Influence of morphology on the fracture toughness of isotactic polypropylene

An adaptation of the fracture toughness test method, the J-integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size. © 1995 John Wiley & Sons, Inc.     

Chemical modification of butyl rubber. II. Structure and properties of poly(ethylene oxide)-grafted butyl rubber

Poly(ethylene oxide)-grafted butyl rubbers (IIR-g-PEOs), which were synthesized from potassium salt of polyethylene glycol monomethyl ether (PEGM) and chlorinated butyl rubber, were found to behave like thermoplastic elastomers. The poly(ethylene oxide) (PEO) content of these amphiphilic polymers was ca. 10 wt %, and their PEO lengths were 750, 2000, and 5000, respectively. The grafted segments of PEO in butyl rubber (IIR) aggregated to form the PEO domains in IIR matrix. At constant PEO content, the longer the PEO segment length, the larger the size and the crystallinity of PEO domains became. This PEO domain worked as a cross-linking site and a reinforcing filler. The degree of swelling in water of IIR-g-PEO film that was prepared from PEGM-5000 was largest, but its emulsification ability was smallest among them. © 1995 John Wiley & Sons, Inc.     

Effective magnetoelastic properties of laminated composites

Effective physical parameters of a fine-layered medium whose layers exhibit linearized magnetostriction as ferrites are determined. Ferromagnetic materials of cubic system with ferromagnetic resonance are considered __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 8, pp. 36–43, August 2006.     

Mössbauer spectroscopy study of mechanically alloyed Fe2O3–(Al, Co and WC) systems

Mössbauer spectroscopy revealed that a central hyperfine interaction doublet and an additional sextet characterized the appearance of new phases in the mechanically alloyed Fe₂O₃–Al and Fe₂O₃–Co systems. In the Fe₂O₃–Al system, the intensity of the central super paramagnetic doublet which represents small particles of iron, increased with increasing milling time from 5 to 30 h of mechanical alloying. The magnetic sextet characterizing hematite vanished in the room temperature Mössbauer spectra of samples produced after 25 h of mechanically alloying the 50% Fe₂O₃ and 50% Al system. In general XRD peak broadening was observed as a result of extensive material structural distortion and formation of small particles. Fe, Al₂O₃ and mixed iron–aluminium oxide phases were identified in the XRD patterns with a small persistence of the iron oxide up to 20 h of mechanically alloying the 1:1 system Al–Fe₂O₃. In the 50% Co–50% Fe₂O₃ system, a 55% abundant new phase CoFe₂O₄ was observed, from the Mössbauer spectra of the system. The presence of this new phase was confirmed by the XRD analysis. The high energy ball milling of WC–Fe₂O₃ revealed a more effective grinding compared to hematite alone. The hematite particles were reduced to nanosized particles.     

Improved outer inverses for the numerical solution of Euler–Lagrange equations

In this paper, improved outer inverses are used for solving the overdetermined differential‐algebraic equations that arise in the simulation of mechanical systems. The method is based on Newton‐type iterations using outer inverses. Copyright © 2004 John Wiley & Sons, Ltd.     

Representation of the anelastic behaviour of a solid having a gaussian relaxation spectrum

Summary The approximate representation obtained in a previous paper for the frequency dependence of the energy dissipation taking place in a vibrating solid with a Gaussian relaxation spectrum has been extended, for the same spectrum, to the frequency dependence of elastic modulus as well as to the time dependence of after-effect and creep. The procedure followed in order to obtain these representations appears susceptible of application to other types of spectra.

---

Riassunto La rappresentazione approssimata, ottenuta in un precedente lavoro, della dipendenza dalla frequenza della dissipazione di energia che ha luogo in un solido vibrante dotato di uno spettro di rilassamento del tipo di Gauss è stata estesa, per lo stesso tipo di spettro, alla dipendenza dalla frequenza del modulo elastico, nonché alla dipendenza dal tempo del ≪creep≫ e dell’≪after-effect≫. Il procedimento seguito per ottenere queste rappresentazioni approssimate è suscettibile di applicazione ad altri tipi di spettri.

