ABSTRACT:The influence of soda lignin and thiolignin on the mechanical properties (tensile strength and elongation at rupture) as well as on the dielectric properties (conductivity (), permittivity (Ј), dielectric loss (Љ), and dielectric relaxation time ()) of their composites with natural rubber (NR) was investigated. All measurements were carried out on NR, NR/soda lignin (20 phr), and NR/thiolignin (20, 30, and 40 phr) composites. The mechanical properties reveal that NR/thiolignin composite possesses the best thermal stability and 20 phr is the optimum thiolignin loading. The dielectric study was carried out over a frequency range from 100 Hz to 100 kHz at temperature range from 20 to 80°C. Dielectric data were fitted in the frequency domain using Havriliak-Negami and Frö hlich functions in addition to the conductivity term. The different relaxation mechanisms in the system were also discussed according to these functions.

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ABSTRACT:The dielectric and mechanical properties of polystyrene(PS)/acrylonitrile-butadiene rubber (NBR) blends were studied with the aim of improving the insulation properties of NBR. Compatibility investigations, performed with viscosity and dielectric methods and confirmed with the calculated heat of mixing, indicated that such blends were incompatible. To overcome the problem of phase separation between NBR and PS, we chose epoxidized soya bean oil to act as a compatibilizer and added 3% to the blends under investigation. This led to the conclusion that a sample containing 10% PS (either pure or scrap) possessed the most suitable electrical and mechanical properties. For this reason, the sample was chosen for studying the effect of the addition of three types of fillers (quartz, talc, and calcium carbonate) in increasing quantities (up to 80 phr) on the dielectric and mechanical properties. The variation of the dielectric properties with temperature (20 -60°C) was also investigated.

Polyvinyl chloride (PVC) was chosen to be loaded with various amounts of high abrasion furnace black (HAF). The mechanical as well as electrical properties of the prepared composites were investigated. The dielectric properties of these composites were investigated in the frequency range 102—10 5 Hz at a temperature range of 30—1208C. In addition to the conductivity term, the experimental data of the dielectric losses ε'' were analyzed using a computer program based on both Havriliak—Nagami and Fröhlich equations into two relaxation processes. The first relaxation process in the lower frequency range could be attributed to the Maxwell—Wagner effect. The second relaxation could be attributed to the combination of the large scale mobilization of the chains i.e., the glass—rubber relaxation process in addition to a contribution of the motion of the large aggregates caused by the movement of the main chain, which are expected to be formed by the addition of different ingredients to PVC such as a plasticizer. The percolation threshold concentration, which is the concentration after which the conductivity increases many orders of magnitude with very little increase in the filler amount for PVC/HAF composites, depends upon the measuring temperature, whether it is below or above the glass transition of the polymer matrix. Stress—strain plot, hardness, and other mechanical properties such as stress at yield, stress at rupture, strain at yield, strain at rupture, and Young's modulus were investigated at room temperature. This investigation led to the conclusion that all the mechanical properties are improved by increasing HAF content and reaches its optimum values at about 30 phr HAF loading. On the other hand, the addition of HAF black by concentration up to 40 phr increases the electrical conductivity to be 10-10 Sm-1 at 30°C and 10-9 Sm-1 at 120°C which highly recommends such composites to be used in antistatic applications as the suitable range of electrical conductivity for such application is 10-9—10-14 S m-1.