Polyurethane-nitrolignin (PUNL), a new network polymer, was synthesized from castor oil based-polyurethane (PU) prepolymer and nitrolignin (NL) with weight-average molecular weight 20.6 x 10~4 and content from 1.4 to 10%. The structure and miscibility of PUNL films prepared by solution casting were investigated by infrared spectroscopy (IR) and transmission electron microscopy (TEM). The results indicated that PUNL2 film with the 2.8% NL content was most miscible, and its tensile strength (σ_b) and breaking elongation (ε_b) were two times higher than that of PU film. The crosslink densities of PUNL films increased with the increase of NL content until ca. 3%, similar to the varieties of the mechanical properties. The thermogravimetric analysis (TGA) revealed that the thermal stability of PUNL films was slightly higher than that of PU. The covalent bonds between PU prepolymer and NL in the PUNL films occurred to form crosslink networks, resulting in the enhancement of mechanical properties and thermal stability. NL has far higher reactivity with PU than nitrocellulose.
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