NOVEL HIGH-PERFORMANCE MATERIALS FROM STARCH - 2 - ORIENTATION AND MECHANICAL-PROPERTIES OF LIGHTLY CROSS-LINKED STARCH-ETHER FILMS

Three types of reactants were used to introduce cross-links into the s tarch-ether polymers, specifically hexamethylene diisocyanate, a hydri dosilane, and a silanol-terminated oligosiloxane. The resulting cross- linked starch-ether films in the dry state were extremely brittle (as they are in their un-cross-linked states), with glass transition tempe ratures between 30 and 40 degrees C. The desired chain orientations we re therefore carried out in the swollen state, with an externally appl ied mechanical force, focusing on the diisocyanate-cured triethyl-amyl ose films. The solvents were removed from these materials while they w ere in the stretched state, either uniaxial or biaxial, and the improv ements in the mechanical properties thus achieved were determined as a function of this stretch ratio. It was found that the tensile strengt hs, tensile moduli, and elongations at break increased monotonically a nd frequently dramatically with increase in orientation, as gauged by this ratio. In addition, two solvent-removal processes were investigat ed, drying in air and coagulation in a suitable nonsolvent. Films obta ined from the coagulation processes showed smaller improvements in mec hanical properties and rougher surfaces than those obtained by air-dry ing.