266 HIGH PERFORMANCE POLYMERS
PET. Alternatively, multilayer films can be formed
in a continuous lamination process using heat or
optionally adhesive layers to bond the separate layers.
Press lamination can also be used to form multilayer
films by pressing layers of individual films at elevated
temperature and pressure. Prior to film formation, the
polymers are generally dried by heating to a temper-
ature of 5
◦
C below the crystallization temperature of
the polymer under vacuum or inert atmosphere. The
films can be rapidly cooled after extrusion to inhibit
crystallization [59].
Unoriented multilayer films are useful in a num-
ber of end-uses, including thermoforming processes,
forming shaped articles, such as bottles, or they can
be stretched to form oriented ...