Cellulose-based Superabsorbent Hydrogels Research Articles

MICRO-HETEROGENEITY AND MICRO-RHEOLOGICAL PROPERTIES OF CELLULOSE-BASED HYDROGEL STUDIED BY DIFFUSING WAVE SPECTROSCOPY (DWS)

Cellulose is the most plentiful biopolymer available in the world, and is a natural, biodegradable as well as inexpensive resource for biomaterials. Herein, a cellulose-based superabsorbent hydrogel (CHCCA) was prepared by crosslinking carboxymethyl cellulose (CMCNa) and hydroxyethyl cellulose (HEC) with citric acid, and its micro-heterogeneity and micro-rheological properties were explored by diffusing wave spectroscopy (DWS). The mean-square displacement (MSD) of microspheres imbedded into CHCCA hydrogels prepared at five concentrations was compared. At very low concentration, of 0.1wt%, the CHCCA hydrogel exhibited nearly homogeneous behavior, with slight heterogeneity. The heterogeneity became larger as the CHCCA concentration increased. It was also revealed that the high-frequency viscoelastic moduli magnitude at 0.1wt% CHCCA can be expressed by |G*(ω)| ∝ ω, which is characteristic of a viscoelastic fluid-like behavior. The magnitude of high-frequency viscoelastic moduli for 0.3 wt% and 0.5 wt% CHCCA can be described by |G*(ω)| ∝ ω3/4, which is characteristic of a semi-flexible polymer. The high-frequency viscoelastic moduli magnitude for 1.0 wt% and 1.5 wt% CHCCA described by |G*(ω)| ∝ ω1/2, was characteristic of a flexible polymer. Our results identified unique CHCCA property changes that occurred with changes in concentration, providing new insights for CHCCA derived hydrogels that will be useful in developing new CHCCA applications.

Aloe vera Rind Valorization to Improve the Swelling Capacity of Commercial Acrylic Hydrogels

Acrylic hydrogels have been used in agriculture to increase the availability of water in the soil; cause faster plant growth and increase plant survival to water stress; allow controlled release of fertilizers; and, therefore, increase crop yields. On the other hand, Aloe vera gel production generates a large amount of solid waste as cuticles, which is currently underutilized despite that it is a good source of cellulose nanofibers that could be used to improve the swelling capacity of commercial acrylic hydrogels. In this work, both morphology (SEM) and particle size (TEM) of the cellulose nanofibers obtained from A. vera cuticles by the acid hydrolysis method combined with ultrasound were analyzed; as well as the presence of functional groups (FITR) and thermal stability (TGA). Then, acrylic hydrogels were synthesized by the solution polymerization method, and nanofibers were added to these hydrogels at different concentrations (0% w w−1, 3% w w−1, 5% w w−1, and 10% w w−1). These concentrations had a nonlinear relationship with the swelling capacity, and the hydrogel reinforced at 3% cellulose nanofiber was chosen as the best formulation in this work, as this one improved the swelling capacity of hydrogels at equilibrium (476 g H2O g hydrogel−1) compared to the hydrogel without nanofiber (310 g H2O g hydrogel−1), while hydrogels with 10% nanofiber had a similar swelling capacity to the non-reinforced hydrogel (295 H2O g hydrogel−1). Therefore, cellulose-based superabsorbent hydrogels with potential application in agriculture were developed in this work.

