Covalent Bonding of Surface-modified Montmorillonite Nanoparticle with Polyurethane and its Impact on Shape Memory Effect and Mechanical Properties

The surface-modified nanoparticle, monmorillonite (MMT), was chemically bonded to shape memory polyurethane (SMPU) to improve shape memory and mechanical properties compared to the conventional composite prepared by melt-mixing process. Cloisite 30B was selected as MMT, because the functional group on its surface, methyl tallow bis-2-hydroxyethyl ammonium group, could be used for chemical bonding with SMPU and the reduced surface hydrophilicity rendered MMT disperse better in SMPU matrix during chemical reaction compared to bare MMT. Two types of SMPU, differing according to their soft segment (PTMG) and MMT content, were compared in mechanical and shape memory properties. Maximum stress went up as high as 57 MPa, and strain remained above 1000% for all of SMPUs. Shape recovery improved up to 97%, and did not decrease after four repetitive cyclic tests. Here, results demonstrating the advantages of chemical bonding of MMT-linked SMPU, compared to MMT and PU composite made by melt-mixing method, are discussed.