Thermal stability and crystallization kinetics of poly(ether ether ketone)

Thermogravimetric analysis (TGA), dynamic rheological analysis and polarized light microscopy were used to assess the thermal stability of poly(ether ether ketone) (PEEK). Samples were exposed to temperatures in the range 385-415 degrees C for times up to 30 min in both air and nitrogen atmosphere. The results indicated that neither TGA nor dynamic rheological analysis detected PEEK degradation at temperatures up to 415 degrees C and heating times up to 30 min in nitrogen. It is suspected that degradation, chain branching, and crosslinking occur in PEEK at high temperatures in the melt. In nitrogen atmosphere, the growth rates of spherulites at 290 degrees C and 300 degrees C leveled off for melting temperatures around 400 degrees C and decreased with increasing melting temperature. This study suggests that when the melt of PEEK has been equilibrated at 400 degrees C for 15 min in nitrogen, the subsequent crystallization behavior (isothermal and nonisothermal) is nearly independent of the prior thermal history. The rates of crystallization of PEEK then were measured in the temperature range of 270-325 degrees C. Kinetic analysis indicated that PEEK exhibits a regime II --> III transition at 296 degrees C.