Mettler Toledo DSC 821e/700 was used to carry out thermal analysis. The test were repeated ten times for each type of sample. The tensile tests were performed on a Lloyds EZ20 machine with a crosshead speed of 20 mm min −1 for all samples. The films prepared by the two film preparation methods were sliced into strips with the width of 3 mm and length of 6 cm. The specimens were sputter coated with a 5 nm thick gold layer. The surface of the thin PEEK films fabricated using the two crystallisation methods was examined by Scanning Electron Microscopy (SEM) (Hitachi S-3200N, Japan). Then the transparent PEEK film was air dried at room temperature, followed by annealing on a hotplate at the temperature of 300 ☌ for 5, 10, 30, 60 and 120 mins. To allow the formation of a transparent PEEK film, the molten film on the glass slide was immediately quenched in deionized water in this case. Method 2: Molten PEEK film was prepared in the same method as Method 1. The molten film on the glass slides was quickly transferred to another hot plate and isothermal crystallized at 300 ☌. Then the powder layer was heated up on a hotplate (V14160 Bibby HC500 hotplate) at 400 ☌ for 5 mins. No glass cover was applied on top of the PEEK powder. Method 1: Firstly, the Victrex PEEK 150PF powder was spread evenly on a glass slide (Fisherbrand microscope slides, 0.8–1 mm thickness). The thickness was controlled using an in-house built doctor blade rig. The thickness of the film is approximately 250 µm. Method 1 allows fabrication of the conventional spherulitic crystals through melt crystallisation, used here as reference and method 2 is used for fabrication of the novel fibre like crystals through quench crystallisation. Thin PEEK films were manufactured by melting and crystallization using two different methods. Other investigations also identified the sheaf-like solution grown crystals by using single-stage crystallization method 4, 5, 6, 7. The typical morphology of PPS and PEEK solution growth crystals are shown in Fig. The type of single crystal depends on seeding temperature and molecular weight. The self-seeding procedure includes a dissolution stage (PPS is dissolved in solution at specific temperature), first-stage isothermal crystallisation, seed generation stage, second-stage crystallisation, solution separation and replacement stage (uncrystallised PPS is removed from solution). Similarly, Chung and Cebe reported various forms of single PPS crystals, needle-like PPS isolated single crystal, sheaf-like single crystal aggregates and star-like single crystal aggregates 3 in thin films formed at elevated temperatures in dilute solutions of α- chloronaphthalene using a two-stage self-seeding technique. Microfaceting was observed in the growth of both single crystals and lamella, which has been explained as a disordered structure and fragmentation of crystals 1. prepared PEEK single crystals film from benzophenone and α-chloronaphthalene solution at elevated temperatures 1, 2. Shortly after their invention, several studies investigated the crystal morphology of solution grown PEEK and PPS thin films. PPS as well as PEEK received a lot of attention due to their excellent engineering performance at high temperatures. Semi-crystalline Poly Aryls such as PEEK, PolyEtherKetone (PEK) or PolyPhenyleneSulphide (PPS) demonstrate formation of various crystal morphologies depending on the crystallization condition 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. Based on these results, a crystal growth mechanism describing the development of the fibre-like crystals on the surface of the quenched crystallised films is proposed. The fracture analysis carried out using microscopy revealed an interesting microstructure which evolves as a function of annealing time. These quenched crystallised films show higher elongation at break when compared with conventional melt crystallised thin films incorporating spherulitic crystals, while the tensile strength of both types of films (quenched crystallised and conventional melt) remained the same. This paper presents a simple quench crystallization method for preparation of PEEK thin films with the formation of a novel fibre-like crystal structure on the surface of the films. As a semi-crystalline polymer, PEEK can become very brittle during long crystallisation times and temperatures helped as well by its high content of rigid benzene rings within its chemical structure. Poly Ether Ether Ketone (PEEK) is a high temperature polymer material known for its excellent chemical resistance, high strength and toughness.
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