Shoujuan Wang

Water soluble kraft lignin–acrylic acid copolymer: synthesis and characterization

Lignin produced in the kraft pulping process is insoluble in water at neutral pH, which limits its application in industry. In this paper, kraft lignin (KL) was copolymerized with acrylic acid (AA) in an aqueous solution to produce a water soluble lignin-based copolymer. The copolymerization was carried out using K2S2O8–Na2S2O3 as the initiator under alkaline aqueous conditions, and the influence of the reaction parameters, i.e. initiator dosage, reaction time and temperature, mole ratio of acrylic acid to lignin and reaction concentration, on resultant lignin copolymers were investigated. The mechanism of copolymerization of kraft lignin with acrylic acid was also discussed in this work. The resultant lignin copolymer was characterized by Fourier Transform Infrared (FTIR) spectrophotometry and Nuclear Magnetic Resonance (NMR). The successful copolymerization of AA and KL was confirmed by the new absorption peak of carboxyl anions in the FTIR spectrum and new peaks in the 1H-NMR spectrum. At optimal conditions, the charge density and molecular weight of lignin copolymer reached 1.86 meq g−1 and 46 421 g mol−1, respectively, and the solubility of lignin after reaction was increased from 1.80 g L−1 to 100 g L−1 at neutral pH.

Production of cationic xylan-METAC copolymer as a flocculant for textile industry.

Xylan is a part of hemicelluloses of woody materials and can be converted to value-added products such as flocculants for the textile industry. To assess the production of flocculants from hemicelluloses of woody materials, xylan was selected as a model and rendered cationic via copolymerization. In this study, the copolymerization reaction of xylan and [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) was optimized. The optimum parameters were 3mol/mol METAC/xylose, 3h reaction time, 80°C reaction temperature, pH 7 and 25g/L xylan concentration. The copolymer was characterized by a charge density analyzer, viscometer, gel permeation chromatography (GPC), light scattering instrument, Fourier transform infrared spectroscopy (FTIR) and an elemental analyzer. The application of the cationic xylan copolymer as a flocculant to decolorize the simulated reactive orange 16 azo-dye wastewater was evaluated. The results confirmed that, by having 160mg/L xylan-METAC concentration in the dye solution with the concentration of 100mg/L, 97.8% of dye could be removed.

Cationic xylan–METAC copolymer as a flocculant for clay suspensions

The work presented herein focused on the flocculation of kaolin and bentonite clay suspensions using cationic copolymerized xylan under controlled conditions. Cationic xylan-2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC) copolymers were produced under the conditions of pH 7, 3 h reaction time, 80 °C and 2 or 3 mol mol−1 METAC/xylan ratio. The charge densities of the produced cationic xylan copolymers, CMX1, and CMX2 were +1.8 and +2.4 meq. g−1 while their molecular weights were 88 986 and 102 545 g mol−1, respectively. The attachment of METAC to xylan was confirmed by elemental and gel permeation chromatography analyses. CMX2 was a more efficient flocculant than CMX1 as it adsorbed and removed more clay particles from the clay suspensions. CMX2 also changed the zeta potential and turbidity of the clay suspensions more remarkably than CMX1, which was attributed to its higher charge density and molecular weight. CMX2 was more efficient in flocculating bentonite than kaolin suspensions. The presence of CMX on the clay particles was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) analysis. The size of kaolin particles increased from 3.2 to 9.8 and 11.7 μm, and that of bentonite particles from 5.8 to 13.8 and 15.5 μm by having 16 mg L−1 of CMX1 and CMX2 copolymers in the clay suspensions, respectively. The reversibility of the flocculation process was assessed with a photometric dispersion analyzer. Furthermore, unmodified xylan was ineffective in flocculating clay particles.

Novel pathway to produce high molecular weight kraft lignin–acrylic acid polymers in acidic suspension systems

Kraft lignin (KL) produced in kraft pulping process has a low molecular weight and solubility, which limits its application in industry. For the first time, KL was polymerized with acrylic acid (AA) in an acidic aqueous suspension system to produce a water soluble lignin–AA polymer with a high molecular weight in this work. The polymerization reaction was carried out using K2S2O8 as an initiator, and the influence of reaction conditions on the carboxylate group content and molecular weight of resultant lignin polymers was systematically investigated. The mechanism of polymerization of KL and AA was discussed fundamentally. The resulting lignin–AA polymer was characterized by Fourier Transform Infrared spectrophotometry (FTIR), proton nuclear magnetic resonance (1H-NMR) and elemental analyses. The results showed that the phenolic hydroxyl group (Ph-OH) content of KL promoted the polymerization under an acidic environment. Under the conditions of 1.5 wt% of initiator, 3.5 of pH, 10.0 of AA/lignin molar ratio, 0.15 mol L−1 of lignin concentration, 3 h and 80 °C, the carboxylate group content and the molecular weight of the polymer were 7.37 mmol g−1 and 7.4 × 105 g mol−1, respectively. The lignin–AA polymer was water soluble at a 10 g L−1 concentration and a pH higher than 4.5. Furthermore, the flocculation performance of lignin–AA polymer in an aluminium oxide suspension was evaluated. Compared with polyAA, the lignin–AA polymer was a more efficient flocculant for aluminium oxide suspension, which shows its potential to be used as a green flocculant in industry.

