Effect of intermediate solvents on poly(ether ether ketone)

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Tech


The interaction between poly(ether ether ketone) (PEEK) and three solvents (i.e., methylene chloride, tetrahydrofuran, and acetone) was studied by means of several complementary techniques. A series of eleven 0.3 mm thick PEEK films was produced. Each film had a certain crystallinity index and crystal morphology, as revealed by optical microscopy, differential scanning calorimetry (DSC), and wide angle X-ray scattering (WAXS). Dynamic solvent uptake measurements were performed on each film with the three solvents. Methylene chloride swelled both amorphous and semi-crystalline PEEK to high degrees, while tetrahydrofuran and acetone swelled amorphous PEEK only. After desorption, the samples were carefully analyzed to characterize solvent-induced crystallization (SINC), which occurred in amorphous PEEK exposed to all three solvents. Diffusion of methylene chloride and tetrahydrofuran in amorphous PEEK was observed in fractured specimens by scanning electron microscopy, while SINC was followed by DSC. The SINC process was found to be diffusion controlled. Diffusion of both solvents through the polymeric film took place in the first third of the equilibrium time, while swelling occurred in the remaining time.

The mechanical properties of all solvent-exposed PEEK films were tested by three types of experiment (i.e., glass cone technique, microtensile tests, and tensile test in the environmental scanning electron microscope (ESEM)), which were first verified with another semi-crystalline thermoplastic polymer, isotactic polypropylene. PEEK specimens were stressed in the inside of glass cones and immersed in a series of solvents. Differences among solvent uptakes of stressed and unstressed specimens were explained in terms of crazing and SINC. Microtensile tests were performed on completely swollen PEEK specimens. Plasticization and delocalized crazing were found in the case of amorphous PEEK exposed to the three solvents and semi-crystalline PEEK exposed to methylene chloride, while classical crazing occurred in the other specimens. Finally, an amorphous PEEK specimen was swollen in acetone and stretched in the ESEM in acetone vapor. A very ductile deformation was observed, which occurred at the necked region between two notches. The results are discussed in terms of Tg depression and plasticization.



absorption, crazing, environmental stress cracking