PipeSak®
Chemical Resistance of Polypropylenes
Polypropylene is essentially inert and resistant to a great
variety of chemicals at temperatures much higher than those
tolerated
by
other
thermoplastic
materials.
It
is
unaffected by aqueous solutions of inorganic salts and by
practically all mineral acids and bases, even when highly
concentrated and at temperatures over 140° F. It resists up
to 80% sulfuric acid and concentrated HCL up to 212° F. It
can withstand saline solutions at temperatures over 212° F.
Its resistance to organic solvents below 175° is also good
(see Table 5).
Polypropylene is subject to slow attack by oxidizing acids.
If it is to be used in the presence of strong oxidizing
chemicals, suitable anti oxidants must be added to prevent
degradation.
Effect of Inorganic Compounds
Water and other inorganic environments have essentially no
effect on polypropylene. Only oxidizing compounds have a
significant effect upon polypropylene. They attack the
polymer chain and modify the chemical structure, causing
the material to lose its good mechanical properties. This a
typical
oxidizing
phenomenon.
Temperature
plays
an
important role in this type of reaction.
Sulfuric acid should not exceed 50% concentration up to
140°
F.
Concentrated
nitric
acid,
oleum,
and
chlorosulphonic acid are not recommend for use even at room
temperature. Gaseous bromine will react with polypropylene,
destroy the crystalline structure, and render the material
brittle. Only dilute solutions of free chlorine or bromine
do not attack polypropylene.
The effects of chlorites and hypo chlorites depend largely
upon
temperature
and
concentration.
Salts,
even
in
concentrated aqueous solutions and solutions of alkaline
nature, have no effect up to 212° F, provided they are not
oxidative substances.
Effect of Organic Compounds
Polypropylene is more resistant to organic chemicals than
are most other commercially available thermoplastics. At
room temperature, polypropylene is insoluble in practically
all organic solvents.
The extent to which such solvents are absorbed by
polypropylene depends on a number of factors, notably
temperature and the polarity of the solvents. Absorption
becomes greater as temperature increases and polarity of
the solvent decreases. In other words, polypropylene is
inert to polar compounds such as ethanol and acetone, while
non-polar solvents such as benzene, carbon tetrachloride,
and petroleum ether will cause swelling. Correspondingly,
mechanical properties deteriorate with prolonged exposure.
Table 5 can be used to view how polypropylene reacted with
various substances at various temperatures.