PEI Content Research Articles

Crystallization and Melting Behavior of Nylon 66/Poly(ether imide) Blends

Isothermal crystallization and melting behavior of nylon 66 and its blends with poly(ether imide) (PEI) were investigated by differential scanning calorimetry. Crystallization kinetics such as overall rate constant Z and index n were calculated according to Avrami approach. Crystallization in the blend was retarded with respect to that of pure nylon 66 by incorporation of PEI with high glass transition temperature (T-g). The lowest growth rate of the spherulites was observed in the blends containing 10 and 15 wt% fraction of PEI. A transition temperature where positively birefringent spherulites disappear and negative birefringent spherulites develop was measured by thermal analysis. The transition temperature increased with content of PEI in the blends. A suitable range of isothermally crystallization temperatures, 238.5-246 degrees C, is suggested For determining the equilibrium melting points by means of Hoffman-Weeks approach.

Variable temperature cure polyetherimide epoxy‐based prepreg systems

AbstractThis work identifies the necessary attributes of variable temperature cure epoxybased prepreg systems as they relate to high performance prepreg systems capable for composite repair. Model polyetherimide epoxy blend resins were developed and hot‐melt impregnated into woven carbon fabric and compared with a commercial prepreg system. It was found that when the PEI content was increased from 0 to 14 wt% in the base resin of the prepregs, the GIC and GIIC fracture toughness increased by over 70%. The fracture toughness was found to be similar when the model prepreg was cured at either 121°C or 177°C, a result of only a 9% difference in conversion and complete phase separation of the PEI at both cure temperatures. Void content in vacuum cured laminates were found to decrease as the PEI content was increased because of a large quantity of resin in the interstitial areas between the longitudinal and transverse tows. A comparison of the model and commercial prepreg system demonstrated many similarities and some significant differences. For example, the commercial prepreg had a 15% difference in conversion when cured at 121°C versus 177°C and very little PEI phase separation after both cure cycles. As a result, a significant difference in GIIC for the commercial prepreg was observed for the two cure temperatures.

Exclusion of non-crystalline polymer from the interlamellar region in polymer blends: poly(ether ether ketone)/poly(ether imide) blend by small-angle X-ray scattering

Crystalline morphology in the blends of poly(ether ether ketone) (PEEK) and poly (ether imide) (PEI) was investigated by small-angle X-ray scattering. The lamellar thickness was found to be constant (≈ 6 nm, independent of blend composition). The long period in 80 20 PEEK/PEI blend was greater than that in neat PEEK, whereas 50 50 PEEK/PEI blend showed intermediate value. This result suggests that a large amount of PEI impurity is excluded from interlamellar region in the high PEI content blend, whereas the exclusion is negligible and most PEI chains reside between lamellae in the low PEI content blend. The population of secondary lamellae, estimated by the interface distribution function analysis, was lowest in the 80 20 blend, suggesting that the formation of the secondary lamellae is restricted by the presence of the large amount of impurity between primary lamellae.

Evaluation of interlaminar‐toughened poly(etherlmide)‐modified epoxy/carbon fiber composites

AbstractAmorphous poly(ether imide) has been used as interlaminar toughening particulate agent in laminated carbon fiber/epoxy composites. Mode I and Mode II delamination fracture toughness was characterized using the double cantilever beam (DCB) and end‐notched flexure (ENF) specimens. The delamination surface was examined using a scanning electron microscopy (SEM) to investigate relationships between the morphology and properties. The results revealed that the PEI‐modified composites exhibited a significantly increased fracture toughness, which increased with the PEI content. GIC was improved from 165 to 540 J/m2 (at 1 mm/min crosshead speed). GIIC was improved more significantly from 290 to 1300 J/m2. It is believed that these values could be further improved if the processing cycle were to be optimized.

