Strengthening of a Polymer Interface: Interdiffusion and Crosslinking

In many industrial processes, pieces of the same polymer material are brought into contact at a temperature above the glass transition. Interdiffusion takes place across the interface and leads to a strengthening of the junction. Often, a crosslinker agent is also added in order to improve the global mechanical properties of the material, as in the formation of latex films from dispersed solutions of polymer particles. We studied theoretically the competition between the interdiffusion and the crosslinking reaction, and found that the control parameter tuning the balance between these two processes is α = Qτ0A ∗ 0 N3b3/Ne, where Qτ0 accounts for the reactivity of the crosslinker, A ∗ 0 is the initial concentration of sites capable of crosslinking on the polymer chains, N is the polymerization index, Ne the number of segments between entanglements and b a distance comparable to the segment length. The case of practical interest is α ≪ 1: the reaction locks the interfacial chains once a significant mixing has developed, resulting in films with good mechanical properties.