Mohammed Naffakh

The influence of a compatibilizer on the thermal and dynamic mechanical properties of PEEK/carbon nanotube composites

The effect of polyetherimide (PEI) as a compatibilizing agent on the morphology, thermal, electrical and dynamic mechanical properties of poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT) nanocomposites, has been investigated for different CNT loadings. After a pre-processing step based on ball milling and pre-mixing under mechanical treatment in ethanol, the samples were prepared by melt extrusion. A more homogeneous distribution of the CNTs throughout the matrix is found for composites containing PEI, as revealed by scanning electron microscopy. Thermogravimetric analysis demonstrates an increase in the matrix degradation temperatures under dry air and nitrogen atmospheres with the addition of SWCNTs; the level of thermal stability of these nanocomposites is maintained when PEI is incorporated. Both differential scanning calorimetry and synchrotron x-ray scattering studies indicate a slight decrease in the crystallization temperatures of the compatibilized samples, and suggest the existence of reorganization phenomena during the heating, which are favoured in the composites incorporating the compatibilizer, due to their smaller crystal size. Dynamic mechanical studies show an increase in the glass transition temperature of the nanocomposites upon the addition of PEI. Furthermore, the presence of PEI causes an enhancement in the storage modulus, and hence in the rigidity of these systems, attributed to an improved interfacial adhesion between the reinforcement and the matrix. The electrical and thermal conductivities of these composites decrease with the incorporation of PEI. Overall, the compatibilized samples exhibit improved properties and are promising for their use in industrial applications.

Solvent-Free Preparation of High-Toughness Epoxy−SWNT Composite Materials

Multicomponent nanocomposite materials based on a high-performance epoxy system and single-walled carbon nanotubes (SWNTs) have been prepared. The noncovalent wrapping of nitric acid-treated SWNTs with a PEO-based amphiphilic block copolymer leads to a highly disaggregated filler with a boosted miscibility in the epoxy matrix, allowing its dispersion without organic solvents. Although direct dispersion of acid-treated SWNTs results in modestly improved epoxy matrix mechanical properties, the incorporation of wrapped SWNTs produces a huge increase in toughness (276% improvement at 0.5 wt % loading) and impact strength (193% at 0.5 wt % loading) with no detrimental effect on the elastic properties. A synergistic effect between SWNTs and the block copolymer is revealed on the basis of tensile and impact strength results. Atomic force microscopy has been applied, obtaining stiffness mappings that identify nanostructure features responsible of the dynamic mechanical behavior. The electrical percolation threshold is greatly reduced, from 0.31 to 0.03 wt % SWNTs when block copolymer-wrapped SWNTs are used, and all the measured conductivity values increased up to a maximum of 7 orders of magnitude with respect to the baseline matrix (1 wt % wrapped-SWNTs loading). This approach provides an efficient way to disperse barely dispersible SWNTs without solvents into an epoxy matrix, and to generate substantial improvements with small amounts of SWNTs.

Novel Melt-Processable Poly(ether ether ketone)(PEEK)/Inorganic Fullerene-like WS2 Nanoparticles for Critical Applications

The combination of high-performance thermoplastic poly(ether ether ketone) (PEEK) with inorganic fullerene-like tungsten disulfide (IF-WS(2)) nanoparticles offers an attractive way to combine the merits of organic and inorganic materials into novel polymer nanocomposite materials. Here, we report the processing of novel PEEK/IF-WS(2) nanocomposites, which overcome the nanoparticle agglomerate formation and provide PEEK-particle interactions. The IF-WS(2) nanoparticles do not require exfoliation or modification, making it possible to obtain stronger, lighter materials without the complexity and processing cost associated with these treatments. The nanocomposites were fabricated by melt blending, after a predispersion step based on ball milling and mechanical treatments in organic solvent, which leads to the dispersion of individually IF-WS(2) nanoparticles in the PEEK matrix as confirmed by scanning electron microscopy. In order to determine the performance of the PEEK/IF-WS(2) nanocomposites for potential critical applications, particularly for the aircraft industry, we have extensively investigated these materials with a wide range of structural, thermal, and mechanical techniques using time-resolved synchrotron X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, dynamic-mechanical analysis, and tensile and impact tests as well as thermal measurements. Modulus, tensile strengh, thermal stability, and thermal conductivity of PEEK exhibited remarkable improvement with the addition of IF-WS(2).

