PEEK Resin Research Articles

How to utilize the true performance of monolithic silica columns

Ways of utilizing the true separation efficiency of monolithic silica (MS) columns were studied. The true performance of MS columns, both regular-sized (rod-type clad with PEEK resin, 4.6 mm ID, 10 cm) and capillary sized (in 100 or 200 microm ID fused silica capillary, 25-140 cm) was evaluated by calculating the contribution of extra-column effects. HETP values of 7-9 microm were observed for solutes having retention factors (kvalues) of up to 4 for rod columns and up to 15 for a capillary column. The high permeability of MS columns allowed the use of long columns, with several connected together in the case of rod columns. Narrow-bore connectors gave good results. Peak variance caused by a column connector ranges from 50 to 70% of that caused by one rod-type column for up to three connectors or four columns in 80% methanol, but the addition of a 4th or 5th connector to add a 5th and 6th column, respectively, caused a much greater increase in peak variance, especially for long-retained solutes, which is greater than the variance caused by one rod column. Rod columns seem to show slightly lower efficiency at a pressure higher than 10 MPa or so. The use of acetonitrile-water as a mobile phase better preserved the ability of individual rod columns to generate up to 100,000 theoretical plates with 14 columns connected. Methods for eliminating extra-column effects in micro-HPLC were also studied. Split injection and on-column detection resulted in optimum performance. A long MS capillary measuring 140 cm produced 160,000 theoretical plates. The column efficiency of a capillary column was not affected by the pressure, showing advantages over the rod columns that exhibited peak broadening caused by connectors and pressure.

Crystallization Mechanism in PEEK/Carbon Fiber Composites

The non-isothermal crystallization kinetics of PEEK in the presence of carbon fibers are investigated for PEEK/carbon composites made from both prepreg and commingled systems. The crystallization kinetics under non-isothermal conditions are studied over a wide range of cooling rates, varying from 0.5°C/min to 160'C/min and compared with the pure PEEK matrix resin. For the composite materials as well as for the PEEK resin, the mechanism of crystallization is found to undergo two transitions, at about 5°C/min and 40'C/min. While the presence of carbon fibers affects the temperature and the rate of crystallization of the PEEK matrix, it does not seem to alter the basic crystallization mechanisms. The results are in agreement with some reported morphological studies on PEEK/carbon composites, suggesting that the transcrystalline structure resulting from epitaxial growth of the PEEK matrix at the carbon fiber surface constitutes a small element in the global crystallinity of the PEEK matrix in the molded composite.

Thermal stability of PEEK/carbon fiber in air and its influence on consolidation

AbstractThe thermal stability of carbon fiber‐reinforced polyetheretherketone (PEEK/CF) in air and its influence on consolidation are characterized under simulated processing conditions. The changes in dynamic shear modulus, melting temperature, heat of fusion and glass transition temperature due to chemical reactions and morphology changes were monitored by dynamic rheological analysis and differential scanning calorimetry. Thermal decomposition in air and simultaneous thermooxidative reaction of PEEK resin exposed to temperatures slightly higher than normal processing temperatures were observed by thermogravimetric and dynamic rheological analysis. The initial stage of this thermo‐oxidative reaction, under isothermal and non‐isothermal conditions, was modeled by a exponential‐based Arrhenius expression. The consolidation of PEEK/CF is affected by the thermal oxidation of the resin, which delays time to intimate contact between the plies. A consolidation model, predicting the degree of intimate contact, is extended to also take into account the rheological changes of the system. Finally, a processing limit regarding the thermal stability is defined based on the model and the experimental results.

Three-dimensional effects in fiber-reinforced composites under compression

This article concerns the compressive response of unidirectionally reinforced fibrous composites. Computational results are given for hexagonal arrays of graphite/PEEK composites employing a finite element analysis that accounts for the non-linear response of the PEEK resin. The results demonstrate the three-dimensional features of the stress and displacement fields and exhibit the presence of significant stress concentrations associated with the hexagonal fibrous array. These features are absent in models that assume layered geometries.

