الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Rubber- Plastic blends are a new class of materials in which the properties of vulcanized rubbers are imbedded with the ease of processing of thermoplastics. These blends are insulators and one can achieve the desired properties by the suitable selection of many parameters such as the blend ratio, type of filler, crosslinkers and preparation technique.
It is well known that the electrical behavior of these heterogeneous systems reflects a mechanism of percolation where the performance of these blends with different affinities of carbon black provides an opportunity to control its state of aggregation and connectivity that are in physical contact. Hence, the percolative model gives a suitable explanation, within experimental limits of the dc-electrical properties of that system. Also, the dielectric properties of carbon black loaded EPDM-PP composites follow the percolative type model which are discussed in terms of interfacial Maxwell-Wagner Polarization effects. Therefore, the effect of γ-irradiation on the percolation threshold that explained by several methods has a great importance to optimize the end-use property of the desired blend, where the first induced reaction for polymeric materials by γ-irradiation is used on the industrial scale as dosimeters.
The choice of the two main components of a thermoplastic elastomer blend are ethylene-propylene-diene rubber (EPDM) and (PP) in accordance to their wide applications specially against radiation doses. However, the additional filler such as carbon in the blends are used to enhance the specific properties. All samples should pass the same procedure under the same circumstances during preparation, since sample preparation depends largely on the order of adding the ingredients and time of mixing and processing. In this work, PP is added with maleic anhydride, MAH, in the laboratory internal mixer (PL-2000, C. W. Brabender) with a rotor speed of 80 rpm at temperature 175°C. After two minutes, EPDM, stearic acid, resin, ZnO, paraffin wax, and carbon black are added for about two to three minutes. Mixing is continued with the curatives 137 (sulfur, S, tetramethyl thorium disulphide, TMTD, stannous chloride catalyst, SnCl22H20, and Dibenthiazyl disulfide, MBTS) on a hot two-roll mill at 60-80 °C with a 2-mm nip shortly after they are taken out of the internal mixer. The output sheets are pressed for 10 minutes at 180 °C and a pressure of 13.8 MPa in an electrically heated compression molding press. The moldings are cooled under compression to maintain dimensional stability and flatness.
A60Co source of gamma facility ”Issledovatel” manufactured by the candidate technical science in Russia and represented at the National Center for Radiation Research and Technology (NCRRT) is used for γ-irradiation.
Swelling measurements are performed on uniformly circular cut of the samples with 5-mm diameter and 1.75-mm thick, by the immersion/gain method where the samples are dried overnight in a vacuum desiccator, and then the original weights are taken. The blend specimens are immersed in the desired solvent at room temperature. At regular time intervals, the test samples are dried gently between filter paper wraps to remove any excess solvent on the sample surface, weighted immediately using a digital balance of accuracy 0.1-mg, and placed back into the test bottles. Six organic solvents, liamely, chloroform, toluene, benzene, carbon tetrachloride (Ccl4),dimethyl formamide (DMF), and dimethylsulfoxide (DMS) that used as received, have employed for these measurements.Measurements of the ac-electrical properties for the blend samples that prepared in the form of discs of diameter 0.9 cm are obtained -usmg, z. ”Programmable Automatic RCL meter PM 6304 PHILIPS” at a frequency range 60 Hz - 105 Hz. Good contact is attained through coating the samples on both sides with conducting silver pasteThe dc-electrical conductivity measurements are done on a Kiethley 617 programmable electrometer and using smoothly power supply that can be adjusted between 0-2 KV.
It is found that the maximum degree of swelling of CB/EPDM-PP blends are decreased as a function of y-irradiation dose at different solvents. This behavior reflects the formation of a crosslinked network up to 3 Mrad, while, their behavior starts to saturate with increasing the carbon black concentration. Also, the average diffusion coefficient, Davg, and the penetration rate, P, values suggest an inverse dependence with the molecular weight of the used diffusing solvents. Moreover, these values are found to be clearly dependent upon the carbon black concentration indicating the portion of percolation behavior.
It is clear from the obtained swelling data, that both the (CB/EPDM-PP)-solvent interaction parameter, u,, which is employed the obtained 8 value, and the (EPDM-PP)-filler interaction parameter, m, which is estimated by using Kraus equation confirmed the right choice of the solvents used throughout this work, namely, chloroform, toluene and benzene. Also, fair agreement between theV
simulated and experimental sorption profiles over the entire time scale of the sorption experiment are indicated a slight deviation from a Fickian transport mechanism mode (I).
from the maximum degree of swelling measurements for all samples as a function of y-irradiation, the sample SB7 (60 phr) exhibits a good differentiation where it lies at the portion of higher sensation. Hence, it can be used as a dosimeter in the y-dose range 1-10 Mrad by the investment of the obtained linear relation and employment of the equilibrium swelling data.
