Environmental stress crack resistance of poly(ethylene terephthalate) and poly(ethylene naphthalate)

The environmental stress crack (ESC) resistance of amorphous poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) was determined in a broad spectrum of organic liquids. Absorption studies showed that the amorphous polymers are readily crystallizable if sufficient swelling and concomitant depression of the glass transition temperature to ambient temperature occurs. Critical strains for craze initiation were determined using Bergen elliptical strain rigs and were correlated with the absorption behavior and solubility parameters of the liquids. Crystallization from exposure to liquid was found to play an important role in the formation of stable crazes in critical strain experiments.