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  • 1
    Electronic Resource
    Electronic Resource
    Self-reinforced thermoplastic-LCP prepregs and laminates (1994)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 15 (1994), S. 254-260 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Self-reinforced sheets (prepregs) have been prepared by stretching extruded sheets made of thermoplastic (TP) and a thermotropic liquid crystalline polymer (LCP) blend. The sheets are formed by extrusion through a coathanger die, device. Processing at this stage is done at a temperature at which both components in the blend are melt processable. These prepregs are laid up in multi-layers in a direction parallel to the stretching direction or in the direction of 45° with respect to each previous layer. The lay-ups are compression molded into unidirectional or isotropic laminates at temperatures below the melt processing temperature of the LCP. Various pairs of TP and LCP have been studied. These include polypropylene and an LCP based on p-oxybenzoyl, terephthaloyl and hydroquinone moieties, polyphenylene oxide (PPO) and polystyrene/PPO alloy and a LCP based on 6-oxy-2-naphthoyl and p-oxybenzoyl moieties. Mechanical properties of the prepregs and laminates were measured and compared with those obtained from injection molded samples. Surprisingly, tensile strength and modulus of isotropic laminates are found to be higher than those of injection molded samples in the flow direction. Morphlogical studies of the prepregs and laminates indicate the presence of well-defined LCP fibers in various thermoplastic matrices.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750150403
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  • 2
    Electronic Resource
    Electronic Resource
    Self-Reinforced melt processible polymer composites: Extrusion, compression, and injection molding (1987)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 8 (1987), S. 158-175 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Rheological properties, extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied. Blends were prepared using an internal Banbury mixer and static Koch mixer. Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentrations. During extrusion and injection molding at high strain rates, it has been observed that thermotropic liquid crystal polymer at concentrations 2.5, 5, and 10 percent by weight in situ forms high modulus and high strength fibers within the polycarbonate matrix leading to self-reinforced polymer composites. The tensile strength of the composite containing 10 percent of liquid crystal polymer exceeds that of the pure components. In addition, anisotropy of properties of the injection molded parts has been found to substantially reduce in a comparison with that of liquid crystal polymer. The processing conditions and technique for the production of self-reinforced polymer composite during processing of the blends have been identified. This has been done by measurements of mechanical properties, direct observation of morphology, and by theoretical calculation using simplified composite theory for the unidirectional continuous fiber-reinforced composites. At the high concentrations, 25 and 50 percent by weight, thermotropic liquid crystal polymer forms large spherical droplets inside polycarbonate leading to highly brittle material. This is in distinction from the fibrous, high modulus tough composites formed at the lower concentrations.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750080305
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of ultrasonic waves on foam extrusion (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1051-1056 
    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 effect of ultrasonic waves upon foam extrusion has been investigated by using a special die attached to an extruder. The die consists of a special ultrasonic horn, having a circular channel, that vibrates at 20 KHz. Various ultrasonic amplitudes and flow rates were employed during extrusion of a foamed polystyrene. Ultrasonic waves were found to affect both die pressure as well as physical and mechanical properties of the foam. Increases in the amplitude of the ultrasonic waves resulted in a decrease of the pressure at the die entrance. The density of the foam was found to increase with an increase of the amplitude and a decrease of the flow rate. Extrudate swell was found to decrease with an increase in the amplitude. Ultrasonic waves also influenced cell size and distribution in extruded samples: increases in amplitude resulted in reduced cell size and in narrowing their distribution. These effects are likely caused by break up of large cells or by disruption of coalescence of small cells. The tensile strength and Young's modulus of samples of extruded foam were found to increase with ultrasonic treatment. A unique correlation of these mechanical properties with the density of the foam was established.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311409
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  • 4
    Electronic Resource
    Electronic Resource
    Blends of a liquid crystalline polymer with polyether ether ketone (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 85-93 
    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: Blends of Polyether ether ketone (PEEK) and a thermotropic liquid crystalline Polymer (LCP) based on paraoxy-benzoyl and oxy-biphenylene terepthaloyl units were prepared using a static mixer attached to a single screw extruder at 420°C. Rheological studies indicated an increase in the viscosity of the blends upon the addition of LCP. Thermal studies on these blends demonstrated their poor thermal stability compared to the parent materials. The mechanical properties indicated improvement in Young's tensile and flexural modulus but no improvement in the break strength with the addition of the LCP. Morphological studies indicated the formation of ellipsoids of LCP at low LCP concentration in the matrix of PEEK, with extended ellipsoids being observable at 25 percent LCP composition. Phase inversion was noticeable at higher LCP content blends with the formation of PEEK fibrils in the matrix of the LCP. Dynamic studies on these blends showed an increase in the storage modulus with the addition of LCP.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760320203
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  • 5
    Electronic Resource
    Electronic Resource
    Filling thin cavities of variable gap thickness: A numerical and experimental investigation (1983)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 23 (1983), S. 20-26 
    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 theoretical and experimental investigation is presented for filling thin cavities of variable gap thickness. The modeling is based upon a finite-element/finite-difference formulation for an inelastic power-law fluid and includes the effects of viscous heating and conduction upon the flow dynamics. Extensive results are presented for polypropylene and polystyrene melts injected into two variable-gap-thickness cavities, of which one has an insert. Good agreement is found between the predictions and measurements concerning the shape of the advancing melt front, the location of weld lines, and the temporal pressure trace at various positions in the cavity.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760230106
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  • 6
    Electronic Resource
    Electronic Resource
    Flow of polymeric melts in short tubes (1985)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 264-270 
