Alternative Methods for Accelerating Mechanical Stability of Concentrated Natural Rubber Latex

The mechanical stability time (MST) of latex is an important parameter indicating the colloidal stability of concentrated natural rubber latex (CNRL). This stability is crucial for the transport and storage of CNRL before the product forming processes. A popular method to increase the MST of CNRL in Thailand is by adding laureth soap or other surfactants. Nevertheless, the laureth soap provides a steady but slow increase in the MST without reaching a stable value after 30 days. At the same time, the phospholipids on the surfaces of natural rubber latex particles will naturally undergo hydrolysis reaction leading to even higher MST. For long storage, too high MST leads to coagulation problem in the product-forming step. Therefore, alternative methods were studied in this research to expedite phospholipid hydrolysis, which results in the increase in MST for CNRL without causing problems from excessive negative ions in the product-forming process. The alternative methods including heating in the presence of metal chips and the use of enzyme lipase were compared to the popular laurate soap addition method. It was found that lipase addition was the most effective method to expedite the hydrolysis of phospholipids to reach the standard MST value within 3 days, and reach a plateau within 10 days.