Semicrystalline PEEK Research Articles

Reinforcement effect and molecular motions in semicrystalline PEEK films: Mechanical and physical modelings. I

The influence of the crystalline phase on the viscoelastic behavior of poly (aryl ether ether ketone) (PEEK) films is assessed by dynamic mechanical spectrometry. Prediction of the viscoelastic behavior near T g of semicrystalline films is performed through mechanical and physical modelings. Changes in the a relaxation induced by the crystalline phase are related to both the mechanical coupling between phases and the decrease in the molecular mobility of chains, which is improved for samples showing a broad crystallite size distribution. Crystalline phase also induces some modifications in the characteristics of the β spectrum. The reinforcement effect brought by the crystalline phase in such a temperature range is predicted through a mechanical model. Then, changes in tan δ level in the β 1 region induced by the crystalline phase result from the mechanical coupling between phases. The magnitude of such changes only depends on the crystallinity ratio and it is not controlled by the crystallite size distribution. The crystalline phase also induces changes in the pattern of the β 2 transition, which could be attributed to modifications in the conformations of the chains near the crystalline entities and/or the magnitude of interactions between chains. Such modifications seem to be sensitive to the thermal history of PEEK samples.

Damage depth-profiling of Au + and O + -irradiated amorphous PEEK by monoenergetic positron beams

and O+ ions was exposed to positron beams to measure the positron annihilation Doppler broadening as a function of the positron energy. As in the previous case of O+-irradiated semicrystalline PEEK, the annihilation lines recorded at relatively low positron energies became broader with increasing irradiation dose. The thickness of the damaged layer estimated from the positron data was compared with the mean depth of the implanted ions calculated by the TRIM code. For the Au+-irradiated samples, some discrepancy was observed between the two quantities.

Beta Relaxations in Semicrystalline Poly(aryl ether ether ketone) Films. Mechanical Coupling and Interactions between Phases

Mechanical spectrometry was performed on poly(aryl ether ether ketone) (PEEK) polymer films in order to evaluate the influence of a crystalline phase on the beta-relaxation. The Halpin-Kardos model has been applied to describe the beta dynamic mechanical behavior of semicrystalline PEEK films considered as composite materials. Changes in the low-temperature component of the beta-relaxation induced by the crystalline phase are discussed in terms of mechanical coupling between phases. Moreover, it is found that the pattern of the higher temperature component of the beta transition is governed, in addition, by the rigid amorphous phase.

Scratch hardness studies of poly(ether ether ketone)

This paper describes a study of the surface properties of poly(ether ether ketone) (PEEK) using a scratch hardness technique. A comparison of the scratch friction and the hardness values determined for amorphous and semi-crystalline PEEK shows that the crystalline polymer is harder. Studies carried out on PEEK treated with chloroform indicate that this organic solvent induces plasticization in PEEK evidenced by a change in the frictional properties and a decrease in hardness. Also, blending PEEK with other polymers, poly(ether imide) (PEI) and polytetrafluoroethylene (PTFE), demonstrates that the degree of crystallinity in PEEK is increased by the presence of such polymers.

Transparency enhancement in semicrystalline PEEK through variation of polymer morphology

Transparency enhancement in semicrystalline PEEK through variation of polymer morphology

Transparency enhancement in semicrystalline PEEK through variation of polymer morphology

We report a processing window in which transparent semicrystalline poly(ether ether ketone) (PEEK) can be produced. The transparent PEEK film reported is 100 μm in thickness and has light transmittance of 54% ; while ordinary semicrystalline PEEK film of the same thickness and degree of crystallinity, but produced outside the processing window, is virtually opaque (with the light transmittance close to 0%). First processing conditions for producing the transparent PEEK film are discussed, and second characterization of the transparent PEEK film is detailed. Results suggest that the main processing condition for developing the transparent PEEK film is forming temperature, defined as the highest temperature that the film is exposed to during thermal treatment. Using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and small-angle x-ray scattering (SAXS), we characterized morphology of the PEEK films. TEM shows that the morphology in the transparent PEEK film has a locally oriented lamellar structure, instead of the commonly observed spherulites or sheaves. DSC results suggest that the new morphology is formed in the melt with a high density of residual crystals that act as nucleating agents during the crystallization process, which is known as a self-seeding effect. SAXS spectra show that specimens with higher forming temperature produce broader diffraction peak at larger Q value that is defined as 4π sin θ/λ. We conclude from the study that the light transmittance enhancement is morphology related, and can be achieved through control of processing conditions.