    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: In an attempt to further understand the flow of polymeric melts through gates in injection molding, the present investigation deals with measurement of pressure drops during isothermal extrusion of fiber-filled and unfilled polystyrene, polypropylene, and polycarbonate melts in short tubes with sudden contraction at high shear rates typical of injection molding. Flow curves for these materials have been determined over a wide range of shear rates at various temperatures by using a capillary rheometer and extruder. Measurements indicate that rheological properties of fiber-filled melts after injection molding differ from those of fresh samples. Moreover, it has been found that decreasing the tube length increases the slope of the curve for pressure drop vs. Volumetric flow rate. Extra pressure losses due to end effects have been determined which show that at high shear rates these losses can reach levels as high as 100 bar, with the effect being higher for the fiber-filled melts. By using a viscoelastic consitutive equation, the extra pressure losses have been separated into entrance and exit losses. Model parameters required for this calculation have been determined from viscosity-shear rate curves for the melts. For various polymers, master curves useful for industrial applications have been constructed for the extra pressure losses.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760250503
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  • 7
    Electronic Resource
    Electronic Resource
    Self-Reinforced composites of two thermotropic liquid crystalline polymers (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 32-42 
    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: Blends of two thermotropic liquid crystalline polymers (LCP) based on 6-oxy-2-naphthoyl and p-oxybenzoyl moieties and p-oxybenzoyl, terephthaloyl and hydroquinone moieties have been studied. The blends were prepared by melt mixing using a twin screw extruder. Thermal, rheological, mechanical, and morphological studies were carried out. Based on the dynamic mechanical thermal analysis and the morphological observations, the blends are found to be immiscible. The viscosity ratios of pure LCP melts exceed values of 10 over a wide range of shear rates, with the viscosity of the blends lying between those of the pure components. The prepared blends are shown to be self-reinforced composites in which one LCP enhances the molecular orientation of the other. Studies of the injection molded bars by scanning electron microscopy indicate a complicated hierarchical morphology with microfibrils of submicron level in diameter, bundled, and intertwined into fibrils of a substantially larger diameter. Due to self reinforcement, impact and tensile properties of the blends show significant synergism when compared to those of the pure LCP components. The properties obtained are remarkably higher than those known for any high performance engineering thermoplastics.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330105
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  • 8
    Electronic Resource
    Electronic Resource
    Flow of thermoplastics in an annular die under parallel oscillations (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1574-1584 
    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 sound wave extrusion system has been developed. This system includes a single screw extruder and an annular die having an internal surface oscillating in the sound frequency range. Oscillating shear flow has been imposed in the direction parallel to the main pressure flow. The die characteristics and average melt temperature at the exit from the die for several thermoplastics have been measured with and without imposition of oscillations. Modeling of parallel superposition of sound oscillations upon pressure flow has been performed using the Leonov viscoelastic constitutive equation. Three cases are considered: (i) the process is isothermal and the change in die pressure is only due to a nonlinear interaction of oscillatory and pressure flow; (ii) the process is nonisothermal and adiabatic, and pressure reduction is due to the nonlinear interaction and the dissipation of oscillatory energy leading to the temperature rise in polymer melts; (iii) the process is nonisothermal with heat transfer due to transient heat conduction and the dissipation of oscillatory energy. Pressure reduction occurs due to both nonlinear interaction and temperature rise. It is found that case (i) cannot explain the observed die pressure reduction, while case (ii) describes those data only at high flow rates. The theoretical results from case (iii) are found to be in qualitative agreement with experimental observations. Generally, the theoretical results of case (iii) are better than those of cases (i) and (ii).
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760302404
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  • 9
    Electronic Resource
    Electronic Resource
    Rheology, morphology, and mechanical characteristics of poly(etherether ketone)-liquid crystal polymer blends (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 971-980 
    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: This paper is in continuation of our previous paper on Poly(etherether ketone)-liquid crystal polymer (PEEK-LCP) composites. Rheological, morphological, and mechanical properties of polyetherether ketone and a thermotropic liquid crystalline polymer based on hydroxybenzoic acid/hydroxynaphthoic acid have been reported. Addition of LCP resulted in a marked reduction of viscosity and improved processability. Tensile properties improved with increase in LCP concentration. Synergistic effects have been observed at certain LCP concentrations. The elongation at break was found to reduce drastically above 10% of LCP content. This is a characteristic typical of chopped-fiber-filled composites. Morphology of injection molded and capillary extruded samples of the blends showed that the in-situ formed fibrous LCP phase was preserved in a solidified form. The improvement in tensile properties is likely due to the reinforcement of the PEEK matrix by the fibrous LCP phase as observed by scanning electron microscopy. A distinct skin-core morphology was found to develop in the injection molded samples of these blends. Mechanical properties measured in the flow and transverse direction indicated an increase in the degree of anisotropy with an increase in LCP content.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311307
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamic properties of crosslinked epoxy resin at large cyclic and static deformation (1981)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 566-570 
    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: Measurement of dynamic properties of crosslinked epoxy resin have been performed under torsional cyclic deformation with different amplitudes and frequencies and with extensional creep under different loads. It is found in both cases that the dynamic modulus decreases above a certain critical value of deformation. Truncation of the glassy state region and shifting of the transition zone to lower temperatures and higher frequencies have been observed as effects of large amplitude deformation. The maximum reduction in the modulus value and the minimum in the critical amplitude both occur in the region of Tg Shear fatigue of the material has been observed in the glassy state with a frequency- and temperature-dependent fatigue life. It is found that the loss modulus under extensional creep depends upon the values of the deformation and stress whereas the storage modulus depends solely upon the deformation. The ratio of energy expended during static and cyclic deformations is shown to depend only upon the extensional deformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760210909
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