Use of Inorganic Fullerene-like WS2 to Produce New High-Performance Polyphenylene Sulfide Nanocomposites: Role of the Nanoparticle Concentration

The use of tungsten disulfide (WS2) nanoparticles offers the opportunity to produce novel and advanced polymer-based nanocomposite materials via melt blending. The developed materials, based on the high-performance engineering thermoplastic polyphenylene sulfide (PPS), display a unique nanostructure on variation of the nanoparticle concentration, as confirmed by time-resolved synchrotron X-ray diffraction. The cold-crystallization kinetics and morphology of PPS chains under confined conditions in the nanocomposite, as determined by differential scanning calorimetry (DSC) and atomic force microscopy (AFM), also manifest a dependence on the IF-WS2 concentration which are unexpected for polymer nanocomposites. The addition of IF-WS2 with concentrations greater than or equal to 0.5 wt % of IF-WS2 remarkably improves the mechanical performance of PPS with an increase in the storage modulus of 40-75%.

Unique isothermal crystallization behavior of novel polyphenylene sulfide/inorganic fullerene-like WS2 nanocomposites.

The isothermal crystallization of polyphenylene sulfide (PPS) nanocomposites with inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2) has been studied from a thermal and morphological point of view, using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), polarized optical microscopy (POM) and time-resolved synchrotron X-ray diffraction. All the analyses revealed that the incorporation of the IF-WS2 altered significantly the crystallization behavior of PPS, in a way strongly dependent with the nanocomposite composition. The addition of IF-WS2 in 0.1 wt % proportion retarded the crystallization of PPS by increasing its fold surface free energy in a 10%. However, addition of the nanoparticles in excess of 1 wt % results in a promotion of the crystallization rate with reduction of the fold surface free energy to half the value of pure PPS.

Morphology and thermal properties of novel poly(phenylene sulfide) hybrid nanocomposites based on single-walled carbon nanotubes and inorganic fullerene-like WS2 nanoparticles

We report for the first time the preparation and characterization of novel poly(phenylene sulfide) (PPS) hybrid nanocomposites based on polyetherimide-modified single-walled carbon nanotubes (SWCNT-PEI). A traditional melt processing strategy was employed providing a versatile, economic and scalable route to the creation of new materials with improved properties. The influence of the presence and concentration of SWCNT-PEI on the structure, morphology, dynamic crystallization behaviour, thermal stability and thermal conductivity of PPS in PPS/SWCNT-PEI nanocomposites was investigated in detail. In the presence of SWCNT-PEI, the crystallization rate of the PPS matrix in the nanocomposites was lowered with respect to that of neat PPS, and the thermal stability and thermal conductivity of PPS increased with increasing SWCNT-PEI content. The combination of PPS/SWCNT-PEI with inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles offers an attractive route to combine the merits of organic and inorganic materials into novel hybrid nanocomposite materials. A synergistic improvement in the thermal properties of PPS/SWCNT-PEI nanocomposites was observed with the addition of IF-WS2. As previously observed in PEEK hybrid systems, the dispersion, morphology and thermal properties of PPS/SWCNT nanocomposites could be tuned by the introduction of small amounts of IF-WS2. The results obtained are very promising and suggest that the use of IF-WS2, a cheap and environmentally friendly reinforcing filler, can also provide an effective balance between performance, cost-effectiveness and processability of polymer/CNT nanocomposites based on the PPS matrix.