---

Резюме Приближенное представление, полученное в предыдущей статье для частотной зависимости диссипации энергии, имеющей место для колеблущегося твердого тела с гауссовым релаксационным спектром, обобщается для того же типа спектра на частотную зависимость модуля упругости, а также на временную зависимость последействия и ползучести. Процедура получения зтих представлений оказывается ппименимой для друтих типов спектров.

     

On the accuracy of wavefunctions obtained by the Fourier grid Hamiltonian method

The quality of wavefunctions obtained by the Fourier grid Hamiltonian (FGH) method is analyzed. The criteria used for judging the quality are the extent to which virial, hypervirial and Hellmann-Feynman theorems are satisfied by the numerically computed FGH-wavefunction. The quality of the FGH-wavefunction is also examined from the point of view of local error in the wavefunction. It is shown that high quality wavefunctions can be obtained from the FGH recipe if the grid length (L) and grid spacings are chosen after properly examining the range of the potential and its nature.     

A study of the crystallinity index of polypropylene fibres

Crystallinity measurements were carried out with the help of X-ray diffraction, differential scanning calorimetry (DSC) and density measurements. The results of this study provide a better understanding of the morphology and complex thermal behaviour of polypropylene fibres. Crystallinity studies show that the crystallinity of PP fibres when measured by X-ray and DSC methods as a function of draw-ratios increases with increasing draw-ratios while the crystallinity of the same samples as derived by density measurements shows an inverse trend. These discrepancies are accounted for by the formation of microvoids within the polypropylene fibres due to drawing. In the DSC scan two endothermic peaks were found to occur in some of the samples. This is explained by the presence of two morphological forms i. e. lamellar and fibrillar morphology in the same sample. The crystallinity values obtained from different methods are correlated with mechanical properties, such as tenacity and elongations.Dedicated to Prof. Dr. H. Janeschitz-Kriegl, a pioneer of Polymer Physics in Austria, in honour of his sixtieth birthday.     

Poly(caprolactone triol) as plasticizer agent for cellulose acetate films: influence of the preparation procedure and plasticizer content on the physico‐chemical properties

The influence of the plasticizer content and film preparation procedure on the morphology, density, thermal and mechanical properties of cellulose acetate (CA) films plasticized with poly‐(caprolactone triol) (PCL‐T), were studied. Differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), scanning electron microscopy (SEM), wide‐angle X‐ray diffraction (WAXD) and infrared spectroscopy (FT‐IR) techniques were used. The films were prepared by dry‐casting CA and CA/PCL‐T in acetone or acetone/water solutions, which produced transparent and opaque films, respectively. In contrast to the transparent films, which were dense, the opaque films presented a porous morphology. However, the presence of PCL‐T reduced the opaque film porosity, increasing, in consequence, its bulk density. The TMA results revealed that PCL‐T reduced the glass transition temperature more significantly in the transparent than in opaque films. Only the transparent CA/PCL‐T films presented a melting temperature, that reduced with higher concentrations of PCL‐T, suggesting a higher ordering (crystallinity) when the films were prepared in the absence of water, as observed from WAXD curves. The mechanical properties also showed that the transparent films were more soft and tough than the opaque films. In summary, PCL‐T was a good plasticizer agent for CA films due to the presence of hydrogen bonds between the components (FT‐IR spectra). The presence of water in the dry casting process has a significant effect mainly on film morphology and mechanical properties. Copyright © 2004 John Wiley & Sons, Ltd.     

Electrostatic interactions in peptides. Polarisation effects due to an α-helix

A quantum mechanical/molecular mechanical study of a dodecapeptide made of 11 alanine and one asparagine residues in a helical conformation is carried out by means of the local self-consistent field/molecular mechanical and integrated molecular orbital and molecular mechanics computational schemes. The electronic properties of the asparagine side chain are analysed to extract the influence of electrostatic and induction interaction. One finds that induction may play an important role in the energetic and structural features of the systems modelled with mixed methods. The importance of performing quantum computations which explicitly take account of the electrostatic interactions is pointed out.Contribution to the Jacopo Tomasi Honorary Issue