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ABSTRACT: Wide-angle X-ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the γ phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small-angle X-ray scattering. The content of the γ phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ≥6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature-controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry
Polymer International 08/2004; 53(12):2001 - 2008. · 1.90 Impact Factor
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ABSTRACT: Ten virgin powder samples of poly(tetrafluoroethylene) (PTFE) were examined by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The samples, prepared by emulsion or nanoemulsion polymerization, differed by average molecular weight and particle size. DSC was used to study the trends of the temperature and enthalpy of solid−solid transitions around room temperature. The samples with smaller particle size and lower molecular weight departed heavily from the behavior reported in the literature. The major role of particle size in determining this behavior was established by experiments of crystallization from the melt. WAXS was employed to study the crystalline phases of PTFE as a function of temperature and to confirm the hypotheses put forward in the DSC analysis. WAXS data showed that the degree of order of the crystallites in the virgin powders is controlled by particle size. Therefore, the confinement of the as-polymerized PTFE crystals in small entities (tens of nanometers) has a similar effect on the crystal correlation length and on the solid-state transitions, while it appears that the molecular weight per se is not able to induce such a behavior in the melt-crystallized polymers.
07/2004;
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ABSTRACT: Fiber evidence found on a suspect vehicle was the only useful trace to reconstruct the dynamics of the transportation of two corpses. Optical microscopy, UV-Vis microspectrophotometry and infrared analysis were employed to compare fibers recovered in the trunk of a car to those of the blankets composing the wrapping in which the victims had been hidden. A "pseudo-1:1" taping permitted to reconstruct the spatial distribution of the traces and to further strengthen the support to one of the hypotheses. The Likelihood Ratio (LR) was calculated, in order to quantify the support given by forensic evidence to the explanations proposed. A generalization of the Likelihood Ratio equation to cases analogous to this has been derived. Fibers were the only traces that helped in the corroboration of the crime scenario, being absent any DNA, fingerprints and ballistic evidence.
Forensic Science International 06/2004; 141(2-3):159-70. · 2.30 Impact Factor
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ABSTRACT: Some theoretical models, including lamellar distortions of the second kind, are described. To test the influence of lamellar distortions on the small-angle X-ray scattering (SAXS) of polymers, some theoretical patterns were calculated with different values of the model parameters. SAXS diffraction profiles were recorded for three commercial copolymer samples of linear low-density polyethylene containing different comonomers and one commercial homopolymer sample of high-density polyethylene; these were successively analyzed by a fit to the calculated profiles corresponding to our theoretical models. Transmission electron microscopy images were obtained of the lamellar morphologies of the four samples. From these, we concluded that the homopolymer sample displayed excellent organization on lamellar stacks, whereas the copolymer samples showed more imperfect lamellar morphologies, so it was useful, in the latter case, to introduce a distorted lamellar structure in calculated SAXS diffraction patterns. By use of wide-angle X-ray scattering, we also determined the overall crystallinities of the samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2400–2407, 2003
Journal of Applied Polymer Science 09/2003; 90(9):2400 - 2407. · 1.29 Impact Factor
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ABSTRACT: A structural investigation is described of poly(L-lactic acid) by best fitting of powder X-ray diffraction patterns. The examined sample shows the already known pseudo-orthorhombic α-form, and it was possible to determine the location of the two 103 polymeric helices in the unit cell and the size distribution of the crystallites. Furthermore, a study is reported of the crystallization kinetics of the above cited polymer by light depolarization measurements in an optical microscope. The crystallization kinetic constants in bulk were evaluated in a temperature range (70–165°C) wider than that previously resulting from measurements of radial growth of spherulites.
Die Makromolekulare Chemie 03/2003; 193(7):1599 - 1606.
