Proteins vs Lipids in Natural Rubber Latex

Manufacturer: Can you explain the roles played by both the naturally occurring proteins and fatty materials in natural rubber latex in terms of the latex colloidal properties? Why can't the latex stability sustain over a long period of storage time?

JohnWoon: Freshly obtained latex from natural rubber trees (Hevea Brasiliensis) contains mainly proteins (including phosphoproteins) and lipids (including phospholipids) at the rubber and water (serum) interface.

In the cause of latex production in factories, ammonia is added as a preservative. In the presence of ammonia, the hydrolysis of both protein and lipids (phospholipids) takes place with the latter at a faster rate than the former. The hydrolysis of phospholipids takes about 3 to 5 weeks with the gradual resultant formation of fatty acid soaps. Hence you also see a gradual increase in the mechanical stability. On the other hand, the hydrolysis of proteins, while taking a longer time, would lead to the formation of smaller polypeptides and amino acids (which tend to destabilize latex).

This accounts for the initial build-up of latex colloidal stability followed by the eventual loss of stability with time. Some studies reveal that the artificial replacement of the rubber-water-interface proteins with more surface active materials followed by centrifugation could eliminate or reduce the level of the destructive amino acids.

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