SYNTHESIS OF CELLULOSE-BASED SUPERABSORBENT HYDROGEL FILLED WITH CELLULOSE NANOFIBER FROM OIL PALM EMPTY FRUIT BUNCHES

Oil palm empty fruit bunches (OPEFB) are waste products from the oil palm plantations, which is still an issue in Indonesian plantations. The high cellulose content in OPEFB enables them to be processed into cellulose nanofibers (CNF) that can be applied as fillers in the hydrogel. This research aimed to synthesize cellulose-based superabsorbent hydrogel and observe the optimal condition to produce hydrogel with high absorption and good thermal properties. CNF-based hydrogel is an excellent option to improve the physicochemical characteristics of the hydrogel. In this work, carboxy methyl cellulose hydrogel was firstly prepared by using citric acid. Then, CNF were added as fillers at different ratio variations, such as 0, 1, 3, 5, and 7 wt%. The surface morphology of the hydrogel showed rough surfaces, except for the 7 wt% CNF variation that produced hydrogel with a homogeneous surface. The cross-linking between the hydrogel and the fillers was evaluated by Fourier-Transform Infrared Spectroscopy (FTIR). A peak associated with the carboxylic acid functional group indicated hydrogel formation. The incorporation of CNF did not change the FTIR spectra since both materials had similar structures. Water absorption analysis showed that the developed product could be classified as a superabsorbent since all samples showed a degree of swelling above 200 g.g−1. CNF content at a 1 %wt ratio had the highest water retention and best thermal stability. The hydrogel showed exceptional characteristics, being suitable for various applications, mainly in agricultural sectors that required water delivery to the soil.

Pectin and mucin modified cellulose-based superabsorbent hydrogel for controlled curcumin release

Pectin and mucin modified cellulose-based superabsorbent hydrogel for controlled curcumin release

Synthesis of cellulose-based superabsorbent hydrogel with high salt tolerance for soil conditioning

In this study, cellulose-based superabsorbent hydrogel was synthesized from sodium carboxymethyl cellulose (CMC-Na), acrylic acid (AA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to enhance its water absorbency and salt tolerance for soil-conditioning applications in areas suffering from drought and soil salinization. Superabsorbent hydrogels (SHs) were prepared by CMC-Na and AMPS successfully, using chemical graft technology. Structure, morphology, thermal stability, and water absorbency of SHs were deduced. The cellulose-based hydrogel showed a high salt tolerance that the maximum water absorbency reached 604 and 119% in distilled water and saline water, respectively. The swelling behavior in aqueous solvents indicated that the water absorption of hydrogels was improved with the increasing ratio of CMC-Na. All SHs exhibited adsorption of nitrogen with the maximum adsorption of ammonia nitrogen 30 mg·g−1 and the presence of hydrogels could slow down the loss of nutrients in the soil. This study provided a feasible strategy that AMPS was substituted by CMC-Na to synthesize SHs with strong water absorbency and high salt tolerance which could be efficiently applied in agriculture as a soil conditioner.

Biomimetic cellulose-based superabsorbent hydrogels for treating obesity

In the treatment of obesity, nutritional and behavioral modifications are difficult to implement and maintain. Since vegetable consumption is a fundamental part of many dietary interventions and daily nutrient requirements, we developed a novel cellulose-based superabsorbent hydrogel (CB-SAH) platform, inspired by the composition and mechanical properties of raw vegetables, as a mechanobiological therapy. The CB-SAHs properties were studied in a simulated gastrointestinal environment, while their impact on gut tissue was investigated by an ex vivo organ culture (EVOC) model. Functional fibers and raw vegetables were used as reference. CB-SAHs demonstrated orders of magnitude higher elasticity in comparison to the tested functional fibers, however performed similar to the tested raw vegetables. Notably, the biomimetic CB-SAHs with elasticity levels similar to raw vegetables showed benefits in preserving and regulating the gut tissue in the EVOC model. Non-systemic oral mechanotherapeutics based on this technology were advanced through clinical studies, with a first product cleared as an aid for weight management in the US and Europe.

Synthesis and Properties of Cellulose-based Superabsorbent Hydrogel by a New Crosslinker

Cellulose-based superabsorbent hydrogel (SAH) has been successfully prepared by the grafting method with cellulose and sodium acrylate as well as aluminum hydroxide as a novel crosslinker. The factors influencing water absorption such as the neutralization degree of acrylic acid (AA), the amount of initiator ammonium persulfate (APS) and crosslinker, and the proportion of cellulose to AA were investigated. The chemical structure and thermal behavior of the SAH were analyzed by fourier-transform infrared spectrometry, field-emission scanning electron microscopy, and thermal gravimetry, respectively. Results showed that the water absorbency of the SAH in distilled water and 0.9 wt% NaCl solution reached 922 and 118 g/g when the mass ratio of cellulose to AA, APS to AA, Al(OH) to AA, and the neutralization degree of AA was 39 wt%, 0.67 wt%, 0.89 %, and 76 %, respectively. Under the same condition, the hydrogel synthesized by traditional crosslinker N,N-methylenebisacrylamide was only 530 and 84 g/g in distilled water and 0.9 wt% NaCl solution, respectively. The mechanism of polymerization reaction was analyzed. And the cost and feasibility for the mass-producing the hydrogel were analyzed.

