Effect of poly(etherimide) chemical structures on the properties of epoxy/poly(etherimide) blends and their carbon fiber‐reinforced composites

Poly(etherimide)s (PEIs) with different chemical structures were synthesized and characterized, which were employed to toughen epoxy resins (EP/PEI) and carbon fiber‐reinforced epoxy composites (CF/EP/PEI). Experimental results revealed that the introduction of the fluorinated groups and meta linkages could help to improve the melt processability of EP/PEI resins. The EP/PEI resins showed obviously improved mechanical properties including tensile strength of 89.2 MPa, elongation at break of 4.7% and flexural strength of 144.2 MPa, and good thermal properties including glass transition temperature (T_g) of 211°C and initial decomposition temperature (T_d) of 366°C. Moreover, CF/EP/PEI‐1 and CF/EP/PEI‐4 composites showed significantly improved toughness with impact toughness of 13.8 and 15.5 J/cm², respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and thermal properties of bismaleimide blends based on hydroxyphenyl maleimide

N‐(4‐hydroxyphenyl)maleimide was melt‐blended with the glycidyl ether of bisphenol‐A and various mole percentages of 4, 4′‐(diaminodiphenylsulfone) bismaleimide. The cure behaviour of the resins was evaluated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The blends showed distinct reductions in the onset of cure (T_o) and peak exothermic (T_exo) temperatures. The blends cured at low temperatures exhibited glass transition temperatures (T_gs) higher than the cure temperatures. The cured blends showed high moduli, glass transition temperatures in excess of 250 °C and good thermal stabilities up to 400 °C. Copyright © 2005 Society of Chemical Industry     

Thermal studies of blends of poly(phenylene sulfide) (PPS) with poly(phenylene sulfide sulfone) (PPSS) and with poly(phenylene sulfide ether) (PPSE)

The miscibilities of poly(phenylene) sulfide/poly(phenylene sulfide sulfone) (PPS/PPSS) and poly(phenylene) sulfide/poly(phenylene sulfide ether) (PPS/PPSE) blends were invesigated in terms of shifts of glass transition temperatures T_g of pure PPS, PPSS, a dn PPSE. The crystallization kinetics of PPS/PPSS blends was also studied as a function of molar composition. The PPS/PPSS and PPS/PPSE blends are respectively partially and fully miscible. PPSE shows a plasticizing effect on PPS as does PPS on PPSS, which necessarily improves te processibility in the respective systems. We can control T_g and melting temperature T_m of PPS by varying amounts of PPSE in blends. The melt crystallization temperature T_mc of PPS/PPSE blends was higher than that of the PPSE homopolymer. Therefore, these blends require shorter cycle times in processing than pure PPSE. The overall rate of crystallization for PPS/PPSS blends follows the Avrami equation with an exponent ?2. The maximal rate of crystallization for PPS/PPSS blends occurs at a temperatre higher by 10°C than that for PPS, while the crystallization half time t_1/2 is 4 times shorter. In the cold crystallization range, crystal growth rates increase and Avrami exponents decrease significantly as the temperature increases.     

Reactively formed ENPT copolymers as compatibilizers in ternary blends of poly(ethylene naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide)

The compatibility of ternary blends of poly(ethylene naphthalate)/poly(pentamethylene terephthalate)/poly(ether imide) (PEN/PPT/PEI) was studied by examining the transesterification of PEN and PPT. ENPT copolymers were formed in situ as compatibilizers between PPT and PEI components in ternary blends. Differential scanning calorimetric (DSC) results for ternary blends showed the immiscibility of PEN/PPT/PEI, but ternary blends of all compositions were phase‐homogeneous after heat treatment at 300°C for more than 60 min. Annealing samples at 300°C yielded amorphous blends with a clear, single glass transition temperature (T_g), as the final state. Additionally, ENPT copolymer improved the compatibility of ENPT/PPT/PEI blends, yielding a homogeneous phase in the ENPT‐rich compositions. The morphology of the ENPT/PPT/PEI blends was altered from heterogeneous to homogeneous by controlling the concentration of PPT in the ENPT copolymers as well as the concentration of the ENPT copolymers. Moreover, a homogeneous phase with a clear T_g was observed when the concentration of PPT in the ENPT copolymer fell to 70 wt% in the ENPT/PEI = 50/50 blends. Experimental results indicate how the concentration of PPT in the ENPT copolymer affects miscibility in the ENPT/PEI blends. POLYM. ENG. SCI. 46:337–343, 2006. © 2006 Society of Plastics Engineers     

