Effects of Acids and Alkalis on NR Latex

Manufacturer: Can you please advise us with simple explanation on the effects of acids and alkalis on anionic-stabilized and cationic-stabilized NR Latex?

John Woon (Senior Latex Consultant): Strong acids could cause immediate destabilization of the anionic-stabilized latex through their hydrogen ions. This is because the hydrogen ions would react with the carboxylate ions on the rubber particles (e.g. laurate and caprylate) forming a layer of the corresponding insoluble fatty acids. As a result, the "electrical double layer" surrounding and protecting the rubber particles collapses with the Zeta potential dropping to almost zero.

On the other hand, when acid is added to cationic-stabilized latex, no destabilization occurs. Instead, the latex becomes more stable in the presence of the acid. And the addition of alkali would destabilize the latex. The reverse is true for anionic-stabilized latex (e.g. commercially available NR latex concentrates), i.e. the addition of alkalis stabilizes the latex while acids destabilize  the latex.