الفهرس 
Introduction and Literature reviewOnly 14 pages are availabe for public view
 |  | from | 137 |  |  |
| | | from | 137 | | |
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.