AND THERMICAL PROPERTIES.Chemical modification of cassava starch was conducted through an acylation reaction by using pyridine and propionic anhydride to replace the functional groups of starch.Polyurethane elastomers were prepared using suspensions of the mixture obtained from castor oil and yucca starch that was modified by a propionic anhydride reaction.The suspensions were characterized by means of tests based on The Fourier Transform Infrared Spectroscopy and the Hydroxyl Index.The castor oil-AMP suspensions were used for the PU synthesis.The PUs were characterized by their physical-mechanical properties like tension-deformation and Shore A. hardness, thermal gravimetric analysis and swelling test.The density cross-linking of from swelling tests was determined by applying the Flory-Rehner equation.