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Films of highly syndiotactic polypropylene (sPP) were quenched at different temperatures between 0°C and 100°C and analyzed as soon as prepared and after 1 month of aging at room temperature. Wide-angle X-ray diffractograms (WAXDs) showed that all the samples crystallized in the disordered helical form I, with the crystallinity increasing both on increasing the quenching temperature and on aging, although to a lower extent. The analysis of sorption and diffusion of dichloromethane vapor at low activity shows that, in some samples, the fraction of impermeable phase is consistently higher than the crystalline fraction. This induced us to hypothesize the presence of an intermediate phase, or mesophase, not crystalline, yet impermeable to the vapors. The fraction of mesophase decreases on increasing the quenching temperature, and it is a very small quantity at 100°C. The dynamic-mechanical analysis showed two transitions in the aged samples, which could correspond to the lower and upper glass transitions, already suggested for aged films of isotactic polypropylene (IPP). [ABSTRACT FROM AUTHOR]

In this paper, the effect of the inclusion of ethylene/vinyl alcohol (EvOH) copolymer in nylon 6 is analyzed with particular attention to the transport properties. Water vapor and dichloromethane transport measurements were performed to provide useful information about polymer-polymer interaction and segmental mobility. Sorption and diffusion tests were carried out at 25°C at several activities to determine both sorption isotherm and diffusivities. Moreover, permeability tests to gases (CO2, O2) were carried out at 30°C. The obtained results indicate the existence of strong hydrogen-bonded interactions of the two polar groups (amidic of nylon 6 and hydroxyl of EvOH) within the amorphous phase. This interaction strongly influences the transport properties of the nylon 6 amorphous component. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model is presented in order to analyze the electrical characteristics of polymer composites filled by carbon nanotubes (CNTs) subject to tensile stress and investigate the possible usage of such materials as innovative sensors for small values of strain. The simulated mechano-electrical response of the nanocomposite is obtained through a multi-step approach which, through different modeling stages, provides a simple and effective tool for material analysis and design. In particular, at first, the morphological structures of the composites are numerically simulated by adopting a previously presented model based on a Monte Carlo procedure in which uniform distributions of the CNTs, approximated as of solid cylinders and ensuring some physical constraints, are dispersed inside a cubic volume representing the polymer matrix. Second, a geometrical analysis allows to obtain the percolation paths detected in the simulated structures. Suitable electrical networks composed by resistors and capacitors associated to the complex charge transport and polarization mechanisms occurring in the percolation paths are then identified. Finally, the variations of these circuit parameters, which are differently affected by the mechanical stresses applied to the composites, are considered to analyze the electromechanical characteristics of the composites and hence their performances as stress sensors. The proposed approach is used to investigate the impact on the electro-mechanical response of some physical properties of the base materials, such as the type of carbon nanotube, the height of energy barrier of polymer resin, as well as characteristics of the composite, i.e., the volume fraction of the filler. The tunneling effect between neighboring nanotubes is found to play a dominant role in determining the composite sensitivity to mechanical stresses. The simulation results are also compared with the experimental data obtained by performing stress tests on samples of a multi walled CNT filled composite based on poly (e-caprolactone), a polymer which is of interest for its biocompatibility. Model simulations and measured data show generally satisfactory agreement, confirming the effectiveness of the proposed approach to account for the impact of the interactions between CNTs and the insulating resin on the electromechanical response of the composite. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT–COOH) were prepared and characterized. Dynamic-mechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT–COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes. [Copyright &y& Elsevier]

Abstract: The antifibrinolytic drug trans-4-(aminomethyl)cyclohexanecarboxylate (tranexamic anions) was intercalated by anion exchange into Mg/Al layered double hydroxide (LDH). The hybrid, of formula [Zn0.65Al0.35(OH)2]Trx0.24(CO3)0.055 ×1.5H2O, was characterized by chemical and thermal analyses and X-ray powder diffraction. Different amounts of the hybrid material were incorporated into poly(ε-caprolactone) by high energy ball milling technique and processed as films. The composite materials were analyzed by X-ray diffractometry, thermogravimetry and FT-IR spectroscopy to clarify the filler-polymer structural organization. An investigation of the mechanical properties of the composite showed an improvement of mechanical parameters, in particular the elastic modulus, when compared to of the pristine polymer. Thus, the inorganic component, even in small quantities, beside acting as a reservoir of active molecular anions, can improve the physical properties. A new method for the quantitative determination of tranexamic anions by infrared spectroscopic analysis was proposed and the release process of the tranexamic anions from the composite into a physiological solution was monitored. The release consisted of two stages: a first stage, very rapid as a burst, in which a small fraction of intercalated drug was released and of a second stage over longer time, much slower than the first. The composites are very promising in the preparation of new hybrid polymeric materials to be used for the molecular delivery of drugs in topical applications, as suture threads or medicate scaffolds. [Copyright &y& Elsevier]

Abstract: New polymeric composite materials containing a nanohybrid to be used for the controlled release of an antibiotic molecule, chloramphenicol succinate, have been formulated, prepared and characterised. The nanohybrid consists of a layered double hydroxide of Mg–Al hydrotalcite-type, in which the nitrate anions present in the host galleries were replaced with chloramphenicol succinate anions (CFS−) by a simple ion-exchange reaction. Different amounts of the hybrid material were incorporated in polycaprolactone and processed as films of 0.15mm thickness. The composite materials were analysed by X-ray diffractometry and thermogravimetry and their mechanical properties were determined. They showed properties even better than those of the pristine polymer. The release process of the antibiotic molecules was found to be very interesting and promising for tuneable drug delivery. It consists of two stages: an initial stage of a very rapid burst, in which a small fraction of drug is released; and a second stage that is much slower, extending for a longer and longer time. This behaviour is profoundly different and much slower than that of a sample in which the antibiotic molecule is directly incorporated into the polymeric matrix. The parameters influencing drug release have been individuated and discussed. [Copyright &y& Elsevier]