Path dependent microstructure orientation during strain compression of semicrystalline block copolymers

Abstract

The shear-induced morphologies produced by channel die processing of a semicrystalline ethylene/ethylene–propylene/ethylene (E/EP/E) block copolymer were investigated as a function of processing conditions. The microphase separation of the block constituents under the processing conditions used in this work leads to a lamellar stack morphology, referred to as the B population, whose dimensions are controlled by the block molecular masses. In addition, the crystallizable part of the E polymer forms lamellar stacks which are referred to as the C population. The orientation textures of these two lamellar populations depend upon processing conditions in a complex manner. Two-dimensional small angle X-ray scattering (SAXS) was used to determine the domain spacing and orientation of the B and C populations relative to the process directions. The rate at which the channel die assembly was cooled following compression was found to strongly affect the microstructure of the end product. Using a cooling rate of 0.27°C/s, a predominantly perpendicular to the direction of shear orientation of B lamellar populations (Bp) is produced, while a cooling rate of 3.50°C/s yields a predominantly transverse to the direction of shear orientation of C lamellar populations (Ct). Both lamellar microstructures are oriented normal to the plane of shear. This Ct microstructure is novel to semicrystalline block copolymers and is attributed to deformation of preexisting crystallites.