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  • 1
    Digitale Medien
    Digitale Medien
    Environmental stress cracking in impact polystyrene (1981)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 624-633 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Environmental stress cracking (ESC) measurements for various impact polystyrenes were performed using a constant load technique with the specimens in contact with a 50/50 solution of cotton seed oil and oleic acid. It was shown that ESC in impact polystyrene is controlled by the transport of the aggressive liquid through a pre-established dry craze structure where capillary pressure is the driving force. At moderate stress levels just above the critical stress for environmental cracking, there is an apparent incubation time for the dry craze formation. The craze incubation time is strongly influenced by thermal stresses induced by the gel particles. As a consequence, ESC is two-stage process involving both an incubation time and actual crack growth. Control of the craze structure to maximize fibril content is essential for good ESC resistance. The craze fibril content can be altered by variables such as gel particle size, matrix molecular weight, plasticizer content, and rubber content.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760211009
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  • 2
    Digitale Medien
    Digitale Medien
    Changes in yield and deformation of polycarbonates caused by physical aging (1984)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 1142-1148 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Change in yield and deformation associated with physical aging was studied on a series of polycarbonates (bisphenol-A polycarbonate, polyestercarbonates, and phenolphthalein-bisphenol-A copolycarbonates) and a polysulfone. A combination of tensile and biaxial yield measurements, dynamical mechanical analysis, and high-resolution density measurements were performed. These data indicate that both free volume arguments and molecular entanglement arguments are inadequate for explaining the differences in large-scale deformation associated with physical aging for the polymers and the superiority of polyestercarbonates over the other resins. The local intramolecular and intermolecular conformation in the glassy state, as predicated by molecular structure, is apparently an important key to understanding physical aging in polycarbonate-type polymers.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760241411
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  • 3
    Digitale Medien
    Digitale Medien
    The effect of processing conditions on the fracture behavior of syndiotactic polystyrene films (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 1483-1490 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A fracture behavior map for syndiotactic polystyrene (sPS) film as a function of annealing temperature and the extension ratio has been developed. The fracture initiation and propagation processes of the film were characterized by a specialized video-based real-time thin-film fracture technique. An unusual layered complex deformation mechanism has been observed for the films fabricated at high extension ratios. This mechanism enhances the resistance to crack growth in sPS films. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Physical aging in thermosets of differing degrees of cure - master curve generation and the relation to mechanical properties (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 1-5 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Physical aging of a thermoset system based on bisphenol-A epoxy (DERTrademark of The Dow Chemical Company. 383) and tetrabromobisphenol-A cured with sulfanilamide and diaminodiphenylsulfone was studied as a function of cure history. Changes in the dynamic mechanical spectra for the thermoset system were correlated to changes in relative toughness associated with physical aging as determined by plane-strain biaxial tension-compression yield measurements. It was found that master curves, generated by using tan δ data obtained in the β relaxation temperature regime, are well related to the corresponding changes in mechanical properties and, hence, have predictive value. Relative toughness decreases and compressive yield increases with decreasing tan 5 because of decreased molecular segmental mobility. The relative extent of physical aging for the as-cast thermosets was shown to be linearly related to the cure time.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760280102
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  • 5
    Digitale Medien
    Digitale Medien
    Coagulation of poly(p-phenylene benzobisoxazole) in polyphosphoric acid using aqueous and nonaqueous solutions (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1621-1626 
    Details
    ISSN: 0887-6266
    Schlagwort(e): poly(p-phenylene benzobisoxazole) ; PBO ; polyphosphoric acid ; diffusion ; fluorescence microscopy ; aqueous coagulants ; nonaqueous coagulants ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Diffusion of aqueous and nonaqueous coagulants into lyotropic/nematic solutions of poly(phenylene benzobisoxazole) in polyphosphoric acid using fluorescence microscopy is reported. The fluorescence microscopy technique offers advantages in that the experiment is independent of the coagulant and the experiments can be performed in a front surface mode so that optically thin samples are not required. The diffusion process is modeled as Case II diffusion as described by Crank and Park. The apparent diffusion coefficients are found to range from ∼ 2 × 10-6 cm2/s to ∼ 2 × 10-7 cm2/s for aqueous and nonaqueous coagulants. The apparent diffusion coefficients can be varied by several orders of magnitude (e.g., down to ∼ 3 × 10-10 cm2/s) by varying the concentration of polyphosphoric acid in the coagulant. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1995.090331106
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  • 6
    Digitale Medien
    Digitale Medien
    SANS from hot-stretched polystyrene revisited (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 1607-1612 
    Details
    ISSN: 0887-6266
    Schlagwort(e): neutron scattering (SANS) from hot stretched polystyrene ; polystyrene, hot stretched, SANS study of ; chain deformation in hot stretched polystyrene, SANS study of ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Small-angle neutron scattering (SANS) has been used to investigate macromolecular orientation of uniaxially hot-stretched partially deuterated polystyrene. Principle radii of gyration and degree of eccentricity were measured over a range of hot-stretch temperatures, strain rates, and external draw ratios (EDR). Results show affine deformation for EDR 〈4 and an increase in the degree of local molecular orientation with increasing rate of strain and decreasing stretching temperature. It also is found that although the macromolecules follow the external stretching affinely on average, they do not deform uniformly.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1991.090291306
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  • 7
    Digitale Medien
    Digitale Medien
    In situ X-ray scattering studies of lyotropic liquid crystalline PBO and PBZT monofilament drawing (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2567-2573 
    Details
    ISSN: 0887-6266
    Schlagwort(e): poly(cis-benzoxazole) ; poly(trans-benzothiazole) ; lyotropic ; liquid crystalline ; monofilament ; x-ray scattering ; compressive strength ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The results of a series of novel synchrontron-based in situ x-ray scattering experiments of monofilament fiber drawing from lyotropic solutions of poly(cis-benzoxazole) (PBO) and poly(trans-benzothiazole) (PBZT) are reported. The purpose of the study is to determine orientation and microstructure development in the draw zone as a function of shear rate in the capillary die, and spin draw ratio (SDR). The transition of the extrudate from opaque to the transparent is complete at about a SDR = 3 and f of 0.9. The filament orientation parameter (f) was found to depend strongly on spin draw ratio, but not shear rate. The orientation was found to increase down the extrudate toward completion of the draw down as one proceeds further from the die face up to an extrudate length of 3.8 cm. Coherence lengths on the order of 19 nm (axial), and 4.5 nm (lateral) have been observed. These “microdomain” sizes are consistent with the “crystallite” sizes typically observed in coagulated fiber. The occurrence of these microdomains in the draw zone as a precursor to the microfibrillar structure is believed to be the origin of low filament compressive strength. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1994.090321602
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