Effect of PEKK oligomers sizing on the dynamic mechanical behavior of poly(ether ketone ketone)/carbon fiber composites

Poly(ether ketone ketone) (PEKK)/unidirectional carbon fiber (CF) composites have a poor interface. Accordingly, PEKK oligomer (PEKKo) sizing with a chemical compatibility with PEKK is proposed for promoting interfacial interactions in order to enhance mechanical performances. The thermal stability until 500 °C has been shown by thermogravimetric analysis (TGA). In order to compare static and dynamic sizing methods, “lab sizing” and “pilot sizing” were carried out. Scanning electron microscopy images of freeze fractures of PEKK/unsized CF, PEKK/PEKKo lab-sized CF and PEKK/PEKKo pilot-sized CF show that the PEKKo sizing causes an improvement of fiber/PEKK interactions, regardless of the sizing method. Indeed, in both cases, there is a continuity of matter at the interface while we observe a poor wetting of CF by matrix in PEKK/unsized CF. Dynamic mechanical relaxations in shear were analyzed as a function of temperature. The increase of storage modulus upon sizing is observed for both methods but it is more important for PEKKo pilot sizing. In the same way, the mechanical energy loss increases, it reflects the optimization of stress transfer between matrix and fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48818.     

Influence of carbon nanotubes on the thermal, electrical and mechanical properties of poly(ether ether ketone)/glass fiber laminates

Novel poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT)/glass fiber laminates incorporating polysulfone as a compatibilizing agent were fabricated by melt-blending and hot-press processing. Their morphology, mechanical, thermal and electrical properties were investigated and compared with the behavior of similar non-compatibilized composites. Scanning electron micrographs demonstrated better SWCNT dispersion for samples with polysulfone. Thermogravimetric analysis indicated a remarkable improvement in the thermal stability of PEEK/glass fiber by the incorporation of SWCNTs wrapped in the compatibilizer, ascribed to a significant thermal conductivity enhancement. Differential scanning calorimetry showed a decrease in the crystallization temperature and crystallinity of the polymer with the addition of both wrapped and non-wrapped SWCNTs. The laminates exhibit anisotropic electrical behavior; their conductivity out-of-plane is lower than that in-plane. Dynamic mechanical studies revealed an increase in the storage modulus and glass transition temperature in the presence of polysulfone. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the incorporation of wrapped nanofillers, whilst the mechanical properties of non-compatibilized composites only improved marginally. Samples with laser-grown SWCNTs exhibit enhanced overall performance. This investigation confirms that SWCNT-reinforced PEEK/glass fiber compatibilized composites possess excellent potential to be used as multifunctional engineering materials in industrial applications.     

Enhanced electrical properties by tuning the phase morphology of multiwalled carbon nanotube‐filled poly(ether ether ketone)/polyimide composites

A novel high‐performance material with enhanced electrical properties was obtained by tuning the phase morphology of poly(ether ether ketone) (PEEK)/thermoplastic polyimide (TPI)/multiwalled carbon nanotube (MWCNT) composites. MWCNTs were selectively located in the TPI phase due to discrepant affinity of MWCNTs between PEEK and TPI. The dependence of the electrical properties of the PEEK/TPI/MWCNT composites on the phase morphology was investigated by changing the PEEK/TPI ratio, and the maximum conductivity was achieved with a PEEK/TPI ratio of 50/50, which could be explained by the selective location of MWCNTs and the co‐continuous phase morphology of the composites. © 2015 Society of Chemical Industry     

Morphology and dynamical mechanical properties of poly ether ketone ketone (PEKK) with meta phenyl links

Poly ether ketone ketone (PEKK) with different proportion of meta phenyl links were investigated by combining differential scanning calorimetry and dynamic mechanical analysis. The influence of the Terephthalyl/Isophthalyl isomers (T/I) ratio on the vitreous phase is mild, the shift of the glass transition is limited to a few degrees and the vitreous G′ is only sensitive to the content of the crystalline phase. Contrarily, the increase of meta isomers is responsible for a significant decrease of the melting temperature (T_m) by 60 °C, which considerably facilitates processing. The modification of interchain interactions in the crystalline phase might be implied. A series of thermal protocols evidenced that the difference of crystallization behavior is also dependent upon the T/I isomer ratio. A time and temperature dependence of annealing on the double melting behavior of PEKK was observed. Regarding the mechanical behavior, the observed reinforcing effect due to the crystalline phase was more prominent in the rubbery state than in the glassy state. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43396.     