Characterization and modeling of nonlinear viscoelastic response of PEEK resin and PEEK composites

The viscoelastic properties of PEEK resin and unidirectional PEEK composite APC-2 were characterized by an accelerated testing procedure based on the time-temperature and time-stress superposition principles. The results obtained by creep and recovery tests are presented, and the constitutive modeling of the nonlinear viscoelastic response is discussed. The stress-dependent viscoelastic responses of the composite were modeled by a special case of Schapery's nonlinear viscoelastic equation with a kernel of the general power law. The relations for the temperature-time scale shift factors and stress-time scale factors are given. With the equations and parameters presented, the linear and nonlinear viscoelastic behaviors of APC-2 composite laminate from ambient temperature up to the glass transition temperature can be described analytically. Comparisons were made on the nonlinear properties of the 15° off-axis laminate, transverse laminate and pure resin. The results agree with the theory that the matrix octahedral shear stress is the main variable determining the nonlinearity of polymers and polymer-based composites.

Blends of semicrystalline and amorphous polymeric matrices for high performance composites

AbstractThe compatibility and crystallization behavior of blends of semicrystalline and amorphous polymers, traditionally used as matrices of high performance composites, has been studied. The analysis has been focused on blends of semicrystalline poly(etheretherketone) (PEEK) with amorphous poly(etherimide) (PEI) prepared by melt mixing. Differential scanning calorimetry and thermogravimetric analysis have been used to analyze the influence of blend constituents and processing conditions on the compatibility, on the crystallization kinetics and on the final crystalline content. An Avrami model has been applied to the crystallization of PEEK in a PEEK/PEI 50/50 blend and the results have been compared with the behavior of the neat PEEK resin. The results of the characterization can be applied to predict the behavior of such blends when processed as matrix of composites or when used in the “amorphous bonding” procedure.

Kinetics of strain‐induced crystallization during injection molding of short fiber composites of poly(ether ether ketone)

AbstractCrystallization kinetics of short glass and carbon fiber composites of poly(ether ether ketone) (PEEK) under melt‐strain conditions have been obtained for the first time, using in‐situ wide angle X‐ray scattering, and have been correlated to a model based on the Avrami equation in order to enable minimization of the processing time for injection molding of these materials. It has been demonstrated that increased flow rate of the melt in the mold and, consequently, increased shear rate accelerates the crystallization process of PEEK composites, analogous to similar trends observed previously in PEEK resin. Short glass fiber composites of PEEK crystallize slower than the resin under identical processing conditions, while short carbon fiber composites crystallize faster than the resin, except at the highest mold temperatures and the lowest flow rates. A model based on the Avrami equation has been proposed to fit the kinetics data obtained experimentally. The Avrami coefficient has been calculated and Arrhenius plots have been used to predict the crystallization kinetics at temperatures lower than those at which experimental data have been obtained here. Fiber orientation, flexural elastic modulus, and flexural fracture toughness of the composites have also been evaluated.

Transport of methylene chloride in poly(aryl‐ether‐ether‐ketone) (PEEK) resin and composite during alternate sorption/desorption cycles

AbstractThe transport of methylene chloride into PEEK resin systems following six successive sorption/desorption cycles was investigated. The sorption and desorption processes in neat PEEK with different morphologies and with varying degrees of crystallinity (from 1 to 29%) were compared to chopped‐carbon‐fiber and carbon‐fiber‐laminate composites. The amount of methylene chloride sorbed during an 80‐min immersion varied from less than 1 wt % in the composites to 37 wt % in the amorphous neat PEEK. During each cycle the solvent was desorbed at 95°C for 338 h. With the exception of the laminate, the sorption/desorption process is essentially independent of cycling. Furthermore, when the desorption processes are viewed in normalized form, i.e., fractional weight loss as a function of time, the desorption appears identical in all samples investigated. Although the maximum amount of solvent retained by the laminate was small, less than 0.1 wt % after the first cycle, it did increase to almost 0.15 wt % after 5 cycles.

Resistance to transverse tension of a commingled carbon fiber/poly(ether ether ketone) composite.

