Effects of NCO/OH molar ratio on structure and properties of graft-interpenetrating polymer networks from polyurethane and nitrolignin

A series of graft-interpenetrating polymer networks (graft-IPNs) with different NCO/OH molar ratio was synthesized from castor oil-based polyurethane (PU) and nitrolignin (NL) by changing the content of 1,4-butanediol as chain-extender. The effects of NCO/OH molar ratio on the morphology and properties of the PU-NL films (UL) were investigated by infrared, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry, dynamic mechanical analysis, and tensile test. WAXD patterns showed that all the UL films were nearly amorphous. With an increase in NCO/OH molar ratio, the glass transition temperature (T-g), the stiffness and tensile strength (sigma(b)) increased, while the breaking elongation (epsilon(b)) and strain recoverability (Re) decreased. The UL films with 1.20 of NCO/OH molar ratio exhibited the maximum value of tensile strength (sigma(b) = 30.2 MPa; epsilon(b) = 152%). 2.8 wt% NL plays an important role in the simultaneous enhancement of sigma(b) and epsilon(b) of the UL films. Solid-state C-13 nuclear magnetic resonance (C-13 NMR) showed that the introduction of NL into PU restricted the motion of PU molecules, indicating a relatively high cross-link network structure in the UL films. Therefore, a relatively great network structure like a star by grafting with multi-PU networks on a NL molecule as the graft-IPNs model was deduced in this work. (C) 2002 Elsevier Science Ltd. All rights reserved.