The preparation and thermomechanical properties of high-temperature foams based on thermoplastic poly(phthalazinone ether ketone)

Poly(phthalazinone ether ketone) (PPEK) is an amorphous thermoplastic polymer with a high glass transition temperature (T_g) exceeding 250°C. We describe the preparation of foams from PPEK and characterize their properties. PPEK foams were prepared using dichloromethane as a foaming agent. The foaming agent was swollen into discs of the PPEK, which were then foamed by heating. Foams could be prepared at temperatures far below the T_g of the PPEK due to plasticization of the polymer by the foaming agent. Foams with densities ranging from 0.1 to 0.65 g/cm³ were prepared. Their thermal conductivity and modulus (measured approximately by indentation tests) were found to decrease with density, and the trends were similar to those expected from existing models. The foams could be annealed at 200°C without collapse suggesting that they may be useful in structural or insulation applications where stability at high temperature is essential.     

Influence of new thermoplastic sizing agents on the mechanical behavior of poly(ether ketone ketone)/carbon fiber composites

In this study, unidirectional poly(ether ether ketone)/carbon fiber (CF) composite sheets were elaborated with unsized, epoxy‐sized, and thermoplastic‐sized CFs by hot‐press molding. The thermoplastic sizings that we used were poly(ether imide) (PEI) and poly(ether ketone ketone) oligomer aqueous dispersions. Scanning electron microscopy observation of the composites freeze fractures showed that unlike unsized or epoxy‐sized CFs, the thermoplastic sizings improved the interaction between the fibers and the matrix. A comparative study of the mechanical relaxations by dynamic mechanical analysis was carried out on the different composites before and after immersion in kerosene. At low temperature, the PEI sizing had a significant influence on the β relaxation, particularly after kerosene immersion. The thermoplastic sizings did not modify the glass‐transition temperature but improved the kerosene resistance on the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42550.     

Improvement of the mechanical and electrical properties of waste rubber with carbon nanotubes

The effect of carbon nanotubes (CNTs) on the stability of the mechanical and electrical properties of recycled waste rubber was experimentally investigated. The stress–strain curves of the composites were studied. The results show that the toughness, the area under the stress–strain curve, of the recycled rubber increased monotonically as a result of the addition of CNTs. The modulus of the nanocomposites increased by 28 times when only 5 wt % CNTs was added to the recycled rubber matrix. The effects of the cyclic fatigue and hysteresis for the composites were also examined. The strain energy density, dissipation energy, and linear damage accumulation versus the number of cycles are discussed for all of the samples. The analysis of the results showed that the strain energy density increased by 15 times at a CNT concentration of 5 wt %. The electrical properties were measured for all of the samples. The results indicate that the addition of CNTs to the recycled rubber improved its electrical conductivity by more than two orders. © 2011 Wiley Periodicals, Inc. J Polym Sci, 2011     

Polypropylene/multiwall carbon nanotubes nanocomposites: Nanoindentation,dynamic mechanical,and electrical properties

Polypropylene (PP)/Multiwall carbon nanotubes (MWCNTs) nanocomposites were fabricated via melt compounding that utilizes a corotating twin‐screw extruder. Two commercially available MWCNTs, Baytubes C150P and C70P, were incorporated into PP matrix at concentration of 3 wt %. The nanocomposites samples were analyzed using scanning electron microscopy, dynamic mechanical analysis (DMA), nanoindentation test, and picoammeter. It was found that both MWCNTs types were well distributed and dispersed in the PP matrix and no agglomeration of MWCNTs was observed. The DMA analysis results showed that the incorporation of MWCNTs enhanced the storage modulus and thermal stability of the PP matrix. Whereas, nanoindentation creep results showed that the creep rate and displacement of the PP/MWCNTs nanocomposites was lower than the neat PP, in which C70P < C150P < PP. The reduction of creep rate and creep displacement was associated to the improvement of creep resistance. There were also improvements on hardness and stiffness of the nanocomposites. Additionally, the electrical resistivity of the neat PP decreased with the incorporation of MWCNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45293.     

