Path Dependent Microstructure Orientation During Strain Compression of Semicrystalline Block Copolymers
P L. Drzal, J D. Barnes, P Kofinas
The shear-induced morphologies produced by channel die processing of a semicrystalline ethylene/ethylene-propylene/ethylene (E/EP/E) triblock 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 weights. 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 populations depend upon processing 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 was cooled following compression was found to strongly affect the microstructure of the end product. Using a cooling rate of 0.27 C/s produces a B population oriented predominantly perpendicular to the direction of shear [Bp], while a cooling rate of 3.50 C/s yields a population [Ct] of C lamellae which are oriented predominantly transverse to the direction of shear. This Ct microstructure is novel for block copolymers and is attributed to deformation of preexisting crystallites. This study clearly demonstrated that dramatic morphological control of both B and C populations is possible through changes in melt processing of semicrystalline block copolymers.