الفهرس 
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Abstract
The aim of the present work was to detect the percolation threshold value for natural rubber (NR) loaded with different concentrations of conducting graphite filler. For this task two methods were used: Method (1): In which the electrical resistivity of (p) NR composites were measured as a function of graphite content (F). An empirical formula on the form log (p/p*)= log po/p*) / [1+exp(F-Fo)/∆F] was suggested to fit the dependence of electrical resistivity (p). on graphite content (F). As a result the percolation threshold was (50 phr). Method(2): In which Laser-Induced Plasma Spectroscopy technique has been utilized for determination of the percolation threshold. from the relation of the intensity of the neutral carbon line C(I) at247.857 nm against the graphite filler concentrations. Percolation threshold was confirmed at the value of 50 phr. This confirms the validity of the result obtained by method (1). The effect of graphite concentration on the electrical DC properties was studied. It showed an Ohmic behavior for both high as well as low graphite concentration. For moderate concentrations of graphite around critical concentration (Fo) the I-V characteristics can be fitted to three stages: (i) the 1st stage IaV. (ii) the 2nd stage IaV2. (iii) the 3rd stage IaV3Measurements of AC at 100Hz to 5 MHz had the greatest impact on determining the quality of the mechanical conduction by jumping (hopping). By measuring the change of electrical conductivity (σac) and dielectric constant (ε’) with frequency (f), both showed a behavior as follows (ε’) f-v , σac fs. The peak value of the summation s+v =1 confirm the percolation threshold value at 50 (phr) of grapfite content * the physico chemical test of the invetigated samples is also measured in order to show the effect of filler on the degree of swelling. The calculation of tome-constant values(t) and swelling values (Qm) showed a clear decrease for both with increased graphite concentration. * The tensile strength as well as the elongation at break foe graphite/NR composites show a marked decrease upon increasing the graphite conttent while the modules of elasticity increase by increasing of graphite content. There is a direct relation between filler concentrations and electron density for both lines; the neutral C line was found to be self-absorbed in comparison to the Ha-line. The neutral C line intensity was rectified using the electron density ratio of neutral C line and the free self-absorbed Ha- line. Also, it was shown that surface hardness is the most perceptible properties that can be affected, and will be marked up with increased crosslink density by increasing graphite filler concentration. This phenomenon designates that graphite fillers improve the chemical cross-linking of rubber chain. The results demonstrated that there is a direct proportionality of the laser-induced plasma temperature versus the shore A mechanical hardness test.