Molecular Weight Effects on Properties of Polyurethane/Nitrokonjac Glucomannan Semiinterpenetrating Polymer Networks

Semiinterpenetrating polymer networks (semi-IPNs) were synthesized from castor oil-based polyurethane (PU) and 20 wt % nitrokonjac glucomannan (NKGM) with weight-average molecular weights ( M w ) from 2.86 × 10 4 to 14.1 × 10 4 . Results from the dynamic mechanical analysis, differential scanning calorimetry, wide-angle X-ray diffraction, and ultraviolet spectrometer showed that the semi-IPNs have a single broad α-relaxation peak, one glass transition, and higher optical transmittance (Tr) in the wavelength range of 400−800 nm than PU, suggesting good miscibility in the range of NKGM M w used. Noted that tensile strength (σ b ) of the semi-IPNs films was much higher than that of films PU and NKGM, and the Tr, σ b, and breaking elongation (ε b ) obviously increased with decrease of NKGM M w from 8.44 × 10 4 to 4.75 × 10 4 (Tr = 88% at 800 nm, σ b = 34 MPa, ε b = 110%). This indicated that the NKGM with relatively lower M w plays an important role in plasticizing, accelerating cure, and enhancement of intermolecular interaction between two polymers in the semi-IPNs films. The semi-IPNs system provided a novel way for modification and exploitation of natural polymers such as polysaccharides.