Superabsorbent polymers: A review on the characteristics and applications of synthetic, polysaccharide-based, semi-synthetic and ‘smart’ derivatives

Abstract

The current review provides an overview of different types of superabsorbent polymers (SAPs) together with appropriate strategies elaborated to enable their synthesis. The main focus will be on polysaccharide-based, semi-synthetic and 'smart' SAPs along with their derivatives. SAPs have already shown their use in a plethora of applications including diapers, the biomedical field, agriculture, etc.The different polymer classification possibilities are discussed, as well as the classification of the constituting building blocks. The main part of SAPs still has a synthetic origin. However, as they are often not biocompatible, biodegradable or renewable, natural SAPs based on polysaccharides have gained increasing interest. Due to the low solubility of synthetic polymers, purification problems or the need for organic solvents, a trend has emerged towards combining polysaccharides with synthetic monomers to create semi-synthetic, hybrid SAPs for specialized applications with fine-tuned properties including wound dressings, fertilizers or self-healing concrete. These specialized, semi-synthetic SAPs offer strong potential for a series of applications in the future. However, future research in this respect is still needed to optimize homogeneity and to increase gel fractions. A final part of this review includes 'smart' SAPs such as SAPs with a T-, electro-and pH-sensitivity. These 'smart' SAPs are especially becoming useful for certain biomedical applications such as drug release for which an in vivo location can be targeted. The use of 'smart', semi-synthetic SAPs with fine-tuned characteristics combining the best characteristics of both synthetic and natural SAPs, offer the greatest potential for the future.

Functional starch-based hydrogels: renewable material solutions for wastewater and agriculture industries

“…The sample with 2.7 wt.% MBA content again showed the highest WAC (~34 g/g) in ES, which was achieved at KOH mole ratio of 0.25. Though similar observations have been reported in the past (Zain et al, 2018) (Mignon et al, 2019;Witono et al, 2012), the exact reason for this optimum is not clear. However, since the ampholytic hydrogels'…”

“…Biodegradability of agricultural polymers is a key characteristic that need to be assessed in order to protect the local environment from negative impacts, including the soil and its microbial and other communities, the plants grown in this soil, and the groundwater and other water resources that could accumulate contaminants or toxic loads from leachates and degradation products (Huttermann et al, 2009). In addition to biological activities, biodegradation of agricultural polymers is often influenced by various environmental factors, including exposure to ultraviolet radiation, chemical oxidisers, fertiliser salts, mechanical abrasion, and freeze-thaw events, which result in the breakdown of the polymer into smaller fragments, leading to a decline and ultimately loss of functional properties in these materials (Mignon et al, 2019). In most previous studies, biodegradability has been highlighted as a unique advantage of starch-based polymeric materials as a better alternative to traditional petroleum-based polymers (Sarmah & Karak, 2019).…”

Design and Preparation of New Multifunctional Hydrogels Based on Chitosan/Acrylic Polymers for Drug Delivery and Wound Dressing Applications

“…The fast swelling, favored by the presence of arginine, and the large volumes retained in the hydrogel networks, due to the chitosan/acrylate cross-linking, indicated a superabsorbent behavior [ 12 , 29 , 30 , 31 , 32 , 33 , 34 ] for the prepared hydrogels, which is a highly advantageous characteristic for applications such as drug delivery and wound dressing, as intended.…”

A Mini-Review on Chitosan-Based Hydrogels with Potential for Sustainable Agricultural Applications

“…When swollen, hydrogels maintain the stability of their networks because of their crosslinked structure, thus allowing them to remain stable in a variety of environments. Some hydrogels can absorb aqueous fluids up to thousands of times their own weight and therefore they are called superabsorbents [ 4 , 5 ]. In general superabsorbent polymer hydrogels are based on ionic monomers and are lightly crosslinked; therefore, they display an exceptional capacity of water absorption, significantly higher than highly crosslinked hydrogels made of nonionic monomers.…”

“…Additionally, their natural origin makes them inherently biocompatible, biodegradable, and non-toxic, so they are often used in the synthesis of hydrogel materials with potential applications in agriculture and horticulture [ 10 , 11 ]. Polysaccharides are widely used in the preparation of hydrogels due to the presence of hydrophilic functional groups, which can absorb water and are easily modified by grafting copolymerization reactions and/or crosslinking using established chemical and physical methods [ 5 , 8 , 10 ]. Chitosan (CS) [ 12 , 13 , 14 ], cellulose (Cell) [ 15 , 16 ], starch (ST) [ 17 , 18 ], and alginates (Alg) [ 19 ] are among the most important polysaccharides incorporated into hydrogels with potential for large-scale agricultural applications.…”