Impact of the heating/quenching process on the mechanical, optical and thermodynamic properties of polyetheretherketone (PEEK) films

Abstract

Objective: The aim of this study was to investigate the impact of a heating/quenching process on the optical, mechanical and thermodynamic properties of filled (20%_4000) and unfilled PEEK films (0%_2000 and 0%_4000). Heating/quenching was performed to simulate thermoforming as possible method to process thermoplastic polymers for dental application.

Methods: For the investigation, films of different PEEK qualities (0%_2000, 0%_4000, 20%_4000) were produced using isostatic pressing (n=10/quality). From each PEEK film, round specimens (n=20/PEEK film) with a diameter of 34mm were cut and following parameters were determined: translucency (T%), Martens-Hardness (HM), indentation modulus (E_IT), glass transition temperature (T_G), melting temperature (T_M) and enthalpy of fusion (ΔH_f). Same specimens were exposed to heating/quenching using defined parameters. Afterwards, T%, HM, E_IT, TG, TM and ΔH_f were determined again. Data were analysed using Kolmogorov-Smirnov test, univariate ANOVA followed by post-hoc Scheffé test with partial eta squared (η_p²), Kruskal-Wallis and Mann Whitney U test. Level of significance was defined to 95%.

Results: Materials showed significant differences for all investigated parameters in the initial state, except of T_G (p=0.249). The heating/quenching process showed a significant increase on T% for the unfilled materials 0%_2000 and 0%_4000. HM and E_IT decreased significantly through heating/quenching for all materials. Moreover, heating/quenching showed a reduction of T_G for 0%_2000 and 20%_4000, while T_M decreased for 0%_2000 and 0%_4000. ΔH_f confirms different crystallinities of tested materials.

Significance: The heating/quenching process showed a significant impact on all investigated parameters. The highest impact was found for mechanical properties resulting in decreased values of HM and E_IT.

Keywords: DSC measurements; Enthalpy of fusion; Glass transition and melting temperature; Heating/quenching; Indentation modulus; Martens-Hardness; Polyetheretherketone; Thermoforming; Translucency.