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ABSTRACT: By X-ray diffraction on polycrystalline powders and Fourier-transform IR spectroscopy, some adducts MgCl2(C2H5OH)x were studied, having different composition in the range from x = 0 (α-MgCl2) to x = 6. For 2 < x ≤ 6, the structure of such adducts shows prevalently ionic MgCl bonds. For x ≤ 2, covalent bonds are observed among chlorine and magnesium atoms, which give rise to chain compounds through chlorine bridges among the Mg-atoms. The obtained structural data are also discussed in terms of the synthesis of some MgCl2-based supports which are very active in the Ziegler-Natta process of olefin polymerization, after a treatment with titanium halides and a successive addition of a cocatalyst and of other suitable donors.
Die Makromolekulare Chemie 03/2003; 193(7):1653 - 1663.
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ABSTRACT: The pure γ-form of isotactic poly(propylene) can be obtained by melt-crystallization starting from a fraction of a random ethylene-propene copolymer (ethylene content 4 wt.-%) soluble in p-xylene at 28°C. Some structural models previously reported are tested by comparing calculated wide-angle X-ray diffraction patterns with the experimental ones. A method for the quantitative determination of the γ-form crystallinity by X-ray line profiles is proposed. The original copolymer and its fractions are characterized by differential scanning calorimetry and 13C NMR techniques.
Die Makromolekulare Chemie 03/2003; 190(11):2805 - 2813.
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ABSTRACT: Some adducts of MgCl2 and Lewis bases (or donors) B were examined, having a composition MgCl2 · 2B, where B = Ethyl (Et) formate, Et acetate, Et propionate, Et benzoate, Et crotonate, acetone, 2-butanone and EtOH. The crystallographic investigation of these adducts, carried out on polycrystalline powders and some single crystals, shows some remarkable structural analogies for all examined donors. In particular, the X-ray diffraction patterns of the adducts indicate the total absence of the close-packing of chlorine which characterizes α-MgCl2 and the presence of covalent Cl-Mg-Cl chains. The obtained data are correlated with the preparation of active supports for Ziegler-Natta olefin polymerization: after total elimination of B, a disordered structure of MgCl2 is obtained, which is coincident with the reported one for the mechanically activated (by ball-milling) MgCl2 and previously described both in the scientific and in the patent literature.
Die Makromolekulare Chemie 03/2003; 193(1):123 - 131.
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ABSTRACT: Synchrotron radiation measurements were employed in recording wide- and small-angle X-ray diffraction patterns during the crystallization of isotactic poly(propylene) in γ-form. In particular, crystallization phenomena of this form are reported for a fraction of a random propylene-ethylene copolymer (4 wt.-% of ethylene) previously investigated by traditional diffraction methods. On slow cooling from the melt, the main decrease in long period L occurs between 88 and 76°C where the degree of crystallinity is almost constant. This may be explained by a flattening of lamellae.
Die Makromolekulare Chemie 03/2003; 191(8):1967 - 1971.
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Macromolecular Rapid Communications 03/2003; 15(3):225 - 232. · 4.60 Impact Factor
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ABSTRACT: New poly(propylene-ran-1-butene) copolymers were analyzed to study the influence of different processing techniques on their structure and morphology. Wide-angle X-ray diffraction allowed determination of the percentage of the γ form and the crystallinity in the samples and also the influence of the percentage of 1-butene on the cell parameters. Furthermore, it was possible to appraise the contributions of different stacks of lamellae to the small-angle X-ray diffraction patterns.© 2001 Society of Chemical Industry
Polymer International 03/2001; 50(4):442 - 448. · 1.90 Impact Factor
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ABSTRACT: Seven samples of isotactic polypropylene were examined to study the influence on the formation of the γ crystalline phase of possible regiodefects along the chain. Wide-angle X-ray diffraction allowed the determination of the percentage of the γ phase in the samples and 13C-NMR spectroscopy was used to correlate the development of the γ phase with the existence of regioirregular structural units along the chain. Furthermore, it was possible to appraise the contributions given by the different families of lamellae to the small-angle X-ray diffraction patterns. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 375–384, 2001
Journal of Applied Polymer Science 11/2000; 79(2):375 - 384. · 1.29 Impact Factor
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ABSTRACT: Some quenched and annealed samples of tetrafluoroethylene copolymers containing perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and hexafluoropropene were studied by small-angle X-ray scattering and differential scanning calorimetry. Small-angle X-ray scattering experimental spectra were analyzed by a fitting method with the profiles calculated from some theoretical distribution models of the lamellar thickness. The mathematical evaluation of small-angle X-ray scattering patterns has provided crystallinity values which were compared with those obtained by wide-angle X-ray scattering in order to obtain information on the organization of the lamellar stacks. The experimental results allow one to conclude that, during the annealing of the quenched fluorinated copolymers, at increasing temperatures, the melting of the thin lamellae takes place together with the appearance and the growth of nonlamellar crystallites.
