Showing papers on "Polystyrene published in 1978"

Contact electrification of polymers: A quantitative model

Abstract: An explicit model of contact‐charge exchange in polymers is proposed in which the steady‐state exchanged charge resides in intrinsic molecular‐ion states. The eigenvalue spectra of these states are inferred from metal/polymer contact‐charge measurements using a theoretical formalism constructed for this purpose. This model of metal/polymer contact‐charge exchange is extended to encompass the description of polymer/polymer contact‐charge exchange as well. Utilizing the metal/polymer contact‐charge‐exchange spectra as input data, the model predicts correctly both the sign and order of magnitude of measured contact‐charge exchange between polystyrene and copolymers of styrene and methyl methacrylate.

Studies of Ordered Monodisperse Polystyrene Latexes. I. Shear Ultrasonic Measurements

Abstract: The rigidity G and the viscosity ? of monodisperse polystyrene latexes were measured by the torsional quartz crystal method at 70 kHz, and an abrupt change in G and ? was found at the order-disorder transition of the latexes. The torsional quartz crystal method was improved for measurements with aqueous conductive samples, and a careful calibration showed that G and ? are obtained if the dielectric constant of the sample is known. In the ordered state of latex with a volume concentration of 9.3%, the apparent rigidity G and the viscosity ? were about 1.5?103 dyne/cm2 and 0.6 cp, respectively, while in the disordered state G was small and ? was 0.95 cp. Ordered latex is a ?crystal? formed by the screened Coulomb repulsion and is a good model not only for crystals but also for ordered structures in some biological systems.

Mechanical α-dispersion and interaction in filled polystyrene and polymethylmethacrylate

Abstract: Dynamic mechanical properties of polystyrene (PS) and polymethylmethacrylate (PMMA) filled with glass beads and mica flakes have been investigated. The α-dispersion temperature (Tα) increases with filler content in each system. The increase in Tα is larger for PMMA than for PS in the case of the same filler; the increase in Tα is larger for mica than for glass in the case of the same polymer. Polymer-filler interaction energies have been estimated from heats of adsorption of the monomers of the filler surfaces determined by solid gas adsorption chromatography. The increase in Tα can be related to the extent of polymer-filler interaction energy. The thickness of the partially immobilized layer on the filler surface has been estimated to be the orders of 0.1 and 1.0 μm, respectively, for the mica and the glass-filled systems.

Influence of glass fibers on the extrusion and injection molding characteristics of polyethylene and polystyrene melts

Abstract: A basic study is reported of extrusion and injection molding for melts of polyethylene and polystyrene filled with glass fibers. It is shown that glass fibers cause large increases in end pressure losses and decreases in extrudate swell. Flow visualization of injection molding studies indicates that polymer melts containing high loadings of glass fibers exhibit jetting in end gated molds. This is attributed to the reduction in extrudate swell. To avoid jetting, special care is required in design of gating.

Transport Phenomena in Polymer Blends

Abstract: Publisher Summary This chapter describes the phenomena of low molecular weight penetrant transport, in and through polymer blends, in terms of the miscibility of the blend system. Polymer blending is an effective means for constructively altering transport properties of polymeric materials. The chapter discusses the general principles of mass transport in polymeric materials. It provides an overview of the membranes prepared from polymer blends. Although membranes are usually supported, they must exhibit sufficient mechanical stability to permit normal handling during installation, use, and maintenance, and selective membranes, in addition, must be resistant to biological attack. The chapter discusses poly (vinyl pyrrolidone) that has been blended with polyurethane to form a blend membrane suitable for dialysis. Reverse osmosis membranes prepared by blending a hydrophilic-hydrophobic block or graft copolymer with a homo-polymer composed of the corresponding hydrophilic moieties in the block or graft copolymer. Under specific conditions of temperature and hexane activity, blends of polystyrene and poly (phenylene oxide) exhibit solubility and sorption rates that are significantly lower than those measured for the parent homopolymers, and the tendency of either of these homopolymers to undergo deleterious morphological changes consequent to solvent contact is reduced significantly by blending.

Adsorption studies of polystyrene on silica I. Polydisperse adsorbate

Abstract: In the course of adsorption measurements, the molecular weight distributions of the polymer in the supernatant solution and in the adsorbed layer have been established by means of gel permeation chromatography analysis for the polystyrene/cyclohexane or carbon tetrachloride/amorphous silica systems at 35°C. Significant changes occur in the surface layer during the approach towards equilibrium as well as in the plateau region, displaying a strong preferential adsorption of the longer chains.

Styrene use and occupational exposure in the plastics industry.

Abstract: The commercial production of styrene was started in the 1930s. Currently 7 million tons of styrene a year is made worldwide by the catalytic dehydrogenation of ethylbenzene or by a process in which styrene is produced as a coproduct with propylene oxide. An estimated 62% of the styrene monomer is consumed in the manufacture of polystyrene, 12% in acrylonitrile-butadiene-styrene resins, 17% in styrene-butadiene rubber and latex, 7% in unsaturated polyester resins, and 2% in other applications. Occupational exposure to styrene occurs in monomer production and polymerization plants, during the fabrication of plastic products from monomeric or partly prepolymerized styrene, and during the transportation and handling of liquid styrene. Due to unreacted residual monomer or thermal degradation of the polymer, low concentrations of styrene can be detected during the use of plastic products. The most extensive and intensive exposure occurs in the reinforced plastics industry, in which over 200,000 workers are exposed to a styrene concentration typically ranging from 20 to 300 ppm.