The thermoelastic behaviour of semicrystalline and of glassy poly(ether-ether-ketone)

A thermoelastic evaluation, based on simultaneous measurements of the mechanical work and of the concomitant heat of deformation by a stretching micro calorimeter, was performed on semicrystalline and glassy PEEK. The objective of this study was to utilize the sensitive technique to detect differences that would account for observed effects of micro structure on mechanical performance. A clear difference was detected beyond a 0.6% strain, where the behaviour of glassy PEEK began to exhibit inelastic features such as yielding and plastic deformation. This difference between the glassy and the semicrystalline polymers was considered the reason for the superior mechanical fatigue and fracture properties produced by the latter micro structure.

Solubility, diffusion and swelling of fluids in thermoplastic resin systems

The transport of liquids into semicrystalline thermoplastic resins such as poly(aryl ether ether ketone) (PEEK) is an extremely complex process, markedly dependent upon the temperature, crystallinity and concentration of the penetrant at the surface. Similarities and differences in the sorption, desorption, resorption, swelling and solvent-induced crystallinity of toluene and carbon disulfide into amorphous and semicrystalline PEEK are reported. The transport of these two liquids into PEEK illustrates many of the complexities associated with non-Fickian diffusion: sharp penetration front, slow relaxation processes, solvent-induced crystallinity and anisotropic swelling and deswelling. Desorption is a two-step process in which 30–50% of the penetrant is rapidly desorbed in a few hours. The rate of CS 2 sorption and desorption is much greater than that of toluene. The rate of resorption is significantly less than that of the initial sorption but the desorption process is essentially unchanged.

Deformation of thin films of poly(ether ether ketone)

Adaptation of sample preparation methods used previously for amorphous glassy polymers has also allowed us to examine tensile deformation of thin films of poly(ether ether ketone) (PEEK), which is of particular interest given the commercial importance of this polymer. As the preliminary results presented here suggest, this appears to be a promising technique, particularly in view of the possibility of examining such films using transmission electron microscopy. In amorphous PEEK films, the dominant mode of deformation is simple shear at all temperatures below T g. In semicrystalline PEEK, however, deformation at room temperature is characterized by both shear and crazing. Shear becomes gradually more dominant as the temperature is raised, and replaces crazing altogether above T g.

Dynamics of excess free volume in semicrystalline PEEK studied by positron annihilation

The dynamical behavior of the free volume creation and its relaxation in the amorphous regions of two-phase PEEK were monitored during isothermal crystallization as a function of annealing time . The kinetics of the isothermal crystallization was analyzed by the Avrami equation. The developement of the relative crystallinity, mean free-volume hole size and relative free volume fraction were obtained.

Crystallization of poly(ether ether ketone) oriented by solid-state extrusion

Semi crystalline and amorphous PEEK were drawn at 154 and 149°C, respectively, using the solid-state extrusion technique. The crystal orientation and total orientation of drawn PEEK were determined. The relationships between deformation history and crystallization have been investigated. Previously drawn PEEK was crystallized nonisothermally and isothermally from the melt. Results show that the crystallization of drawn PEEK is slower than that of the undrawn initial films. An orientation-induced crystallization was found during the solid-state extrusion of amorphous PEEK films at 149°C

Thermoplastic interlayer bonding of aromatic polymer composites—methods for using semi-crystallized polymers

