Plastic deformation and structure of extruded polymer solids

During extrusion the main deformation and orientation of macromolecules is achieved by the flow component with longitudinal gradient. The orientation increases drastically if some solidification occurs during flow, yielding row‐nucleated cylindrites and even fully oriented hard elastomers. In all cases the basic elements are stacks of very thin (∼100Å) folded‐chain lamellae connected by very few tie molecules. The plastic deformation of the solid transforms the original lamellar material into the extremely well oriented fibrous structure with high anisotropy of physical properties. The basic element are the highly aligned, very long and thin microfibrils bundled into fibrils. The axial strength of microfibrils is caused by the great many taut tie molecules connecting as almost crystalline bridges the crystalline blocks across the interposed amorphous layers. In plastic deformation of fibrous material the fibrils are sheared and longitudinally displaced. The latter mode is responsible for almost all the observed elongation. It smooths the structural defects on the surface of fibrils caused by the ends of microfibrils and thus produces a better lateral fit of fibrils resulting in rapidly increasing resistance to plastic deformation. The former mode extends the interfibrillar tie molecules and hence drastically increases their fraction per amorphous layer.