Triaxially oriented shape memory natural rubber

Shape memory natural rubber (SMNR) is crystalline natural rubber (NR) which is stable at room temperature even after releasing from tensile force. In this study, preparation of triaxially oriented SMNR and its properties are reported. A series of wide-angle X-ray diffraction (WAXD) patterns was successfully obtained from this sample by changing the zone axis. The clear WAXD pattern corresponding to hk0 reciprocal lattice was also successfully obtained. The lattice constants of NR crystal reported in the previous studies were compared with those estimated from the specimen free from tensile stress, and as a result, distortion of the crystal lattice was found to be negligible. The triaxially oriented SMNR is thought to be useful for future refinement of crystal structure of NR. In the DSC measurements, multiple melting peaks of the crystallized SMNR appeared at temperature much higher than reported equilibrium melting temperature. An unidentified step similar to glass transition was also found in the DSC traces at about 20 degrees C.