Synthesis, characterization and properties of self-healable ionomeric carboxylated styrene-butadiene polymer

The paper describes synthesis and properties of carboxylated styrene-butadiene rubber (XSBR) and its ionomer using the reaction between carboxyl groups of XSBR and zinc stearate. The self-aggregation of Zn2+ ion pairs resulted in the formation of an ionic cross-linked network, which gave excellent properties to XSBR. The transitions due to the self-association of the ionic cross-links in the ionomers in addition to the glass transition were observed in the dynamic mechanical analysis. The cross-linked XSBR with 1 and 3 wt% of zinc stearate showed a tensile strength value of 4.2 and 5.2 MPa, which were much higher than that (2.5 MPa) of pristine XSBR. Self-healing test was done for the ionomer, where a tensile strength value of 5.2 MPa (before healing) and a value of 3.5 MPa (after healing) were observed, which indicated that the ionic cross-links could heal the interphase. The ionic network polymers also displayed excellent self-healing ability, triggered by heating at 100 degrees C for 3 h via atomic force microscopy. The healing efficiency of the XSBR/Zn stearate compound was calculated as 68%. Thermoreversible behaviour of the polymer via ionic cross-links showed regular reversal of storage modulus (E') with varying temperature at constant frequency and strain. This study thus opens up a route for developing the self-healable ionic cross-linked XSBR with considerable mechanical properties for various engineering applications.