2.1. Material Rice straw was harvested in an agricultural field of Nanjing, Jiangsu Province in China. Methylene diphenyl diisocyanate(MDI) resin (100% solid) was provided by the Huntsman Company (Germany), and it was a dark yellow liquid with a viscosity of 275 MPa s (25◦C). Acetone purchased from Nanjing Chemicals Reagents Company in China was used as a diluent for MDI.