الفهرس 
I: IntroductionOnly 14 pages are availabe for public view
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Abstract
The present work includes three chapters which involve the theoretical, the experimental background and the results and discussion.
Chapter one: Introduction Blending of a thermoplastic and an elastomer gives a class of rubbery materials known as thermoplastic elastomers which possess the good physical properties of elastomers along which the processing characteristics of thermoplastics. The introduction contains a theoretical background about the effect of radiation on the polymers and the polymer blends and the different techniques used for blends modification.. In this work we attempt to enhance the compatibility to attain a modified physico-chemical properties for blends of LDPE with different polymeric materials such as ethylene vinyl acetate (EVA), ethylene propylene diene rubber (EPDM), and styrene butadiene rubber (SBR), via electron beam irradiation with various irradiation doses. In addition, another compatibilization process throughout the incorporation of dicumyl peroxide (DCP), will be investigated Chapter two: Experimental The investigated LDPE blends were prepared by mixing an accurate weight of LDPE pellets (70 wt %) and other copolymers {EVA, EPDM or SBR (30 wt %)} in extruder mixture at 130 oC for 10 minutes. For DCP-vulcanized samples, an accurate weight of DCP (2 wt %) was added to the molten mixture after 8 minutes till complete mixing. The mixture was immediately transferred from the mixer to an open roll-mill to make a sheet. Then this sheet was pressed in a hot press at 160 oC under 15 Mpa pressure for 5 min (20 minutes for DCP samples) to obtain a rectangular sheet, (15 x 20 cm), of 1-1.2 mm thickness. The molded sheet was then transferred to water-cooled press at the same pressure for further 5 min. The changes in the physico-chemical properties, (degree of crosslinking, hot elongation, mechanical properties, thermal stability and morphology), were estimated using different techniques and the obtained results are summarized as follows: Chapter three: Results and Discussion Part one: Gel fraction and swelling characterization The gel fraction percent increases as the irradiation dose increase whereas the blank LDPE and LDPE/SBR blends have the lowest value at all irradiation doses. In addition, blends containing either EPDM or EVA have the highest gel fraction percent respectively. The maximum degree of gelatin, (gmax), for LDPE blends increase to reach 97% for LDPE/EPDM blend. The volume swelling ratio decrease with highly rate up to 150 kGy irradiation dose. LDPE/EPDM and LDPE/EVA shows the minimum rate of volume swelling ratio decrease. Finally, the rate and magnitude of induced crosslinked units are dependent on the type of compounded polymer into LDPE sample. Part two: Hot set measurements from the hot set measurements it was found that unirradiated LDPE samples failed the test immediately under elevated temperature (200 0C) and at load 20 N/mm2 for 15 minutes. 150 kGy irradiated blank LDPE and LDPE blend containing SBR still failed the test but after longer time (8-13 minutes). Also, LDPE/EVA and LDPE/EPDM blends irradiated at 150 kGy exhibited the excellent test data confirming the occurrence of higher degree of crosslinking density. On the other hand, one can notices that the peroxide cured samples exhibited much more performance at all than irradiated samples in spit of the gel fraction for both were comparable. This behaviour was believed to be due to only DCP-induced crosslinking reaction in the presence or absence of copolymer. Part three: Mechanical properties The value of yield stress as well as cold drawing were decreased as a result of addition of rubber component in the LDPE blends. For LDPE blends crosslinked by either EB irradiation or DCP vulcanization, it obvious that the yield stress and length of cold drawing are higher for EB irradiated LDPE sample than that crosslinked with DCP one, this may reflects the higher crystallinity of LDPE crosslinked by irradiation. Irradiation or DCP vulcanization of LDPE samples improve the tensile stress at break, (Ts), up to 150-200 kGy and then decrease slightly. The increase in tensile strength is attributed to the increase in crosslinking density whereas the reduction in Ts may be due to degradation (chain scission) at higher irradiation doses which causes bond rupture either in the side or in the main chains. Unlike stress at break which goes through a pronounced maximum at certain irradiation dose then rapidly decrease, the elongation at break, (Eb), is continuously decrease with increasing irradiation dose and this is due to the inverse proportional to crosslinking density. Highest elongation at break, (Eb), attained for LDPE/EPDM and the lowest for blank LDPE. Part four: Thermal stability measurement The oxygen and nitrogen DSC analysis of blank LDPE and their blends showed that there is a reduction in the melting temperature point (Tm), onset temperature (Ti) and heat of fusion (∆Hf) of the EB-irradiated blank LDPE sample is observed as compared with that of the unirradiated one. Also, the reduction in the thermal DSC parameters are continued for irradiated LDPE blends due to the blending of LDPE with various copolymers, and this reduction was also observed for DCP vulcanized samples. Moreover, the reduction for vulcanized samples (chemically crosslinked) are higher than that EB-irradiated ones (radiation-induced crosslinking). Also, the level of the reduction in the nitrogen thermographs parameter is lower than that oxygen thermographs. The reduction could be attributed to the decrease of the crystallinity as a result of crosslinking. The decrease in the crystallinity is largely dependent on the type of crosslinking reaction (radiation or vulcanized-induced crosslinking) and the type of incorporated copolymer Part five: FTIR characterization The spectroscopic analysis, (FTIR) regarding the change in the degree of unsaturation, (vinyl, vinylidine, and trans-vinylene double bonds), and sharp increase in the carbonyl, C=O upto 150 kGy then slightly decrease. The initial increase was due to the aerial oxidation of the samples during irradiation, as the irradiation dose increased the probability of chain scission and degradation increased along with the oxidation and crosslinking. The obtained spectroscopic data goes in line with the above mentioned thermal and mechanical results. Part six: Morphology The morphology reveals that the dispersion of the copolymer in the blend mixture was found to increase as a result of irradiation. The segmental miscibility of EVA and EPDM in LDPE seem to be higher than those of SBR because of higher ethylene contents in both EVA and EPDM chains.