Hydrogels Based on Cellulose and its Derivatives: Applications, Synthesis, and Characteristics

Hydrogels are mainly structures formed from biopolymers and/or polyelectrolytes, and contain large amounts of trapped water. Smart cellulose-based superabsorbent hydrogels are the new generation of scaffold which fabricated directly from native cellulose (including bacterial cellulose) via cellulose dissolution. Cellulose has many hydroxyl groups and can be used to prepare hydrogels with fascinating structures and properties. Cellulose hydrogels based on its derivatives, including methyl cellulose (MC), hydroxypropyl cellulose (HPC), hydroxypropylmethyl cellulose (HPMC), and carboxymethyl cellulose (CMC) can be fabricated by various methods. On the basis of the cross-linking method, the hydrogels can be divided into chemical and physical gels. Physical gels are formed by molecular self-assembly through ionic or hydrogen bonds, while chemical gels are formed by covalent bonds. Composite smart hydrogels are prepared using cellulose in conjunction with other polymers through blending, formation of polyelectrolyte complexes, and interpenetrating polymer networks (IPNs) technology. According to type of superabsorbent cellulose-based hydrogels fabrication methods, there are many various techniques to evaluate quality of them. Briefly, some of these means generally used to assess the hydrogel are described as following. The obtained gel membranes are characterized by infrared spectroscopy, scanning electron microscopy, thermo gravimetric analysis, and mechanical tests in order to investigate the crosslinking occurrence and modifications of cellulose resulting from the synthetic process, morphology of the hydrogels, their thermal stability, and viscoelastic extensional properties, respectively. This review highlights the recent progress in smart cellulose-based superabsorbent hydrogel designs, fabrication approaches and characterization methods, leading to the development of cellulose based smart superabsorbent hydrogels.

Highly Effective Removal of Methylene Blue Using a Chemi-Mechanical Pretreated Cellulose-based Superabsorbent Hydrogel

Eucalyptus bleached chemical pulp was fibrillated using a PFI pulp beater and ball mill method and was modified by acryloyl chloride. A novel porous cellulose-based hydrogel was prepared from the modified cellulose and acrylic acid for the removal of methylene blue (MB) from aqueous solution. The structure and morphology of the hydrogel were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), respectively. The influence of various parameters, such as pH value, hydrogel dosage, initial MB concentration, and contact time on the dye adsorption, were investigated. The equilibrium experimental data fitted well to the Langmuir isotherm model, and the maximum adsorption capacity of the hydrogel reached 3003 mg/g. In addition, the reusability study suggested that the hydrogel showed great adsorption capacity and a high removal ratio, even after the 5th adsorption-desorption cycle. Thus, the modified cellulose-based hydrogel is a potential superabsorbent for the removal of MB from wastewater.

Carboxymethyl cellulose-based superabsorbent hydrogels containing carboxymehtyl β-cyclodextrin for enhanced mechanical strength and effective drug delivery

