Simple One Pot Preparation of Chemical Hydrogels from Cellulose Dissolved in Cold LiOH/Urea

Abstract

In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) and chemically cross-linked with methylenebisacrylamide (MBA) to form a robust hydrogel with superior water absorption properties. Different cellulose concentrations (i.e., 2, 3 and 4 wt%) and MBA/glucose molar ratios (i.e., 0.26, 0.53 and 1.05) were tested. The cellulose hydrogel cured at 60 • C for 30 min, with a MBA/glucose molar ratio of 1.05, exhibited the highest water swelling capacity absorbing ca. 220 g H 2 O/g dry hydrogel. Moreover, the data suggest that the cross-linking occurs via a basic Michael addition mechanism. This innovative procedure based on the direct dissolution of unmodified cellulose in LiOH/urea followed by MBA cross-linking provides a simple and fast approach to prepare chemically cross-linked non-derivatized high-molecular-weight cellulose hydrogels with superior water uptake capacity.Polymers 2020, 12, 373 2 of 15 enhance their potentials for applications, affect their release profiles and even allow specific processing, such as their injection [19]. In this respect, the mechanical and flow properties cannot be neglected when judging the feasibility of a hydrogel for a specific biological application. For instance, suitable flow properties allow hydrogels to be exciting candidates as injectable therapeutic delivery carriers if they are capable of shear-thinning during application at a proper shear stress; rapid self-healing; and adopting a solid-like behavior once the stress is removed [20].The general processing of cellulose, including the hydrogel formation, is challenging, since the biopolymer does not dissolve in water or in common organic solvents. Cellulose dissolution requires the disruption of the relatively extended inter-and intramolecular hydrogen bond network within its structure, as well as the van der Waals and hydrophobic interactions among the less polar faces of the anhydroglucose units [21][22][23][24].It is thus not surprising that for cellulose-based hydrogels the majority of studies have mainly focused on systems involving cellulose derivatives that can be easily dissolved in aqueous media [3,5,25,26]. Some studies have focused on physical hydrogels from several cellulose derivatives [27,28], while chemical cross-linking is more commonly used [3]. In this respect, chemically crosslinked cellulose-based hydrogels have been prepared using different methodologies, such as esterification [29], and radical and graft polymerization [30,31]. Methods involving free-radical initiation using an initiator compound or a high energy irradiation source, such as microwaves, γ-rays or glow discharge by electrolysis plasma, have also been suggested [29,[32][33][34][35][36][37][38][39]. Most of these processes involve time-consuming procedures requiring large quantities of chemicals, which make the post-treatment challenging. Consequently, these are generally expensive and poorly efficient strategies [32].Chemical cross-linking overcomes the problem of poor robustness of physical hydro...

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation

“…This crosslinking is dependent on degree and type of substitution and at higher dose hydrogels can be formed [375][376][377]408,409]. Other polysaccharides have also been studied including substituted chitin and chitosan, and gum arabic [382,410,411].…”

Polyvinylpyrrolidone K-30-Based Crosslinked Fast Swelling Nanogels: An Impeccable Approach for Drug’s Solubility Improvement

“…According to Flory's theory, excessive crosslinking causes generation of additional crosslinking points during polymerization process which result in enhanced gelling network and swelling index [65]. The hydrophilic groups (-OH) of polymer (PVP-K30) and monomer (AMPS) and -NH groups introduced by the MBA during radical polymerization are responsible for favorable polymeric network-solvent interaction triggering solvent uptake [66]. Slight decrease was observed in swelling index with increasing mass ratio (Table 1) of polymer/ monomer to MBA (PNG1-PNG5) that was due to the availability of less crosslinking points in the solution produced during free radical polymerization which resulted in inadequate gelling structure as shown in Figures 6(a) and 6(b).…”

Nanocellulose-Based Biomaterial Ink Hydrogel for Uptake/Release of Bovine Serum Albumin

“…Using LiOH/urea to partially dissolve CNF allows for self-forming gelation through changes in temperature, pH, and time, but additional crosslinking is necessary for better observation and gelation [ 40 ]. In this study, ionic crosslinking using H 2 SO 4 and CaCl 2 was performed after the printing process.…”