Phase and crystallization behavior of solution-blended poly(ether ether ketone) and poly(ether imide)

Results on solution-blended poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) blends are reported. Dichloroacetic acid was used as the cosolvent for blending. PEEK and PEI are confirmed to be miscible in the melt. The glass transition, T_g, behavior obeys the simple Fox equation or the Gordon-Taylor equation with the adjustable coefficient k = 0.86. This agrees with prior data on melt-blended PEEK/PEI blends. The T_g width of the amorphous PEEK/PEI blends was found to be broader than that of the pure components. The maximum broadening is about 10°C. The specific volume of the amorphous PEEK/PEI blends shows a slight negative deviation from linearity, indicating favorable interaction between PEEK and PEI. The spherulitic growth and resultant blend morphology at 270°C were studied by a cross-polarized optical microscope. The radial growth rate of PEEK spherulites formed from the miscible melt at 270°C decreases from 3.04 μm/min for PEEK/PEI 90/10 blend to 0.77 μm/min for PEEK/PEI 70/30 blend. The decrease in crystalization rate of PEEK from PEEK/PEI blends is attributable to the increase in blend T_g. A linear growth was observed for PEEK spherulites formed from miscible melt at 270°C in the early growth stage. The spherulitic growth deviated from linearity in the late stage of growth. PEEK spherulites formed from the miscible PEEK/PEI melt at 270°C are essentially volume-filling. The branches of the spherulites become more clear for PEEK spherulites formed from the blend than that formed from pure PEEK melt.     

Investigation of non-isothermal crystallization,dynamic mechanical and dielectric properties of poly(ether-ketone) matrix composites

ABSTRACT

Poly(ether-ketone)/hexagonal boron nitride (h-BN) composites reinforced with micrometer-sized h-BN particles were investigated. The composites exhibited glass transition temperature (T_g) and thermal stability over 160°C and 560°C, respectively. The melting point and peak crystallization temperatures of the composites decreased up to 17°C and 12°C, respectively. The linear CTE of the composites decreased both below and above the T_g. The storage modulus increased with increasing h-BN content at all temperatures (50–250°C). The composites possessed excellent dielectric properties with insignificant dispersion with increasing frequency. Thus, resultant composites are promising candidates for the printed circuit boards/electronic substrates.     

Highly reversible and repeatable PTCR characteristics of PMMA/Ag‐coated glass bead composites based on CTE mismatch phenomena

Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)‐coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115°C, close to the glass transition temperature (T _g, 113°C) of the PMMA. However, the PTC trip temperature (92°C) of PMMA/Ag‐coated glass bead composites was appeared well below the T _g of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120°C, close to the T _g (118°C) of PMMA/clay nanocomposites, while PMMA/clay/Ag‐coated glass bead nanocomposites showed the PTC trip at 98°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag‐coated glass beads even at a temperature well below the T _g of PMMA. The decrease in dielectric permittivity of PMMA/Ag‐coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Sulfonated poly(ether imide) and poly(ether sulfone) blends for direct methanol fuel cells. I. Sulfonation of PEI and characterization of the products

This investigation examines characteristics of sulfonated polyether imides (SPEI) with various ion exchange capacity values (IEC) and completes previous work to enable its blends to be adopted as polyelectrolyte in direct methanol fuel cells (DMFC). Polyether imides (PEI) were sulfonated by using chlorosulfonic acid as the sulfonating agent and chloroform as the solvent. The structure of SPEI was observed by FTIR and ¹H NMR. The sulfonate or sulfonic acid content of the polymers, expressed as a number per repeat unit of the polymer, was accurately determined by elemental analysis and conductometric titration. Physical properties such as solubility, intrinsic viscosities, thermal stability, and glass transition temperature (T_g) were studied for both PEI and SPEI. TGA‐FTIR verified that sulfonic groups, attached to the aromatic ring in the PEI backbone, are split at 230–350°C, but the main‐chain splitting temperature of SPEI is similar to that of pure polymer. The sulfonated samples exhibited good solubilities and increased glass transition temperatures (T_g values) as degree of sulfonation (DS) increased; two T_g values were detected when IEC was sufficiently high. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of polycaprolactone molecular weights on thermal and mechanical properties of polybenzoxazine

