Yuxia Pang

Sulfonation of Alkali Lignin and Its Potential Use in Dispersant for Cement

Sulfonation modification of alkali lignin from wheat straw pulping spent liquid, carried out under normal pressure and medium temperature, was investigated, and the properties of the resulting sulfonated lignin were characterized. It was found that condensed lignin was degraded into lignin fragments with lower molecular weight by oxidation reaction, producing more active sites to react with formaldehyde, consequently forming more active hydroxymethyl groups for sulfonation. Therefore, it is feasible to carry out the sulfonation of alkali lignin under conditions of normal pressure and medium temperature. As higher contents of sulfonic group were introduced, sulfonated lignin with 1.49 mmol/g of sulfonation degree exhibits 96.9% of solubility at neutral aqueous solution and good surface activity. Compared to commercial lignosulfonate, sulfonated lignin produced by the present work contributes higher adsorption amount and zeta potential to cement particles, and hence shows better dispersion effect to the cement matrix.

Physicochemical Properties of Calcium Lignosulfonate with Different Molecular Weights as Dispersant in Aqueous Suspension

Five purified calcium lignosulfonate (CL) fractions with different molecular weights were obtained by fractionation using ultrafiltration and dialysis. The influence of molecular weight on their physicochemical properties was investigated by determining the properties of five fractions. TEM and ESEM imaging indicated that CL has a globular structure to form locally regular colloidal assemblies with the diameter of approximately 200 ∼ 300 nm. Fraction3 (M w is 7621) with the molecular weight of 5,000–l0,000 has more sulfonic and carboxyl group, so the highest zeta potential (−36 mV) can be charged on the TiO2 particles. With the increase of molecular weight, the hydrophobicity and surface activity of CL in aqueous solution increase, so Fraction5 (M w is 21646) which molecular weight is more than 30000 has the biggest adsorption amount. The adsorption characteristic of CL on solid-water interface have great impact on the dispersive properties of TiO2 particle in aqueous solution and the higher adsorption capacity is helpful to improve the dispersive ability of CL. On the other hand, the surface charge of TiO2 particle absorbing CL is another important factor to the dispersive ability of CL. Furthermore, when the CL concentration in TiO2 suspension is less than 4 mg/mL, Fraction3 has the best dispersive ability because the electrostatic repulsion effect is controlling factor. The dispersive ability of CL increases with the increase of molecular weight when the CL concentration in TiO2 suspension is more than 4 mg/mL, so Fraction5 has the best dispersive ability owing to the steric hindrance effect.

Effect of straight-chain alcohols on the physicochemical properties of calcium lignosulfonate

Lignosulfonate is an anionic surfactant from pulp processing industries. Alcohols are often used as cosurfactants in the application of surfactant. The improvement of straight-chain alcohols with different alkyl chain lengths as cosurfactant on the physicochemical properties of calcium lignosulfonate (CL) aqueous solution has been investigated. The results indicate that small amounts of straight-chain alcohols with longer alkyl chains are helpful in improving the surface activity of CL, especially when the number of carbon atoms in alcohols is 10 or larger. The adsorption amount of CL solutions with additives of longer chain alcohols on TiO(2) particles increases greatly, and the zeta potential of TiO(2) particles adsorbing CL rises significantly. It can be concluded that there is a cooperative effect of the longer chain alcohols on lignosulfonate to form a tighter adsorption layer at the interface. The steric hindrance increases with the increasing amount of adsorption, and the static repulsive force increases with the increasing zeta potential. Therefore, the effect of CL on the stability of the TiO(2) suspension is enhanced dramatically by addition of longer chain alcohols. This understanding can lead to further development in expanding the functionalities of the lignosulfonate through manipulation of the adsorption capacity of CL on solid particles and enhance the dispersive ability of CL on solid suspensions by adding longer straight-chain alcohols.

Improving enzymatic hydrolysis of lignocellulosic substrates with pre-hydrolysates by adding cetyltrimethylammonium bromide to neutralize lignosulfonate.

Two pretreatment methods to overcome recalcitrance of lignocelluloses, sulfite pretreatment (SPORL) and dilute acid (DA), were conducted to pretreat softwood masson pine and hardwood eucalyptus for enzymatic hydrolysis. In the presence of corresponding pre-hydrolysates, adding moderate cetyltrimethylammonium bromide (CTAB) could enhance the enzymatic hydrolysis of the SPORL-pretreated substrates, but had no enhancement for the DA-pretreated substrates. The results showed that sodium lignosulfonate (SL) in pre-hydrolysates and CTAB together had a strong enhancement on the enzymatic hydrolysis of lignocelluloses. The compound of commercial lignosulfonate SXSL and CTAB (SXSL-CTAB) could enhance the substrate enzymatic digestibility (SED) of SPORL-pretreated masson pine from 27.1% to 71.0%, and that of DA-pretreated eucalyptus from 37.6% to 67.9%. The mechanism that CTAB increased the adsorption of SL on lignin to form more effective steric hindrance and reduced the non-productive adsorption of cellulase on lignin by neutralizing the negative charge of SL was proposed.

Depolymerization of lignin by microwave-assisted methylation of benzylic alcohols.

A new two-step lignin depolymerization strategy was developed, in which the benzylic alcohols in lignin was methylated under microwave irradiation, followed by a hydrogenolysis for the cleavage of βO4 bond with Pd/C as the catalyst. The results showed that an efficient and selective catalytic methylation of benzylic alcohols was achieved with various lignin model compounds, and the acidic environment promoted the methylation of benzylic alcohol. Methylation of benzylic alcohol increased the βO4 bond cleavage rate by 55.9%, and improved products selectivity. Preliminary study of lignin depolymerization illustrated that methylation pretreatment of benzylic alcohols facilitated lignin depolymerization to produce aromatic monomers and reduced the oxygen content of aromatic monomers.

