Doubts About Air Bubbles in Natural Rubber Latex

Student:  I'm actually a student of University Malaya. Currently, I am studying the cause of bubble formation in natural rubber latex and attempting to control and diminish it.

Referring to journals, bubble forms when gas is introduced into solution which containing either surfactant or protein.

Below are some doubts from me:

1) What are the surfactant that usually applied in latex processing? Is that Tween 80, Trixton 100?. 2) Hevein and Ovalbumin are the protein in the natural rubber latex ? 3) Besides Biuret test, any other simpler to test the protein level? As I know, oil based antifoam is usually used to control bubble. However, is there any other ways?

Thank you. Hope to hear from you soon.


John Woon (Senior Latex Consultant): The followings are my answers to your questions:

1) The surfactant usually used by both the latex producers and latex products manufacturers is ammonium laurate. Occasionally, latex products manufacturers also uses potassium laurate, oleate and other anionic surfactants such as sodium lauryl sulphate.

Non-ionic surfactants such as Tween 80, Trixton 100 are seldom added into the latex unless one encounters a severe loss of chemical stability.

2) Proteins in latex are found on both the rubber particles and the aqueous phase of the latex. These are mainly the alpha-globulin and hevein.

To measure the total protein level, you could determine the Nitrogen content using the Kjedahl method and multiply the result by a factor of 6.25.

For water extractable protein, you can use the so-called Modified Lowry method as that used by the medical glove industry, namely, ASTM D5712 - 10 (Standard Test Method for Analysis of Aqueous Extractable Protein in Natural Rubber and Its Products Using the Modified Lowry Method)

3) Although foaming is due to reduced surface tension as a result of the addition of surfactants, there are other factors that could lead to foaming tendency. Pure liquids do not foam while a solution and a mixture often do.Hence, you have to also study the effect of other ingredients in the latex besides the surfactants.

Not all antifoam agents are oil based. Carefully selected non-ionic surfactants with the right HLB ratio could act as an effective anti-foaming agent.