Recovery of amorphous poly(ethylene terephthalate) film uniaxially drawn just below the glass transition temperature

Isothermal recovery in the macroscopic length of homogeneously deformed spe cimens of amorphous poly(ethylene terephthalate) (PET) film sample uniaxial ly drawn at 69 degrees C to the draw ratios lambda(0) = 1.26-2.20 were stud ied at temperatures around the glass transition temperature (T-g = 73 degre es C). Experimental results indicate that the length recovery look place in two distinct steps: a fast first step (fast relaxation) followed by a slow second step (slow relaxation). The relaxation processes were accompanied b y the reversion of trans-conformers (1340 cm(-1)) to gauche, and the dichro ic function of the 1340 cm(-1) band characterizing the segmental orientatio n along the chain direction decreased to a very low value at the end of the fast relaxation. This fact led us to assign the fast relaxation as the seg mental orientation while the slow relaxation as relaxation of the global ch ain orientation. It was found that the slow relaxation follows a single exp onential function, with relaxation times strongly dependent on the temperat ure resembling the glass transition process. The fast relaxation does not f ollow a single exponential decay, presumably a distribution of relaxation t imes is involved.