Tensile yield in phenolphthalein polyether ketone

Uniaxial tension tests to the yield point were performed on phenolphthalein polyether ketone (PEK-C) from room temperature to near the glass transition temperature (T_g) at a constant rate of 0.02 min^?1. At room temperature, some measurements were also made at strain rates from 0.002 min^?1 to 2 min^?1. Yield stress was a linear function of temperature and log strain rate. The temperature and the strain rate dependence of yield stress could be modeled using Eyring theory. Yield energy was found to be a linear function of temperature. Young's modulus, yield strain, elastic strain, and plastic strain all decreased with temperature. © 1994 John Wiley & Sons, Inc.     

Mechanical properties of phenolphthalein polyether ketone: Yield stress,young's modulus,and fracture toughness

A series of tensile and three-point bending studies was conducted at various temperatures and loading rates using phenolphthalein polyether ketone (PEK-C). Yield stress, Young's modulus, fracture toughness, and crack opening displacement data were obtained for various conditions. In general, both yield stress and Young's modulus increase with decreasing temperature. However, the relationships between fracture toughness, loading rate, and temperature are very complex. This behavior is due to the simultaneous intersection of viscoelasticity and localized plastic deformation. The increased yield stress is the main factor contributing to the reduction in fracture toughness and crack opening displacement. The relationship between fracture toughness and yield stress are discussed. © 1995 John Wiley & Sons, Inc.     

The charpy impact fracture behavior of phenolphthalein polyether ketone

The Charpy impact fracture behavior of notched specimens of phenolphthalein poly(ether ketone) (PEK-C) has been studied over a range of temperature using a JJ-20 Model instrumented impact tester. For PEK-C, there exist two temperature regions which distinguish the fracture mechanism, and the brittle fracture was preferentially governed by slip or shear bands at relatively high temperatures, but by crazes at low temperatures. The temperature dependence of the ductility index (DI) shows similar peaks to the tan δ loss.     

J-integral studies of crack initiation and crack tip-blunting of phenolphthalein polyether ketone

The J-integral is applied to characterize the fracture initiation of phenolphthalein polyether ketone (PEK-C) for which the concepts of linear elastic fracture mechanics (LEFM) are inapplicable at high temperatures for reasonably-sized specimens due to extensive plasticity. The multiple-specimen resistance curve technique recommended by the ASTM is the basic method employed. The values of J_IC increase with increasing temperature. The crack tipblunting of PEK-C is observed. The parameters, such as crack opening displacement (COD), δ₀, and the stretching increment Δa_b1 are introduced to describe the blunting phenomenon. The δ₀ increases with increasing temperature, as does Δa_b1. This indicates that the blunting occurs easily as the temperature increases; i.e., as the material's yield stress, σ_y steadily falls. The relationships between δ₀, Δa_b1, and σ_y are also discussed. © 1994 John Wiley & Sons, Inc.     

Plastic zone in front of mode I crack in phenolphthalein polyether ketone

The plastic zone size and crack opening displacement of phenolphthalein polyether ketone (PEK-C) at various conditions were investigated. Both of them increase with increasing temperature (decreasing strain rate), i.e. yield stress steadily falls. Thus, the mechanism increasing the yield stress leads to increased constraint in the crack tip and a corresponding reduction in the crack opening displacement and the plastic deformation zone. The effect of the plastic deformation on the fracture toughness is also discussed.     

Fracture toughness of carbon fiber/polyether ether ketone composites manufactured by autoclave and laser‐assisted automated tape placement

A comparative study is presented on the fracture toughness of carbon fiber/PEEK composites manufactured by autoclave and laser‐assisted automated tape placement (LATP). Formation of a good inter‐laminar bond is always a concern in ATP due to the short time available for intimate contact development and polymer healing, yet our double cantilever beam (DCB) tests reveal 60–80% higher Mode I fracture toughness for the LATP processed specimens than for the autoclave processed specimens. This magnitude of difference was unexpected, so specimens were further examined via differential scanning calorimetry, dynamic mechanical analysis, nano‐indentation, and scanning electron microscopy. The results indicate that the LATP process has been very effective in heating and consolidating the surface of plies, creating an excellent bond. However, it has been less effective in processing the interior of plies, where a low crystallinity and poor fiber–matrix bonding are evident. The higher fracture toughness of the LATP processed specimens is also not solely due to a better bond, but is partially due to significant plastic deformation in the interior of plies during the DCB test. The findings indicate there is still considerable scope for optimizing the laser‐assisted ATP process, before the optimum balance between strength and toughness is achieved at favorable lay‐down speeds. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41643.     

