PP Chemical Resistance

HMC Polymers’ polypropylene resin portfolio (Moplen, Adstif, Clyrell and Purell), like most polyolefins, are highly resistant to solvents and chemicals.

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Moplen Chemical Resistance PDF download
Chemical resistance data presented for a range of over 260 chemicals and substances is based on ASTM D543.

Testing method
Unstressed resin specimens are used measuring 76mm (3") long x 0.635mm (0.025") thick, in the shape of dumbbells. Results are reported after 1 month immersion.

Important: As it is difficult to create actual service conditions in the laboratory, the results of many of the environments should be taken only as an indication of behaviour in service.

Polypropylene chemical resistance capability
Polypropylene resins have outstanding resistance to water and other inorganic environments. In most aqueous environments, its weight increase is less than 0.2% when it has been stored for 6 months at ambient temperatures. When the temperature is increased to 60°C (140°F), the weight increase is less than 0.5% for a similar period. According to ASTM D570, its 24 hr water absorption rate is 0.03%. It resists most strong mineral acids and bases, but, like the other polyolefins, it is subject to attack by oxidizing agents.

Polypropylene resins are appreciably affected by chlorosulfonic acid and oleum at room temperature, 98% sulfuric acid, 30% hydrochloric acid, and 30% hydrogen peroxide at 100°C (212°F). They are also affected by 98% sulfuric acid at 60°C (140°F) and fuming nitric acid and liquid bromine at room temperatures. Under strain, failure could occur with strong oxidizing acids at temperatures lower than those mentioned. With few exceptions however, inorganic chemicals produce little or no effect on PP resins over a period of 6 months at temperatures up to 120°C (248°F).

The permeation resistance of PP resins to organic chemicals depends on the rate and extent to which absorption occurs. This, in turn, affects the suitability of the resin to serve in a particular environment. When the resin is removed from the environment, evaporation will take place and cause it to return almost to its original dimensions. Property changes resulting from the absorption will be reversed if evaporation is complete.

Temperature and polarity of the organic medium are the foremost factors in determining the extent of absorption by polypropylene. Absorption becomes greater as temperatures are increased and polarity of the medium is decreased. PP copolymers swell more than homopolymers, indicating greater absorption. Such nonpolar liquids as benzene, carbon tetrachloride, and petroleum ether have a higher absorption rate with PP than polar media such as ethanol and acetone.

Some reduction in tensile strength and an increase in flexibility and elongation-to-break in tension can be expected, depending on the nature and amount of the organic medium absorbed.

PP resins have excellent resistance to environmental stress-cracking. When they are tested according to ASTM D1693 the brittle fractures that occur with certain polyethylenes in contact with polar organic liquids, detergents, and silicone fluids are not observed. Failure of this type with polypropylene is rare. Those environments known to cause such cracking to polypropylene are 98% sulfuric acid, concentrated chromic/sulfuric acid mixtures, and concentrated hydrochloric acid/chlorine mixtures.

The useful life of PP resins at elevated temperatures is limited by oxidative degradation. The expected life of PP at any given temperature is also determined by the nature of the environment, and by the extraction of some of the antioxidant system. Any environment that tends to extract the antioxidants may lead to more rapid breakdown of the polypropylene, especially at elevated temperatures.