Polymer blends of polybenzoxazine (PBA‐a) and polycaprolactone (PCL) of different molecular weights (M_n = 10,000, 45,000, and 80,000 Da) were prepared at various PBA‐a/PCL mass ratios and their properties were characterized. The results from dynamic mechanical analyzer (DMA) revealed two glass transition temperatures implying phase separation of the two polymers in the studied range of the PCL contents. Moreover, a synergistic behavior in glass transition temperature (T_g) was evidently observed in these blends with a maximum T_g value of 281°C compared with the T_g value of 169°C of the PBA‐a and about ?50°C of the PCL used. The blends with higher M_n of PCL tended to provide greater T_g value than those with lower M_n of PCL. The modulus and hardness values of PBA‐a were decreased while the elongation at break and area under the stress?strain curve were increased with an increase of the content and M_n of PCL, suggesting an enhancement of toughness of the PBA‐a. Scanning electron micrographs (SEM) of the sample fracture surface are also used to confirm the improvement in toughness of the blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41915.     

An apparent double glass transition of polyphenylene sulfide in blends with polyarylate

Summary Injection molded blends of polyphenylene sulfide (PPS) and polyarylate (PAR) are phase separated as evidenced by transmission electron microscopy (TEM) micrographs and the existence of glass transition temperatures (T_g's) near 100 °C (PPS) and 190 °C (PAR). Upon annealing, blends that contain 15% to 40% by weight PPS exhibited unusual double glass transition temperatures (aside from PAR's T_g at 190 °C) at ca. 88 °C and 110 °C. These transitions coincide, respectively, with the T_g's of amorphous and crystalline PPS homopolymer. PPS crystallinity and average domain size distribution were found to be larger in the skin region than in the core region. It is believed that the double T_g's are brought about by different PPS domains with two types of amorphous material.     

Reorganization of the chain packing between poly(ethylene isophthalate) chains via coalescence from their inclusion compound formed with γ‐cyclodextrin

Amorphous poly(ethylene isophthalate) (PEI) was synthesized, and was used for preparing an inclusion compound (IC) with γ‐cyclodextrin (γ‐CD). Coalesced polymer was produced by washing the PEI‐γ‐CD‐IC with hot water. Wide angle X‐ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses were employed to verify formation of PEI‐γ‐CD‐IC and to compare the as‐synthesized and coalesced PEI samples. These observations suggested that the conformations and morphology/chain‐packing of PEI were changed via coalescence from its γ‐CD inclusion compound. The glass‐transition temperature of the amorphous coalesced PEI is 15–20°C higher than the T_g observed for the as‐synthesized sample, even when observed in the second heat after cooling from well above T_g at 260°C. The amorphous as‐synthesized PEI retains its randomly‐coiling structure, while coalesced PEI has at least partially retained, the highly extended and parallel chains from the narrow channels of the inclusion compound, resulting in better/tighter packing among the PEI chains manifested by a higher T_g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6049–6053, 2006     

Anomalies,influencing factors,and guidelines for DMA testing of fiber reinforced composites

This study systematically assessed the measurement of dynamic properties of a range of fiber reinforced composite materials using dynamic mechanical analysis (DMA) instrument. The discrepancy in the moduli from DMA to ASTM tests was investigated. The study showed that proper specimen preparation, maintaining appropriate aspect ratio (span to thickness ratio) to reduce the transverse shear deformation, and sufficient loading are critical to measure correct properties from DMA test. The guidelines on aspect ratio and loading for plastics to high-modulus carbon fiber composites are presented as a design chart and equations, respectively. The study also found that the glass transition temperature (T_g) was independent of specimen aspect ratio and T_g is lower for multidirectional composites when compared with its unidirectional composites. The particle interleaved T800H/3900-2 composite showed two glass transition temperatures (140 and 198°C), the lower value is due to the effect of interleaving by thermoplastic particles, and the higher value is the T_g of its base matrix. This lowering of T_g would have significant effect on the application temperature of the material. This phenomenon was not observed here to fore in the literature. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Thermal,mechanical, and dielectric studies on the DGEBA epoxy blends by using liquid oxidized poly(1,2‐butadiene) as a reactive component