Temperature effect on impact fracture toughness and fracture mechanism of phenolphthalein poly(ether ketone)

Phenolphthalein poly(ether ketone) (PEK-C) was tested using an instrumented impact tester to determine the temperature effect on the fracture toughness K_c and critical strain energy release rate G_c. Two different mechanisms, namely the relaxation processes and thermal blunting of the crack tip were used to explain the temperature effect on the fracture toughness. Examination of the fracture surfaces revealed the presence of crack growth bands. It is suggested that these bands are the consequence of variations in crack growth along crazes that are formed in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances.     

Cell structures,phase morphologies and impact toughness of phenolphthalein poly(ether ether ketone)/epoxy composite foams

Thermoplastic phenolphthalein poly(ether ether ketone) (PEK-C) /epoxy composite foams were prepared by free foaming process (Fre-foams) and limited foaming process (Lim-foams), respectively, and the effects of PEK-C content and foaming methods on the cell structures, phase morphologies, and impact strength of epoxy foams were investigated. The results showed that the gas pressure in the bubbles promoted the resin curing process and polymerization-induced phase separation process (PIPS) during the free foaming process, while the resin curing process and PIPS were highly constrained in Lim-foams. The incorporation of PEK-C in the Fre-foams showed superior improvement in impact strength compared with the PEK-C/epoxy Lim-foams. By adding 12 wt% PEK-C, the specific impact strength of Fre-foams could be enhanced by 72%, and the improved specific impact strength was because the phase-inverted structures could prevent crack initiation and propagation, and moreover the presence of PEK-C led to significantly refine cell structure and reduce foam density. Interestingly, the impact strength of Lim-foams was nearly independent on the PEK-C content, it was attributed to the obviously increased cell size with increasing PEK-C content, and also that the phase separation process was not carried out.     

Viscoelastic properties of phenolphthalein poly(ether ketone)

Stress relaxation and dynamic mechanical behavior of phenolphthalein poly(ether ketone) (PEK-C) have been investigated. Using Ferry's reduction method, the master curve was obtained. From the experimental results, we found that the WLF equation is not appropriate in the lower-temperature range (T < T_g). The relaxation spectrum was calculated according to the first approximation method proposed by Schwarzl and Staverman. In addition to the α-transition region, a second transition zone is revealed at low temperature. This transition is probably due to a restricted motion of its main chain. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of a new polyether ketone

Summary A new polyether ketone has been synthesized (via addition polymerization) by reacting N,N-bispropargyl-4,4-diaminobenzophenone and Bisphenol A. The polymer is soluble in both polar and ketonic solvents. The inherent viscosity data indicates the molecular weight of the polymer to be low and thermogravimetric analysis suggests it to be a fairly thermostable polymer.     

Fracture toughness and morphology of phenolphthalein poly(ether sulfone)–thermotropic liquid crystalline polymer blends

Blends of a new phenolphthalein poly(ether sulfone) (PES-C) and a thermotropic liquid crystalline polymer (LCP) were prepared by melt-blending in a twin-screw extruder. Rheological properties, fracture toughness, K_IC, and morphology of the blends were studied. It was found that the addition of LCP could reduce the melting viscosity and improve the fracture toughness of the PES-C matrix. The morphology of the LCP phase for the fractured section changed with increasing LCP content in the blend from dropletlike to fibrillar and layered structure. Strong interfacial adhesion could be observed at a lower content of LCP. The toughening mechanisms by blending LCP were also discussed. © 1994 John Wiley & Sons, Inc.     

