Impact of Lignin Content on the Properties of Hemicellulose Hydrogels

Thermosensitive TMPO-oxidized lignocellulose/cationic agarose hydrogel loaded with deferasirox nanoparticles for photothermal therapy in melanoma

Deferasirox (DFX) is an iron-chelating agent effective in treating various kinds of cancers, which inhibits iron metabolism in cancer cells. The recent study aimed to prepare an injectable thermosensitive hydrogel based on lignocellulose and agarose containing deferasirox-loaded polypyrrole nanoparticles for local drug delivery in a combined chemo-photothermal therapy by laser light irradiation. Polypyrrole nanoparticles containing DFX were made by the emulsification method and optimized. Thermosensitive hydrogels were prepared by quaternary ammonium substituted agarose and TMPO-oxidized lignocellulose at different ratios, and the optimal hydrogel was selected based on gelation time, gelation temperature, and injectability. DFX- loaded polypyrrole nanoparticles were then added to the hydrogel, and the drug release, rheology test, injectability, degradation, and swelling percent, as well as cytotoxicity, and photothermal properties, were studied on B16F10, human melanoma cells. The hydrogel with 2 % anionic lignocellulose and 0.5 % cationic agarose showed the shortest gelation time and the highest mechanical strength. It transferred from a liquid state at 4 °C into a semisolid form at 37 °C with a gelation time of 10.3 min. The nanoparticles loaded in hydrogel showed dose-dependent cytotoxicity. The cytotoxic dose of the drug was reduced by laser light irradiation.

High-Performance Hydrogel Adsorbent Based on Cellulose, Hemicellulose, and Lignin for Copper(II) Ion Removal

Cellulose, hemicellulose, and lignin are three kinds of biopolymer in lignocellulosic biomass, and the utilization of the three biopolymers to synthesize hydrogel adsorbent could protect the environment and enhance the economic value of the biomass. A novel hydrogel adsorbent was prepared using cellulose, lignin, and hemicellulose of wheat straw by a one-pot method, and the adsorbent showed excellent adsorption performance for copper(II) ions. Scanning electron microscopy and Fourier transform infrared spectroscopy analysis showed that the prepared straw-biopolymer-based hydrogel had porous structure, and cellulose fibrils had crosslinked with lignin and hemicellulose by poly(acrylic acid) chains. The effects of contact time, initial concentration, and temperature on the copper(II) ion removal using the prepared hydrogels were investigated, and the obtained results indicated that the adsorption kinetics conformed to the pseudo-second-order and Elovich equation models and the adsorption isotherm was in accord with the Freundlich model. The adsorption thermodynamics study indicated that the adsorption process was spontaneous and accompanied by heat. X-ray photoelectron spectroscopy analysis revealed that the adsorption behavior resulted from ion exchange. The prepared hydrogel based on cellulose, hemicellulose, and lignin could be used for water treatment and soil remediation because of its high performances of excellent heavy metal ion removal and water retention.

Bio-Based Hydrogels With Ion Exchange Properties Applied to Remove Cu(II), Cr(VI), and As(V) Ions From Water

Hydrogels with ion exchange properties were synthesized from compounds derived from wood biopolymer hemicellulose and from commercial vinyl monomers to be tested as active materials for the removal of Cu(II), Cr(VI), and As(V) ions. The hemicellulose O-acetyl galactoglucomannan (GGM) was used as the precursor material, and through a transesterification reaction, GGM was converted into a macromonomer GGM–glycidyl methacrylate (GGM-GMA). Subsequently, the GGM-GMA macromonomer, containing more than one methacrylate group, was used as a crosslinking agent in the synthesis of hydrogels through free-radical polymerization reactions in combination with a 2-acrylamido-2-methyl-1-propanesulfonic acid monomer to produce a cation exchange hydrogel. Also, (3-acrylamidopropyl)trimethylammonium chloride monomer was applied together with the GGM-GMA to form hydrogels that can be used as anion exchange hydrogel. The hydrogels were characterized by Fourier transform-infrared (FT-IR), ¹H-NMR spectroscopy, and thermogravimetric analysis (TGA), as well as derivative thermogravimetry (DTG). The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM) analysis with X-ray microanalysis energy-dispersive spectroscopy (EDS). The results obtained regarding the absorption capacity of the Cu(II), Cr(VI), and As(V) ions were studied as a function of the pH value and the initial concentration of the metal ions in the solutions. Absorption was carried out in consecutive batches, and it was found that the poly(GGM-GMA/AMPSH) hydrogel reached an absorption capacity of 90 mg g^–1 for Cu(II). The poly(GGM-GMA/APTACl) hydrogel reached values of 69 and 60 mg g^–1 for Cr(VI) and As(V) oxyanions, respectively. Tests with polymer blends (mixtures of anionic and cationic hydrogels) were also carried out to remove Cu(II), Cr(VI), and As(V) ions from multi-ionic solutions, obtaining satisfactory results.

