Shape memory effect of polyethylene nylon 6 graft copolymers

A series of maleated polyethylene/nylon 6 blends with nylon as the dispersed phase was prepared at 230 degrees C in a batched Haake mixer, and their shape memory effect was investigated. The nylon contents of the blends are in the range from 5 to 20 wt%. The Molau testing was used to verify the in situ formation of polyethylene-g-nylon 6 graft copolymers bridged by maleic anhydride in the melt-blending process. Differential scanning calorimetry, dynamic mechanical thermal analysis and scanning electron microscopy have been used to investigate the crystallization and melting behaviour, dynamic mechanical properties and phase morphology for all the specimens. The results indicate that the maleated polyethylene/nylon 6 blend specimens are able to show good shape memory effect under normal experimental conditions. The high crystallinity of the polyethylene segments at room temperature and the formation of a network structure in these specimens are the two necessary conditions for their good shape memory effect. The nylon domains, which serve as physical crosslinks, play a predominent role in the formation of a stable network structure for the graft copolymers. The studies show that shape memory materials with thermoplastic characteristics can be prepared not only by segmented copolymers but also by graft copolymers, and the reaction processing method might be a promising and powerful technique for this purpose. (C) 1998 Elsevier Science Ltd. All rights reserved.