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  • Chemical Engineering  (8)
  • Polymer and Materials Science  (8)
  • 1
    Electronic Resource
    Electronic Resource
    A simple model of nonisothermal coextrusion (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 408-415 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A numerical method has been developed that takes the streamline finite difference method for modeling fully developed multilayer polymer flows and adds to it a simple means of accounting for nonisothermal conditions. In industrial practice, temperature control is often used to match material viscosities and, thereby, to avoid flow instabilities. By numerically calculating both viscosity ratios and normal stress difference ratios, the numerical method allows one to judge the relative stability of different flows and to choose an intelligent set of experiments when designing a coextrusion process. The algorithm has been successfully tested for a number of polymer melt constitutive equations in flows where the viscosity jumps no more than two orders of magnitude between fluids. Results for a rheologically well characterized polystyrene low-density polyethylene system and for an industrially interesting high-density polyethylene/Ultem system show that the common practice of matching zero-shear viscosities is overly simplistic when interface shear rate, conduction, normal stress, and flow rate effects are taken into account.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760300705
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  • 2
    Electronic Resource
    Electronic Resource
    Flow-induced structure and rheology of a triblock copolymer (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 1585-1600 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Linear viscoelastic properties are found to be a sensitive measure of flow-induced structural changes in a block copolymer. Styrene-butadiene-styrene block copolymer (SBS) with 26% polystyrene (PS) forms a macrostructure in the quiescent state with grains of the order of 1-10 μm. Within each grain, phase separation gives rise to a regular two-phase microstructure with cylindrical PS domains with radius of the order of 200 Å. Large-amplitude oscillatory shear (γ = 4.5) at temperatures between 139 and 181°C was applied to after the grain structure with the objectives of removing the discontinuities at the grain boundaries and of aligning the domains into a continuous ultrastructure. The SBS behaved like a solid (tan δ 〈 1 at low ω) before and like a liquid (tan δ 〉 1) after shear modification. This change expressed itself in the removal of the long relaxation times from the linear viscoelastic spectrum; the intermediate and low relaxation times were not affected by the shear modification. The viscoelastic spectrum slowly recovered during annealing with recovery times of the order of the longest relaxation time of the quiescent structure. Birefringence studies showed that the SBS did not recover into its original grain structure but into a highly oriented domain structure. The discontinuities at the grain boundaries could not be removed completely.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070330514
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  • 3
    Electronic Resource
    Electronic Resource
    Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl)(1-η5-indenyl)dimethyltitanium: A two-state propagationSee Reference 1. (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2601-2617 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalysts ; ansa-metallocene catalyst ; thermoplastic elastomeric poly(propylene) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic-anti-[ethylidene(1-η5-tetramethylcyclopentadienyl) (1-η5-indenyl)dimethyltitanium (6) has been synthesized and its molecular structure determined by x-ray diffraction methods. The two Ti=Me(1) and Ti=Me(2) units have bond distances differing by 0.08 Å and their proton NMR resonances are separated by over 1 ppm. Using this compound and methylaluminoxane (MAO) as the activator, at 25°C the 6/MAO catalyst produced polypropylene having crystalline domain with physical crosslinks. The polymers obtained at lower polymerization temperatures are rheologically liquids. The behaviors of this catalyst system resembles closely the previously reported rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl) (1-η5-indenyl)dichlorotitanium (4)/MAO system. The structure of 6 determined here furnishes tangible support for the proposed two-state (isomeric)-switching propagation mechanism. Addition of MAO to 6 causes broadening of the Me(1) resonance in the 1H-NMR spectra, and 6 is decomposed by Ph3C+B(C6F5)-4. © 1992 John Wiley & Sons, Inc.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301215
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  • 4
    Electronic Resource
    Electronic Resource
    Rheology of phase separated blends of two thermotropic liquid crystalline copolyestersPresented at “Liquid Crystal Polymer Symposium,” Amherst, Mass., July 1990. (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 773-776 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The melt rheology of phase separated blends of two thermotropic liquid crystalline polymers (LCPs) have been studied. The two components are a random copolyesters consisting of 73 mol% 4-hydrobenzoic acid (HBA) and 27 mol% 6-hydroxy-2-napthoic acid (Vectra A900 of Hoechst Celanese Corp.) and a poly(ethylene terephalate-co-4-oxybenzoate) containing 60 mol% HBA units (PET/60HBA of Eastman Kodak Corp.). Most striking is the effect of adding 10% PET/60HBA to Vectra A900: The viscosity at 290°C drops by a factor of 4 and the terminal zone of the relaxation time spectrum is shifted to much shorter times. This is an interesting effect that could be used for LCP processing even if its origin is not yet understood. Differential scanning calorimetry measurements support the hypothesis that the blend is phase separated and that no transestification reaction occurs during the experiments.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321203
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  • 5
    Electronic Resource
    Electronic Resource
    Fully developed multilayer polymer flows in slits and annuli (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 444-452 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A numerical method has been developed for simulating fully developed multilayer shear flows of non-Newtonian fluids with arbitrary viscosity functions. Poiseuille and combined Poiseuille/Couette flows in both slits arid annuli may be modeled. The method employs a finite difference system where grid points lie on streamlines and move to their correct positions as the solution procedure converges. Interfaces are easily handled as particular stream lines with the equation of motion replaced by a boundary condition. The method is stable for high interface viscosity ratios and readily handles a large number of layers. Many authors have employed power law models to model multi-layer non-Newtonian flows. We find that the power law is sufficient to predict pressure gradients and interface positions in most cases, but gives unrealistically flat velocity profiles, even when truncated at finite viscosity. Results are presented for the Carreau fluid and for the rubber-like liquid with shear thinning via Wagner's strain functional.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760280707