Liquid oxidized poly(1,2‐butadiene) (LOPB) with multi epoxy groups is synthesized to modify diglycidyl end‐caped poly(bisphenol A‐co‐epichlorohydrin) (DGEBA) cured by 4,4′‐diaminodiphenyl sulfone (DDS). FTIR spectra shows that DGEBA and LOPB can be effectively cured by DDS, and the epoxide rubber particles are evenly distributed in the composites till their addition up to 20 wt % of DGEBA as seen from the scanning electron microscope (SEM). Their decomposition temperatures (Td) increase with the increase in LOPB addition at around 10 wt % of DGEBA while the Td for the composite containing 20 wt % LOPB of DGEBA is lower than that of the neat epoxy. The addition of LOPB improves their storage moduli and especially these values at temperatures higher above 150 °C; all the composites exhibit higher glass transition temperature (T_g) than that of the neat epoxy, and the maximum T_g reaches up to 255 °C for the composite containing 15 wt % LOPB of DGEBA. The incorporation of LOPB effectively decreases their dielectric constants and the composite with 10 wt % LOPB of DGEBA possesses the lowest one. The synergic improvements in their various properties are attributed to the networks formation via covalent linkage between the two phases in these reactive blends. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44689.     

Processing and properties of injection molded thermoplastic composites reinforced with melt processable glasses

This work was concerned with evaluating the properties of injection molded composites comprising polyetherimide (PEI) and polyetheretherketone (PEEK) reinforced with various lower T_g melt processable phosphate glasses. Composites were produced utilizing a variety of glass and resin combinations in order to ascertain the effects of factors such as glass concentration and viscosity of the components on the mechanical properties of the composite blends. Changes in the rheological and interfacial properties of the blends obtained by varying the resins and phosphate glasses used during processing resulted in a variety of reinforcing morphologies consisting of glass beads, ribbons, and an interpenetrating network structure. The large variations in the glass phase morphologies obtained during injection molding led to composites that displayed a wide range of properties. Generally, it was found that the use of resin/glass combinations that minimized the viscosity difference between the components resulted in composites displaying the best overall mechanical properties. The stiffness of the composites was found to increase with glass concentration with loadings up to 45 vol% glass, leading to moduli 3‐4 times greater than those of the neat resins. While the addition of the phosphate glasses produced significant enhancements in the stiffness of the composite blends, the strength often fell to values 2‐3 times lower than those of the neat resins.     

In situ composites based on blends of a polyetherimide and thermotropic liquid crystalline polymers subjected to shearfree deformations

The effects of shearfree elongational flows on the morphology and mechanical properties of blends of a polyetherimide (PEI) with thermotropic liquid crystalline polymers (TLCP) have been investigated. Extruded sheets and injection molded plaques of PEI/Vectra A and PEI/HX1000 blends, with a TLCP concentration of ≤30 wt%, were subjected to uniaxial elongation, planar and biaxial deformations at 240°C, above the glass transition temperature of the PEI, and at 265°C, which is below the melting point of the TLCPs. Experimental results revealed that each particular mode of shearfree deformation had a distinct effect on the morphology and properties of the blends. For instance, TLCP droplets were deformed into elongated fibrils by application of uniaxial elongation, deformed into elongated ribbon-like structures after planar deformation, and deformed into a disc-like shape by application of equibiaxial flow. Regarding mechanical properties, it was observed that the tensile modulus and strength of molded plaques of PEI/HX1000 80/20 wt% increased to about twice their initial values (from 5.13 to 10.40 GPa and from 105 to 198 MPa, respectively) after a strain of 0.75 was applied in a direction parallel to the initial direction of the TLCP fibers. In addition, samples exhibiting equal values of flow and transverse direction tensile modulus of ∼5.0 GPa were obtained when molded plaques of PEI/HX1000 80/20 wt% were subjected to planar stretching in a direction transverse to the initial direction of the fibers. Thus, by subjecting injection molded plaques to planar stretching, it was possible to obtain a sample exhibiting balanced flow and transverse direction mechanical properties and, consequently, reduced anisotropy.     

Effects of fibers on the glass transition temperature of polyphenylene sulfide composites

The glass transition temperature (T_g) of polyphenylene sulfide (PPS), and of several commercial and model PPS prepregs with aramid, carbon, and glass fibers was studied by means of differential scanning calorimetry. The T_g of unreinforced PPS was found to range between 83–90°C, depending on source and molecular weight. The T_g of the commercial prepregs was depressed by about 3–5°C from that of the corresponding unfilled PPS, an effect that was ascribed to the plasticization of the PPS by one or more components of the fiber finish (size) that was assumed to have diffused into the PPS polymer. In the case of model prepregs prepared with finish-free reinforcing fibers, an expected increase in T_g was observed. In model prepregs prepared with finished (sized) aramid fibers, the T_g was depressed as in the case of the commercial prepregs. With sized AS-4 carbon fibers, the T_g was increased, but significantly less so than with unsized AS-4 fibers. With sized glass fibers, the same slight increase in T_g was observed as with unsized glass fibers. The increase or decrease of T_g in all cases was a function of the fiber content in the model PPS prepregs.     

