Relation between spherulites and water trees in polypropylene

Using polypropylene specimens, a water needle is inserted into both the spherulite region and the amorphous region to observe patterns and growth of water trees. All experimental results indicate that a water tree is more easily initiated and grown in the amorphous region than in spherulites. This can be explained by the fatigue effect of local forces. Also, special trees, referred to as "transient trees", were found.