Improving Rheology and Enzymatic Hydrolysis of High-Solid Corncob Slurries by Adding Lignosulfonate and Long-Chain Fatty Alcohols

The effects of lignosulfonate (SXSL) and long-chain fatty alcohols (LFAs) on the rheology and enzymatic hydrolysis of high-solid corncob slurries were investigated. The application of 2.5% (w/w) SXSL increased the substrate enzymatic digestibility (SED) of high-solid corncob slurries at 72 h from 31.7 to 54.0%, but meanwhile it increased the slurrys yield stress and complex viscosity to make the slurry difficult to stir and pump. The smallest molecular weight (MW) SXSL fraction had the strongest enhancement on SED. The SXSL fraction with large MW had a negative effect on rheology. n-Octanol (C8) and n-decanol (C10) improved the rheological properties of high-solid slurry and are strong enough to counteract the negative effect of SXSL. Furthermore, C8 and C10 clearly enhanced the enzymatic hydrolysis of high-solid corncob slurries with and without SXSL. A mechanism was proposed to explain the observed negative effect of SXSL and the positive effect of LFAs on the rheological properties.

Using polyvinylpyrrolidone to enhance the enzymatic hydrolysis of lignocelluloses by reducing the cellulase non-productive adsorption on lignin

Polyvinylpyrrolidone (PVP) is an antifouling polymer to resist the adsorption of protein on solid surface. Effects of PVP on the enzymatic hydrolysis of pretreated lignocelluloses and its mechanism were studied. Adding 1g/L of PVP8000, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) was increased from 28.9% to 73.4%, which is stronger than the classic additives, such as PEG, Tween and bovine serum albumin. Compared with PEG4600, the adsorption of PVP8000 on lignin was larger, and the adsorption layer was more stable and hydrophilic. Therefore, PVP8000 reduced 73.1% of the cellulase non-productive adsorption on lignin and enhanced the enzymatic hydrolysis of lignocelluloses greatly.

Enhancing enzymatic hydrolysis of xylan by adding sodium lignosulfonate and long-chain fatty alcohols.

Sodium lignosulfonate (SXSL) and long-chain fatty alcohols (LFAs) could enhance the enzymatic hydrolysis of xylan, and the compound of SXSL and LFAs have synergies on the enzymatic hydrolysis. SXSL shows a strong enhancement in buffer pH range from 4.0 to 6.0. The enhancement increased with the SXSL dosage and the xylanase loading. The cellulose and lignin in corncob substrate could not only adsorb xylanase nonproductively, but also seriously reduce the accessibility of xylanase on xylan to impede the enzymatic hydrolysis of xylan. Cellulase could break the plant cell wall structure of corncob and make additives work better. The xylose yield of corncob at 72h increased from 59.4% to 73.7% by adding the compound of 5g/L SXSL and 0.01% (v/v) n-decanol, which was higher than that without cellulase and additives by 30.7%. Meanwhile, the glucose yield at 72h of corncob increased from 45.8% to 62.3%.

Slow relaxation mode of sodium lignosulfonate in saline solutions

Abstract Sodium lignosulfonate (NaLS) was dissolved in saline solutions, and the dissolving process was examined by a combination of static and dynamic light scattering. When NaLS was dissolved in 1.2 mol l-1 NaCl solution for 24 h and filtered through a 0.45 μm syringe filter, only a fast relaxation mode was observed, which was attributed to the co-diffusion of NaLS molecular ions and counterions. When the concentration of NaCl was below 1.2 mol l-1 or the dissolving time was <24 h, an additional slow relaxation mode (SRM) appeared due to hindered motions of electrostatically interacting chains. Without filtering or filtering followed by rising temperature to 38°C, SRM appeared due to aggregation, which occurred at a position similar to that caused by electrostatic interaction. For poly(sodium styrenesulfonate) (NaPSS) and modified bamboo lignin derivate with open polyelectrolyte structures, 0.1 mol l-1 NaCl was enough to inhibit the electrostatic interaction. For NaLS with a closed polyelectrolyte structure, the SRM could not be removed until the concentration of NaCl reached 1.2 mol l-1. Above observations give insights for the first time into the relationship between the SRM caused by electrostatically interacting chains and the diffusion mode due to NaLS aggregation, and the influence of the closed polyelectrolyte structure on the SRM.

Preparation of Lignin/Sodium Dodecyl Sulfate Composite Nanoparticles and Their Application in Pickering Emulsion Template-Based Microencapsulation

Lignin is a vastly underutilized biomass resource. The preparation of water-dispersed lignin nanoparticles is an effective way to realize the high-value utilization of lignin. However, the currently reported preparation methods of lignin nanoparticles still have some drawbacks, such as the requirement for toxic organic solvent or chemical modification, complicated operation process, and poor dispersibility. Here, lignin/sodium dodecyl sulfate (SDS) composite nanoparticles (LSNPs) with outstanding water dispersibility and a size range of 70-200 nm were facilely prepared via acidifying the mixed basic solution of alkaline lignin and SDS. No harsh chemical was needed. The formation mechanism was systematically studied. Results indicated that the LSNPs were obtained by acid precipitation of the mixed micelles formed by the self-assembly of lignin and SDS. In addition, on the basis of the LSNP-stabilized Pickering emulsions, lignin/polyurea composite microcapsules combining the excellent chemical stability of a synthetic polyurea shell with the fantastic antiphotolysis and antioxidant properties of lignin were successfully prepared.