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 POLYPROPYLENE Polypropylene has excellent dielectric strength, excellent chemical resistance and outstanding heat resistance. Its moisture absorption is practically nil and unsurpassed in flexural strength. Unlike polyethylene, polypropylene is not prone to environmental stress cracking. It is harder than polyethylene and has greater tensile strength. Although its heat resistance allows usage is up to 80°C, it does tend to become brittle below 0°C. The chemical resistance of polypropylene is outstanding. At room temperature it is essentially insoluble in common solvents. Polypropylene resists acids, alkalies, moisture and salt solutions. It is attacked by strong oxidizing agents such as concentrated nitric acid, hydrogen peroxide and wet chlorine especially at higher temperatures. Ultra violet light and direct sunlight degrade polypropylene unless it is modified by additives. Welding of polypropylene should be done with nitrogen or dry air as oxygen at high temperatures tends to degrade the material. Common mill shapes are: sheet, rod, pipe, tubing and spheres.
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