Laser light-scattering study of novel thermoplastics .1. Phenolphthalein poly(aryl ether ketone)

Five different molecular weight phenolphthalein poly(aryl ether ketone) (PEK-C) fractions in CHCl3 were studied by static and dynamic laser light scattering(LLS). The dynamic LLS revealed that the PEK-C samples contain some large polymer clusters. These large clusters can be removed by filtering the solution with a 0.1-mu m filter. We found that the persistence length of PEK-C in CHCl3 at 25 degrees C is similar to 2 nm and the Flory characteristic ratio, C-infinity is similar to 25. Our results showed that [R(g)(2)](1/2)(z) = (3.50+/-0.20) x 10(-2)M(w)(0.54+/-0.01) and [D] = (2.37+/-0.05) x 10(-4)M(w)(-0.55+/-0.01), with [R(g)(2)](1/2)(z), M(w), and [D] being the z-average radius of gyration, the weight-average molecular weight, and the z-average translational diffusion coefficient, respectively. A combination of static and dynamic LLS results enabled us to determine D = (2.20+/-0.10) x 10(-4)M(-0.555+/-0.015), where D and M correspond to monodisperse species. Using this calibration between D and M,we have determined molecular weight distributions of five PEK-C fractions from their corresponding translational diffusion coefficient distribution.

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.

Structural study on poly(ether ether ketone ketone)-poly(ether biphenyl ether ketone ketone) copolymers

Structures of poly(ether ether ketone ketone)-poly(ether biphenyl ether ketone ketone) copolymers were studied by using small angle X-ray scattering and the one-dimensional electron density correlation function method. The results revealed that structures of the aggregated state of the copolymers depend closely on the biphenyl content (n(b)). When n(b) = 0.35, invariant Q, long period L, average thickness of crystal lamellae (d) over bar, electron density difference eta(c) - eta(a) and degree of crystallinity W-c,W-x assume minimum values.

Enhanced glass fiber-reinforced phenolphthalein poly(ether ketone) composites by blending poly(phenylene sulfide)

The mechanical properties of glass fiber-reinforced phenolphthalein poly(ether ketone)/poly(phenylene sulfide) (PEK-C/PPS) composites have been studied. The morphologies of fracture surfaces were observed by scanning electron microscope. Blending a semicrystalline component, PPS, can improve markedly the mechanical properties of glass fiber-reinforced PEK-C composites. These results can be attributed to the improvement of fiber/matrix interfacial adhesion and higher fiber aspect ratio. (C) 1996 John Wiley & Sons, Inc.

TEMPERATURE AND STRAIN-RATE DEPENDENCE OF FRACTURE-TOUGHNESS OF PHENOLPHTHALEIN POLYETHER KETONE

A strong strain-rate and temperature dependence was observed for the fracture toughness of phenolphthalein polyether ketone (PEK-C). Two separate crack-blunting mechanisms have been proposed to account for the fracture-toughness data. The first mechanism involves thermal blunting due to adiabatic heating at the crack tip for the high temperatures studied. In the high-temperature range, thermal blunting increases the fracture toughness corresponding to an effectively higher test temperature. However, in the low-temperature range, the adiabatic temperature rise is insufficient to cause softening and Jic increases with increasing temperature owing to viscoelastic losses associated with the p-relaxation there. The second mechanism involves plastic blunting due to shear yield/flow processes at the crack tip and this takes place at slow strain testing of the single-edge notched bending (SENB) samples. The temperature and strain-rate dependence of the plastic zone size may also be responsible for the temperature and strain-rate dependence of fracture toughness.

FRACTURE-TOUGHNESS OF PHENOLPHTHALEIN POLYETHER KETONE

The static and impact fracture toughness of phenolphthalein polyether ketone (PEK-C) were studied at different temperatures. The static fracture toughness of PEK-C was evaluated via the linear elastic fracture mechanics (LEFM) and the J-integral analysis. Impact fracture toughness was also analyzed using the LEFM approach. Temperature and strain rate effects on the fracture toughness were also studied. The enhancement in static fracture toughness at 70 degrees C was thought to be caused by plastic crack tip blunting. The increase in impact fracture toughness with temperature was attributed two different mechanisms, namely, the relaxation process in a relatively low temperature and thermal blunting of the crack tip at higher temperature. The temperature-dependent fracture toughness data obtained in static tests could be horizontally shifted to match roughly the data for impact tests, indicating the existence of a time-temperature equivalence relationship. (C) 1995 John Wiley & Sons, Inc.

