Polymeric Shape Memory Nanocomposites with Heterogeneous Twin Switches
(1981–1986)Macromolecular Chemistry and Physics 212 #18 (2011)
Luo, Hu and Zhu ofThe Hong Kong Polytechnic University, China, developed a smart nanocomposite featuring a heterogeneous-twin-switch shape memory effect using cellulose-whiskers as reinforcement and segmented shape-memory-polyurethane as matrix.  The composite maintains the thermal-induced shape switchable effect originally existing in the polymer matrix and simultaneously possesses water-induced shape memory effect due to the percolation network of the cellulose whiskers whose hydrogen bonding can be regulated by water reversibly.  The composite is capable of fixing the total temporary shape (shape A) through cooling and drying after the extension in a warm water condition.  Reversibly, the extended composite partially recovers to the temporary shape (shape B) triggered by thermal stimuli solely and consequently from there to the original shape (shape C) triggered by thermal and water stimulus.  This is a new strategy to combine two different types of switches into one material and the responsiveness of the composite is different from the conventional ones being able to response to one external stimulus only.  (RDC 9/15/2011)

Covalent Bonding of Surface-modified Montmorillonite Nanoparticle with Polyurethane and its Impact on Shape Memory Effect and Mechanical Properties
(477-497) Journal of Thermoplastic Composite Materials 24 #4 (2011)
Abstract
Chung et al , South Korea, chemically bondedsurface-modified nanoparticle, monmorillonite (MMT), 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.  (RDC 7/14/2011)

Covalent Bonding of Surface-modified Montmorillonite Nanoparticle with Polyurethane and its Impact on Shape Memory Effect and Mechanical Properties
(477-497) Journal of Thermoplastic Composite Materials 24 #3 (2011)
Abstract
Chung et al, South Korea, chemically bonded surface-modified nanoparticle, monmorillonite (MMT) 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.  (RDC 7/5/2011)

Waterborne polyurethane nanocomposites having shape memory effects
(634–641)Journal of Polymer Science Part A: Polymer  Chemistry 49 #3 (2011)
Lee et al developed UV curable waterborne polyurethane/silica nanocomposites with functionalized silicas, where the functionalization was made with allyl isocyanate.  The incorporated silica particles gave triple effects of multifunctional chemical cross-links, reinforcing fillers, and stress relaxation retarders. Notably, over 99% shape fixity and shape recovery with minimum cyclic hysteresis were obtained for the repeated cycles at 1% loading of the modified silica.  (RDC 1/12/2011)