Carboxymethyl cellulose (CMC)-based hydrogels have superabsorbent properties but low mechanical strength. Variation of other hydrogel components might improve the mechanical strength, but has been occasionally seen to decrease the swelling and drug-loading capacity. To address these problems, we designed a dual-component system, consisting of both carboxymethyl β-cyclodextrin (cmβCD) and CMC. We synthesized the hydrogels by crosslinking βCD or cmβCD with both cellulose (CEL) and CMC to evaluate their intrinsic mechanical strength and swelling capacity. The characteristic structure and morphology of each hydrogel was determined by Fourier- transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and field emission scanning electron microscopy. The storage modulus of the cmβCD/CMC gel was nearly eight-fold higher than that of the CMC gel only in rheology tests; the compressive strength was also enhanced while still retaining high swelling ability. We also investigated the drug-loading capacity and subsequent release properties, using tetracycline as a drug model. The cmβCD/CMC hydrogels showed the most effective tetracycline-loading capacity with the highest antibacterial activity among all hydrogels. They also showed the highest mechanical strength and the best drug release properties apart from the appreciable swelling capacity. Furthermore, cmβCD/CMC hydrogels are non-cytotoxic towards human dermal fibroblasts, suggesting their safe use as nontoxic, bio-friendly, and effective drug delivery systems.

A facile and efficient strategy for the fabrication of porous linseed gum/cellulose superabsorbent hydrogels for water conservation

The linseed gum/cellulose composite hydrogels were successfully fabricated by mixing cellulose and linseed gum solutions dissolved in the NaOH/urea aqueous system and cross-linked with epichlorohydrin. The morphology and structure of the composite hydrogels were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD) and thermogravimetric analysis (TGA). The swelling ratio and water retention properties were investigated. The results revealed that linseed gum mainly contributed to water adsorption, whereas the cellulose acted as a backbone to strengthen the porous structure. This work provided a simple way to prepare cellulose-based superabsorbent hydrogels, which could be potentially applied as an effective water conservation material in agriculture.

Biocompatible cellulose-based superabsorbent hydrogels with antimicrobial activity

Current superabsorbent hydrogels commercially applied in the disposable diapers have disadvantages such as weak mechanical strength, poor biocompatibility, and lack of antimicrobial activity, which may induce skin allergy of body. To overcome these hassles, we have developed novel cellulose based hydrogels via simple chemical cross-linking of quaternized cellulose (QC) and native cellulose in NaOH/urea aqueous solution. The prepared hydrogel showed superabsorbent property, high mechanical strength, good biocompatibility, and excellent antimicrobial efficacy against Saccharomyces cerevisiae. The presence of QC in the hydrogel networks not only improved their swelling ratio via electrostatic repulsion of quaternary ammonium groups, but also endowed their antimicrobial activity by attraction of sections of anionic microbial membrane into internal pores of poly cationic hydrogel leading to the disruption of microbial membrane. Moreover, the swelling properties, mechanical strength, and antibacterial activity of hydrogels strongly depended on the contents of quaternary ammonium groups in hydrogel networks. The obtained data encouraged the use of these hydrogels for hygienic application such as disposable diapers.

Synthesis of cellulose-based superabsorbent hydrogels by high-energy irradiation in the presence of crosslinking agent

Superabsorbent hydrogels were prepared from aqueous solutions of four cellulose derivatives (carboxymethylcellulose Na-salt – CMC, methylcellulose – MC, hydroxyethylcellulose – HEC and hydroxypropylcellulose – HPC) by gamma irradiation initiated crosslinking. CMC was used for the majority of the measurements. N,N’-methylene-bis-acrylamide (MBA) crosslinking agent was used to modify the gel properties. The crosslink density increased with the MBA concentration, leading to an improved gel fraction and lower water uptake. The crosslinking efficiency was the highest up to 1 w/wpolymer% MBA concentration. Very high MBA content (10 w/wpolymer%) led to a heterogeneous gel structure. Gelation also occurred under milder conditions in the presence of MBA: good gel properties were achieved at significantly lower doses and solute concentrations as compared to crosslinker-free solutions. The time required to reach maximum water uptake increased with the degree of swelling in equilibrium. Swelling properties of CMC gels with lower water uptake showed lower sensitivity to the ionic strength of the solvent.

Advances in cellulose-based superabsorbent hydrogels

This contribution provides a brief overview of recent progress in cellulose-based superabsorbent hydrogels, fabrication approaches, materials and promising applications.

