摘要:

AbstractThe ultrasonic properties of PVC (S‐27/R63) in the glassy region have been investigated as a function of temperature. The propagation velocities and absorption of the longitudinal and transverse ultrasonic waves have been measured at constant frequency of 2 MHz and at temperatures varying between −5°C and 75°C, using the ultrasonic immersion technique. The variation of the elastic moduli with temperature has been derived from these measurements. The results thus obtained have been compared to those previously published in the literature for different PVC and other polymer samples. ©1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330701

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractVarious aspects of the kinetics of sorption of acetone vapor by cellulose acetate films at 30°C have been studied in detail, the principal aim being to understand more thoroughly the physical nature and causes of non‐Fickian behavior in this and other similar polymer‐micromolecular penetrant systems. Particular attention was given to the changes in sorption (including absorption, desorption, and resorption) kinetics caused by (a) systematic variation of the vapor pressure of acetone in different ways and (b) changes in membrane thickness. It has been shown that both viscous volume swelling relaxation and longitudinal differential swelling stress effects must be invoked, in order to explain fully the observed behavior. Detailed analysis of two‐stage sorption kinetics indicated (1) reasonable agreement between estimates of the diffusion coefficient reported by different authors, as long as a consistent analysis of the first stage is used, although the significance of the values given is open to some doubt, because the said first stage is found not to be free of non‐Fickian features; and (2) reasonable conformity of the second stage to a first‐order volume relaxation process (except a long times), with a relaxation frequency strongly dependent on the width of the concentration interval covered by the sorption experiment (and hence on the applied “osmotic stress”). The close similarity of second‐stage sorption to nonlinear viscoelastic creep behavior, previously found in the cellulose‐water system was confirmed and is taken further here, by demonstrating semiquantitative agreement between the corresponding “elastic swelling” and mechanical bulk moduli. ©19

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330702

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractChitosan powders and fibrids were prepared by shear precipitation of dissolved chitosan in a coagulating solution of sodium hydroxide. Following neutralization by washing and an alcohol dehydration step, the white to off‐white powders were fine and free flowing. The dried fibrids had a highly oriented, ribbon‐like shape that in bulk gave a lofty appearance and soft hand. Chitosan fibrids were readily converted to sheet structures by typical paper‐making procedures. The resulting chitosan papers were either smooth, flexible, and largely translucent when pressed dry from the moist mat, or were soft and opaque white when the moist mat was soaked in alcohol before drying. X‐ray diffraction, SEM, and optical microscopy were used to characterize the different chitosan powders, fibrids, and papers. Chitosan fibrid papers were found to have tensile properties comparable to that of cellulosic papers, though the wet strength and water sorption of chitosan fibrid papers was higher than that of the cellulose controls. ©1995 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330703

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe viscosity behavior of polyelectrolyte solutions induced by borate or phenylboronate complexation with poly(glyceryl methacrylate) (PGM) has been investigated. In dilute solutions borate ions can form monodiol (1/1) complexes and didiol (2/1) intramolecular complexes. Both types of complex are anionic. Thus, the polymer is characterized by the existence of charged sites on the chain and loops formed by intramolecular complexation. On the contrary, phenylboronate can only give monodiol 1/1 complexes. In the presence of passive salt, the charges are screened. By addition of borate ion to a PGM solution, a decrease of the initial polymer viscosity due to loop formation is first observed, then the anionic charges fixed on the chain by complex formation induce an expansion of the polyelectrolyte and the viscosity of the solution increases. The situation is different for the PGM‐phenyl boronate system, where no intramolecular crosslink is present. In this case the viscosity of the solution increases with phenyl boronate concentration. But for a fixed complexing ion concentration it will tend to that of the neutral polymer when NaCl is added. ©1995 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330704

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA peculiar phenomenon is reported whereby a melt‐extruded, low‐crystallinity, unoriented film of poly(chlorotrifluoroethylene) upon unconstrained thermal treatment, self‐extends in the machine direction (MD) while shrinking along the transverse (TD) and normal/thickness (ND) directions. In addition to the expected increase in crystallinity, the annealing process leads to an unexpected development of crystalline orientation along the MD. This phenomenon is an example of “processing‐induced memory effects” since it depends on the processing history of the starting film, e.g., melt‐extrusion leads to the subject behavior whereas compression molding does not. We must mention that the melt‐extruded films of poly(chlorotrifluoroethylene) are isotropic to start with, that is, MD and TD are indistinguishable prior to the annealing process. Furthermore, this phenomenon has not been observed for any other semicrystalline polymer and is believed to be the first citation for poly(chlorotrifluoroethylene) since its commercialization in 1957. Thermomechanical analysis (TMA) is the analytical technique that led to this novel phenomenon which was later substantiated by x‐ray diffraction (XRD). ©1995 Jo

