Thermal and Crystallization Properties of the Alternated Tere/Iso PEKK Copolymer: Importance in High-Temperature Laser Sintering

Abstract

High-temperature laser sintering (HT-LS) is a very promising additive manufacturing process for the production of parts of complex geometry for highly demanding applications. Poly(aryl ether ketone) polymers such as poly(ether ketone), poly(ether ether ketone), and poly(ether ketone ketone) (PEKK) have attracted increasing interest during the last decade for use in HT-LS. Among them, PEKK offers the advantage of exhibiting tunable melting temperature and crystallization rate due to its copolymer structure. Indeed, PEKK is synthesized by Friedel-Crafts polyacylation condensation of diphenyl ether with terephthaloyl chloride (T units) and isophthaloyl chloride (I units). In this work, we focus on a specific member of the PEKK family having a regular alternated T/I structure, PEKK 50/50, and study its isothermal crystallization from the melt at various crystallization temperatures (TC), from 200 °C to 290 °C. A quantitative analysis based on X-ray scattering and differential scanning calorimetry experiments is performed. Primary crystallization dominates the process with a half-time of crystallization higher than 6 min and an Avrami exponent between 2.2 and 3. Stacks of periodic crystalline lamellae are first created, followed by lateral growth of these crystalline lamellae, leading to a gradual increase of the weight crystallinity. Crystalline form I, with traces of form III, is mostly observed regardless of TC. The amount and perfection of the crystalline phase increase with TC. The crystalline state achieved, as well as the thermal and rheological behavior of PEKK 50/50 during crystallization at high TC(∼280-290 °C), are promising for use in HT-LS manufacturing.