الفهرس 
coverOnly 14 pages are availabe for public view
 |  | from | 141 |  |  |
| | | from | 141 | | |
Abstract
All kinds of rubber have shortcomings in one or more properties. To develop their properties there are two ways, synthesizing a new rubber with new chemical structure or blending different types of rubbers having different properties to obtain rubber blend with desirable properties. The first way is very difficult, expensive, needs more time and not guaranteed. On the other hand blending is not expensive, not risky and very easy to realize. Thus, there are technical reasons for blending two types of rubber in order to obtain best compromise. Processing difficulties may be overcome by blending and appreciable differences in the price of different rubbers emphasize economical reason for blends. However, preparation and selection of rubber components of the blends in sulphur vulcanization or other conventional vulcanization systems differ from that in radiation induced cross-linking of rubber blends. For this purpose, the present work is aiming to study the characteristics of NR/ SBR blends in different ratio and vulcanized by gamma irradiation. The change in mechanical properties namely tensile strength (TS), modulus at 100% elongation (M100) elongation at break (Eb) and hardness; physical properties namely swelling number, gel fraction and thermal properties such as thermogravimetric analysis TGA of these blends under the effects of γ-radiation were followed up.
Section 1: of this investigation is directed to study the effect of gamma irradiation on physico- mechanical properties of raw NR/SBR blends in different ratios.
from all results obtained the following conclusions can be derived: The magnitude of improvement is a function of irradiation dose as well as the amount of natural rubber in the blend
1- The improvement attained in mechanical properties of raw blend has been certified by measurements of physical properties of prepared blends.
2-The thermal stability of vulcanized NR/SBR blend (50/50) was improved with respect to that of NR alone
Section 2: deals with the effect of gamma irradiation dose on the physico-mechanical properties of NR/SBR blends loaded with different types of fillers namely, Hisil, HAF carbon black, clay and TiO2. SEM was used to study the topography of the composites surfaced Hisil, HAF carbon black, clay and titanium were used as fillers at fixed content (40 phr) in NR / SBR (50/50) blend and vulcanized by gamma irradiation up to 250 kGy.
The following conclusions can be made:
1-The reinforcing ability of the four different filler can be followed using mechanical, physical and scanning electron microscopy (SEM)
2-Noticeable improvement was observed for all properties with the increase of irradiation dose up to 200 kGy and with the incorporation of different fillers.
It was established that Hisil possesses a high reinforcing effect in NR/SBR blend followed by HAF carbon black with respect to semi- reinforcing effect of clay and limited reinforcing effect of TiO2 .The efficiency of the fillers can be arranged in the following order:
Hisil > HAF carbon black > Clay > TiO2
Section 3: deals with the effect of different kinds of polyfunctional monomers on radiation vulcanization of NR/SBR (50/50) blend loaded with 40 phr HAF carbon Black to show the possibility of reducing the irradiation dose necessary to obtain vulcanized blend with reasonable mechanical properties. In this section N, N- methylene diacrylamide (MDA),trimethylol propane-trimethacrylate (TMPTMA) and tetramethylol - methane tetraacrylate (TMMT) are used as coagents at concentration of 5 phr. 3- N, N- methylene diacrylamide (MDA),trimethylol propane-trimethacrylate (TMPTMA) and trimethylol- methane tetraacrylate (TMMT) are used as coagents at concentration of 5 phr in NR/SBR (50/50) blend and vulcanized by gamma irradiation dose up to 200 kGy.
The following conclusions can be made:
1-The addition of polyfunctional monomers was found to enhance the irradiation crosslinking process of NR/SBR blend. Moreover, the efficiency of TMMT coagent on increasing the GF% values of the blend is more than that of, TMPTMA and MDA coagents. Such behavior is affiliated with the higher functionality of TMMT with respect to that of, TMPTMA and MDA. As expected, the formation of more crosslinking has improved the thermal stability of the composites which is in accordance with mechanical improved properties.
General conclusion
It can be generally concluded that the radiation vulcanized NR/SBR (50/50) blends loaded with 40 phr of HAF and 5phr TMMT coagent have pronounced good mechanical, physical and thermal properties which make it feasible for several industrial applications.