Direct observations of differential lamellar deformation on drawing isolated polyethylene spherulites.

The deformation of isolated linear polyethylene spherulites, to at least 7 times extension, has been observed with lamellar resolution in a dilute blend with branched polyethylene as matrix. Drawing occurs in two temperature ranges. In the low temperature range, from 25 to 100 °C, spherulites deform as a whole within a solid matrix with longitudinal dimensions increasing by the draw ratio. From 120 °C to 130 °C, when the matrix is fully molten, the principal effect is to detach lamellar fragments along the line of greatest extensional stress while leaving the majority of the spherulite little affected. In the low temperature range, deformation differs according to the inclination of lamellae to the tensile axis. Under tension or shear, lamellae rotate, disrupt and/or fragment; under compression they buckle then kink co-operatively where the stress is highest. After deformation, spherulites tend to have become cylindrical within well demarcated lateral boundaries parallel to the draw direction. It is suggested that this reflects differences in the extensibility of the molecular networks on either side of the boundary. [ABSTRACT FROM AUTHOR]