Gelation thermally irreversible gels

The thermally-reversible gel returns to the solution because the droving forces are noncovalent bonds such as hydrogen bonding, hydrophobic interaction, n-n interaction and electrostatic interaction. These noncovalent bonds are broken down by heating, so the gel reverts to the sol. Since the thermally-irreversible gel forms a network structure by firm chemical covalent bonds, the gel formed never changes to the sol. This is why the thermally-irreversible gel is called physical gel and the thermally-irreversible gel is referred to as chemical gel. Moreover, the gelation ability is found in not only biopolymers but also low molecular weight compounds. 

In chemical gels the network connection (crosslink) is usually a covalent bond, which leads to a thermally irreversible gel. When the crosslinking is purely physical in nature, a physical gel is formed which is thermally reversible. There have been at least two excellent works published in the last few years. Reversible Polymeric Gels and Related Systems by Russo [2] and Thermoreversible Gelation of Polymers and... 

Konjac mannan dissolves in water to form highly viscous solutions. It is acetylated ( 1 acetyl group for every 19 sugar residues) and in the presence of alkali, deacetylation occurs and thermally irreversible gels are produced. The rate of gelation is dependent on the polymer and alkali concentration and also on the temperature. This is illustrated in Figure 4.20... 

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