Extended study on the thermal stability and crystallization behavior of aliphatic polyketone under physical and chemical exposure

In this paper the processing stability, environmental and chemical aging of aliphatic polyketone (POK) were systematically investigated with particular emphasis on degradation mechanisms and structure–property relationships. Environmental exposure was found to influence POK behavoir, with the observed changes being associated with modified intermolecular interactions, chain mobility, and crystallization kinetics. Differential Scanning Calorimetry (DSC) and Karl–Fischer titration indicated that moisture uptake and freezing influence crystallization behavior, suggesting heterogeneous nucleation and possible structural rearrangements. Crystallinity decreased from 22 to 36% to 12–21%. Regranulation improved crystallization stability and promoted the formation of more ordered crystalline phases, as suggested by DSC. Accelerated aging in various liquid resulted in no detectable backbone degradation directly according to FT-IR analysis; however, significant reductions in melting and crystallization temperatures and crystallinity were observed after cooling-heating cycles by DSC in the order: NaOH > H₂SO₄ > butyl acetate > water > xylene. Thermogravimetric Analysis (TGA) showed a corresponding decrease in thermal stability, with decomposition onset temperatures reduced from 408.0 °C to 368.3 °C. FT-IR analysis indicated chemical changes associated with medium-dependent structural modifications during thermal cycles. Hydrolytic effects were suggested for NaOH and water-treated samples, while butyl acetate also promoted chemical modification. Sulfuric acid produced changes consistent with acid-catalyzed chain scission, leading to a near-complete loss of crystallinity. In contrast, xylene mainly acted as a non-reactive plasticizer, increasing chain mobility without detectable chemical degradation, thereby supporting long-term stability in nonpolar environments. These findings provide mechanistic insight into the combined effects of chemical exposure and thermal cycling, highlighting limitations and long-term performance conditions for POK applications.