Anisotropic linear thermal expansivity of poly(ether-ether-ketone)

This paper deals with anisotropic behavior of thermal expansivity (α) of poly(ether-ether-ketone) (PEEK) sample prepared by compression molding above the melting point of polymer. The α was determined using thermo mechanical analyzer (TMA) for the temperature interval 50–250 °C in expansion mode. It is found that out-of-plane thermal expansivity (αz) is 3.8-fold of the in-plane thermal expansivity (αxy) below the glass transition temperature (Tg) of PEEK while αz is decreased to 1.8-fold of the αxy above the Tg. Moreover, the average αz over the range studied is about 2.2-fold of the αxy. This anisotropic behavior may be attributed to the alignment of polymer spherulites and chains along in-plane direction due to compressive forces under hot compression molding.