Recrystallization process of branched Polyethylene during stretching and a statistical explanation

Summary

A new statistical theory leads to a simple relation [eq. 3] between the crystallinity and the branching ratio e for polyethylene (PE) cold drawn to the natural draw ratio. Three assumptions are made:

• 1) The branches all are incorporated in the amorphous phase,

• 2) they are distributed randomly along the chain and

• 3) the sample tends to obtain the highest possible crystallinity during the stretching process.

Ifm is the mean number of monomers in chain direction within one paracrystal, then this optimum can never be attained, ifmε during the whole process of necking is larger than 1. Now the theory gives no answer and the experiments give a crystallinity of ∼ 0.55 for all observed cases. Formε < 1, where the optimal crystallinity is established the volume occupied by the direct backfolds is about two third of the volume of the amorphous phase. Comparison with the crystallinity obtained from other methods proves that the superstructure consists of paracrystalline lamellae and not of clusters of lamellae imbedded into a amorphous matrix.