Both PEEK and PEKK are members of the polyaryletherketone (PAEK) family, commonly referred to as polyketones. Henri de Vries, Senior Composites Scientist, Structural Technology Department, Netherlands Aerospace Center (NLR), said: "PEKK and PEEK are very similar in appearance and crystallization behavior, but the process temperature is different, PEKK is 375°C, while PEEK is 385°C. °C.” NLR and GKN Aerospace’s Fokker Technologies are very interested in the development of thermoplastic composite (TPC) technology in the first and second phases of the project “Thermoplastic Affordable Aircraft Primary Bearing Structures (TAPAS)” He has made achievements, successfully developed a torsion box with a span of 12m, and recently made a 6m long and 28mm thick carbon fiber reinforced PEEK engine hanger upper beam by using automatic fiber placement technology (AFP) and autoclave curing technology. De Vries found that PEKK was more suitable for AFP because of its wider process window.

In contrast, the process window of PEEK is in the range of 385-390°C, and the process requirements are relatively harsh, and the process conditions of 360°C are obviously not ideal. For PEKK, 355°C is also a good processing temperature. So not only is the lower temperature limit of the process window lower, but it also spends a little longer in the liquid state and cures better. De Vries added that pressure forming is a faster two-step curing process than vacuum bag autoclaving. And for pressure forming, PEKK is an interesting material. The old specification system of PEKK is too slow for pressure forming, and the new specification of PEKK is better and cheaper than PEEK.