Electron microscope observations of fibrillar-to-lamellar transformations in melt-drawn polymers

Abstract

Electron-transmissible polybutene-1 films were produced by drawing from an already thin molten film on a microscope slide. The films exhibitab initio a microstructure composed of fine fibrils of the stable (hexagonal) phase. Films from various stages of heat-treatment in air were examined in the transmission electron microscope. Two types of microstructural charge were seen. In one, crystallites appearing within the fibrils gradually order themselves to lie in rows normal to the chain (fiber) axis. The laterally aligned crystallites do not merge to form crystallographically homogeneous lamellae. In the other observed process, patches of fully lamellar metastable phase crystals form. These lamellae are oriented normal to the surface and grow both parallel and normal to the surface. These crystals grow by the incorporation of relaxed chains and require substantial molecular diffusion. It is suggested that entanglements or other physical pinning of the long molecules used here inhibit the full lamellarization of the intrafibrillar crystallites and cause the system to transform by means which utilize the chains which are most easily disengaged and transported.