J.G. Fatou

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.

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.

The crystallization kinetics of low-molecular-weight polyethylene fractions

Abstract Overall crystallization rates of low-molecular-weight fractions of linear polyethylene have been measured. The molecular weights range from MN = 2900 to MN = 11 400 and quantitative data were obtained in the temperature interval of 110 to 127°C, depending on the molecular weight. Crystallization kinetics obey nucleation theory appropriate to chains of finite length. Definite continuity is found between the kinetics of fractions with molecular weights greater than 8000 and high-molecular-weight fractions. The three lowest molecular-weight fractions appear to display some unique kinetic features. All the fractions display three distinct regimes and the transition temperature between regimes can be identified with characteristics in nucleation rates and do not correspond to an integral change in crystallite thickness.

α, β and γ relaxations of functionalized HD polyethylene: a TSDC and a mechanical study

The relaxation behavior of high density polyethylene functionalized with diethylmaleate has been determined by dynamic mechanical method and thermally stimulated depolarization technique. The transitions observed have been related to the structural parameters as well as the α-olefin comonomer content and degree of grafting, and compared with previous TSDC results on LLPE functionalized with the same polar group. The lowest relaxation is composed of a sub-γ and a γ mode assigned to localized motions of the polar groups and to the glass transition (at 137 K), respectively. The β-relaxation intensity grows with the grafting degree in agreement with its assignment to motions taking place in the interfacial regions. The behavior of the α-mode with different content of diethylmaleate has confirmed its dependence with the crystallite size.

Vickers microhardness related to mechanical properties of polypropylene

Vickers micro-indentation of polymers is a method that yields information about their microstructure and some aspects of their mechanical behaviour. In the case of polyethylenes of different types, a monotonic increase of the microhardness with increasing degree of crystallinity has been observed and it has been proved that the microhardness is related to the elastic modulus and the yield stress [1, 2]. Microhardness has been also shown to be an adequate technique for establishing precisely the glass-transition temperature of isotactic polypropylene [3] or for studying the delayed elastic recovery of polyethylenes [4, 5]. Moreover, microhardness is a suitable tool for investigating oriented polymers, because it has been demonstrated that the microhardness anisotropy can be related either to changes in the preferred orientation in injection-moulded poly(4-methyl pentene-1) [6] or to birefringence and draw ratio in stretched poly(ethylene terephthalate) [7]. The dependence of the microhardness on structure and the relationships between the microhardness and the mechanical properties have not been analysed in polypropylene. For this reason the main purpose of this work was to present the results obtained for this polymer and to discuss these results in terms of structural parameters. A series of nine commercial isotactic polypropylenes whose nominal densities and melt indices ranged from 0.897 to 0.904gcm -3 and from 0.82 to 29.7, respectively, were studied. The materials were placed between the plates of a Collin press, heated to 5°C above their melting temperatures and pressed at 1.5 MPa for 10min. The mouldings were quenched in ice-water and fihns about 200/~m thick were obtained. The densilLy of the samples was measured by using a gradient column filled with ethanol-water which was calibrated with glass floats, and the degree of crystallinity was calculated by means of the twophase model using the values vj = 1.142cm3g -I and vc = 1.070cm3g L for the specific volumes of the amorphous and crystalline phases, respectively [8]. Dumb-bell shaped specimens with a gauge length of 2cm and a width of 0.4cm were cut out of the moulded sheets. The drawing of the samples was carried out on an Instron tensile testing machine at 20 ° C and at a strain rate of 0.25 min- ~. The moduli of elasticity were calculated from the initial slope of the stress-strain curves and the yield points were considered to occur where the stress went through a maxi

Crystallization regimes in poly(3,3-dimethylthietane) fractions

Overall crystallization rates of poly(3,3-dimethylthietane) fractions ranging in molecular weight from 6.5 × 103 to 1.04 × 105 have been analysed over the temperature range from −30 to 7°C. Kinetic analysis of the temperature coefficient shows that this polymer presents all three regimes of crystallization. The ratios of the temperature coefficients for Regime I to Regime II and of Regime III to Regime II are close to the theoretical value of 2. The transitions occur at an undercooling of 15–16°C for Regime I-Regime II and ΔT = 23−26°C for Regime II-Regime III.

Miscibility of poly(vinyl chloride)/poly(ethylene oxide) blends—I. Thermal properties and solid state 13C-NMR study

Abstract Blends of poly(vinyl chloride), PVC, and poly(ethylene oxide), PEO, have been studied for a complete range of composition, by differential scanning calorimetry and high-resolution solid state 13C-NMR spectroscopy. Proton spin-lattice relaxation times in the rotating frame, T1ρ(H), as well as calorimetric data indicate miscibility of the components of these blends in the amorphous phase for mixtures containing ≥40% PVC. In this range of composition and from the melting point depression for PEO in the mixtures, the binary interaction parameter is found to be −0.094.

Miscibility of poly(vinyl chloride)/poly(ethylene oxide) blends—II. An inverse gas chromatography study

The application of inverse gas chromatography (IGC) to measure polymer-polymer interaction parameters (X or B) requires attention to the dependence of these parameters for the selected probes. A phenomenological alternative to solve this problem, recently proposed, has been applied to poly(vinyl chloride)/poly(ethylene oxide) blends. A composition dependent B parameter was obtained, in reasonable agreement with the results reported in the previous paper of this series.

FT Raman study of orientation and crystallization processes in poly(ethylene terephthalate)

Abstract FT Raman spectroscopy is used to study a series of commercial samples of poly(ethylene terephthalate) (PET) with controlled thermal history, as a function of the degree of extension. Some observations are made with regard to bands which appear in the spectra of the drawn samples, and seem to be associated with the presence of trans conformers which are introduced into the non-crystalline regions of the material by the drawing process.