الفهرس 
Introduction and Literature reviewOnly 14 pages are availabe for public view
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Abstract
Polymers have emerged as the most important materials in the recently time by virtue of their properties with possibility to modify these to the desired extent through various means like irradiation and chemical doping. It is well documented that the polymers with improved properties find extensive and technological fields. Gamma irradiation attracts special attention in improving the bulk properties of the polymers. Irradiation induces bond breaking, main chain scission, creation of unsaturated bonds, intermolecular crosslinking radical formation and loss of volatile fragments. All these processes are responsible for the modification of structure, thermal, optical and color properties of polymers leading to their applications in different fields.
from the x-ray diffraction we see that, the increase in integral intensity in the gamma doses range 0-100 kGy indicates an increase in crystallinity (ordering character) which can be attributed to degradation induced by gamma irradiation. This degradation reduces the number of entanglements per molecule, thus increasing chain mobility. On the other hand, the decrease in integral intensity at the dose range from 100 kGy to 400 kGy denotes a decrease in the amount of crystalline phase, indicating that the crystalline structure has been destroyed due to crosslinking.
The dose range in which the intrinsic viscosity decreases can be explained by the formation of shorter molecules as a result of degradation which causes both a random breaking of bonds and the formation of stable molecules with a lower molecular weight. While the increases in intrinsic viscosity in the doses range 100-400 kGy, indicates an increase in the molecular mass of the polymer due to crosslinking process.
We see from FTIR that the intensity of the peak corresponding to hydroxyl group OH (3560 cm-1) increases with the gamma doses up to 100 kGy and then decreases with increasing the doses up to 400 kGy. The increase in the hydroxyl groups means an increase in the end groups of macromolecules indicating that degradation process prevails in this dose range. These results indicate that scission takes place at the carbonate site with elimination of carbon dioxide.
The result of TGA support that the degradation is the dominant phenomenon in the dose range 0-100 kGy. Degradation led to formation of low molecular weight products, which decrease the strength of the polymer, thereby decreasing its ability to withstand high temperatures. At the dose range 100-400 kGy, the opposite trend was observed indicating that the samples re-gain their thermal stabilities due to crosslinking process which strength the polymer against thermal degradation.
The refractive index showed a decrease in magnitude until a minimum value around 100 kGy followed by an increase on increasing the gamma doses up to 400 kGy. This behavior can be explained in terms of degradation and cross-linking induced by gamma irradiation. Such behavior facilitates the formation of free radicals that are chemically active. This allows the formation of covalent bonds between different chains (crosslinking), leading to the increase in refractive index. Also, the scission of chains and crosslinking may cause variations in chain orientation, which may lead to the observed changes in the refractive index. These results are in good agreement with those obtained by Shams-Eldin et al. Where, they illustrated that the irradiations implies chain scission which leads to a decrease of the refractive index.
The color intensity DE was greatly increased with increasing the gamma dose, and accompanied by a significant increase in the red and yellow color components (+a*), (+b*). This indicates that the CR 6-2 polymer has more response to color change by gamma irradiation. These changes in color can be attributed to the trapping of the excited free radicals that are formed by ionization. Also, the trapped free radicals resulting from radiation-induced rupture of polymer molecules have electrons with unpaired spin. Such species may also give optical coloration.
The aim of this research work is to study the effect of gamma rays irradiation with a wide range of doses on structural, thermal, optical and surface wettability properties of SSNTD CR 6-2.