Creaming of latex

Manufacturer: We are adhesive manufacturer and started to buy NR latex in 200 kg steel drums about a year ago. Whenever we want to use the latex, we always find a thick layer of latex at the top of the drums. This has given us some problems. How can we prevent this?

JohnWoon: Before I start advising you how to overcome this problem, perhaps it'd better if I give some basics about the latex colloidal properties. Latex is basically a dispersion of the rubber particles in the serum (i.e. the aqueous phase of the latex). The rubber particles, being lighter than the serum, would tend to move upwards and rise to the top of the latex especially when left alone without agitation. This would result in a thick layer with very high solid content that can be as high as 70% and more while the normal solid content is about 60%.

This is what we call the "creaming process" which occurs faster at higher temperatures (25C to 30C). The rate of creaming is lower at lower temperature (10C to 25C). I suggest you agitate the latex by stirring it with a collapsible stirrer or by rolling the drums. If possible, empty some drums of latex into a tank and stir the latex in this tank periodically, say every 2 to 3 days for about half an hour each time.

Do not discard the "thickened" or "creamed" latex unless it has dried to solid state. This latex is still reversible when remix in normal latex.