الفهرس | Only 14 pages are availabe for public view |
Abstract Polyurethane elastomers are the most important class of polymeric materials due to its wide range of applications. They produce in many forms such as foams, adhesives, fibers, synthetic leathers and others. Also it can be employed in many industries e.g. cars, building, constructions, shoes and medical devices. Polyurethanes are multi block copolymers with alternative sequence of hard segments and soft segments. The hard segments are built from short chain diols and diisocyanets. The hard segment provides a physical cross links via hydrogen bond. The soft segments usually comprised polyether, polyester polyol. The soft segments provide flexibility in the polymer backbone , the hard segment affect modulus, hardness and tear strength , while the soft segment control flexibility, softening and low temperature resistance. By controlling variables such as functionality, chemical composition and molecular weight of reactants, a wide class of materials of varying properties can be obtained .polyurethanes with best mechanical properties are preparing from aromatic diisocyanate , polyether, polyester and 1,4-butane diole. On the other hand aromatic diisocyanate based polymer suffering from degradation upon expose to uv-irradiation when used for outdoor applications. Many studies are deal with the effect of diisocyanate type on the various properties of polyurethanes with polyester and polyether’s polyols. Polyester urethanes are no longer used for medical devices that are required for long implantation, due to poor hydrolytic solubility, polyether are hydrolytically stable but can undergo oxidative degradation. There are different types of radiation can affect the properties of polyurethanes e.g. formation of qinioed structure and photo rearrangement with C-N cleavage. When polyurethanes are subjected to UVirradiation a deterioration in their crystalline structure was observed. Photo II degradation affect the backbone of polyurethane structure and can initiate embrittlness, crazing of the surface and discoloration. from literature survey it is noticed that little information about the effect of electron beam and gamma irradiation on the properties of polyurethane. Therefore the objective of this study is to improve the drawback properties of polyurethane by using gamma irradiation at different doses ranging from 100 to 600 kGy. The effect of gamma irradiation on the properties of urethanes such as physical, mechanical, thermal and FT-IR were investigated. |