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  • 1
    Electronic Resource
    Electronic Resource
    The effect of a magnetic tape coating process on the structure and properties of a semi-crystalline polymer (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 683-690 
    Details
    ISSN: 1435-1536
    Keywords: Semi-Crystalline Polymers ; orientation ; crystallinity ; magnetic coating ; processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A combination of structure identifying and bulk property experiments were combined with a two-phase analytical methodology to elucidate the influence of a magnetic tape coating process on the substrate polymer film. Employing a typical tape manufacturing process that utilizes coating, drying, and calendering stages, polyethylenete-rephthalate polymer film samples with and without the magnetic coating were prepared. Experiments and modeling studies performed on these samples demonstrate that the drying and calendering processes may increase the crystallinity and noncrystalline orientation of the substrate film. In addition, dynamic mechanical experiments identified a viscoelastic transition at 50 °C for the PET substrate film sample which is near the glass transition of the magnetic coating utilized. Overall, the results of this investigation provide a basis for evaluating structure property interrelations of polymer-based magnetic tapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01469529
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  • 2
    Electronic Resource
    Electronic Resource
    Activation energy determinations from dielectric thermal analysis of reacting polymeric systems (1991)
    Springer
    Journal of thermal analysis and calorimetry 37 (1991), S. 2407-2421 
    Details
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurden Verfahren zur Berechnung der Aktivierungsenergien aus dielektrischen Messungen der isothermen bzw. nichtisothermen Aushärtung von Duroplasten entwickelt. Dabei wurde angenommen, daß die dielektrische Antwort bei einem einzelnen Wert der Reaktionswerte erfolgt. Die Aktivierungsenergie-Ergebnisse wurden für zwei Duroplast-Harze ermittelt: ein Epoxysystem — Tetraglycidyl-4,4′-diamonidiphenylmethan, gehärtet mit 25% 4,4′-Diaminodiphenylsulfonhärter; und ein Dicyanatmischharz aus 55 Gew.% Bisphenol A Dicyanat und aus 45 Gew.% Tetra-o-methylbisphenol F Dicyanat. Die Ergebnisse stehen in guter Übereinstimmung mit den aus DSC-Messungen erhaltenen Werten.
    Notes: Abstract Methods were developed for calculating reaction activation energies from dielectric property measurements during isothermal and nonisothermal cure of thermosetting polymers. These methods were derived by assuming that features of the dielectric response occurred at unique extent of reaction values. Activation energy results were obtained through dielectric analysis for two thermosetting resin systems: a model epoxy system — tetraglycidyl-4, 4′-diaminodiphenylmethane cured with 25 parts per hundred of 4,4′-diaminiphenylsulfone hardener; and a model dicyanate blend resin, 55% (by weight) of bisphenol A dicyanate and 45% of tetrao-methyl bisphenol F dicyanate. Results were in excellent agreement with activation energies determined from differential scanning calorimetry measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01913743
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  • 3
    Electronic Resource
    Electronic Resource
    Thermal and mechanical characterization of high performance epoxy systems with extended cure times (1996)
    Springer
    Journal of thermal analysis and calorimetry 46 (1996), S. 1511-1525 
    Details
    ISSN: 1572-8943
    Keywords: characterization ; epoxy ; extended cure time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Five epoxy resins of different chemistry and functionality were cured with DDS (4,4′-diaminodiphenyl sulfone) using 2, 8 and 14 h curecycles. Both Differential Scanning Calorimetry (DSC) and Thermomechanical Analysis (TMA) were used to characterize reaction behavior and cured properties of the resin systems. In addition, static mechanical tests and density measurements were integrated with the thermal characterization methods to correlate resin properties with process time. Flexural three-point bending experiments showed that the resins tended to have higher yield stress and toughness values at extended cure times. The improved mechanical properties could be attributed to the full development of the epoxy molecular structure, in the form of cross-linked networks and molecular rearrangement. These results suggest that extended cure times or high temperature post-curing may be required to obtain the resin's ultimate mechanical properties for high performance composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01980758
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  • 4
    Electronic Resource
    Electronic Resource
