Effects of hard-segment compositions on properties of polyurethane-nitrolignin films

Segmented polyurethane (PU) films from easter-oil-based PU prepolymer with different hard-segment compositions and nitrolignin (NL) were synthesized. Diisocyanates (DIs), such as 2,4-tolylene DI (TDI) and 4,4 ' -diphenylmethane DI (MDI), 1,4-butanediol (BDO) as a chain extender, and trimethanol propane (TMP) as a crosslinker were used to obtain PU films containing NL (UL) which were named as UL-TB for TDI and BDO, UL-TT for TDI and TMP, UL-MB for MDI and BDO, and UL-MT for MDI and TMP, respectively. The mechanical properties and thermal stability of the films were characterized by a tensile test and thermogravimetric analysis, respectively. The MDI-based UL films exhibited a higher tensile strength (sigma (b)) and thermal stability than TDI-based UL. However, the recoverability of the TDI-based UL films was better than that of others. The UL films with TMP (UL-TT and UL-MT) had higher sigma (b) and lower breaking elongation (epsilon (b)) than the UL films with BDO (UL-TB and UL-MB), caused by enhancement in the crosslinking network of hard segments and microphase separation between soft and hard segments. The values of sigma (b) and epsilon (b) of the UL films that contained NL were much higher than those of the PU films, which indicates that the introduction of NL increased the interaction between hard segments by crosslinking. The hydrogen bonding in the UL films was studied by infrared spectroscopy, which indicated that MDI favored the formation of hydrogen bonds, especially in the ordered domain. Differential scanning calorimetry, dynamic mechanical analysis, and wide-angle X-ray diffraction indicated that the UL films were compatible as a whole, but microphase separation existed between soft and hard segments and significantly affected the mechanical properties. (C) 2001 John Wiley & Sons, Inc.