Binary blends of a new wholly aromatic thermoplastic polyimide and poly(ether imide)

This present investigation deals with the miscibility, phase behaviour and semicrystalline morphology of new thermoplastic polyimide (N-TPI)/poly(ether imide) (PEI) blends with different compositions. Melt-quenched amorphous blends were used as the raw materials. The phase behaviour of the blends has been studied by means of differential scanning calorimetry (d.s.c.). It has been found that the following four states develop depending upon the heat-treatment temperature and the blend composition: (1) a miscible amorphous state in the melt-quenched blends, (2) a phase-separated amorphous state in the blend that had been heat treated at 260°C, (3) a semicrystalline state with phase-separated amorphous regions in the blends that had been heat treated at 290–340°C, and (4) a semicrystalline state with miscible amorphous regions in the blends that had been heat treated at temperatures above 350°C. The semicrystalline morphology of the blends corresponding to the above four states was studied by means of small-angle X-ray scattering (SAXS). The results were analysed on the basis of the one-dimensional correlation function proposed by Stroble and coworkers. It has been found that the long-period and the amorphous thickness of the blends increase with increasing PEI content. The d.s.c. and SAXS studies of the blends lead to the conclusion that the PEI segments are incorporated in the amorphous layer between the stacked N-TPI crystals, regardless of the phase separation.

Miscible blends containing a crystallizable component: poly(vinyl alcohol)/poly(ethyleneimine)

AbstractBlends of poly(vinyl alcohol) (PVAI) with poly(ethyleneimine) (PEI) were prepared by casting from a common solvent. All blends show a single, composition dependent glass transition temperature (Tg), indicating that the blends are miscible in the amorphous state and in the melt. The overall crystallization rate of PVAI in the blend decreases with increasing PEI content. The crystallinity index of PVAI in the blend does not decrease greatly with PEI content up to a composition of 70/30 PVAI/PEI, since the Tg of the crystallizable component PVAI is larger than that of the non‐crystallizable component PEI. The Tg of the system PVAI/PEI decreases with increasing PEI content. The interaction parameter B of the two polymers in the melt was found to be −24 J/cm3.

Morphology and dynamic mechanical properties of nylon 66/ poly(ether imide) blends

AbstractThe morphology and dynamic mechanical properties of blends of poly(ether imide) (PEI) and nylon 66 over the full composition range have been invesigated. Torque changes during mixing were also measured. Lowertorque values than those calculated by the log‐additivity rule were ontained, resulting from the slip at the interface due to low interaction between the componeents. The particle size of the dispersed phase and morphology of the blends were examined by scanning electron microscopy. The composition of each phase was calculated. The blends of PEI and nylon 66 showed phase‐seoarated structures with small spherical domains of 0.3 ∼ 0.7 μm. The glass transition temperatures (Tgg) of the blends were shifted inward, compared with those of the homopolymers, which implied that the blends were partially imiscible over a range of compositions. Tg1, corresponding to nylon 66‐rich phase. This indicated that the fraction of PEI mixed into nylon 66‐rich phase increased with decreasing PEI content and that nylon 66 was rerely mixed into the PEI‐rich phase. The effect of composition of the secondary relaxations was examined. Both Tβ, corresponding to the motion of amide groups in nylon 66. and Tγ′, corresponding to that of either groups in PEI, were shifted to higher temperature, probably because of the formation of intermolecular interactions between the components.

Miscibility and Crystallization Behavior of Poly(ethylene terephthalate)/Poly(ether imide) Blends

The miscibility and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends have been investigated by DSC and optical microscopy. PET/PEI blends were prepared by solution precipitation from two solvents: a phenol/ tetrachloroethane mixed solvent and dichloroacetic acid. It was found that the compatibility of the as-prepared blends depended on the solvent used. Dichloroacetic acid appeared to provide better segmental mixing for PET and PEI than the mixed solvent of phenol and tetrachloroethane. The compatibility of the blends as prepared from both solvents could be enhanced by melt annealing. The composition dependence of T g of PET/PEI blends exhibited a cusp at the composition of ω PEI > 0.60 and was analyzed using the classical Gordon-Taylor's equation and the free volume theory of Braun-Kovacs. The PET crystallinity measured from the enthalpy of melting displayed a monotonic drop with increasing PEI content in the composition range of ω PEI > 0.4, while it stayed approximately constant for ω PEI < 0.4. The effect of blending with PEI on the multiple melting behavior of PET was also investigated. The highest melting endotherm was found to diminish with increasing PEI content in the blends, showing that the recrystallization of PET after the initial melting was hindered by the presence of PEI. After the crystallization of PET, a strong segregation of PEI was observed. Such segregation of PEI was accompanied with a significant increase in spherulitic nucleation density. The monitoring of the T g shift during crystallization and the morphological observation by optical microscopy suggested that the crystallization was coupled with a liquid-liquid phase separation, where the miscible melt demixed into the PET-enriched phase and the PEI-rich phase. The morphology created by the liquid-liquid phase separation and the nucleation at the domain interfaces may account for the drastic increase in nucleation density