    A viscoelastic description of the glass transition-conversion relationship for reactive polymers (1991)
    Springer
    Journal of thermal analysis and calorimetry 37 (1991), S. 463-478 
    Details
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Der GlasumwandlungspunktT g ist eine empfindliche und praktische Grö\e zum Verfolgen der AushÄrtung reaktiver Duroplaste. Basierend auf dem viskoelastischen Steifigkeitsmodell von Dillman-Seferis wurde eine neue Gleichung zur Vorhersage der Beziehung zwischenT g und Konversion entwickelt. Dabei wird angenommen, da\ die Änderung vonT g in erster Linie durch eine Änderung der Relaxationszeit bedingt ist, da KettenverlÄngerung und Vernetzung die Beweglichkeit des Polymergefüges herabsetzen. Bei einer Kombination von kinetischen und viskoelastischen Messungen, mit denen die Umwandlungen wÄhrend des AushÄrtens von Duroplasten verfolgt werden können, ist diese Erkenntnis von gro\er Bedeutung. Die auf der Basis des viskoelastischen Modelles erhaltene Gleichung ist für eine gro\e Breite von experimentellen Daten anwendbar. Den Erfolg dieser Methodik zeigt weiterhin ein Vergleich bewÄhrter Beziehungen, wie z.B. der Foxschen Gleichung und der Gleichung von DiBenedetto, mit Aussagen, die durch Anpassung zweier viskoelastischer Parameter ermöglicht wurden. Die StÄrke der vorgeschlagenen Gleichung wird letztlich durch Anpassen von Epoxy-Daten aus der Literatur sowie von experimentellen Daten eines relativ neuen und in dieser Untersuchung als Modell benutzten Harzsystemes gezeigt.
    Notes: Abstract The glass transition temperature,T g is a sensitive and practical parameter for following cure of reactive thermosetting systems. A new equation was developed for predicting theT g -conversion relationship based on the Dillman-Seferis viscoelastic compliance model. It assumes that the changes inT g are primarily due to changes in relaxation time as chain extension and crosslinking reduce the mobility of a polymer network. Such information is essential in combining kinetic and viscoelastic measurements, which monitor transformations of thermosets during cure. The equation derived from the viscoelastic model was shown to be applicable for a variety of experimental data. The success of the methodology was further demonstrated by comparing well-established relations, such as the Fox equation and the Di-Benedetto equation, to predictions made possible by adjusting two viscoelastic model parameters. Finally, the fitting power of the proposed equation was shown by fitting published epoxy data from the literature as well as experimental data on a relatively new resin system such as dicyanates used as a model in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01913098
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature-Modulated Differential Scanning Calorimetry through Heat Diffusion Analysis (1998)
    Springer
    Journal of thermal analysis and calorimetry 54 (1998), S. 501-519 
    Details
    ISSN: 1572-8943
    Keywords: complex heat capacity ; heat transfer ; phase lag ; TMDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the present study, a complete model of thermal diffusion in a TMDSC specimen is presented. The governing equation takes into account thermal conductivity and does not neglect temperature gradients. This model is solved analytically for a specimen of cylindrical geometry with two surfaces following the block temperature and considering the third surface insulated. The full analytical solution consists of a transient and an asymptotic expression. The asymptotic expression is divided into an underlying and a cyclic part to allow comparison with existing models. The present model finds that the phase angle between the temperatures of sample and block are dependent upon the sample material, which has not been predicted by existing models. Moreover, the present model does not require the use of an experimentally determined constant as long as the cell is ideal. It was found that the phase lag between sample and block temperatures could be described by two effective thermal diffusivities, Λ′ and Λ″, instead of complex heat capacities $$c'_p {\text{ and }}c''_{\text{p}} $$ and $$c'_p {\text{ and }}c''_{\text{p}} $$ . These heat capacity parameters were viewed as mathematical artifacts arising from the use of an over-simplified governing equation that does not take into account thermal conductivity and thermal gradients within the specimen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010134307537
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  • 6
    Electronic Resource
    Electronic Resource
    Processing-structure relationships for multiphase epoxy matrix systems (1991)
    Springer