Preparation and Characterization of Softwood Kraft Lignin Copolymers as a Paper Strength Additive

Softwood kraft lignin is a renewable type of woody material that can be converted to value-added products, for example, as a paper strength additive in the paper industry. In this study, the monomers of methacryloxyethyltrimethyl ammonium chloride (DMC), acrylic acid (AA), and acrylamide (AM) were grafted on softwood kraft lignin (SKL) to prepare three different SKL copolymers. Fourier-transform infrared, proton nuclear magnetic resonance, charge density, elemental, and molecular weight analyses confirmed that the monomers were successfully grafted onto SKL. The grafting rates of SKL-DMC, SKL-AA, and SKL-AM copolymers were 80.35%, 82.70%, and 79.48%, respectively. The application of SKL copolymers as a paper additive for enhancing paper physical properties was studied. The results indicated that at a 2 wt % dosage of SKL copolymers, the increase in the physical properties of paper is maximum.

Preparation and Application of Phosphorylated Xylan as a Flocculant for Cationic Ethyl Violet Dye

In this study, phosphorylated birchwood xylan was produced under alkali conditions using trisodium trimetaphosphate. Three single-factor experiments were used to explore the influences of time, temperature, and the molar ratio of trisodium trimetaphosphate to xylan on the degree of substitution (DS) and charge density of xylan. The response surface methodology was used to explore the interaction of these three factors. Phosphorylated xylan with a maximum DS of 0.79 and a charge density of −3.40 mmol/g was produced under the optimal conditions of 80 °C, 4 h, and a molar ratio of xylan/sodium trimetaphosphate (STMP) of 1/3. Fourier transform infrared (FTIR), ascorbic acid method analyses, and inductively coupled plasma–atomic emission spectrometer (ICP-AES) analyses confirmed that the phosphate groups were successfully attached to xylan. Thermogravimetric analysis confirmed that phosphorylated xylan was less stable than birchwood xylan. Furthermore, the phosphorylated xylan was applied as a flocculant for removing ethyl violet dye from a simulated dye solution. The results indicated that more than 95% of the dye was removed from the solution. The theoretical and experimental values of charge neutralization for the dye removal were close to one another, confirming that charge neutralization was the main mechanism for the interaction of dye and phosphorylated xylan. The impacts of salts on the flocculation efficiency of phosphorylated xylan were also analyzed.

Cationic High Molecular Weight Lignin Polymer: A Flocculant for the Removal of Anionic Azo-Dyes from Simulated Wastewater

The presence of dyes in wastewater effluents made from the textile industry is a major environmental problem due to their complex structure and poor biodegradability. In this study, a cationic lignin polymer was synthesized via the free radical polymerization of lignin with [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride (METAC) and used to remove anionic azo-dyes (reactive black 5, RB5, and reactive orange 16, RO16) from simulated wastewater. The effects of pH, salt, and concentration of dyes, as well as the charge density and molecular weight of lignin-METAC polymer on dye removal were examined. Results demonstrated that lignin-METAC was an effective flocculant for the removal of dye via charge neutralization and bridging mechanisms. The dye removal efficiency of lignin-METAC polymer was independent of pH. The dosage of the lignin polymer required for reaching the maximum removal had a linear relationship with the dye concentration. The presence of inorganic salts including NaCl, NaNO3, and Na2SO4 had a marginal effect on the dye removal. Under the optimized conditions, greater than 98% of RB5 and 94% of RO16 were removed at lignin-METAC concentrations of 120 mg/L and 105 mg/L in the dye solutions, respectively.

Preparation and Application of Carboxymethylated Xylan as a Flocculant for Ethyl Violet Dye in Aqueous Systems

Hemicellulose is one of the most abundant renewable biopolymers on earth. Xylan is the main hemicellulose of hardwood species, but it is under utilized. In this work, carboxymethylated xylan (CMX) with the maximum degree of substitution (DS) of 0.95 and charge density of −4.57 mmol/g was produced. Fourier transmittance infrared (FTIR) and nuclear magnetic resonance (NMR) analyses confirmed the success of carboxylemthylation reaction. Thermogravimetric analysis confirmed that CMX was less thermo-stable than xylan. Furthermore, the CMX was applied as a coagulant for removing cationic ethyl violet dye from a simulated dye solution. The results showed that more than 95% of dye was removed from the solution. The theoretical and experimental values for the removal of the dye were close confirming that the charge neutralization was the main mechanism for interaction of dye and CMX. The impact of salt in the coagulation efficiency of CMX was also analyzed.

Preparation and application of sulfated xylan as a flocculant for dye solution

The main purpose of this study is to explore the sulfation of xylan to produce an anionic flocculant, sulfated xylan, for removing ethyl violet dye from simulated dye solutions. In this work, xylan was sulfated with chlorosulfonic acid in N, N‐dimethylformamide solvent and the reaction conditions were optimized using a response surface methodology. It was observed that the maximum degree of substitution of 1.1 was obtained for sulfated xylan under the conditions of 3.71 chlorosulfonic acid/xylan molar ratio, 70°C and 7 h reaction time. The resulting sulfated xylan had a charge density of −3.12 mmol/g and molecular weight (Mw) of 22,300 g/mol. Furthermore, elemental and thermogravimetric analyses, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (1H‐NMR) confirmed the sulfation of xylan. The application of sulfated xylan as a flocculant for decolorizing the simulated ethyl violet dye wastewater was studied. The results indicated that 97% of dye was removed from 50 mg/L dye solution at the sulfated concentration of 175 mg/L and pH 9, but unmodified xylan was ineffective in flocculating and removing dye segments.