Development of structural hierarchy during uniaxial drawing of PEEK/PEI blends from amorphous precursors

When poly(ether ether ketone)/poly(ether imide) (PEEK/PEI) blends are drawn in their rubbery region, prior to the critical draw ratio, they remain amorphous. Subsequent to the onset of strain hardening, the stress rises rapidly as a result of strain-induced crystallization of the chains highly oriented in the direction of strain. It is during this stage of deformation process that a highly structured physical network is formed where oriented crystallites act as nodes in the network structure. The wide angle X-ray scattering data indicate that chains in these ‘nodes’ are highly oriented and the three dimensional crystalline lattice is not well established due to poor axial registry of these highly oriented chains. This is evidenced by the absence of off-equatorial peaks. During this period, the effectiveness of drawing arises from the existence of the tie chains aligned in the direction of draw and forming the net between the crystallites. PEI, though a stiff and bulky chain, is found to delay the oriented crystallization rate of PEEK, but has little effect on its crystalline orientation in the composition range investigated.