Environmental Engineering Reference
In-Depth Information
also yield the soft, pliable feel to some types of “cling” films (Sablani and
Rahman, 2007).
14
Molecules such as phthalates have polar structural features that can
molecules are able to readily mix with the long-chain polymer molecules
weakening the polymer-polymer attractive forces (van der Waals forces)
that impart rigidity to the material. In so doing, the plasticizers increase
the “free volume” or the interchain space available in the plastic, making it
easierforsegmentsofthelongchainstoflexandslidepasteachothereasily.
These molecular-level changes are reflected in corresponding changes in
lowering of the modulus (or increasing flexibility) as well as the glass
transition temperature Tg (C) of the plastic material (
Fig. 4.13
).
