Effect of storage on the mechanical properties of propylene-ethylene copolymers

The effect of storage at room temperature on the mechanical properties of the low ethylene content propylene-ethylene copolymers was investigated. The experimental results showed that the storage modulus increased and the loss tangent decreased on storage. The glass transition temperature shifted to higher temperature compared to unstored samples. From the tensile results, it was seen that storage produced a stiffer and more brittle material. The stress relaxation behavior was investigated. It is suggested that all the effects resulted from the occurring of secondary crystallization during the storage process.