The particles of polymer produced in the dispersion polymerisation process are of the order of 0.2µm in size, whilst those from a granular polymerisation are hundreds of µm in size, built up from smaller particles.They are both highly crystalline – about 90 to 95%.
The dispersion particles can be studied directly in a conventional transmission electron microscope, providing the electron intensity is kept low. On raising the electron beam intensity the particles change rapidly in appearance to become transparent with a crumpled texture. At this stage the crystallinity has disappeared and the ‘particles’ probably consist of a shell of carbon. Electron diffraction patterns and dark field micrographs suggest that the particles are composed of a pile of small single crystals with the molecular axis along the axis of the brick-shaped particles . The particles also appear to have a striated surface structure generally parallel to the long axis. A replica of some dispersion particles. During coagulation, the dispersion particles aggregate to form a larger particle, made up of a loose structure of agglomerates of the primary particles. During cold, lubricated extrusion the agglomerated particles are highly distorted, with their primary particles becoming aligned and also drawn into fibrous material.
During the early stages of polymerisation granular particles form as aggregates of smaller particles. This process continues and large irregular fibrous structures are produced.This material is then modified mechanically to reduce it to the familiar form suitable for processing.