Reactive coupling between immiscible polymer chains: Acceleration by compressive flow

It is demonstrated that processing flow affects the kinetics of the interfacial coupling reaction between functional groups that are grafted to polymer chains. At melt temperatures the amine group on the end of nylon 6 chains reacts with maleic anhydride grafted polyethylene (PE-MA) and forms graft copolymers. Bilayers were made by lamination and coextrusion and adhesion was measured using asymmetric dual cantilever beam (ADCB). The amount of graft copolymer in the interface was quantified by X-ray photon spectroscopy (XPS). With quiescent lamination, adhesion increased with temperature and the concentration of PE-MA. The adhesion metric, G_c (critical energy release rate), plotted as a function of Σ (interfacial copolymer density) fell on the same master curve, unifying reaction process, temperature and time. G_c was a linear function of Σ for low-copolymer coverage and weak adhesion. For relatively high coverage and strong adhesion, G_c scaled with Σ. Coextrusion with compressive flow resulted in a reaction rate strikingly two-orders of magnitude faster than that without compressive flow. The rate in the noncompressive die was close to quiescent lamination. Even for lamination, when compressive flow was applied normal to the interface, the coupling reaction rate was also greatly accelerated. Several mechanisms are speculated for this remarkable acceleration in polymer chain coupling.