Effects of crosslinking density on structure and properties of interpenetrating polymer networks from polyurethane and nitroguar gum

Semi-interpenetrating polymer networks (semi-IPNs) of castor oil-based polyurethane prepolymer and nitroguar gum (NGG) with different crosslinking density of the PU network, coded as UNG films, were prepared through varying the trimethanol propane (TMP)/1,4-butanediol (BDO) molar ratios in the chain extender mixture. The effects of crosslinking density on the structure and properties of the UNG films was investigated by attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, crosslinking density measurements, solvent-extracting tests, and tensile tests. The experimental results revealed that incorporation of TMP crosslinker into the hard segments of polyurethane resulted in a decrease in the aggregation of hard segments. With an increase of the TMP/BDO molar ratios, the semi-IPN films exhibited the higher crosslinking density, glass temperature (T-g), stiffness, and tensile strength (sigma(b)). Furthermore, the experimental results also indicated that NGG restricted the formation of crosslinking networks when the TMP content is relatively high, which led to the negative deviation of the theoretically predicted crosslinking density and Dibenedetto's equation.