SIMPLE-MODELS FOR STRESS-RELAXATION AND YIELD PHENOMENON OF PHENOLPHTHALEIN POLY(ETHER KETONE)

According to stress relaxation curves of phenolphthalein poly(ether ketone) (PEK-C) at different temperatures and the principle of time-temperature equivalence, the master curves of PEK-C at arbitrary reference temperatures are obtained. A coupling model (Kohlrausch-Williams-Watts) is applied to explain quantitatively the different temperature dependence of stress relaxation behavior and the relationship between stress relaxation and yield phenomenon is established through the coupling model.

CHEMICAL-IONIZATION MASS-SPECTROMETRY OF SOME NITRO-CONTAINING BIFUNCTIONAL AROMATIC-COMPOUNDS - LOCATION OF PROTONATION SITE

It is found that the nitro substituent of some aromatic bifunctional compounds shows unusual reactivity towards protonation. In the chemical ionization mass spectra of nitrobenzoic acids and their esters and amides, and of nitrophenols and their ethers, protonations on the carboxyl, ester, amide, hydroxyl or alkoxyl groups are highly suppressed by that on the nitro group. As a result, fragmentations based on protonation on these groups unexpectedly become negligible. Ortho effects were observed for all the ortho isomers where the initial protonation on the nitro group is followed by an intramolecular proton transfer reaction, which leads to the expected 'normal' fragmentations. Protonation on the nitro substituent is much more favourable in energy than on any of the other substituents. The interaction of the two substituents through the conjugating benzene ring is found to be responsible for this 'unfair' competitive protonation. The electron-attracting nitro group strongly destabilizes the MH+ ions formed through protonation on the other substituent; although the COR (R = OH, OMe, OEt, NH2) groups are also electron-withdrawing, their effects are weaker than that of NO2; thus protonation on the latter group produces more-stable MH+ ions. On the other hand, an electron-releasing group OR (R = H, Me, Et) stabilizes the nitro-protonated species; the stronger the electron-donating effect of this group the more stable the nitro-protonated ions.

THE IZOD IMPACT FRACTURE-BEHAVIOR OF PHENOLPHTHALEIN POLY(ETHER KETONE)

The Izod impact fracture behaviour of notched specimens of phenolphthalein poly(ether ketone) (PEK-C) has been studied over a temperature range from room temperature to 240 degrees C by using an instrumented impact tester. The temperature dependence of the maximum load, total impact energy, initiation energy, propagation energy, ductility index (DI) and the relationships between these parameters and the relaxation processes have been investigated.

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 delta loss. (C) 1995 John Wiley and Sons, Inc.

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 alpha-transition region, a second transition zone is revealed at low temperature. This transition is probably due to a restricted motion of its main chain. (C) 1995 John Wiley and Sons, Inc.

MECHANICAL-PROPERTIES OF PHENOLPHTHALEIN POLYETHER KETONE - YIELD STRESS, YOUNGS 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. (C) 1995 John Wiley and Sons, Inc.

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.

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 degrees 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.

THE FRACTURE-BEHAVIOR OF PHENOLPHTHALEIN POLYETHER ETHER KETONE AT ELEVATED-TEMPERATURE FOR LONG TERMS

The fracture behavior of phenolphthalein polyether-ether ketone (PEK-C) affected by physical aging at 200 degrees C was studied by tensile experiments, scanning electron microscopy, and differential scanning calorimetry observations. The ductile-brittle fracture transition (DBT) caused by physical aging can be considered as a competition between fracture mechanisms of crazing and shear yielding. The aging time required for the DBT is found to be around 400 h, based on the morphological studies and tensile experiments. The shear yielding component of the mechanical deformation could erase the aging effect, thus a deaging phenomenon occurs. We found that the deaging phenomenon has an intrinsic relationship with the extent of aging in the specimen and as a result of the fracture behavior. (C) 1995 John Wiley and Sons, Inc.