. The deposition kinetics were mainly controlled by electrostatics, since both the latex particles and the PEO-SKL complexes formed at the surface are negatively charged. The detachment kinetics were strongly affected by SKL as the fraction of very strongly bound particles increased. At SKL concentrations above 1 mg l −1 it took longer for the weakly bound particles to detach. These studies show that SKL strengthens the PEO bridge between latex and glass.

Studies on water solubilization of lignin (2).

In the previous paper, the authors have reported the water solubilization of kraft lignin by various kinds of oxidizing catalysts-sodium sulfite combination treatment. However, because of the toxic moieties from oxidizing catalysts, those processes might be very difficult to be feasible. In this study, ferrous (or ferric) compound-sodium persulfate-sodium sulfite combination which is completely free from toxicity, was found to be a hopeful system for the water solubilization of kraft lignin. Dispersing properties of sulfonated kraft lignin thus prepared, were also evaluated in comparison with those of lignin sulfonate.