الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Polymer industry represents one of the fastest growing area of technology • A considerable portion of this growth has taken place in the area of electrical insulation , where the high resistivity, high dielec¬tric breakdown strength , and cost had been a prime importance •
Theories concerned with electrical conduction in polymers have recently received considerable interest and have been much developed •
One of the major problems of polymers science is to set up a complete analysis of the composition , stru¬cture , and the correlation between them and the physical properties of a given polymer .
Moreover , the electrical response of a polymer is profoundly affected by the mechanical stress applied to a given Dolymer .
The major rubber used throughout this work is styrene-butadiene rubber in view of its large application in rubber industry • The crumbs of 40 HAP/SBH were used as a compounded ingredient after a simple grinding process
All samples Passed the same procedure under the same circumstances during preparation , since sample properties depend largly on the order of adding the mater¬ials and the time of mixing and processing • All rubber mix cures were prepared on a two-roll mill l70 mm dia.,
working distance 300 mm , speed of slow roll 24 rev./min. and gear ratio 1.4 •
The compounded rubber was left for at 1 east 24
hours before vulcanization . The rubber vulcanization wasconducted at 143 -2cº under a pressure of about 40 Kg/cm and the time of vulcanization was 20 min., to ensure stable properties without affecting the electrical properties . Different concentrations of the pre-vulcanized 40 HAF/SBR powder having a certain particle size ( 200 - 500µm ) were introduced into SBR •
Simple devices were proposed to allow for measur¬ing electrical resistivity of the above samples under different types of mechanical stresses (compression & extension )
The temperature was controlled by means of an
electrical oven in the range ( 20 - 140 cº ) .
A Keithley digital electrometer 616 was employed for low-conductivity measurements .
This work deals mainly with two subjects • One is concerned with studying the effect of both thermally accelerated ageing and filler concentration on the electr- ical properties of SBR vulcanizates .
The second subject is studying the effect of applying static strain ( compression & extension ) in cycles on the electrical properties of the above samples.
During the thermally accelerated ageing at 70 Cº in air for 60 days, the above samples- were subjected to repe¬ated measurements of the degree of swelling: Q Vs. -time of swelling in Kerosene , t •
The maximum degree of swelling . Qmax was found to
Decrease by increasing the filler concentration up to 40
phr ( Fº ) owing to the formation of chemical high-energy
carbon-rubber bonds . Meanwhile , by further increasing of
filler concentration ( 40 - 200 phr ) Qmax increases due
to the presence of physical adsorption of rubber on carbon
black forming low-energy rubber-carbon bonds which are easily breakable by the action of solvent molecules •
It was found that the dependence of the electrical
resistivityᵩ of filler-SBR composites on the concentrat-
ion (F ) of the filler at 35 Cº illustrates peculiar behaviour which in turn reflects also a minimum point that confirms the suggestion that upon increasing the filler concentration ( F ) , the carbon-carbon bonds contribute to the conduction process ( till F ≈F , and upon increas¬ing filler concentration ( F ) , the probability of form-ation of carbon-rubber bonds hinders the formation of carbon-carbon bonds
An empirical formula was proposed to account for the relation between the electrical resistivity p and filler concentration ( F ) .
It WRS ’found that , the thermally activated nature of conduction is a characteristic behaviour of poorly con-ductive compositions . This in turn may confirm the sugge-stion that the conduction is independent of the conductive filler and is mainly related to the host SBR material •
The ohmic behaviour in IxVn curves obtained for
all samples could be judged by the value of the index n
which is highly affected by filler concentration . The dependence of the index n on the filler concentration (F) at 35cº also exhibits a minimum point which -in turn -reflectsthe type of the predominating contact ( carbon -rubber bonds ) •
The effect of static cyclic strain ( compression & extension ) on the electrical resistivityp of ( 10, 40, and 80 phr ) of filler-SBR vulcanizates was studied
In the case of compression , large fluctuations of electrical resistivity p upon loading and unloading were recorded and ascribed to breakdown and alignment of the filler chains in the direction of strain , i.e. the elec-trical resistivity p decreases uponloading •
In the case of cyclic static extension , an inverse influence compared with that of static cyclic compression was detected •
Finally , the effect of pre-coraT>ression on the temperature-dependence on electrical resistivity p of the above three samples was studied • .
.At low Tiller concentration , a slight decrease in resistivity p was found due to the change in contact resis tance between the adjacent carbon particles in the rubber But at higher concentration of filler , a smaller effect could be detected due to the closer packing of the filler particles ,
Microvoids and cracks were detected even by ordin¬ary optical microscope during electrical measurements upon increasing the siiatic compression cycles which reflected the low influence of the filler in the reinforcement of the SBR vulcanizates.