A hydrogel product constitutes of a group of polymeric materials. A hydrogel structure will allow this group the capability of holding a large amount of water or liquid in a 3 dimensional network. There recently has been extensive employment of these type of products in a number of environmental and industrial areas of application. This type of employment is considered to be of very great importance.

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As anticipated, a natural hydrogel has been replaced gradually by synthetic types of hydrogels. The synthetic hydrogels have a longer service life, higher water absorption capacity, and a wide variety of raw chemical resources. There has been an expanding amount of literature on the subject especially in regards to scientific areas of research.

However, a number of earlier technical reports and publications that have dealt with various hydrogel products, in regards to an engineering point of view, have been recently re-examined. This re-examination is due to the technological overview aspect that covers this growing multidisciplinary field of research.

The main focus of this article is to take a look at various pieces of literature that explain the classification of hydrogels on different bases, look at the chemical and physical characteristics of hydrogel products and investigate their modern utilization and technical feasibility. This article will also consider the various technologies used in hydrogel production in regards to block diagrams, process design implications, and the different conditions of a preparation process.

The main material of interest in this review are hydrogels. A hydrogel is a hydrophilic gel that is a network of polymer chains which are often seen as colloidal gels. These type of gels use water as the dispersion medium. Throughout the years, researchers have used different ways to classify hydrogels. The most common definition is that a hydrogel is a cross-linked polymeric network that is water-swollen. Another definition that is used is that it is a polymeric substance that has the ability to swell or de-swell as well as retaining a significant fraction of water within the structure. However, it should be mentioned that hydrogels will not dissolve in water.

Hydrogels have been under the scrutiny of scientists for the past half of a century because of their exceptional potential in a wide range of applications. Hydrogels have a degree of flexibility that is quite similar to natural tissue. The reason for this is primarily because of a hydrogel large water content.

During the last 20 years, a natural hydrogel was gradually replaced by a synthetic hydrogel. A synthetic hydrogel besides having a long service life also has a well-defined structure that can be easily modified so as to yield tailor-made functionality. A hydrogel can be synthesized from a purely synthetic component. It also is quite stable in conditions where there are strong or sharp fluctuations of temperatures.

More recently, a hydrogel has been defined as either a two or multi-component system which consists of a network of polymer chains that is 3 dimensional. Depending on the polymer properties used and the density and nature of the network joints, a structure that is in an equilibrium has the capability of containing various amounts of water (normally in a swollen state) so that the hydrogels mass fraction of water is higher than the mass fraction of polymer. To achieve a high degree of swelling it is typical to use a synthetic polymer that is water soluble when it is in a non-cross-linked form.

A hydrogel can be synthesized in a variety of classical chemical ways. Some of these ways include a multi-step procedure or a one-step procedure. A polymer engineer will be able to design and synthesize a polymer network that has a molecular scale type control over the structure.

As mentioned previously, a hydrogel as a cross-linked, 3 dimensional hydrophilic network has the capability of swelling or de-swelling in water while pertaining a large water volume. A hydrogel can be designed and created with controllable responses that will allow it to expand or shrink during any change in external environmental conditions.

The extent of the swelling or de-swelling in response to a change in the external environment of hydrogels can be quite dramatic. This dramatic change is often referred to as phase transition or volume collapse. Synthetic hydrogels are continuing to be an active area of research and will undoubtedly continue in the future to be so.

Since the first synthetic hydrogel was established by Wichterle and Lim in 1954, hydrogel technologies have been utilized in many hygienic products including agriculture, drug delivery systems, artificial snow, food additives, coal de-watering, sealing, bio-medical applications, regenerative medicines, diagnostics, wound dressing, biological infusions, and biosensors.

In addition, there is an ever growing spectrum of functional macromeres and monomers that are widening hydrogels applicability. Synthetic hydrogels were utilized in early agricultural water absorbents. Hydrogel products from RD Medical Products that have been used for hygienic applications are primarily based on acrylic acids and their salts. For example, acrylamide is a main component that has been used as a preparation of agricultural hydrogel products.

There have been many publications about hydrogels and synthetic applications. For instance, there was a comprehensive review of the various synthetic schemes and chemistries that were employed for hydrogel preparations found in sections of a compilation that was edited by Peppas.

More recently, there has been information about radiation grafting and polymerization published by Khoylou. Another publication by Mi-Ran Park looked further into the chemical properties and preparation of hydrogels when used in various agricultural applications. The potential of hydrogels when used in sensor utilization has also been explored by Kenichi and Vijayalakshmi.

In summary, a hydrogel technical feature can include features such as it has the highest absorption capacity in saline, it has the highest absorbency when under a load, it offers the lowest price, it has the lowest residual monomer and soluble content, it is pH neutral after swelling in water, it has photo stability, it is odorless, it is colorless, it is absolutely non-toxic, and it has the highest stability and durability during storage and while in a swelling environment.