Mild sulfonated polyether ketone ether ketone ketone incorporated polysulfone membranes for microbial fuel cell application

To address the impediments of low power generation of Nafion, which is the main hurdle in the commercialization of microbial fuel cells (MFC), the current study focuses on developing a new PEM for MFC from mild sulfonation of PEKEKK with relatively improved physiochemical properties. In this study, mild post sulfonation of a polyether ketone ether ketone ketone (PEKEKK) has been successfully achieved using 98% H2SO4 at 90°C under reflux. 5%–30% (wt%) of sulfonated PEKEKK (SPEKEKK) loaded polysulfone (PSU) composite membranes were fabricated via a solution casting method. Ingeminating evidence of the sulfonation and structure of sulfonated polymer was proved by ¹H NMR peaks integration data and FTIR, respectively. The addition of SPEKEKK to PSU showed significant improvement in conductivity owing to the availability of more protonated sites ( SO3H) and water mediated pathways for the conduction of protons. The composite membrane containing 30 wt% SPEKEKK exhibits the highest conductivity of 0.12 S/cm at 90°C. The water uptakes and swelling ratio of the composite membranes are all higher than that of the pristine PSU membrane and show an increasing trend with increasing SPEKEKK content, thus validating the availability of water domains. Meanwhile, the lowest initial decomposition temperatures assigned to sulfonic acid groups and main chain degradation of the polysulfone/polyether ketone ether ketone ketone (PSU/SPEKEKK) composite membranes occurred at ~300°C and ~500°C respectively, which reflects an excellent thermal stability property. The experimental results indicate that the PSU/SPEKEKK membrane has the potential to greatly enhance the efficiency of MFCs.     

Ductile tearing instability in phenolphthalein poly(ether ketone)

Phenolphthalein poly(ether ketone) (PEK-C) can fail by tearing instability when the elastic contraction is greater than the plastic extension due to crack growth. Tearing instability (TIS) theory developed by Paris and coworkers describes the effect of specimen geometry on the ductile fracture properties of polymers. The stability of crack growth in three-point bend specimens depends on the specimen's dimensions. In this article, tearing instability theory is applied to describe the ductile tearing instability of PEK-C at different temperatures. The temperature dependence of tearing modulus T_m, dJ/dδa, and the relationship between dJ/dδa and yield stress are discussed. © 1994 John Wiley & Sons, Inc.     

Reinforced effect of wollastonite on phenolphthalein poly(ether ketone)

The mechanical properties of wollastonite-filled phenolphthalein poly-(ether ketone) (PEK-C) composites have been studied at room temperature and 200°C. The dispersion of wollastonite particles in PEK-C matrix were investigated by means of scanning electron microscope. The modulus and strength of the composites increased with filler content. The reinforced effect of wollastonite on PEK-C is more marked at elevated temperature. The glass transition temperature of the composites is higher than that of PEK-C and is independent of filler content. The restriction effect of filler particles on the molecular mobility of the polymer matrix should be attributed to the reinforcement. © 1997 John Wiley & Sons, Inc. J Appl Polym 65: 649–653, 1997     

聚醚酮不同结晶温度对其精制的影响

为了更有利于聚醚酮从结晶混合物中分离出来,探索了其结晶条件对其结晶物形态及精制时间的影响。采用特制的恒温制片板,在不同温度、不同恒温时间下获得聚醚酮结晶物,用液泛提取器对其进行精制。结果表明:聚醚酮产物在速冷时晶体类似层岩状,晶体间隙小,精制时间长;在130—155℃及165—190℃,晶体为球形,晶体间有小的孔洞;在160℃左右时,聚醚酮在混合物中的晶型类似海绵状,晶体间孔隙较大,空隙率高,形成均匀纳微结构界面,更有利于精制过程的传质,其精制时间是12.6 h.为速冷精制时间的69.3%。对同批次不同温度下结晶的聚醚酮进行物性检测,其性能未发生变化。此结果对聚醚酮结晶工艺的设计、达到节能降耗、提高生产效益具有指导意义。     

Direct observation of the fracture behavior of the polyether ketone ketone (PEKK) spherulites