On the interaction of softwood hemicellulose with cellulose surfaces in relation to molecular structure and physicochemical properties of hemicellulose

The substantial part of the water-soluble hemicellulose fraction, obtained when processing cellulose to produce paper and other products, has so far been discarded. The aim of this work is to reveal the interfacial properties of softwood hemicellulose (galactoglucomannan, GGM) in relation to their molecular and solution structure. In this study the sugar composition of GGM was characterised by chemical analysis as well as 1D and 2D NMR spectroscopy. Previously it has been demonstrated that hemicellulose has high affinity towards cellulose and has the ability to alter the properties of cellulose based products. This study is focused on the interactions between hemicellulose and the cellulose surface. Therefore, adsorption to hydrophobized silica and cellulose surfaces of two softwood hemicellulose samples and structurally similar seed hemicelluloses (galactomannans, GMs) was studied with ellipsometry, QCM-D and neutron reflectometry. Aqueous solutions of all samples were characterized with light scattering to determine how the degree of side-group substitution and molecular weight affect the conformation and aggregation of these polymers in the bulk. In addition, hemicellulose samples were studied with SAXS to investigate backbone flexibility. Light scattering results indicated that GM polymers form globular particles while GGMs were found to form rod-like aggregates in the solution. The polysaccharides exhibit higher adsorption to cellulose than on hydrophobic surfaces. A clear correlation between the increase in molecular weight of polysaccharides and increasing adsorbed amount on cellulose was observed, while the adsorbed amount on the hydrophobic surface was fairly independent of the molecular weight. The obtained layer thickness was compared with bulk scattering data and the results indicated flat conformation of the polysaccharides on the surface.

Hemicellulose Recovery from Spent-Sulfite-Liquor: Lignin Removal by Adsorption to Resins for Improvement of the Ultrafiltration Process

In this work, three polymeric resins were examined as alternatives for the separation of hemicellulose and lignin. The aim was to remove the lignin from spent-sulfite-liquor (SSL) prior to ultrafiltration, producing a hemicellulose-rich retentate with high purity, and increase the capacity of the membrane filtration. The lignin in the SSL was sulfonated; thus, two of the resins were anion exchangers and 1 was hydrophobic. The data from the equilibrium studies and adsorption kinetics were fitted to established models, and the results were interpreted based on these observations. The strongly basic anion exchanger performed best with regard to lignin removal. The adsorption followed the Sips isotherm, indicating that the process was cooperative with chemisorption as the main reaction between the adsorbate and adsorbent based on the kinetics. Regeneration of the adsorbent was also possible, wherein 100 g/L NaCl was sufficient to recover 98% of the lignin. The lignin removal had a positive effect on the ultrafiltration process, in which the flux increased by 38% and the extent of separation between the hemicellulose and lignin rose from 17% to 59%.

Analysis of membrane fouling by Brunauer-Emmet-Teller nitrogen adsorption/desorption technique

Membrane fouling is the major factor limiting the wider applicability of the membrane-based technologies in water treatment and in separation and purification processes of biorefineries, pulp and paper industry, food industry and other sectors. Endeavors to prevent and minimize fouling requires a deep understanding on the fouling mechanisms and their relative effects. In this study, Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique was applied to get an insight into pore-level membrane fouling phenomena occurring in ultrafiltration of wood-based streams. The fouling of commercial polysulfone and polyethersulfone membranes by black liquor, thermomechanical pulping process water and pressurized hot-water extract was investigated with BET analysis, infrared spectroscopy, contact angle analysis and pure water permeability measurements. Particular emphasis was paid to the applicability of BET for membrane fouling characterization. The formation of a fouling layer was detected as an increase in cumulative pore volumes and pore areas in the meso-pores region. Pore blocking was seen as disappearance of meso-pores and micro-pores. The results indicate that the presented approach of using BET analysis combined with IR spectroscopy can provide complementary information revealing both the structure of fouling layer and the chemical nature of foulants.

Pretreatment for biorefineries: a review of common methods for efficient utilisation of lignocellulosic materials

The implementation of biorefineries based on lignocellulosic materials as an alternative to fossil-based refineries calls for efficient methods for fractionation and recovery of the products. The focus for the biorefinery concept for utilisation of biomass has shifted, from design of more or less energy-driven biorefineries, to much more versatile facilities where chemicals and energy carriers can be produced. The sugar-based biorefinery platform requires pretreatment of lignocellulosic materials, which can be very recalcitrant, to improve further processing through enzymatic hydrolysis, and for other downstream unit operations. This review summarises the development in the field of pretreatment (and to some extent, of fractionation) of various lignocellulosic materials. The number of publications indicates that biomass pretreatment plays a very important role for the biorefinery concept to be realised in full scale. The traditional pretreatment methods, for example, steam pretreatment (explosion), organosolv and hydrothermal treatment are covered in the review. In addition, the rapidly increasing interest for chemical treatment employing ionic liquids and deep-eutectic solvents are discussed and reviewed. It can be concluded that the huge variation of lignocellulosic materials makes it difficult to find a general process design for a biorefinery. Therefore, it is difficult to define "the best pretreatment" method. In the end, this depends on the proposed application, and any recommendation of a suitable pretreatment method must be based on a thorough techno-economic evaluation.

Galactoglucomannan Recovery with Hydrophilic and Hydrophobic Membranes: Process Performance and Cost Estimations

In this study, we compared the GR51PP (hydrophobic/polysulfone) membrane with a series of hydrophilic (regenerated cellulose) membranes with the aim of increasing the retention of products and decreasing membrane fouling. The raw material used was a sodium-based spent sulfite liquor from the sulfite pulping process of spruce and pine. The results show that the hydrophilic membranes were superior to the hydrophobic membranes in terms of higher fluxes (up to twice the magnitude), higher product retentions and less fouling (up to five times lower fouling). The fouling was probably caused by pore blocking as observed in earlier studies. However, the hydrophilic membranes had a lower affinity for lignin, which was indicated by the lower retention and fouling. This also resulted in a separation degree, which was higher compared with the hydrophobic membrane, thus yielding a higher galactoglucomannan (GGM) purity. 2D HSQC NMR results show that no major structural differences were present in the hydrophilic and hydrophobic retentates. A techno-economical evaluation resulted in the RC70PP being chosen as the most cost-efficient membrane in terms of flux and product recovery.