Toughness improvement of tetrafunctional epoxy resin by using hydrolysed poly(ether imide)

Toughened epoxy resins were prepared by dissolving poly(ether imide) (PEI) in the EPON HPT 1071 based resin with EPON HPT 1061M as a curing agent. Open tension tests showed an increase in fracture toughness with PEI content, from 0.61 GPa m 1 2 in the pristine resin to 1.32 GPa m 1 2 at 15 wt% PEI. Similar results were obtained for the flexural properties of the epoxy resin. In order to improve the fracture toughness of epoxy resins, increasing the interfacial adhesion strength between the dispersed PEI phase and tetrafunctional epoxy resin was necessary. Improved interfacial adhesion of the modified epoxy resin was obtained through the hydrolysis of PEI. At a concentration of 5 wt% PEI, hydrolysed PEI/epoxy resin had 40% more fracture toughness than the unhydrolysed PEI/epoxy resin. The effect of PEI hydrolysis on the flexural properties of the cured epoxy resins was also studied. Scanning electron microscopy was used to investigate the relationship between the morphological study of the fractured epoxy resins and mechanical properties of the modified epoxy resins.

Miscibility of poly(ether imide)/poly(ethylene terephthalate) blends

Miscibility of blends of poly(ether imide) (PEI) and poly(ethylene terephthalate) (PET) were studied by differential scanning calorimetry (DSC). Single and composition-dependent Tg's are observed over the entire composition range, indicating that the blends are miscible in the amorphous region. The overall crystallization rate of PET in the blends decreased with increasing the PEI content. The interaction energy density B, which was calculated from the melting point depression of the blends using Nishi-Wang equation, was-5.5 cal/cm3.

Effects of morphology on toughening of tetrafunctional epoxy resins with poly(ether imide)

Tetraglycidyl-4,4′-diaminodiphenyl methane based resin with 30 phr diaminodiphenyl sulfone as curing agent was toughened with poly(ether imide) (PEI). The effects of morphology on the fracture toughness of modified epoxy resins were investigated. Morphology was controlled by changing the curing conditions. The co-continuous structure and morphology of the PEI spherical domain dispersed in the epoxy matrix were obtained. Phase-inversed morphology with PEI matrix was also obtained with 30 phr PEI content. The cured resin with phase-inversed morphology showed the highest fracture toughness. The modified epoxy resins with enhanced fracture toughness exhibited other improved mechanical properties such as flexural strength, flexural modulus and strain at break.

Relation between neck-like deformation and fiber structure formation in high-speed melt spinning of ethylene terephthalate/ethnylene isophthalate copolymers.

Four kinds of ethylene terephthalate/ethylene isophthalate copolymers (PET/PEI, PEI=0, 2, 5, 10mol%) were prepared and melt spun at take-up velocities from 1 to 7km/min. Birefringence and density of as-spun fibers increased with increasing take-up velocity. Density showed abrupt increase due to oriented crystallization at take-up velocities above 5km/min, where birefringence and density became lower for higher PEI contents. Radial variation of birefringence in filament cross-section measured with an interference microscope was also lower for the higher PET content fibers. Moreover, increase in PEI content caused the decrease in Young's modulus and tenacity and the increase in extension at break. These results suggest that development of fiber structure through the oriented crystallization was suppressed by the existence of the ethylene isophthalate component.Filament diameter profiles in the spinline were measured using a diameter monitor. Below 4km/min, filaments attenuated smoothly along the spinline, while above 5km/min, neck-like deformation was observed. With increasing PEI content, position of the neck-like deformation moved downward in the spinline, and necking draw ratio decreased. From the relation between the neck-like deformation in the spinline and the physical and mechanical properties of high-speed spun fibers, it is concluded that birefringence, density, Young's modulus, tenacity and extension at break of as-spun fibers are governed by the necking draw ratio, and that the radial variation of birefringence is governed by the position of neck-like deformation.