INVESTIGATION OF THE VULCANIZATION CHARACTERISTICS OF NATURAL RUBBER COAGULATED BY MICROORGANISMS

The network variations of NR during the vulcanization process were investigated by ¹H chemical shift by liquid-state ¹H-NMR spectroscopy. NR latexes coagulated by microorganisms (NR-m) or acid (NR-a) were contrasted. The influences of coagulation on the structures, vulcanization characteristics, and mechanical properties of NR were analyzed. The results show that the cross-link density (XLD) and mass percentage of cross-link network [A(M_c)] increased with the increment of the vulcanization time, whereas the mass percentage of bangling free ends of the hydrocarbon and small molecules [A(T₂)], the longitudinal relaxation time (T₁), the transverse relaxation time (T₂), and the molecular mass of inter–cross-link chains (M_c) decreased with the prolonging of vulcanization time for both NR-m and NR-a. Although NR-m exhibits shorter scorch times and optimum cure time, it shows higher maximum torque and minimum torque than that of NR-a. It is obvious that the higher XLD and A(M_c), the lower the A(T₂), T₁, T₂, and M_c values of NR-m, resulting in higher stress, tensile strength, and tear strength of NR compounds.