Influence of melt deformation history on orientation in vitrified polymers

Abstract: An experimental study of the development of orientation in polystyrene melts during flow and its retention in vitrified parts is described. It is shown on the basis of elongational and shear flow experiments that orientation in vitrified polystyrenes may be predicted from a knowledge of the stress field at the time of vitrification and application of stress-optical laws. More generally a relationship between birefringence and principal stress difference is found which correlates (1) on-line isothermal shear flow, (2) on-line non-isothermal elongational flow (melt spinning), and (3) vitrified samples formed in both shear and elongational flow. It is further proposed that orientation in polymer chains in deforming melts is uniquely dependent on stress—specifically, that the ratio of the stress-optical constant C to the intrinsic birefringence Δ° is approximately a constant.

Effects of Pressure, Temperature, Adsorbent Surface, and Mobile Phase Composition on the Supercritical Fluid Chromatographic Fractionation of Monodisperse Polystyrenes

Abstract: No significant differences have been found in the separation behavior of oligomers of monodisperse polystyrene samples when using n-pentane as the mobile phase and a phenyl or an n-octadecyl bonded stationary phase. For low-molecular weight polystyrenes used in this study, there was no evidence of steric exclusion effects when using non-derivatized silica. In all cases, the addition of either isopropanol or cyclohexane as a moderator was found to produce more nearly complete elution of the polystyrene oligomers from the stationary phases. Concentrations of isopropanol above 5% v/v caused no further change while increasingly higher percentages of cyclohexane caused capacity ratios of higher molecular weight species to decrease. Finally, non-linear pressure programming was found to produce more nearly regular elution of an oligomeric series while linear downward temperature programming was found to produce irregular elution behavior near the critical temperature. 14 figures, 2 tables.

Investigation of the size distribution of non-ionic micelles formed from a polystyrene–polyisoprene block copolymer in N,N-dimethylacetamide

Abstract: Solutions of a polystyrene–polyisoprene block copolymer in N,N-dimethylacetamide were studied by gel permeation chromatography. The effect of temperature on the equilibrium between free copolymer chains and micelles was studied qualitatively from 26 to 110°C. Micelles studied in detail at T= 26°C were monodisperse in size, as judged by the reverse flow method. This result was supported by electron microscopy of micelles isolated from solution. Comparison with light scattering results showed that the universal calibration method of calibration was not applicable to the micelles.The application of gel permeation chromatography in a relatively bad solvent to the analysis of a mixture of a block copolymer with a component homopolymer was demonstrated.

Mutagenicity study of workers employed in the styrene and polystyrene processing and manufacturing industry.

Abstract: Mutagenicity studies were undertaken on lymphocytes from the following groups of persons exposed to styrene or polystyrene: one group from a styrene manufacturing plant, one from a polystyrene plant, and three from plants processing unsaturated polyester resins with different manufacturing methods. For all the groups the concentration of styrene in the atmosphere of the workplace was measured at various points and the amount of urinary mandelic acid was determined. In each case 100 metaphases were analyzed for chromosomal aberrations. The results were compared with reference groups.

Microbial degradation of [14C]polystyrene and 1,3-diphenylbutane

Abstract: Microbial degradation of [β-14C]polystyrene and 1,3-diphenylbutane, a compound structurally representing the smallest repeating unit of styrene (dimer), was investigated in soil and liquid enrichme...

Time-resolved fluorescence spectroscopy of polystyrene and poly(1-vinylnaphthalene)

Abstract: An apparatus is described which enables the rapid recording of time-resolved emission spectra on a nanosecond time scale. The instrument permits detailed study of the time-dependent photo-physical processes occurring in many polymer systems. The technique has been used to investigate the kinetics of excimer formation in methylene chloride solutions of polystyrene and poly(1-vinyl-naphthalene). Unambiguous evidence for excimer dissociation is observed in poly(1-vinylnaphthalene) but the process appears unimportant in solutions of polystyrene.

Thermoplastic elastomer compositions

Abstract: Thermoplastic elastomer compositions of the present invention comprise a blend of from about 10 to about 48 parts by weight of a crystalline 1-olefin polymer, from about 90 to about 10 parts by weight of a styrene-butadiene rubber, and a triblock copolymer or a diblock copolymer in the amount of from about 0.1 to about 80 parts by weight or a polystyrene in the amount of from 0.1 to about 50 parts by weight. The thermoplastic elastomer blends have good physical properties, especially tensile strength, elongation at break, and tear strength. Moreover, the compositions can be repeatedly processed and yet maintain their good physical properties. The compositions, which may be partially cured, have excellent aging properties as well as paint adhesion.