PROPERTIES OF AMMONIA-FREE CONCENTRATED NR LATEX PRESERVED WITH N,N′-METHYLENEBISMORPHOLINE

ABSTRACT The NR latex (NRL) industry contributes to ammonia pollution, a problem that is difficult to solve. To address this issue, N,N-methylenebismorpholine (MBM) was used to prepare ammonia-free concentrated NRL (CNRL). The effect of MBM on the preservation and properties of CNRL was studied through comparison with high-ammonia (HA) CNRL. Results showed that MBM had an excellent preservation effect on ammonia-free CNRL. When the MBM dosage exceeded 0.35%, the volatile fatty acid value of CNRL was relatively stable and was consistently less than 0.06 over 180 days of storage. The prepared ammonia-free CNRL had lower viscosity and pH, and its mechanical stability test (MST) was moderate. The control results of the stabilization system showed that sodium dodecyl sulfate can significantly reduce the viscosity and improve the MST of the ammonia-free CNRL. KOH can significantly improve the pH and thermal stability of latex, but has little effect on improving MST. The ammonia-free CNRL had a lower pH after prevulcanization, but higher MST than the HA latex. The viscosity of the ammonia-free prevulcanized latex increased rapidly. The physico-mechanical properties of the vulcanizate films were slightly different from those of the HA latex samples. In addition, the infrared spectrum of the ammonia-free CNRL dry film was basically consistent with that of HA latex dry film. The thermal degradation curve and characteristic temperature of the ammonia-free CNRL dry film were basically the same as those of the HA-preserved film. Biosafety tests showed that the cytotoxicity of the MBM-preserved, ammonia-free CNRL dry film was slightly higher than that of the HA latex film. However, both films did not irritate the skin. All of these results illustrate that MBM has an excellent preservation effect on CNRL and the prepared ammonia-free CNRL has good processability, environmental protection, and safety.