Een Uitgebreide Studie van PCCD-gebaseerde Materialen: Morfologie, Kristallisatie en Fysische Veroudering

Amphora™ SP1621 was recently introduced to the market by Eastman Chemical Company as a material for selective laser sintering (SLS). SLS, one of the most widely used additive manufacturing techniques, employs a high-power laser to sinter polymer powders in a layer-by-layer fashion, producing solid printed parts. The method is well known for its ability to fabricate components with complex geometries and favorable mechanical properties. Amphora SP1621 is marketed as recyclable and, being a thermoplastic elastomer, it offers elastomeric properties—an attractive feature in a market largely dominated by thermoplastic materials such as PA12 and PA11. Amphora SP1621 is a semi-crystalline segmented copolyesterether consisting of crystallizable poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD) blocks and amorphous polytetrahydrofuran (PTHF) blocks. PCCD as a homopolymer is known as a crystallizable, tough, and rigid polyester. However, literature on PCCD-PTHF block copolymers is very limited, and almost no data are available on their semi-crystalline morphology or crystallization kinetics. This lack of information hinders the optimization of thermal processing protocols and complicates property assessments of Amphora SP1621. In the context of SLS, two thermal phenomena are particularly critical for print quality: crystallization and physical ageing. To address these gaps, a full morphological and phase-behavior study of PCCD-PTHF was carried out using NMR, DSC, time-resolved SAXS/WAXS, FSC, POM, and AFM. At a cooling rate of 10 K/min, the copolymer was found to crystallize in a triclinic unit cell via a two-step mechanism: primary crystallization produced spherulites with amorphous pools between primary lamellar stacks, followed by secondary crystallization forming new stacks in these amorphous regions with lamellae of the same thickness. To isolate the crystalline behavior of PCCD without the influence of amorphous PTHF, a PCCD homopolymer was synthesized. It also crystallized into spherulites from lamellae, but the extent of secondary crystallization was far less pronounced than in the copolymer. Both PCCD and PCCD-PTHF were found to be thermally unstable under prolonged high-temperature annealing. The main mechanisms were identified as transesterification for PCCD-PTHF and a combination of condensation reactions and isomerization for PCCD, increasing the molar mass. Stabilization strategies were developed and successfully applied, which was crucial for enabling reliable crystallization kinetics studies requiring long heating times. Crystallization kinetics were then investigated using FSC, POM, and SAXS/WAXS, with a focus on PCCD-PTHF. This material exhibited two distinct temperature regimes, where different nucleation pathways dominated depending on the crystallization temperature when crystallization occurred isothermally from the melt or during non-isothermal cooling at different rates. This bimodal behavior was absent in crystallizations from the glassy state and in PCCD homopolymer, which crystallized similarly regardless of whether it originated from the melt or glass. To complete the analysis, Amphora SP1621 powder was also studied; unlike PCCD-PTHF, it did not display strong rate dependence in the studied rate range, likely due to additives present in the commercial formulation. Finally, a low-molecular-weight, fully amorphous PCCD was synthesized to study physical ageing via FSC. Ageing, defined as structural relaxation in the supercooled liquid state near and below the glass transition, leads to embrittlement of the material. While polystyrene has been extensively studied in this context, no data previously existed for PCCD-based materials. Therefore, PS samples of varying characteristics were included as references. Temperature-dependent relaxation behavior was mapped, revealing that, similar to PS, PCCD relaxes through more complex mechanisms far below Tg than can be explained by the standard α-relaxation alone.