Biodegradable Superabsorbent Hydrogel IncreasesWater Retention Properties of Growing Media and Plant Growth

Abstract Superabsorbent hydrogels are a particular class of gels, obtained by chemical stabilization of hydrophilic polymers in a tridimensional network. Hydrogels have been widely proposed over the last 40 years for agricultural use with the aim to ameliorate water availability for plants, by increasing water holding properties of growing media (soils or soilless substrates). Most of the traditional hydrogels on the market are acrylate-based products, thus not biodegradable. Due to the increasing attention for environmental protection issues, biodegradable hydrogels arise lively interest for potential commercial application in agriculture. In this study, we evaluated a novel class of cellulose-based superabsorbent hydrogels, totally biodegradable and biocompatible, for agricultural use. The objectives of the tests carried out were: 1) to verify the ability of the hydrogel to modify the water retention properties of the growing media (soils and soilless substrates); 2) to study the effects on the growth of plants grown on media amended with the hydrogel. Water retention curve of a sandy soil amended with 0, 0.5, 1.0 and 2.0% (w/w) of hydrogel was determined using a Richard's pressure plate apparatus. The hydrogel modified the soil water retention properties. The soil moisture at field capacity increased with the highest hydrogel percentage up to 400% compared to the not amended soil, and at wilting point (-15 bar) was similar to that at field capacity of the not amended soil. When added to perlite, a low water holding capacity soilless substrate, 1 or 2% (w/w) of hydrogel increased the container capacity of 28 and 48%, respectively, with no decrease of air capacity. Tests revealed absence of phytotoxicity of the hydrogel, and cultivation trials on cucumber (on soil) and sweet basil (in soilless conditions) showed a general overall enhancement of plant growth and quality when hydrogel was added to growing media. The tested hydrogel showed to be suitable for potential use in agriculture. Its employment should be further evaluated under a cost-effective perspective.

Potential of Cellulose-Based Superabsorbent Hydrogels as Water Reservoir in Agriculture

The present work deals with the development of a biodegradable superabsorbent hydrogel, based on cellulose derivatives, for the optimization of water resources in agriculture, horticulture and, more in general, for instilling a wiser and savvier approach to water consumption. The sorption capability of the proposed hydrogel was firstly assessed, with specific regard to two variables that might play a key role in the soil environment, that is, ionic strength and pH. Moreover, a preliminary evaluation of the hydrogel potential as water reservoir in agriculture was performed by using the hydrogel in experimental greenhouses, for the cultivation of tomatoes. The soil-water retention curve, in the presence of different hydrogel amounts, was also analysed. The preliminary results showed that the material allowed an efficient storage and sustained release of water to the soil and the plant roots. Although further investigations should be performed to completely characterize the interaction between the hydrogel and the soil, such findings suggest that the envisaged use of the hydrogel on a large scale might have a revolutionary impact on the optimization of water resources management in agriculture.

Environmentally sustainable production of cellulose-based superabsorbent hydrogels

The development of new products and materials, especially those which are non-petrolchemical reserves and based on renewable organic resources, using innovative sustainable processes is nowadays of increasing interest and deserves the attention of both academic and industrial research. Cellulose and its derivatives, as renewable organic resources, have been used to synthesize novel superabsorbent hydrogels. Although the production of cellulose is one of the causes connected to deforestation, the production of suitably engineered cellulose superabsorbent hydrogel materials has been proposed to preserve water in typically arid areas in the world. Paradoxically, divinylsulfone (DVS), a small di-functional highly toxic molecule, was used as a crosslinker for the preparation of the hydrogel. An environmentally sustainable heterogeneous TiO2 photo-catalysed process has been performed in order to achieve the detoxification (and a possible re-use) of washing waters deriving from the purification process carried out after the synthesis of a bio-degradable cellulose based superabsorbent hydrogel. The main species present in the washing water was DVS. DVS is a well known toxic agent and it was efficiently removed along with the unreacted polymers and oligomers by irradiating the washing waters in the presence of suspended polycrystalline TiO2. The photoprocess was studied not only by monitoring the total organic carbon (TOC) present in the solution but also by following the evolution of sulfate anions.