Journal of Macromolecular Science, Part B 

About: Journal of Macromolecular Science, Part B is an academic journal published by Taylor & Francis. The journal publishes majorly in the area(s): Crystallization & Differential scanning calorimetry. It has an ISSN identifier of 0022-2348. Over the lifetime, 3736 publications have been published receiving 52488 citations. The journal is also known as: Journal of macromolecular science. & Physics.

β-MODIFICATION OF ISOTACTIC POLYPROPYLENE: PREPARATION, STRUCTURE, PROCESSING, PROPERTIES, AND APPLICATION

Abstract: The methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the β-modification of isotactic polypropylene (β-iPP) are reviewed. The introduction of selective β-nucleants is the most reliable method for preparation of samples rich in β-modification or of pure β-iPP. The advantages and drawbacks of the known β-nucleating agents are summarized. It is emphasized that pure β-iPP can be prepared under laboratory and processing conditions in the presence of highly active and selective β-nucleants. Nevertheless, there are no literature data—apart from that of the author's groups—which evidenced unambiguously the formation of pure β-iPP. It hints at the insufficient selectivity of β-nucleants used or at the inappropriate crystallization or melting conditions applied by other scientists. The structure formation during the high-temperature hedritic crystallization is discussed comprehensively and illustrated by polarized light microscopy and scanning ele...

Oriented crystallization of polymers

Abstract: Molten crystallizable polymer is extruded through an orifice. Opposite the orifice on the upstream side is a fixed surface arranged so as to provide in the molten polymer a line of uniaxial extension or a plane of pure shear passing through the orifice. The polymer is extruded at a temperature and flow rate such as to cause a core of crystalline polymer to form in the melt along said line or plane. It is particularly suitable for extruding a continuous filament having a highly crystalline core in a generally less crystalline matrix of the polymer.

α to β Phase Transformation and Microestructural Changes of PVDF Films Induced by Uniaxial Stretch

Abstract: The phase transformation from α to β poly(vinylidene fluoride) (PVDF) through a stretching process at different temperatures was investigated. Samples of originally α-PVDF were stretched uniaxially at different temperatures at draw ratios from 1 to 5. The stretched samples were studied and characterized by infrared spectroscopy, scanning electron microscopy, and differential scanning calorimetry. The maximum β-phase content was achieved at 80°C and a stretch ratio of 5, but the samples still showed 20% of the original α-phase. Accompanying the phase transformation, an orientation of the polymer chains was observed. The stretching process also influenced the degree of crystallinity of the polymer. Poling of the samples also improves the α- to β-phase transformation.

Swelling kinetics of polymers

Abstract: The equilibrium swelling of semicrystalline or crosslinked polymers and of their gels upon immersion in liquids has been investigated extensively. On the other hand, few studies have dealt with the kinetics of swelling. Swelling kinetics are important for designing controlled-release devices for drugs and agricultural pesticides based on swellable polymer matrices, and for predicting the release rates of the active ingredients. Theoretical considerations, based on diffusion-controlled swelling, show that first-order kinetics does not apply, even though deviations during the initial and even middle stages of the swelling process may be relatively small. Extensive studies of swelling rate and equilibrium swelling of supported and unsupported gelatin films have been published. The rate is controlled by stress relaxation in the swelling polymer network. The rate equations of these studies, which have also been reported to apply to cellulose, are shown to represent second-order kinetics with respect t...

FTIR AND DSC STUDIES OF MECHANICALLY DEFORMED β-PVDF FILMS

Abstract: Films of semicrystalline poly(vinylidene fluoride) (PVDF) in the β-phase were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The main goal of this study was to improve the understanding of the structural changes that occur in β-PVDF during a mechanical deformation process. FTIR spectroscopy was used to examine the structural variations as a function of strain. DSC data allowed measurement of the melting temperatures and enthalpies of the material before and after deformation, providing information about the changes in the crystalline fraction. After the molecular vibrations were assigned to the corresponding vibrational modes, we investigated the energy and intensity variations of these vibrations at different deformations. A reorientation of the chains from perpendicular to parallel to the stress direction was observed to occur in the plastic region. During the deformation, a decrease in the degree of crystallinity of the material was observed, but ...