Effect of multiwall carbon nanotubes on thermomechanical and electrical properties of poly(trimethylene terephthalate)

Multiwalled carbon nanotubes (MWCNTs) were synthesized using chemical vapor deposition and poly(trimethylene terephthalate) (PTT)/MWCNT composites with varying amounts of MWCNTs were prepared by melt compounding using DSM micro‐compounder. Morphological characterization by SEM and TEM showed uniform dispersion of MWCNTs in PTT matrix upto 2% (w/w) MWCNT loading. Incorporation of MWCNTs showed no effect on percent crystallinity but affected the crystallite dimensions and increased the crystallization temperature. Dynamic mechanical characterization of composites showed an increase in storage modulus of PTT upon incorporation of MWCNTs above glass transition temperature. The electrical conductivity of PTT/MWCNT composites increased upon incorporation of MWCNTs and percolation threshold concentration was obtained at a loading of MWCNTs in the range of 1–1.5% (w/w). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication and dielectric properties of poly(ether ether ketone)/polyimide blends with selectively distributed multi‐walled carbon nanotubes

The distribution and contents of conductive fillers have a decisive influence on the dielectric properties of polymer/conductive filler composites. Herein, we clarified how the phase morphology and filler contents affect the dielectric properties of poly(ether ether ketone) (PEEK)/polyimide (TPI)/multi‐walled carbon nanotubes (MWCNTs) composites, in which MWCNTs were selectively located in the TPI phase. Firstly, PEEK/TPI/MWCNTs composites with identical MWCNTs content but different PEEK/TPI ratios were prepared. The composites with co‐continuous phase structure exhibited much better dielectric properties than those with sea–island structure. Then, PEEK/TPI/MWCNTs composites with the same PEEK/TPI ratio but various MWCNTs contents were prepared. The dielectric constant of the composite with 2 wt% MWCNTs reached 11306, which is because the formation of a co‐continuous phase structure benefited the mini‐capacitor network. Our results provide an effective method to develop high‐dielectric‐constant composites using the concept of double percolation. © 2015 Society of Chemical Industry     

Enhanced mechanical and electrical properties of nylon‐6 composite by using carbon fiber/graphene multiscale structure as additive

In order to improve the mechanical properties and electrical conductivity of nylon‐6 (PA6) composites, a highly effective multiscale structure filler comprising poly(diallyldimethylammonium chloride) (PDDA)‐modified graphene and negatively surface‐charged carbon fiber was synthesized in this study. For this, the graphene used a top‐down method for synthesis by exfoliating graphite oxide (GO) through focused solar radiation on it and then modified its surface by using a polyelectrolyte. The carbon fiber (CF) surface was functionalized by an acid oxidation method. The multiscale structure was manufactured via the electrostatic interaction between the positively charged solar graphene (SG) and oppositely charged CF by homogeneous mixing. Scanning electron microscopy (SEM) images of the fracture surface of the PA6 composites exhibited that the carbon fiber/graphene multiscale structure possessed better dispersion and compatibility than those of individual CF and SG did. Thus, the impact strength, bending properties, and electrical conductivity of the PA6 composites were enhanced. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41968.     

Tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO4/SPEEK membranes

A study to evaluate the tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO₄/SPEEK composite membranes has been carried out. It is aimed to give an assessment of these materials for applications in proton exchange membrane fuel cells. The stress–strain response of the membranes was measured as a function of the degree of sulfonation (DS) and the filler–matrix ratio. In addition, the effects of immersion in water at various temperatures were explored in situ by means of a homemade testing chamber fitted to the tensile analyzer. The results indicate that the DS has an important influence on the final mechanical behavior of the membranes. The introduction of the BPO₄ solid filler leads to deterioration in mechanical performance compared to unfilled SPEEK. A general picture of the microstructural features influencing the mechanical properties of SPEEK and BPO₄/SPEEK membranes is proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2380–2393, 2005     

Studies of electrical and mechanical properties of semiconductive poly(vinyl chloride) compositions

A sample of poly(vinyl chloride) (PVC) and a polar plasticizer consisting of dioctylphthalate (DOP) and triisopropylphenylphosphate (TIPPP) was prepared and found to possess some electrical conductivity. Different samples of PVC compositions were formulated from the PVC-DOP-TIPPP system and also variable proportions of the conductive materials polyaniline or the Ni salt of ethylene glycol bisadipate ester. Dibutyltindilaurate as a heat stabilizer, titanium oxide as a filler, and sandorin red 20 pigment were added. The effect of the structure of polyaniline and Ni adipate ester on the electrical and mechanical properties of the PVC–DOP–TIPPP system was studied to obtain a semiconductive plasticized PVC with good mechanical properties. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 685–693, 1998     

Poly(ether ether ketone)/poly(aryl ether sulfone) blends: Relationships between morphology and mechanical properties

Mechanical properties such as the tensile modulus, yield (break) strength, and elongation to break (or yield) are measured for multiphase poly(ether ether ketone) (PEEK)/poly(aryl ether sulfone) (PES) blends. Specimens with three different levels of thermal histories (quenched, as‐molded, and annealed) are prepared in order to study their effects on the mechanical properties of PEEK/PES blends. Synergistic behavior is observed in the tensile modulus and tensile strength of the blends in almost the whole range of compositions. The ductility of quenched blends measured as the elongation to break (yield) shows an unexpected synergistic behavior in the blend containing 90 wt % PEEK, although a negative deviation from additive behavior is observed in the rest of the compositions. A ductile–brittle transition is observed between 50 and 75 wt % PEEK in the blend. The ductile–brittle transition in as‐molded blends shifts to 75–90 wt % PEEK. Annealed blends show predominantly brittle behavior in the whole composition range. The experimental data are further correlated with the theoretically predicted results based on various composite models. Although the prediction based on these equations fails to fit the experimental data in the whole composition range, the simplex equations that are normally used for blends showing synergistic behavior produced a reasonable fit to the experimental data. The mechanical properties obtained for different blend compositions are further correlated with their morphology as observed by scanning electron microscopy. Morphological observation shows a two‐phase morphology in PES‐rich blends, which is an interlocked morphology in which the disperse phase is not clearly visible in PEEK‐rich blends, and a cocontinuous type of morphology for a 50/50 composition. Considerable permanent deformation of both the disperse and matrix phase, especially in the case of quenched tensile specimens, demonstrates the remarkable adhesion present between the two phases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2887–2905, 2003     

Improving the thermal and mechanical properties of poly(vinyl butyral) through the incorporation of acid‐treated single‐walled carbon nanotubes

In this study, to investigate the effect of functionalized carbon nanotubes on the thermal and mechanical properties of the poly(vinyl butyral) (PVB) resin, PVB/functionalized single‐walled carbon nanotube (f‐SWCNT) composites were fabricated by a solution casting method. The functionalized nanotubes were prepared by acid treatment. The formation of oxygen‐containing functional groups on the surface of the nanotubes was confirmed by Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, and scanning electron microscopy (SEM) measurements. SEM analysis also showed that the nanotubes were dispersed well in the PVB matrix. The thermal stability of the composites were investigated with thermogravimetric analysis, and the results show better stability for PVB in the presence of a very low content of the f‐SWCNTs. The prepared composites exhibited a significant increase in the temperature of degradation at 50 wt % loss and also in the onset temperature and decomposition temperature at the maximum rate of weight loss of butyral degradation. A significant enhancement in the mechanical properties was also achieved for these prepared composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40481.     

Dynamic rheological behavior of poly(ether ketone ketone) from solid state to melt state

High performance thermoplastic poly(ether ketone ketone) (PEKK) polymers with various meta phenyl links ratio were investigated by dynamical mechanical analysis. Analyses were carried out in a wide range of temperature from solid state (torsion rectangular mode) to the melt state (torsion parallel plates mode) as function of thermal history and environmental conditions. In the solid state, this study was focused on the secondary relaxations in the vitreous state. A complementary investigation conducted with different poly(aryl ether ketones) allowed us to propose a molecular interpretation of PEKK sub‐vitreous relaxations. In the molten state, storage modulus (G′), loss modulus (G″), storage viscosity (η′), and loss viscosity (η″) were studied to determine zero shear‐rate viscosity (η₀) and thermal activation energy E_a. Master curves were built and the shift factor a_T was determined. Thermal activation energies were extracted from an Arrhenius model on the shift factor temperature's dependency. Finally, E_a and η₀ were determined thanks to the dynamic viscosity fit with Cross model and Cole–Cole representation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46456.     

Poly(ether ether ketone)/wrapped graphite nanosheets with poly(ether sulfone) composites: Preparation,mechanical properties,and tribological behavior

Antiwear composites with extraordinary tribological performances and good mechanical/thermal properties were developed by the dispersion of poly(ether sulfone) (PES) wrapped graphite nanosheets (GNSs) inside a poly(ether ether ketone) (PEEK) matrix via melt blending. The tribological behaviors and the mechanical/thermal properties of the composites were carefully investigated. Compared with pure PEEK and PEEK/GNS composites, the PEEK/wrapped GNS composites exhibited considerable enhancements in those performances; these were attributed to the eliminated layer of PES; this elimination not only eliminated the GNS aggregation inside the PEEK matrix for homogeneous distribution inside the PEEK matrix but also enhanced the interfacial adhesion between the PEEK and wrapped GNSs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41728.     

Synthesis and properties of copolymers of poly(ether ketone ketone) and poly(ether amide ether amide ether ketone ketone)

Poly(aryl ether ketone)s (PAEKs) are a class of high‐performance engineering thermoplastics known for their excellent combination of chemical, physical and mechanical properties, and the synthesis of semicrystalline PAEKs with increased glass transition temperatures (T_g) is of much interest. In the work reported, a series of novel copolymers of poly(ether ketone ketone) (PEKK) and poly(ether amide ether amide ether ketone ketone) were synthesized by electrophilic solution polycondensation of terephthaloyl chloride with a mixture of diphenyl ether and N,N′‐bis(4‐phenoxybenzoyl)‐4,4′‐diaminodiphenyl ether (BPBDAE) under mild conditions. The copolymers obtained were characterized using various physicochemical techniques. The copolymers with 10–35 mol% BPBDAE are semicrystalline and have markedly increased T_g over commercially available poly(ether ether ketone) and PEKK due to the incorporation of amide linkages in the main chain. The copolymers with 30–35 mol% BPBDAE not only have high T_g of 178–186 °C, but also moderate melting temperatures of 335–339 °C, having good potential for melt processing. The copolymers with 30–35 mol% BPBDAE have tensile strengths of 102.4–103.8 MPa, Young's moduli of 2.33–2.45 GPa and elongations at break of 11.7–13.2%, and exhibit high thermal stability and good resistance to organic solvents. Copyright © 2010 Society of Chemical Industry     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwalled carbon nanotubes composites

Poly(ethylene terephthalate)/multiwalled carbon nanotubes (PET/MWCNTs) with different MWCNTs loadings have been prepared by in situ polymerization of ethylene glycol (EG) containing dispersed MWCNTs and terephthalic acid (TPA). From scanning electronic microscopy images of nanocomposites, it can be clearly seen that the PET/MWCNTs composites with low‐MWCNTs contents (0.2 and 0.4 wt %) get better MWCNTs dispersion than analogous with high‐tube loadings (0.6 and 0.8 wt %). The nonisothermal crystallization kinetics was analyzed by differential scanning calorimetry using Mo kinetics equation, and the results showed that the incorporation of MWCNTs accelerates the crystallization process obviously. Mechanical testing shows that, in comparison with neat PET, the Young's modulus and the yield strength of the PET nanocomposites with incorporating 0.4 wt % MWCNTs are effectively improved by about 25% and 15%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic mechanical properties of Al2O3/poly(ether ether ketone) composites

The dynamic mechanical properties of high‐performance polymer matrix composites based on semicrystalline poly(ether ether ketone) (PEEK) and aluminum oxide (Al₂O₃) were evaluated in the temperature range of 30–250°C with a three‐point‐bending mode at a frequency of 1 Hz. The storage modulus and loss modulus changed significantly with the variation of the Al₂O₃ content in the PEEK matrix. The Al₂O₃ reinforcement was more pronounced above the glass‐transition temperature (T_g). A composite containing 60 wt % (33 vol %) Al₂O₃ exhibited about a 78% increase in the storage modulus at 50°C and about a 200% increase at 200°C. However, there was no significant change in the mechanical loss factor and T_g associated with the peak of the mechanical loss factor or loss modulus with the addition of Al₂O₃. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 568–575, 2007