Carlos Marco

Structure and thermal properties of blends of nylon 6 and a liquid crystal copolyester

Abstract Blends of nylon 6 with the liquid crystal copolyester Vectra have been prepared from the melt with different compositions, and their thermal behaviour has been analysed by differential scanning calorimetry (d.s.c.) and X-ray diffraction (WAXS) using syncrotron radiation, as a function of temperature and thermal treatment. The structural properties of these blends have been found to be very sensitive to the thermal history, and particular attention has been paid to the effect of the liquid crystal content in the polymorphic transformations of nylon 6.

Crystallization kinetics of polypropylene-polyamide compatibilized blends

Abstract Polypropylene and polyamide blends (composition 70/30) have been studied with and without the addition of maleic anhydride functionalized polypropylene at different levels, 1, 3, 5 and 10% by weight. The influence of the compatibilizing agent on the thermal transitions and on the morphology has been determined by X-ray diffraction, differential scanning calorimetry in dynamic and isothermal conditions and by dynamic mechanical analysis. The crystallization kinetics of these blends have been systematically investigated. The isothermal crystallization of the PA component is influenced by the presence of PP, reducing the crystallization rate due to the diluent effect originated by this polymer. On the contrary, the crystallization rate of PP in the blends is higher than the corresponding value for pure PP. This effect is higher in the blends without compatibilizer This behaviour is related to the nucleating activity by the PA component.

Rheological properties, crystallization, and morphology of compatibilized blends of isotactic polypropylene and polyamide

Blends of isotactic polypropylene (iPP) with the polyamide nylon-6 (N6), prepared by extrusion, were studied with a composition of up to 30% by weight polyamide. In the case of a 70/30 iPP/N6 blend, the influence of a compatibilizing agent based on polypropylene functionalized with maleic anhydride (PP-g-MA), with compositions of 1, 3, 5, and 10% by weight in polypropylene, was followed. The influence of the concentration of N6 and the compatibilizing agent on the rheological and thermal properties, and the morphology of the blends, was analyzed by monitoring the melt viscosity at different shear rates, differential scanning calorimetry, and polarized light microscopy. Vibrational spectroscopy was used to characterize the blends and to study the effect of the compatibilizing agent. The viscosity—composition curves for the iPP/N6 blends, in the composition and shear rate ranges analyzed, show a negative deviation from the additive rule, while the opposite trend is observed for the blends compatibilized with PP-g-MA. Important variations in the spectroscopic behavior was observed between compatibilized and noncompatibilized blends, which varied as a function of the compatibilizing agent concentration. The crystallization rates of iPP in the iPP/N6 blends, under both dynamic and isothermal conditions, are much greater than are those observed for pure iPP and are directly related to the nucleating activity of the polyamide. This effect is much smaller in the presence of the compatibilizing agent. The isothermal crystallization of the polyamide N6 in compatibilized blends is affected by the presence of iPP, reducing the crystallization rate due to the diluent effect of the polypropylene.

Water effect on the morphology of EVOH copolymers

The effect of water on the morphology of four ethylene vinyl alcohol copolymers (EVOH) with different ethylene contents was studied by differential scanning calorimetry (DSC). EVOH film samples equilibrated in controlled atmospheres at different relative humidities (RH) and 23°C were analyzed. Under dry conditions, the glass transition temperature (Tg) was unaffected by copolymer ethylene content. As RH increases, Tg decreases. It seems that the presence of water within the polymer matrix results in plasticization of the polymer. Tg varies from around 50°C (dry) to below room temperature. EVOH copolymers are glassy polymers when dry and rubbery polymers at high RHs. Fox and Gordon–Taylors equations well describe Tg depletion at low water uptake, although severe water gain results in a considerable Tg decrease, which is not predicted by these theories. Melting temperature, Tm, and enthalpy, ΔHm, were also analyzed. When dry, Tm decreases as ethylene content increases. No significant water effect was found on either Tm or ΔHm. Hence, crystallinity seems to be unaffected by water presence.

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.

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%.

The influence of molecular weight on the regime crystallization of linear polyethylene

Overall crystallization rates of polyethylene fractions, ranging in molecular weight from 1.95 × 104 to 8.0 × 106, have been measured over the temperature range from 114 to 128°C. From kinetic analysis of these data, three distinct regimes have been detected. The assignment of the regimes has been made based on several mechanistic situations, which lead to the same temperature coefficient. The influence of molecular weight on the regime behaviour has been found to be very profound. It changes the type of regime that is observed, the slope of the temperature coefficient in regime II and the location of the transition temperature from one regime to another.

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.