Resistance to transverse tension of the unidirectional carbon fiber/Poly(ether ether ketone) (PEEK) composites was examined by uniaxial tensile and cleavage tests. Three types of unidirectional carbon fiber/PEEK composites were fabricated from: (a) prepreg sheet, (b) plain weave cloth (warp: commingled yarn of 1800d of carbon fiber with PEEK fiber, weft: PEEK yarn of 70d), or (c) 5-shaft sateen weave cloth (warp: carbon yarn of 1800d, weft: PEEK yarn of 900d). The initial Young's modulus and the breaking strength measured by the transverse tensile tests were the highest on the specimen (a). Those of the specimen (c) were the lowest because of the lack of the carbon fiber/PEEK interfacial adhesion. On the other hand, the mode I intralaminar fracture toughness estimated from the cleavage test was the highest on the specimen (b). The interfacial adhesion between the carbon fiber and PEEK resin was also investigated by scanning electron microscopic observation of the fractured surface after transverse tensioning. For specimen (b) the fracture surface was rough and irregular, and the fibers were twisted with one another. The fracture surface of specimen (a) was flat and smooth, and the fibers were parallel to one another. It was concluded that the undulation and twisting of the carbon fibers enhanced the fracture toughness of specimen (b).

Effect of melting history on the crystalline characteristics of poly(etheretherketone) aromatic polymer composite

The effect of melt temperature on the crystalline characteristics of poly(etheretherketone) (PEEK) composite APC-2 has been studied using a differential scanning calorimeter, wide angle X-ray scattering and small angle X-ray scattering. Melting at a temperature close to the melting point of PEEK resin resulted in an increase of crystallinity and lamellar thickness. The internal process during a low melt temperature treatment was suggested to be similar to a high temperaature annealing treatment.

混繊糸および交織布を用いた一方向炭素繊維／ＰＥＥＫ複合材の試作と横方向引張り特性

Three types of unidirectional carbon fiber/PEEK composites are fabricated from : (a) prepreg sheet, (b) plain weave cloth ; warp : commingled yarn (1800 d) of carbon fiber with PEEK fiber, weft : PEEK yarn (70 d), (c) 5-shaft sateen weave cloth ; warp : carbon yarn (1800 d), weft : PEEK yarn (900 d). The transverse tensile properties are measured and compared with the theoretical predictions based on the perfect adhesion and interfacial slippage models. The transverse Young's moduli of the composites fabricated from (a) and (b) are in good agreement with the theoretical values based on the perfect adhesion model at the fiber/matrix interface. On the other hand, Young's modulus of the composite from (c) rather coincides with the prediction by the interfacial slippage model. The wettability and the interfacial adhesion between the carbon fiber and the PEEK resin are also investigated by the SEM observation of the fracture surface.

The effect of morphology on the transport of dichloromethane in poly(aryl‐ether‐ether‐ketone)

AbstractA study of the transport of the dichloromethane in neat poly(aryl‐ether‐ether‐ketone) (PEEK) samples with thicknesses from 0.08 to 3.0 mm with different morphologies was conducted at 35°C. Both sorption and desorption of the solvent were studied. Thermal annealing was used to vary the sample morphology, and density measurements were used to determine the crystallinity of the samples. The equilibrium concentration of solvent and rate of solvent sorption were found to vary with sample morphology. The density of the dichloromethane when in the PEEK resin was found to be 1.65 g/cm3. Solvent desorption was independent of sample morphology or any previous sample treatment and depended only upon desorption temperature. Solvent sorption appears to alter the morphology of amorphous samples by increasing the crystallinity to about 20% after one sorption/desorption cycle. Small amounts of the solvent, less than 0.5 wt.%, remain trapped in fully desorbed samples. The micromorphology of solvent‐induced crystallization appears to be different from that induced by thermal treatment.

Studies on Thermogravimetric Properties of Polyphenylene Sulfide and Polyetherether Ketone Resins and Composites

Polyphenylene sulfide (PPS) and Polyetherether ketone are high performance engineer ing thermoplastics with a unique combination of excellent thermal, mechanical and en vironmental properties. This paper presents the thermogravimetric properties of PPS and PEEK resins and carbon fiber reinforced composites. The addition of carbon fiber and the effects of environment on the thermal stability are presented. Crosslinking of Polypheny lene sulfide in air enhances thermal stability is discussed. PEEK resin and its composite show higher thermal stability than PPS by 70°C to 100°C is also described.