Synthesis and characterization of super-absorbent hydrogels based on hemicellulose

Fabrications and applications of hemicellulose-based bio-adsorbents

Super adsorbents exhibit great potential to remove pollutants from media or store considerable amounts of water, which may undermine the pressure triggered by environmental pollution and shortage of water resources. Super adsorbents made from biopolymers have been an attractive topic because of biodegradability, renewability and outstanding adsorption capacity. Hemicelluloses are a type of biopolymers very abundant in agricultural, forestry and pulping industrial wastes. Hemicellulose-based bio-adsorbents are thriving because the inherent chemical structures and physical properties of hemicelluloses make themselves easy to be processed into matrix materials applicable in super adsorbents. This review summarizes recent studies in hemicellulose-based bio-adsorbents, i.e. hydrogels and activated carbons, from the perspectives of types, applications, fabrication methods, the elements affecting the adsorption performance and the kinetics of adsorption process, which thus helps to further improve the properties of hemicellulose-based bio-adsorbents and to promote the industrial production and utilization of hemicelluloses and hemicellulose-based bio-adsorbents.

Multifunctional Ginger Nanofiber Hydrogels with Tunable Absorption: The Potential for Advanced Wound Dressing Applications

In this study, ginger residue from juice production was evaluated as a raw material resource for preparation of nanofiber hydrogels with multifunctional properties for advanced wound dressing applications. Alkali treatment was applied to adjust the chemical composition of ginger fibers followed by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation prior to nanofiber isolation. The effect of alkali treatment on hydrogel properties assembled through vacuum filtration without addition of any chemical cross-linker was evaluated. An outstanding absorption ability of 6200% combined with excellent mechanical properties, tensile strength of 2.1 ± 0.2 MPa, elastic modulus of 15.3 ± 0.3 MPa, and elongation at break of 25.1%, was achieved without alkali treatment. Furthermore, the absorption capacity was tunable by applying alkali treatment at different concentrations and by adjusting the hydrogel grammage. Cytocompatibility evaluation of the hydrogels showed no significant effect on human fibroblast proliferation in vitro. Ginger essential oil was used to functionalize the hydrogels by providing antimicrobial activity, furthering their potential as a multifunctional wound dressing.

Hydrogels as potential drug-delivery systems: network design and applications

Hydrogels are 3D crosslinked polymer matrices having a colossal tendency to imbibe water and exhibit swelling under physiological conditions without deformation in their hydrophilic network. Hydrogels being biodegradable and biocompatible, gained consideration due to some unique characteristics: responsiveness to external stimuli (pH, temperature) and swelling in aqueous solutions. Hydrogels offer a promising option for various pharmaceutical and biomedical applications, including tissue-specific drug delivery at a predetermined, controlled rate. This article presents a brief review of the recent and fundamental advances to design hydrogels, the swelling and deswelling mechanism, various crosslinking methods and their use as an intelligent carrier in the pharmaceutical field. Recent applications of hydrogels are also briefly discussed and exemplified.

Biosourced Polysaccharide-Based Superabsorbents

In the last decades, many studies have been conducted on new materials to meet a growing industrial demand and to move scientific research forward. Superabsorbents are good examples of materials that have generated special attention in many fields for their ability to absorb and retain water up to 1000 times of their dry weight. They found many applications in hygiene products and other products, for a fast growing market of USD 9.58 Billion in 2019. Most of them are composed of synthetic polymers, which are often not environmentally friendly. Therefore, natural superabsorbents and particularly those based on polysaccharides have received a recent increased interest for their biodegradability, biocompatibility, and renewability. This review focuses on polysaccharide-based superabsorbents, on their properties, synthesis methods, and characterization. Their potential applications in many fields, such as biomedical and hygiene, agriculture, water treatment, and the building sector, are also reported with an interest in products already marketed.

Synthesis of Grafted Nanofibrillated Cellulose-Based Hydrogel and Study of Its Thermodynamic, Kinetic, and Electronic Properties

Hydrogels were synthesized by a copolymerization reaction of nanofibrillated cellulose (CNF) with acrylic acid (AA) and acrylamide (AM) and N,N-methylene-bis-acrylamide (MBA) as a cross-linker and their absorption performance as a function of composition was determined. Hydrogels with 4% by weight CNF had swelling of about 250 g/g and with 7% CNF about 200 g/g for water. Thermodynamic and kinetic studies of the reaction pathways and the electronic properties of the cellulose and monomers were investigated through density functional theory calculations. Thermodynamic investigations revealed that the radical formation of cellulose that initiates the hydrogel process can occur through the breaking of the homolytic covalent bonds C6-OH and C3-OH. The results show that the reaction of CNF with monomers is thermodynamically favorable in the decreasing order of AM, AA, and MBA. The kinetic study also indicates that the reaction kinetics of CNF with AM is faster than with AA which is much faster than with MBA. Overall, this study has elucidated some of the key chemical characteristics that impact the derivatization of nanocellulose structures to produce advanced renewable bioproducts.

Utilization of waste hemicelluloses lye for superabsorbent hydrogel synthesis

A high-performance superabsorbent hydrogel have been successfully fabricated by using waste hemicelluloses lye. Not any extra base was added into the synthesis system for achieving hydrophilic polymer composite. In addition, polyvinyl alcohol (PVA) was added the reaction system to entrap within the hemicelluloses-g-AA/bentonite matrix and form a semi-interpenetrating polymer networks (semi-IPN) for enhancing the swelling properties of the as-prepared polymer composite. SEM, FTIR, and TG were employed to characterize the morphologies, structure, and thermal stability of as-synthesized hydrogel composite. Moreover, liquid absorbency in distilled water and saline solutions, water absorption rate, water retainability, and water reusability of hemicelluloses-g-AA/bentonite (HAB) and hemicelluloses-g-AA/bentonite-PVA (HAB-PVA) hydrogels were also investigated systematically. The adsorption kinetics and isotherms of the composites were studied, and the synergy effect of PVA and bentonite were also proposed. This method provides a new avenue to design the new structure of superabsorbent hydrogel and treat the waste lye in green and sustainable chemical engineering processes.

Hydrothermal extraction of hemicellulose: from lab to pilot scale

A flow-through reactor for hemicelluloses extraction with hot pressurized water was scaled with a factor of 73. System performance was evaluated by comparing the temperature profile, extraction yield and kinetics of the two systems, performing experiments at 160 and 170°C, 11barg for 90min, using catalpa wood as raw material. Hemicellulose yields were 33.9% and 38.8% (lab scale 160°C and 170°C) and 35.7% and 41.7% (pilot scale 160°C and 170°C). The pilot reactor was upgraded by designing a manifold system capable to provide samples with different liquid residence time during the same experiment. Tests at 140, 150, 160 and 170°C were carried for 90min. Increasing yields (9.3-40.6%) and decreasing molecular weights (4078-1417Da) were obtained at increasing the temperature. Biomass/water ratio of 1/27 gave total average concentration of xylose of 0.4g/L (140°C) to 1.8g/L (170°C).