Amorphous thermoplastic interlayer bonding techniques involve coating laminates to be bonded with a layer of amorphous polymer, using the mechanisms of molecular diffusion, mechanical keying, and fibre migration to achieve firm integration. By correct selection of that interlayer material components may then be fused at temperatures below the melting point of the composite matrix without leading to distortion of the components being bonded, thereby negating the need for complex tooling. The overall properties of the structure are therefore not compromised. Although cases where a joint may encounter extremes of environmental hostility are usually avoided, methods have been developed whereby the interlayer is able to exhibit a similar level of chemical resistance to that of a semi-crystalline peek matrix. Two methods exploiting the melting mechanisms associated with novel, semi-crystalline, polyketones exist. Excellent resistance to a range of commonly encountered aerospace fluids is demonstrated.

Thermal expansion of poly(ether‐ether‐ketone) (PEEK)

AbstractThermal expansivities along the a, b, and c axes of the orthorhombic unit cell of poly (ether‐ether‐ketone (PEEK) crystals have been determined from 160 to 470 K by wide‐angle x‐ray diffraction. The expansivities along the a and b axes are positive while the expansivity along the c (chain) direction is negative, with values of \[ \alpha _a^c = 11.3 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,{\rm }\alpha _b^c = 4.6 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} , \] and \[ \alpha _\parallel ^c = ‐ 1.4 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} \] at 300 K. The negative α arises from the effective shortening along the chain axis caused by the torsional and bending motions of the chain, whereas the large and positive α and α reflect the weak interactions across the chains. Using a dilatometric technique we have also studied the expansion behavior of isotropic PEEK as a function of crystallinity (X = 0−0.34) and have measured thermal expansivities of oriented PEEK (draw ratio 1–4) parallel and perpendicular to the draw direction. The effects of crystallinity and orientation can be understood by treating semicrystalline PEEK as a composite consisting of crystallites embedded in an amorphous matrix.

Positronium formation at free‐volume sites in the amorphous regions of semicrystalline PEEK

Etude de la correlation entre la cristallinite d'un PEEK et l'intensite de l'orthopositronium par spectrometrie PAL

Water sorption kinetics in poly(aryl ether ether ketone)

AbstractThe kinetics of diffusion of water from different activity vapors and liquid phase have been investigated in glassy amorphous poly(aryl ether ether ketcne) (PEEK) films at the temperature of 60°C and in glassy semicrystalline PEEK sheets at different temperatures, respectively. In the case of the amorphous PEEK films (250 μm thick) the data at low activity levels were interpreted by means of a purely Fickian mechanism. At higher activity levels the material has shown the presence of a relaxation process; in this case the data have been interpreted using a model proposed by Berens and Hopfenberg. Equilibrium sorption isotherm is also reported. Liquid water sorption in semicrystalline (30%) PEEK sheets (2 mm thick) has been determined to follow the classical Fickian mechanism. The water uptake values obtained for both amorphous and semicrystalline PEEK, confirm the good moisture and liquid water resistance of this kind of high performance thermoplastic polymer.

Mechanical relaxation of crystalline poly(aryl-ether-ether-ketone) (PEEK) and influence of electron beam irradiation

Mechanical relaxation of semicrystalline PEEK and influence of electron beam irradiation on molecular motions were studied by measuring dynamic viscoelastic properties in the temperature range from − 160°C to 350°C. Irradiation caused the glass transition temperature (β relaxation) to shift upwards, and β′ relaxation, related to loosened chain packing, to appear just below the glass transition temperature, and a small shoulder that appeared at − 40°C to 0°C on the γ relaxation peak and disappeared in the first run after irradiation to reappear in the second run. It was concluded that both crosslinking and chain scission take place under irradiation. The shoulder on the γ relaxation was assigned to segmental motion of the chains at the crystalline-non-crystalline interface. The inferior radiation resistance of semicrystalline PEEK with respect to non-crystalline PEEK is ascribed to preferential disintegration of tie-molecules between crystalline and non-crystalline phases.