12/1997;
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ABSTRACT: Some samples of tetrafluoroethylene copolymers, containing perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and hexafluoropropene, were studied by small-angle X-ray scattering in order to investigate the correlation among the crystalline lamellar thickness and both the comonomer content and the molecular weight. The lamellar thickness was determined from the identity period of the one-dimensional scattering function and from the analysis of the one-dimensional correlation function. The crystallinity and the volume of the crystalline unit cell were determined by wide-angle X-ray scattering. Some considerations are reported on the partial inclusion in the crystall cell of the −CF3 groups and on the expulsion into the amorphous regions of the −O(CF2)2CF3 groups.
03/1996;
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Computer Physics Communications 10/1984; 34:145-151. · 3.27 Impact Factor
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Computer Physics Communications 06/1982; 27:49-55. · 3.27 Impact Factor
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European Polymer Journal 45(8):2155-2163. · 2.74 Impact Factor
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ABSTRACT: A case of failure of an epoxy flooring is presented. The cause of the damage has been found in a wrong formulation of one of the layers, that contained an anomalous quantity of solvents, which produced a plasticization of the resin with a consequent loss in mechanical properties. Differential scanning calorimetry, solid phase micro-extraction–gas chromatography–mass spectrometry and wide angle X-ray diffraction were employed. No significant difference in the degree of reticulation was detected between the defective samples and a reference specimen coming from the manufacturer. After evaporation of the solvents in excess, the resins completely recovered their mechanical properties. The responsibility of the failure was charged to the negligence of the manufacturer in the formulation of the resins.
Engineering Failure Analysis 14(7):1394-1400. · 1.09 Impact Factor
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ABSTRACT: An analysis was carried out of some Ziegler–Natta catalysts precursors by small- and wide-angle X-ray scattering in order to get information on the crystallites dimensions, structural disorder and surface areas. The results were correlated with catalytic activities in polymerization of propylene. It was shown that the structural variations, which mainly influence the catalytic activity, are associated with the rotational disorder of the Cl–Mg–Cl triple layers and that the crystallites dimensions and surface areas play a determinant role in the same activity.Furthermore it was shown that the surface areas of the examined samples, determined by BET, are less meaningful than the data obtained by small-angle X-ray scattering, probably for the presence of intra-particle closed pores and/or microporosity.
European Polymer Journal 36(9):1921-1926. · 2.74 Impact Factor
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ABSTRACT: Nanocomposites based on isotactic polypropylene and montmorillonite were studied, investigating the polymorphism of the polymer, and examining the interaction between polypropylene and silicate. Wide angle X-ray diffraction (WAXD) was used to study the crystallization of the matrix, particularly the influence of additives and processing. Small angle X-ray scattering (SAXS) was employed to assess the lamellar morphology, estimating how silicate dispersion could affect this factor. Interaction between polymer and clay was quantified from WAXD and SAXS profiles; by the position and shape of the clay basal peaks, two different degrees of interaction were identified, characterized by a different affinity between the constituents. Observation of the samples' morphology by transmission electron microscopy (TEM) confirmed the results of X-ray diffraction methods. A fitting procedure was applied to SAXS profiles and the dimensions of the clay stratifications were estimated. These results were successfully compared with those drawn by application of Scherrer equation on (001) WAXD peaks.
Polymer. 46(19):8275-8285.