Toughness optimization of elastomer‐modified glass–fiber reinforced PA6 materials

To investigate the influence of moisture and EPR‐g‐MA content on the fracture behavior of glass–fiber reinforced PA6 materials, brittle‐to‐tough transition temperatures (T_btt) were determined. Water absorption was taken into account by conditioning the analyzed materials. Tensile tests could reveal the temperature range of the largest moisture dependence of mechanical properties between 10 and 50°C. J‐integral values were used to describe the fracture behavior under conditions of impact load as a function of temperature. The brittle‐to‐tough transition of reinforced polyamides was found to be less approximate than in unreinforced materials. Two different characteristic temperature points T_s and T_e were identified, which were the intercept between elastic and elastic–plastic deformation on the one hand and the starting point of dominating stable crack propagation with strong plastic deformation on the other hand. Characteristic brittle‐to‐tough transition temperatures T_btt could be calculated as the arithmetic average of these two points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The dynamic mechanical behaviour of blends of polyphenylene sulfide with acetylene terminated sulfone

The dynamic mechanical behaviour of blends of poly(phenylene sulfide) (PPS) with the acetylene terminated sulfone bis(4-(4-ethynylphenoxy)phenyl)sulfone (ESF) was investigated by torsional braid analysis (TBA). A uniform dispersed system of ESF/PPS may be obtained by a solution process at 200°C, and can be maintained during the heat treatment up to 400°C. The increase of T_g of the blended system was found to be inappreciable by one-step and short time (e.g. 1 h) heat treatment, whatever the ESF fraction is. By a long term heat treatment or by step-curing, the T_g of the system may be raised from 180 to 220°C, in company with the increase of rigidity at 300°C, compared with pure PPS. The flexural modulus and interlaminar shear strength of continuous unidirectional carbon fibre composites with a blended matrix of ESF/PPS = 10/90 are significantly higher than those of composites with pure PPS matrix.     

Crystallization kinetics of poly(trimethylene terephthalate)/poly(ether imide) blends

The crystallization kinetics of a melt‐miscible blend, consisting of poly(trimethylene terephthalate) (PTT) and poly(ether imide) (PEI) prepared by solution precipitation, has been investigated by means of optical polarized microscopy and differential scanning calorimeter. It was found that both the PTT spherulitic growth rate (G) and overall crystallization rate constant (k_n) were depressed, with increasing PEI composition or crystallization temperature (T_c). The kinetic retardation was attributed to the decrease in PTT molecular mobility, and the dilution of PTT concentration due to the addition of PEI, which has a higher glass transition temperature (T_g). According to the Lauritzen–Hoffman theory of secondary nucleation, the crystallization of PTT in blends was similar to that of neat PTT as regime III, n = 4 and regime II, n = 2 growth processes, while the transition point of regime III to II has been shifted from 194°C for neat PTT to 190°C for blends. POLYM. ENG. SCI. 46:89–96, 2006. © 2005 Society of Plastics Engineers     

Thermophysical properties of anhydride‐cured epoxy/nano‐clay composites

Polymer nano‐composites made with a matrix of anhydride‐cured diglycidyl ether of bisphenol A (DGEBA) and reinforced with organo‐montmorillonite clay were investigated. A sonication technique was used to process the epoxy/clay nano‐composites. The thermal properties of the nano‐composites were measured with dynamic mechanical analysis (DMA). The glass transition temperature T_g of the anhydride‐cured epoxy was higher than the room temperature (RT). For samples with 6.25 wt% (4.0 vol%) of clay, the storage modulus at 30°C and at (T_g + 15)°C was observed to increase 43% and 230%, respectively, relative to the value of unfilled epoxy. The clay reinforcing effect was evaluated using the Tandon‐Weng model for randomly oriented particulate filled composites. Transmission electron microscopy (TEM) examination of the nano‐composites prepared by sonication of clays in acetone showed well‐dispersed platelets in the nano‐composites. The clay nano‐platelets were observed to be well‐intercalated/expanded in the anhydride‐cured epoxy resin system. POLYM. COMPOS., 26:42–51, 2005. © 2004 Society of Plastics Engineers.