Gamma and ultraviolet radiation effects on hardness, elastic modulus and viscoelastic properties of polyurethane derived from castor oil (PU) were investigated by nanoindentation tests. Modifications on surface morphology, induced by radiation, were observed by atomic force microscopy. The polyurethane derivate from castor oil shows good resistance to gamma radiation, with only small changes in hardness, elastic modulus, viscoelastic properties and contact angle. The hardness of PU increases at the near surface region due to UVA radiation and decreases after UVC radiation. The contact angle for water drop decreases after UVC radiation, but not after gamma radiation, despite a significant increase in roughness. Such results are attributed to different responses from polyurethane to radiation energy. Increase in hardness due to UVA is attributed to a higher crosslinking at shallow depths, while a decrease in mechanical properties may be attributed to chain scission. These results are consistent with the modifications on viscoelastic properties. Shore D hardness did not show the same trend as observed by nanoindentation results. Hardness, viscoelastic properties and contact angle of castor oil polyurethane are more severely influenced by UVC radiation, while gamma radiation does not have a significant effect.
Polyurethanes; castor oil; hardness; gamma radiation; UV radiation; nanoindentation