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330705

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractRetardation of dissolution of highly oriented polyethylene fibers exposed to solvent under a constant tensile force has been investigated in comparison to free conditions. Beyond a critical value of the applied force, the time for dissolution increases sharply by several orders of magnitude. This effect is significant only in fibers with high initial orientation. It is attributed to the existence of a network of oriented crystallites. We have utilized this effect for surface modification of highly oriented PE fibers, by exposure to solvent at different temperatures and applied stress. At a relatively low load the action of the solvent displays pronounced effects: roughening of the fiber surface, formation of a nonoriented crystalline phase, enhancement of adhesion to epoxy resin with some loss of strength. ©1995 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330706

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractNylon 6‐clay hybrid (NCH) is a molecular composite of Nylon 6 and uniformly dispersed silicate monolayers of montmorillonite. In this study the preferred orientation of montmorillonite and Nylon‐6 crystallites in a thick (3 mm) injection‐molded bar of NCH has been investigated using x‐ray diffraction and electron micrography (TEM). It is clear that this bar has a triple layer structure consisting of surface, intermediate, and middle layers which have different preferred orientation. In the surface layer both the silicate monolayers and the chain axes of Nylon‐6 crystallites are parallel to the bar surface though the latter are randomly oriented within the plane. In the intermediate layer the silicate monolayers remain parallel to the bar surface but the Nylon‐6 crystallites rotate by 90° so that the chain axes would be perpendicular to the bar surface or the silicate monolayers. In the middle layer the silicate monolayers are randomly oriented around the flow axis of the NCH bar while remaining parallel to it, and the Nylon crystallites are randomly oriented around the flow axis while keeping their chain axes perpendicular to the silicate monolayers. It may be concluded that such preferred orientation of Nylon 6 crystallites is induced by the clay because the crystallites in the pure Nylon 6 bar have no preferred orientation. ©1995 John Wi

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330707

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe resistance to slow crack growth (SCG) was measured in binary blends of high density polyethylene (HDPE) and 5–10% concentrations of model ethylene‐butene random copolymers by measuring the time to failure (tf) under a constant stress intensity. An increase oftfwith the addition of the copolymer if the copolymer could crystallize and the increase was greater the higher branch density. The copolymer with 117 branches/1000C could not crystallize and therefore its blend had atfthat was less than that of the HDPE. The fracture energies of the blends as determined by their resistance to SCG were compared with the energy by rapid fracture,Jc, as previously measured by Rhee and Crist. It is concluded that SCG is more sensitive to variations in the microstructure than is rapid fracture and that the differences in SCG behavior can be qualitatively explained in terms of the differences in microstructure of the blends. ©1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330708

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe morphologies of solvent‐free, microporous, mechanically self‐supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330709

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAttenuated total reflectance FTIR spectroscopy was used to compare the influence of hydrophilic and hydrophobic counterions on the vibrational behavior of the sulfonate and perfluoroether groups in 1100 equivalent weight (EW) Nafion®and 808 EW Dow perfluorosulfonate ionomer membranes. For dry, Na+‐form membranes, the infrared band attributed to the —SO3−symmetric stretching vibration was found to shift to higher frequencies with an increase in the degree of neutralization. In contrast, neutralization with tetrabutlyammonium ions caused the —SO3−vibrational band to shift to lower frequencies with increasing neutralization. This behavior is attributed to a diminished polarization of the —SO3−groups by the hydrophobic and diffusely charged TBA+cations, relative to the strong polarization observed with Na+ions. Vibrational bands attributed to perfluoroether groups in close proximity to the sulfonate groups were also found to be influenced by Coulombic interactions within the clusters. The frequency shifts of these bands followed a trend that was virtually identical to that observed for the —SO3−symmetric stretch. This behavior is attributed to a combination of through‐space, dipolar field effects, and through‐bond inductive effects, from the neighboring ionic groups. In Nafion®, the ether groups directly attached to the backbone are shielded from the Coulombic interactions within the clusters, while the ether groups within three bonds of the terminal ionic groups are very sensitive to the state of polarization of the sulfonate anion. ©1

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330710

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY