Influence of the samarium impurity on the structure and surface morphology of Se<Subscript>95</Subscript>Te<Subscript>5</Subscript> chalcogenide glassy semiconductor

X-ray diffraction and atomic-force microscopy are used to study the structure and surface morphology of Se₉₅Te₅ chalcogenide glassy semiconductor films and the influence exerted on these films by doping with samarium. The parameters of the first sharp diffraction peak (FSDP), observed in X-ray diffraction patterns, are used to determine the numerical values of the local structure parameters, such as the “quasiperiod” of density fluctuations, correlation length [size of medium-range-order (MRO) regions], and nanovoid diameters. In addition, the numerical values of the roughness-amplitude parameters are determined. It is found that the disorder in the atomic structure and the irregularities on the surface of the films under study become more pronounced with increasing percentage content of the samarium impurity.     

Injection molding of semicrystalline polymers. II. Modeling and experiments

The injection molding of an isotactic polypropylene was computer-simulated with both quiescent and shear-induced crystallization taken into account. A one-dimensional finite difference model was used to simulate the filling, packing, and cooling stages of the injection-molding cycle. The Spencer-Gilmore equation was used to relate the density variations to the pressure and temperature traces in the packing simulation. The quiescent crystallization kinetics was modeled by the differential form of the Nakamura equation. The theory developed by Janeschitz-Kriegl and co-workers was used to model the shear-induced crystallization kinetics. The pressure traces during the filling and packing stages of the molding cycle, the thickness of the shear-induced crystallization layer, and the crystallinity profile throughout the thickness of the part were measured and compared with predicted values. © 1995 John Wiley & Sons, Inc.     

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of various polyesters

A novel approach to predict anisotropic shrinkage of slow crystallizing polymers in injection moldings was proposed, using the flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. In the present study, three different polyesters, polyethylene terephthalate, polybutylene terephthalate, and polyethylene‐2,6‐naphthalate (PEN), are used. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from the amorphous contribution based on the frozen‐in and intrinsic amorphous birefringence and crystalline contribution based on the crystalline orientation function determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with the temperature‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs were carried out by varying the packing time, packing pressure, flow rate, melt and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data and found in a fair agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3526–3544, 2006     

Recycling of tire‐curing bladder by ultrasonic devulcanization

The recycling of butyl rubber‐based tire‐curing bladder was carried out by means of a grooved barrel ultrasonic extruder. Die pressure and ultrasonic power consumption were measured as a function of flow rate and ultrasonic amplitude. Gel fraction and crosslink density of the ultrasonically devulcanized rubber were substantially reduced. In turn, this led to some reduction in gel fraction and crosslink density in the revulcanized rubber. These findings were correlated with dynamic properties and the cure behavior of the devulcanized rubber. The mechanical properties of the revulcanized rubber, dependent on processing conditions during devulcanization, were compared with that of the virgin vulcanizate. Good mechanical properties of revulcanized rubber was achieved with 86 and 71% retention of the tensile strength and the elongation at break respectively, and with modulus increased by 44%. The devulcanized rubber was found to contain tiny gel particles of a wide size distribution with a predominant size of <4 μm. POLYM. ENG. SCI., 46:8–18, 2006. © 2005 Society of Plastics Engineers     

Ultrasonic decrosslinking of crosslinked high‐density polyethylene: Effect of screw design

The effect of screw design on decrosslinking of the crosslinked high‐density polyethylene (XHDPE) by means of ultrasonic twin‐screw extruder with two screw configurations is investigated. Die pressure and ultrasonic power consumption during extrusion are recorded. Swelling characteristics, rheological properties, thermal analysis, scanning electron microscopy, and tensile properties are used to investigate the structure–property relationship of decrosslinked XHDPE. It is found that the screw configuration with conveying elements and reverse conveying elements (decrosslinking screws) is an effective means to reduce the gel fraction and crosslink density of decrosslinked XHDPE and significantly improve its processibility. Rheological properties of decrosslinked XHDPE are correlated with structural changes occurring during ultrasonic decrosslinking. The presence of the highly branched sol in decrosslinked XHDPE is revealed through measurements of the activation energy for flow. Comparison of morphologies of the lamellar structure of HDPE, XHDPE, and decrosslinked XHDPE reveals that the presence of the crosslink network inhibits the lamella growth. Significant improvements in the mechanical performance of decrosslinked XHDPE are obtained by using decrosslinking screws. The molecular structure and morphology of the lamellar structure of decrosslinked XHDPE are used to explain the processing–solid‐state property relationship. The measured results on the gel fraction and crosslink density are compared with those of numerical simulations. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40680.