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 then 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. In these systems, the interdiffusion process and the crosslinking reaction couple strongly, and, in practice, may sometimes interfere in a way that proves unfavorable to the tenacity of the film. We studied theoretically the competition between interdiffusion and crosslinking, and found a control parameter tuning the balance between these two processes, in terms of simple physical quantities. The case of practical interest occurs when this parameter is much smaller than unity: the reaction locks the interfacial chains once a significant mixing has developed, resulting in films with good mechanical properties.