KOH Number of Natural Rubber Latex Concentrates

Manufacturer: Our consultant advised that we should not pay too much attention to the KOH number of our incoming latex concentrates. What is your comment?

John Woon (Senior Latex Consultant): I disagree with your consultant. 

KOH Number is defined as the number of grams of potassium hydroxide equivalent to the acid radicals in the latex combined with ammonia containing 100 gm of total solids.

There are different types of such acid radicals in the latex, which are measured with the KOH Number. Some are good while others are bad. The good ones are the fatty acid soap and protein ions, which are latex stabilizers. The bad ones that can destabilise latex are amino acids (by-products of the breakdown of proteins) and the volatile fatty acids (VFA). Other bad ones include phosphates, carbonates, citrates, and sulphates.

Therefore, this parameter must be accessed together with other parameters to access the quality of the latex.

If you are getting the latex from the same source or plantation, the KOH Number could indicate the age of the latex. The higher the number, the older the latex, and hence, the lower the latex stability.

I suggest you liaise with your suppliers and set the specification of KOH Number at 0.6 (maximum).