Welding Behavior of Semicrystalline Polymers. 2. Effect of Cocrystallization on Autoadhesion

The effect of cocrystallization on the welding behavior of semicrystalline polymers was studied by means of T-peel testing at room temperature, using ultrahigh-molecular-weight polyethylene (UHMWPE) as a model polymer. Solution-cast films of UHMWPE have a very special morphology, consisting of regularly stacked, 107 Å thick lamellae, which exactly double in thickness upon annealing for 15 min below the melting point at 125 °C. This lamellar doubling process was used to introduce a well-defined amount of cocrystallization across the interface, by annealing two stacked, completely wetted solution-cast films. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, reference samples, in which cocrystallization across the interface was prohibited by “preannealing” one side of the film, could still be separated easily. Therefore, it is concluded that cocrystallization across the interface is extremely efficient in enhancing the adhesive fracture energy.