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  • 6
    Electronic Resource
    Electronic Resource
    The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)Parts of this work were presented at the AICHE Annual Meeting, Washington, DC, November, 1988 (1989)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1434-1445 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Shear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow-induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow-induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow-induced phase separation.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760292005
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  • 7
    Electronic Resource
    Electronic Resource
    Optical anisotropy of a thermotropic liquid-crystalline polymer in transient shear (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 1571-1588 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A rheo-optical apparatus, based on a linear shear rheometer, has been constructed to study the deformation of liquid-crystalline polymers. This apparatus uses optical techniques such as flow birefringence, small-angle light scattering, and optical microscopic image analysis. The rheological responses were simultaneously measured under varying temperatures and deformation conditions. The modified Debye-Bueche equation for scattering, in the nonspherically symmetrical form, was adapted to analyze small-angle light-scattering data. The orientation correlation lengths, determined by this method, reveal the deformation mechanism in nematic melts. Flow birefringence results are in agreement with the proposed mechanism.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280912
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  • 8
    Electronic Resource
    Electronic Resource
    Isotactic polypropylene foams crystallized from compressed propane solutions (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 617-627 
    Details
    ISSN: 0887-6266
    Keywords: isotactic polypropylene foams ; supercritical propane solutions ; high surface areas ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crystallization of isotactic polypropylene (iPP) from homogeneous solution in supercritical propane yields open-cell foams of high surface area (120-150 m2/g). Their morphology usually consists of microspheres with a dense core and a porous periphery of radiating fibrils. Pore radii covering the mesopore range (2-50 nm), making their largest contribution at 10-20 nm, were calculated from nitrogen adsorption isotherms. Surface areas of the correct order of magnitude are obtained by assuming that gas adsorption takes place on the surfaces of lamellar crystals. Crystallization of iPP from n-butane and n-heptane generates foams of lower mesoporosity and smaller surface area. These more “liquid-like” solvents do not allow the formation of an open network of mesopores or they promote its collapse upon their removal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 617-627, 1998
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Recycling of sheet-molding compounds by chemical routes (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 57 (1995), S. 1409-1417 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This article describes a number of chemical routes for the recycling of sheet-molding compounds (SMC) consisting of glass fibers, filler (calcium carbonate), and an unsaturated polyester-styrene thermoset resin. Treatment of milled SMC with ethanol/potassium hydroxide at 85°C for 48 h ultimately affords a soluble polymeric fraction, consisting of styrene-fumaric acid copolymers. The excess of potassium hydroxide as well as the filler are removed via a neutralization step, which results in a large stream of waste chemicals. Treatment of SMC chips with ethanolamine at 180°C for 48 h gives a reaction mass that can be split into three fractions, viz., the glass fibers, the filler, and a methanol-soluble polymeric residue. The excess of ethanolamine is recovered by distillation at 220°C and reduced pressure. The polymeric fraction consists of terpolymers of styrene, N,N′-di(2-hydroxyethyl)fumaramide and N-2-hydroxyethylmaleimide monomer units, the latter two bearing two and one hydroxyl groups, respectively. The terpolymer shows little solubility in unsaturated polyester, epoxy, or isocyanate resins. The glass fibers and the filler coated with the polymeric fraction can be used as constituents of bulk-molding compounds (BMC). Replacing half of the original amount of glass fibers or filler of a standard BMC formulation by recycled materials does not significantly alter the mechanical properties. Increasing the amount of recyclate results in processing difficulties in the case of the glass fibers or a serious decline of the mechanical properties in the case of the filler/polymer. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070571116
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  • 10
    Electronic Resource
    Electronic Resource
    Design of dies for the extrusion of sheets and annular parisons: The distribution problem (1986)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 26 (1986), S. 543-553 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A systematic design of the classical “coat hanger” die is proposed and tested experimentally. The objectives of the design are 1. distribution of the polymer over the width of the die before it reaches the final lip section for thickness adjustment, 2. invariance of distribution to flow rate, 3. invariance to changes in polymer viscosity, and 4. uniform average residence time. The die design is based on a flow model which assumes power-law viscosity, steady shear flow In each cross-section, uniform temperature, and separation of the flows into a manifold component and a component in a slit section of uniform height. The design corrects for an oversimplification of the pressure gradient that was applied in previous studies; and it differs from previous designs by suggesting a rectangular cross-section for the manifold. Applications to side-fed dies for extrusion blow molding and to a sheet extrusion die achieved uniform distribution and did not require any additional flow corrections (such as choker bars or flexible lips). With the new design, the lip region of the die can freely be used for thickness control, fine tuning, or further shaping of the extrudate.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760260805
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