Hydrogel: Preparation, characterization, and applications: A review

Abstract

Hydrogel products constitute a group of polymeric materials, the hydrophilic structure of which renders them capable of holding large amounts of water in their three-dimensional networks. Extensive employment of these products in a number of industrial and environmental areas of application is considered to be of prime importance. As expected, natural hydrogels were gradually replaced by synthetic types due to their higher water absorption capacity, long service life, and wide varieties of raw chemical resources. Literature on this subject was found to be expanding, especially in the scientific areas of research. However, a number of publications and technical reports dealing with hydrogel products from the engineering points of view were examined to overview technological aspects covering this growing multidisciplinary field of research. The primary objective of this article is to review the literature concerning classification of hydrogels on different bases, physical and chemical characteristics of these products, and technical feasibility of their utilization. It also involved technologies adopted for hydrogel production together with process design implications, block diagrams, and optimized conditions of the preparation process. An innovated category of recent generations of hydrogel materials was also presented in some details.

Keywords: Hydrogel; Innovation; Optimization; Preparation; Processing.

Graphical abstract

Fig. 1

Stimuli response swelling hydrogel.

Fig. 2

Schematic diagram of hydrogel preparation.

Fig. 3

Hydrogel preparation block diagram (solution polymerization/cross-linking procedure).

Fig. 4

Solution polymerization with recycle loop.

Fig. 5

Block diagram of suspension polymerization process.

Fig. 6

Suspension terpolymerization process with recycle loop.

Fig. 7

Block diagram for the preparation of the high swelling hydrogel.

Fig. 8

Block diagram of the rapid preparation process of superabsorbent hydrogel.

Fig. 9

Preparative flowchart for grafted starch and P(AM-co-IA) hydrogel.

Fig. 10

Preparative steps in the production of SAPs and SPHs.

Fig. 11

Post-preparation steps of SAPs and SPHs.

Fig. 12

Typical swelling and mechanical properties of: first (A and B), second (C and D) and third (E and F) SPH generations.

Fig. 13

Schematic diagram of batch reactor.

Fig. 14

Schematic diagram of impellers used in high viscosity range.