Eco-Friendly Semi-Interpenetrating Polymer Network Hydrogels of Sodium Carboxymethyl Cellulose/Gelatin for Methylene Blue Removal

Characterization Methods to Determine Interpenetrating Polymer Network (IPN) in Hydrogels

Significant developments have been achieved with the invention of hydrogels. They are effective in many fields such as wastewater treatment, food, agriculture, pharmaceutical applications, and drug delivery. Although hydrogels have been used successfully in these areas, there is a need to make them better for future applications. Interpenetrating polymer networks (IPNs) can be created to make hydrogels more adjustable and suitable for a specific purpose. IPN formation is an innovative approach for polymeric systems. It brings two or more polymer networks together with entanglements. The properties of IPNs are controlled by its chemistry, crosslinking density, and morphology. Therefore, it is necessary to understand characterization methods in order to detect the formation of IPN structure and to develop the properties of hydrogels. In recent studies, IPN structure in hydrogels has been determined via chemical, physical, and mechanical methods such as Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and rheology methods. In this paper, these characterization methods will be explained, recent studies will be scrutinized, and the effectiveness of these methods to confirm IPN formation will be evaluated.

Preparation of CMC-poly(N-isopropylacrylamide) semi-interpenetrating hydrogel with temperature-sensitivity for water retention

The CMC-PNIPAM hydrogel with semi-interpenetrating structure and temperature-sensitivity was prepared by in-situ polymerization of N-isopropylacrylamide (NIPAM) in sodium carboxymethylcellulose (CMC) solution at room temperature. The mass ratio of CMC to NIPAM was a key factor influencing the network structure and property of CMC-PNIPAM hydrogel. The low critical phase transition temperature (LCST) of CMC-PNIPAM hydrogels increased from 34.4 °C to 35.8 °C with the mass ratio of CMC to NIPAM rising from 0 to 1.2. The maximum compressive stress of CMC-PNIPAM hydrogel reached to 26.7 kPa and the relaxation elasticity was 52 % at strain of 60 %. The viscoelasticity of CMC-PNIPAM hydrogel was consistent with the generalized Maxwell model. The maximum swelling ratio in deionized water was 170.25 g·g-1 (dried hydrogel) with swelling rate of 2.57 g·g-1·min-1 at 25 °C. CMC-PNIPAM hydrogel hardly absorbed water above LCST, but the swollen hydrogel could release water at the rate of 0.36 g·g-1·min-1 once exceeding LCST. The test of water retention showed that soil mixed with 2 wt% dried CMC-PNIPAM hydrogel could retain 13.08 wt% water after 30 days at 25 °C that was 4.4 times than that of controlled soil without CMC-PNIPAM hydrogel. The semi-interpenetrating CMC-PNIPAM hydrogel showed a potential to conserve water responding to temperature.

Towards superior biopolymer gels by enabling interpenetrating network structures: A review on types, applications, and gelation strategies

Gels derived from single networks of natural polymers (biopolymers) typically exhibit limited physical properties and thus have seen constrained applications in areas like food and medicine. In contrast, gels founded on a synergy of multiple biopolymers, specifically polysaccharides and proteins, with intricate interpenetrating polymer network (IPN) structures, represent a promising avenue for the creation of novel gel materials with significantly enhanced properties and combined advantages. This review begins with the scrutiny of newly devised IPN gels formed through a medley of polysaccharides and/or proteins, alongside an introduction of their practical applications in the realm of food, medicine, and environmentally friendly solutions. Finally, based on the fact that the IPN gelation process and mechanism are driven by different inducing factors entwined with a diverse amalgamation of polysaccharides and proteins, our survey underscores the potency of physical, chemical, and enzymatic triggers in orchestrating the construction of crosslinked networks within these biomacromolecules. In these mixed systems, each specific inducer aligns with distinct polysaccharides and proteins, culminating in the generation of semi-IPN or fully-IPN gels through the intricate interpenetration between single networks and polymer chains or between two networks, respectively. The resultant IPN gels stand as paragons of excellence, characterized by their homogeneity, dense network structures, superior textural properties (e.g., hardness, elasticity, adhesion, cohesion, and chewability), outstanding water-holding capacity, and heightened thermal stability, along with guaranteed biosafety (e.g., nontoxicity and biocompatibility) and biodegradability. Therefore, a judicious selection of polymer combinations allows for the development of IPN gels with customized functional properties, adept at meeting precise application requirements.