Tensile properties electrical insulators

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

A typical cellulose-filled urea plastic has a tensile strength of 55,000 kPa, an Izod impact strength of 16 cm N/per centimeter of notch, and a coefficient of linear expansion of 3 X 10 3 cm/cm C. Urea-formaldehyde plastics have good electric insulating properties. Unlike phenolic plastics, urea plastics do not carbonize when an electric arc is placed on their surfaces. They also have a high dielectric strength. 

Ethylene copolymers were compared with liquid plasticisers for use as additives to improve the flexibility of poly(vinyl chloride) (PVC) for electrical cable insulation applications. The PVCs were assessed by determining smoke generation, flammability, tensile properties and the low temperature brittle point. The ethylene copolymers gave similar peak heat release rates, but the peak smoke and the total smoke generation were lower. They also gave similar or increased strength, similar elongation and flexural modulus, and lower brittle point temperatures. 4 refs. 

Wire and cable Thermoplastics and elastomers are widely used as electrical insulating material due to their physical properties and processability. Cross linking is an effective means for improving e.g. the thermal resistance and tensile strength. EBA-irradiation ( 50 kGy) affords a rapid, well controlled cross linking and is used by several major producers of thin wires and cables. 

Properties Improved/FUlers Chemical Resistance FI eat Resistance Dimensional Stability Tensile Strength Stiffness Impact Strength Hardness Lubricity Electrical Insulation Electrical Conductivity Thermal Conductivity Moisture Resistance Processability Recommend for Use in ... 

The main attributes of properly cured epoxy systems are outstanding adhesion to a wide variety of substrates, including metals and concrete ability to cure over a wide temperature range very low shrinkage on cure excellent resistance to chemicals and corrosion excellent electrical insulation properties and high tensile, compressive, and flexural strengths. 

Fillers may be divided into particulate and fibrous types. Particulates include calcium carbonate, china clay, talc and barium sulphate. Fillers affect shrinkage on moulding and the dimensional stability of the finished plastic, increase tensile strength and hardness, enhance electrical insulation properties and reduce tackiness. They also impart opacity and colour (Figure 3.16). Carbon black is now the most widely used filler for polymers usually in the form of furnace carbon black, which has a particle diameter of 0.08 mm. Fibrous fillers reinforce polymers and greatly increase their tensile strengths. They include fibres of glass, textile and carbon. Plastics filled with fibrous fillers are known as composites. 

Linear Low Density Polyethylene Linear polyethylenes with density 0.91-0.94 g/cm. Has better tensile, tear, and impact strength, and crack-resistance properties, but poorer haze and gloss than branched low-density polyethylene. Processed by extrusion at increased pressure and higher melt temperatures compared to branched low-density polyefliylene, and by molding. Used to manu-faeture film, sheet, pipe, electrical insulation, liners, bags, and food wraps. Also called LLDPE. 

Polymethylpentene Thermoplastie stereoregular polyolefin obtained by polymerizing 4-methyl-1-pentene based on dimerization of propylene has low density, good transpar-eney, rigidity, dieleetrie and tensile properties, and heat and ehemieal resistanee. Proeessed by injection and blowmolding and extrusion. Used in laboratory ware, coated paper, light fixtures, auto parts, and electrical insulation. Also called PMP. 

In their function as fillers, the organic spheres share the performances and benefits of the spherical form, similar to glass and ceramic spheres. However, their effect on a polymer matrix is normally not the enhancement of mechanical strength, such as tensile strength and abrasion resistance. Instead, they can impart new features to thermoplastics and thermosets, such as reduced density, improved resilience and ductility, mechanical and thermal stress absorption, or enhanced thermal and electrical insulating properties. When added to binders and plastisols for coatings, the function of the spheres can be surface modification of the coated surface this may include the creation of a visual effect or antislip properties, or to make a protective coating [2, 3]. 

The final products of cast phenol-formaldehyde polymers have a number or exceptional properties, including high tensile and compressive strengths, good electrical insulating capabilities, and excellent adhesive qualities. Also, they can be polished and machined. Finally, the presence of very small water droplets in the material gives the surface a superb appearance. 

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