KOH Number Vs VFA Number

Manufacturer: Can you explain the importance of testing for VFA and KOH numbers for latex concentrates? Can we test one and omit the other?

John Woon (Senior Latex Consultant): If the field latex or the resultant latex concentrate has been infected by bacteria, the degradation or hydrolysis of the non-rubbers in latex would result in the formation of volatile fatty acids (VFA)which would eventually lead to a drastic drop in the colloidal stabilty of the latex. Hence it is always prudent to measure the VFA number to assess the stability and hence the processability of the latex before, during and after compounding with curatives etc.

KOH number measures the total acid radicals present in the latex. Since this includes VFA, a poorly preserved latex would show a high KOH number. However, a latex with high KOH number might not necessarily mean poor latex preservation because its measurement also includes ions from the “good” higher fatty acids.

Testing for KOH number is usually recommended as an indication of the age of the latex concentrates as it increases from about 0.45 to 0.7 on storage.

Hence my answer to your question: Do both tests.

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