Foams deleterious effects

Alkali treatment has been used to improve the functional properties of the insoluble protein prepared by heat precipitation of an alkaline extract of broken yeast cells (63). Heating yeast protein at pH 11.8 followed by acid precipitation (pH 4.5) yielded a preparation composed of polypeptides with increased aqueous solubility. It also increased foaming capacity of the protein 20-fold. The emulsifying capacity of the modified protein was good whereas the original insoluble protein was incapable of forming an emulsion. Alkali treatment must be carefully controlled to avoid its possible deleterious effects (24,75), e.g. alkaline treatment of yeast protein resulted in a loss (60%) of cysteine (63). 

In Chapter 4, mechanisms by which carbon-to-carbon unsaturation can be introduced onto the ends of poly (alkylene oxide)s were described. Since these end groups can have a deleterious effect on the performance characteristics of polyurethane foams or elastomers, as well as on other derivatives, the degree of unsaturation is a specification often required by manufacturers or a tool for understanding lot-to-lot variation in products produced. 

The effect of crude oil can also be deleterious. In some foam systems the presence of crude oil, even in small amounts, is sufficient to greatly inhibit foam formation and foam stability. A preferred surfactant is either unaffected or its effectiveness is enhanced by the presence of crude oil. 

Consider the application of pressure to the sample. (For many purposes it is satisfactory to immerse the sample in silicone oil, which is used as a pressure-transmitting fluid. This oil is relatively inert, and it can be removed subsequently by washing with acetone (propanone). In circumstances where penetration by silicone oil is deleterious then alternative pressure-transmitting liquids such as water may be useful. If, however, it is inadvisable to have water in direct contact with the pressure vessel then secondary encapsulation, for example, in thin-walled gold tubes, may be an effective alternative. The use of high-pressure gases is often unsatisfactory because they tend to cause various polymers to foam.)... 

The effect of particle concentration on the PMMA foam nucleation was investigated (Zeng, 2004). The ceU density was found to increase linearly versus clay concentration at low clay concentration, and starts to level off as clay concentration further increases, arguably resulting from the deleterious particle dispersion as the concentration increases. 

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