A straight forward indication about the structure improvement from the values of the crosslink density, ve, with y- irradiation dose up to 3 Mrad for EPDM-PP blends loaded with different concentrations of carbon black. In case of good solvents, the behavior is percolative and the critical threshold is determined (-30 phr).
The effect of filler loading on the o”dc values of EPDM-PP blends reflects a mechanism of percolation where a relatively sharp increase above a certain critical concentration (>30 phr) is detected according to the degree of dispersion of carbon black in the blend by either aggregate-aggregate or aggregate-blend upon the interphase. While, the conduction mechanism of carbon black filled EPDM-PP blend
systems are estimated where the ”Poole-Frenkel type”, (3PF, is found
in good agreement with Ptirco above the percolative threshold (30 phr), while the experimental values obey ”Schottky emission” below the threshold carbon-black concentrations.
Evaluation of the average separation distance, d, between carbon black particles/aggregates confirms the blend system on loading.Rubber- Plastic blends are a new class of materials in which the properties of vulcanized rubbers are imbedded with the ease of processing of thermoplastics. These blends are insulators and one can achieve the desired properties by the suitable selection of many parameters such as the blend ratio, type of filler, crosslinkers and preparation technique.
It is well known that the electrical behavior of these heterogeneous systems reflects a mechanism of percolation where the performance of these blends with different affinities of carbon black provides an opportunity to control its state of aggregation and connectivity that are in physical contact. Hence, the percolative model gives a suitable explanation, within experimental limits of the dc-electrical properties of that system. Also, the dielectric properties of carbon black loaded EPDM-PP composites follow the percolative type model which are discussed in terms of interfacial Maxwell-Wagner Polarization effects. Therefore, the effect of y-irradiation on the percolation threshold that explained by several methods has a great importance to optimize the end-use property of the desired blend, where the first induced reaction for polymeric materials by y-irradiation is used on the industrial scale as dosimeters.
The choice of the two main components of a thermoplastic elastomer blend are ethylene-propylene-diene rubber (EPDM) and (PP) in accordance to their wide applications specially against radiation doses. However, the additional filler such as carbon in the blends are used to enhance the specific properties. All samples should pass the same procedure under the same circumstances during preparation, since sample preparation depends largely on the order ofSUMMARY
Rubber- Plastic blends are a new class of materials in which the properties of vulcanized rubbers are imbedded with the ease of processing of thermoplastics. These blends are insulators and one can achieve the desired properties by the suitable selection of many parameters such as the blend ratio, type of filler, crosslinkers and preparation technique.
It is well known that the electrical behavior of these heterogeneous systems reflects a mechanism of percolation where the performance of these blends with different affinities of carbon black provides an opportunity to control its state of aggregation and connectivity that are in physical contact. Hence, the percolative model gives a suitable explanation, within experimental limits of the dc-electrical properties of that system. Also, the dielectric properties of carbon black loaded EPDM-PP composites follow the percolative type model which are discussed in terms of interfacial Maxwell-Wagner Polarization effects. Therefore, the effect of y-irradiation on the percolation threshold that explained by several methods has a great importance to optimize the end-use property of the desired blend, where the first induced reaction for polymeric materials by y-irradiation is used on the industrial scale as dosimeters.
The choice of the two main components of a thermoplastic elastomer blend are ethylene-propylene-diene rubber (EPDM) and (PP) in accordance to their wide applications specially against radiation doses. However, the additional filler such as carbon in the blends are used to enhance the specific properties. All samples should pass the same procedure under the same circumstances during preparation, since sample preparation depends largely on the order of
jrium disulphide, TMTD, stannous chloride catalyst, ad Dibenthiazyl disulfide, MBTS) on a hot two-roll 3C with a 2-mm nip shortly after they are taken out of lixer. The output sheets are pressed for 10 minutes at a pressure of 13.8 MPa in an electrically heated molding press. The moldings are cooled under to maintain dimensional stability and flatness.
a source of gamma facility ”Issledovatel” manufactured date technical science in Russia and represented at the titer for Radiation Research and Technology (NGRRT) is radiation.
----...remsnts performed on uniformly circular cutVI
Good agreement is found between the critical exponent, P, and the fitting parameter, K„, values of both the experimental and the theoretical percolative model reflecting CdC, crac and s’ dependence on loading above the critical percolative threshold.
Finally, a new imagination that relates the o~ac values (at 300 Hz) of the blends above Oc as a function of y-dose is deduced by representing the function P (D) in the percolative model directly as follows:
aac = K01 (0-<Dc)-p(D)Therefore, one can suggest that the CB loaded EPDM-PP blends above Oc (> 30 phr) can be easily used as a dosimeter in the y-dose range of 0- 3 Mrad. While, below 4>c (< 30 phr) can be used as a product that has radiation protect property.