Abstract
ABSTRACTThe network variations of natural rubber (NR) during the vulcanization process were investigated by 1H chemical shift by liquid-state 1H nuclear magnetic resonance (NMR) spectroscopy. NR latex coagulated by microorganisms (NR-m) was contrasted with NR latex coagulated by acid (NR-a). The influences of the coagulation process 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(Mc)) can be increased with the increment of the vulcanization time; while the mass percentage of dangling free ends of the hydrocarbon and small molecules (A(T2)), the longitudinal relaxation time (T1), transverse relaxation time (T2), and molecular mass of inter–cross-link chains (Mc) decreased with the prolonging of vulcanization time both NR-m and NR-a. NR-m exhibits shorter scorch times (ts1, ts2) and optimum cure time (t90) and shows higher maximum torque (MH) and minimum torque (ML) than that of NR-a. It is obvious that the higher XLD and A(Mc) and lower A(T2), T1, T2, and Mc values of NR-m result in higher stress, tensile strength, and tear strength of NR compounds.
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