Thermal decomposition of technological polymer blends 1. Poly(aryl ether ether ketone) with a thermotropic liquid crystalline polymer

The thermal decomposition of blends of poly(aryl ether ether ketone), PEEK, with a thermotropic liquid crystalline polymer (LCP), VECTRA, was investigated using thermogravimetric analysis under dynamic conditions. The activation energies were obtained using integral and differential methods. The thermal analysis of the blends show that thermal stability is clearly affected with respect to the unblended materials, and it was also observed that the degradation process is accelerated by blending. In the case of VECTRA, the LCP is destabilized at high PEEK contents. The degrading polymer blends, at various degrees of conversion, were examined by Fourier transform infrared spectroscopy. The degradation mechanisms were analysed from the changes in the vibrational spectra. Blending appears to modify only the rate of degradation of the component polymers, the mechanisms remaining unchanged.

Unique nucleation activity of inorganic fullerene-like WS2 nanoparticles in polyphenylene sulfide nanocomposites: isokinetic and isoconversional study of dynamic crystallization kinetics.

The dynamic crystallization kinetics of polyphenylene sulfide (PPS) nanocomposites with inorganic fullerene WS2 nanopartices (IF-WS2) content varying from 0.05 to 8 wt % has been studied using differential scanning calorimetry (DSC). The analysis of the crystallization at different cooling rates demonstrates that the completely isokinetic description of the crystallization process is not possible. However, the isoconversional methods in combination with the JMAEK equation provide a better understanding of the kinetics of the dynamic crystallization process. The addition of IF-WS2 influences the crystallization kinetics of PPS but in ways unexpected for polymer nanocomposites. A drastic change from retardation to promotion of crystallization is observed with increasing nanoparticle content. In the same way, the results of the nucleation activity and the effective energy barrier confirmed the unique dependence of the crystallization behavior of PPS on composition. In addition, the morphological data obtained from the polarized optical microscopy (POM) and time-resolved synchrotron X-ray diffraction is consistent with results of the crystallization kinetics of PPS/IF-WS2 nanocomposites.

New hybrid nanocomposites containing carbon nanotubes, inorganic fullerene-like WS2 nanoparticles and poly(ether ether ketone) (PEEK)

Single-walled carbon nanotubes (SWCNTs) and inorganic fullerene-like WS2 nanoparticles were successfully dispersed in poly(ether ether ketone) (PEEK) by advantageously traditional melt processing techniques. This strategy offers an attractive way to combine the merits of organic and inorganic materials into novel hybrid systems that challenge emerging polymer/CNT nanocomposites in terms of performance, cost and processability. In particular, the incorporation of IF-WS2 has shown to be efficient to produce well-dispersed PEEK/SWCNT composites influenced in turn by the processing method. The morphology, thermal stability, crystallization behaviour, thermal conductivity as well as mechanical and electrical properties of PEEK/SWCNT composites were tuneable by the introduction of small amounts of IF-WS2. The overall structural, thermal, mechanical and electrical performances confirm the potential use of SWCNTs and IF-WS2 for the preparation of advanced hybrid nanocomposites as lightweight alternatives for use in critical industrial applications of high-performance and high-temperature thermoplastics like PEEK.

Isothermal crystallization kinetics of novel isotactic polypropylene/MoS2 inorganic nanotube nanocomposites.

Inorganic nanotubes (INT) were used for the first time to prepare advanced polymer nanocomposites by means of the most simple, cost-effective and ecologically friendly way (i.e., melt-processing route). The polymer matrix was isotactic polypropylene (iPP) and the inorganic fillers were molybdenum disulfide nanotubes (MoS(2)). The effect of INT-MoS(2) concentration and the crystallization temperature on the isothermal crystallization behavior of iPP was investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS). It has been observed that INT-MoS(2) affects the crystallization of nanocomposites remarkably, which can be attributed to the nucleating effect of INT-MoS(2) on the monoclinic α-crystal form of iPP. Other parameters such as the Avrami exponent and the fold surface free energy of crystallization of iPP chains in the nanocomposites were obtained in order to determine the effect of the INT-MoS(2) on them. The addition of INT-MoS(2) remarkably influences the kinetics of nucleation and growth of iPP with a decrease in the fold surface free energy of 11-24%.