This article reports the direct observation of the fracture of individual poly-ether-ketone-ketone (PEKK) spherulites. A single layer of PEKK spherulites was obtained by bonding a PEKK film in-between two sandblasted Ti alloy plates using an autoclave. The crack of an individual PEKK spherulite was achieved by opening the Ti/PEKK/Ti sandwich using a double cantilever beam test. The fracture morphology of the PEKK spherulite was characterized using scanning electron microscopy and atomic force microscopy. It was found that under tensile stress the crack of the individual spherulite propagates along the middle plane and crosses the nucleation core. This is due to the symmetric radial structure of the spherulite. Moreover, it was found that the fracture surface morphology at the core of the spherulite is strongly influenced by the local crystalline structure, which is anisotropic and determined by the initial nucleation growth direction. As a result, the area fraction experiencing plastic deformation during the fracture of PEKK spherulites at different orientations may vary by an order of 10. Our results show the important role of the initial nucleation growth direction on the mechanical properties of the polymer crystals and may provide a new approach to the design of high-performance polymer materials with tailored crystalline structures.     

Fracture toughness evaluation of polytetrafluoroethylene

The objective of this preliminary work was to explore the fracture resistance of polytetrafluoroethylene (PTFE) (DuPont tradename Teflon) as part of materials characterization work related to the development of “reactive” material projectiles. Little mechanical property data is available on this material since it is commonly used only as a coating material with the dominant properties being its low friction coefficient and high application temperature. Additional end products of the “7C” derivative, however, includes sheet, gaskets, bearing pads, piston rings, and diaphragms. In this work, standard ASTM E1820 fracture toughness specimens were machined from a 14‐mm‐thick sheet of this material obtained from NSWC Dahlgren Laboratory. These specimens were tested at three test temperatures and four test rates to determine if fracture would occur in this material, and if so, how the fracture toughness depends on the test temperature and specimen loading rate. Standard axial tensile specimens were also tested at quasi‐static and elevated loading rates at temperatures from ambient to ?73°C. The major results are that while crack extension is difficult at ambient (20°C) temperature, for temperatures slightly below ambient, a rapid degradation of fracture resistance occurs. This reduction in fracture resistance is enhanced by rapid loading, and the material loses approximately 75% of its toughness (fracture energy absorption ability) at ?18°C if the crack opening loading rate of the C(T) specimen approaches 0.25 m/s. Further reductions in temperature or increases in the loading rate appear to result in a reduced rate of degradation of fracture toughness.     

Comparison of the crack growth method and the crack stress whitening zone method for the fracture toughness determination of phenolphthalein poly(ether ketone)

Fracture toughness values of phenolphthalein poly(ether ketone) (PEK-C) at 190°C were determined by two different methods, i.e. the conventional crack growth method and the crack stress whitening zone method, which show consistent results. This indicates that the crack stress whitening zone method can be used to determine the crack initiation of some polymers for which the blunting line concept is unsuitable.     

Blends of a liquid crystalline polymer with polyether ether ketone

Blends of Polyether ether ketone (PEEK) and a thermotropic liquid crystalline Polymer (LCP) based on paraoxy-benzoyl and oxy-biphenylene terepthaloyl units were prepared using a static mixer attached to a single screw extruder at 420°C. Rheological studies indicated an increase in the viscosity of the blends upon the addition of LCP. Thermal studies on these blends demonstrated their poor thermal stability compared to the parent materials. The mechanical properties indicated improvement in Young's tensile and flexural modulus but no improvement in the break strength with the addition of the LCP. Morphological studies indicated the formation of ellipsoids of LCP at low LCP concentration in the matrix of PEEK, with extended ellipsoids being observable at 25 percent LCP composition. Phase inversion was noticeable at higher LCP content blends with the formation of PEEK fibrils in the matrix of the LCP. Dynamic studies on these blends showed an increase in the storage modulus with the addition of LCP.     

Mechanical properties of miscible phenolphthalein poly(ether ether ketone)/polysulfone blends

The properties of miscible phenolphthalein poly(ether ether ketone) (PEK-C)/polysulfone blends have been measured by dynamic mechanical analysis and tensile testing. The blends are found to have single glass transitions that vary continuously with the composition. The tensile moduli exhibit positive deviations from simple additivity as expected for miscible blends. Remarkably, positive deviations were also observed for tensile strength. Embrittlement, or transition from the brittle to ductile mode of failure, occurs at 50-30 wt % PEK-C. These observations suggest that mixing on the segmental level has occurred and that there is enough interaction between the components to retard internal mobility significantly.