Research and comparative analysis of the performance of ammonia-free concentrated natural rubber latex with different preservation systems

Ammonia-free concentrated natural rubber latex (CNRL) offers considerable environmental benefits and has wide application potential. However, there are currently several varieties of ammonia-free CNRLs on the market with varying quality characteristics. This study conducts a comparative analysis of four systems: Hexahydrohydroxyethyl triazine (HTT), Benzoisothiazolinone (BIT), N,N'-Methylene-bis-Morpholine (MBM), and Thioacetamide derivative (TD). The HTT system maintains ammonia-free CNRL with the smallest rubber particle size, though it exhibits relatively high viscosity, low mechanical stability time (MST), and limited hardness and constant elongation stress of the vulcanized film. The BIT system offers excellent control over the volatile fatty acid number (VFA No), leading to high MST and heat stability, but its increased latex viscosity contribute to overall poor stability. In the MBM system, the viscosity is reduced; however, the prevulcanized latex shows decreased heat and chemical stability. In contrast, the TD system enhances the MST, reduces viscosity, improves the mechanical properties of the dry film, and bolsters the stability and film-forming characteristics of the prevulcanized latex. Nonetheless, the electrical conductivity in the TD-preserved ammonia-free CNRL is elevated, which may compromise chemical stability. Consequently, selecting the appropriate ammonia-free CNRL for various products is critical and should be guided by specific performance requirements.