Foamed Gelling Hydrocolloids

To a foamed gelling hydrocolloid system a firming agent and a fibrous material are advantageously added. When articles prepared from such compositions are coated with a suitable coating, they are impervious to boiling water and able to withstand microwave heating (33). 

Examples for the foamed gelling hydrocoUoid system are summarized in Table 7.7. 

A foaming agent is added for foaming and the foaming agent should produce a foam that lasts imtU gelling occurs. The time period will depend on the conditions chosen for foam formation, but will typically be about half an hour or less at room temperature. 

Examples of surfactants for foaming include sodium dodecyl sulfate, cleaning compositions, lecithins, as well as pertinent derivatives of cellulose and other polysaccharides (33,34). For physical applications such as wound healing dressings, when a surfactant is included in the dried gelled foam, non-ionic surfactants, such as the ethoxylates of sorbitan esters, are preferred (34). 

Some foaming agents form gels at body temperature. For example, methyl cellulose forms gels above 35°C. When using a foam that comprises methyl cellulose as the foaming agent in an application in which the foam is at body temperature, the methyl cellulose will 

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