Environmental Engineering Reference
In-Depth Information
7.3 PHTHALATE PLASTICIZERS
Worldwide, over 6 million tons of phthalates are produced annually. They
are colorlessliquids having theconsistency ofoil,sparingly solubleinwater,
but very soluble in plastic matrices (as well as in adipose body tissue.)
At least 95% of the production ends up in plastics and other consumer
products. They are also used in cosmetic formulations such as nail polish
(impartscrackresistance)andinhairspray.Itsbest-knownuseisinplastics
as a plasticizer, mostly in PVC, to soften the hard, brittle plastic. It is the
same plastic, PVC, that is used in siding and water pipes that is also used
in soft flexible automobile seat covers and in shower curtains. In the latter
cases, the PVC is intimately compounded with up to 50-60% of an organic
phthalate to plasticize the resin. Notebook covers, children's toys, rainwear,
and backpack components used by children as well as some flexible
transparent medical tubing and blood bags are also made from plasticized
PVCmaterial.Phthalatesbeingonlydissolvedinthepolymer(notcovalently
bound) can leach out into fluids in contact with the vinyl under some
conditions.
Plasticizer molecules as a rule are highly compatible with plastics and, like
all good solvents, easily disperse in between the long chain-like polymer
molecules. This essentially increases the free volume between chains,
reducing interchain attraction and allowing increased mobility in the
polymer chain segments. With reduced interchain attraction, chains can
move about easier resulting in a softer polymer. A plastic such as PVC
becomes progressively softer (and its glass transition temperature Tg (°C)
decreases),anditsmodulusandhardnessalsodecreaseasincreasingweight
fractions of plasticizer are mixed into the plastic (
Fig. 7.4
).
