Morphology-Properties Relationship in High-Renewable Content Polyurethanes

The effect of diisocyanate nature and hard segment content on the morphology and properties of high-renewable content segmented thermoplastic polyurethanes was studied. Vegetable oil-based polyether diol and corn sugar derived chain extender were used as renewable reactants together with an aliphatic (1,6-hexamethylene diisocyanate, HDI) or aromatic (4,4'-diphenylmethane diisocyanate, MDI) diisocyanate as hard segment. Segmented thermoplastic polyurethanes were synthesized by two-step bulk polymerization. Morphology and physicochemical, thermal and mechanical properties were analyzed by Fourier-transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, atomic force microscopy, and mechanical testing. The effect of mechanical deformation over the microstructure was also analyzed. Changes in crystallinity and hard segment hydrogen bonding after mechanical testing were evaluated by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The increase of physical crosslinking sites by aromatic diisocyanate and chain extender ratio in the polyurethane results in hard segment crystalline domains with spherulitic morphology, which enhance the stiffness and hardness whereas percentage elongation at break diminish. The flexible, linear aliphatic nature of HDI favors the arrangement of urethane groups thus creating strong hard segment interactions and hard segment crystal microdomains composed of fibrillar morphology are observed. (C) 2013 Society of Plastics Engineers