    Journal of materials science 26 (1991), S. 1691-1698 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A styrene-modified diglycidyl ether of bisphenol-A (DGEBA) epoxy system cured with trimellitic anhydride (TMA) has been investigated to explore processing and structure relationships. During cure, the reactive styrene precipitated with polymerization into phase domains separate from the epoxy phase. Dynamic mechanical analysis and microscopy studies were performed to gain insight to matrix structure. The DMA studies showed that the styrenemodified epoxy system after cure exhibited two partially overlapped but distinct relaxation peaks, which are associated with the T gs of the polystyrene and epoxy phases. The glass transition of the polystyrene phase was shown to be broadened and the T g to depend strongly on processing temperature profiles. While the T g of the epoxy phase increases with curing agent concentrations, the T g of the polystyrene phase does not. Microscopic studies showed that the styrene-modified system exhibited a rougher fracture surface but did not reveal well defined phase domains in which the precipitated polystyrene component was aggregated. Overall, the study has demonstrated correlations of the kinetic factors in controlling the morphology in reactive modifier-epoxy systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00544684
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of heterogeneous matrix composites using scanning acoustic microscopy (1993)
    Springer
    Journal of materials science 28 (1993), S. 329-336 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Acoustic microscopy was used to examine the morphology of multi-phase matrices and composites. The acoustic microscopy imaging could easily resolve the rubber domains dispersed within a thermosetting or thermoplastic continuous phase. However, because the thermoplastic and thermosetting phase domains had comparable elastic moduli, the resolution between them was not always clear. Rayleigh wave distortion of imaging remained as one of the serious limitations that needed to be overcome in order for this technique to be widely utilized in heterogeneous/anisotropic media. In its present form, the acoustic imaging technique can be used to augment other existing analytical tools in order to generate more detailed morphological information that is useful in understanding structure-property relationships for multi-phase toughened matrices used in advanced composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357803
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of Polymer Specimen Structure on The Reproducibility of Micro-thermomechanical Transitions (2000)
    Springer
    Journal of thermal analysis and calorimetry 62 (2000), S. 599-608 
    Details
    ISSN: 1572-8943
    Keywords: microscale heat transfer ; micro-thermal analysis ; thermosetting polymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glass transitions of amorphous polystyrenes with low polydispersity were evaluated using the modulated Local Thermal Analysis mode of the TA Instruments 2990 µ TA and evaluating the thermomechanical signal. Transition temperature variance and fraction of transitions measured were compared for high molecular mass thermosetting materials and the melt of Nylon 6.6. The transition reproducibility was found to decrease as the molecular size of the polymer samples increased. Reproducibility also decreased for thermosetting materials when the experimental ramp rate was decreased. Heat transfer within the specimen was evaluated using finite element analysis, allowing scaling of microscale experimental results for comparison to bulk transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012085020210
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of epoxy-bismaleimide network matrices (1987)
    Springer
    Journal of materials science 22 (1987), S. 3665-3671 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This study investigated intercrosslinked networks formed by co-curing two thermosets: a tetrafunctional epoxy/amine and a bismaleimide formulation. The mechanical properties and phase behaviour of the intercrosslinked networks were compared with the corresponding neat epoxy and bismaleimide systems. In addition, the reaction scheme of the epoxy-bismaleimide resin mixtures was investigated using differential scanning calorimetry. A homogeneous structure for the networks was suggested by the results of both dynamic mechanical analysis and scanning electron microscopy. In contrast to most epoxy systems modified with rubbers or thermoplastics, phase separation was not observed in these intercrosslinked epoxy-bismaleimide networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01161475
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Gas permeation and viscoelastic deformation of prepregs in composite manufacturing processes (1995)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 16 (1995), S. 370-377 
    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: Gas permeation and creep deformation of a commercial prepreg, which exhibits viscoelastic characteristics, were investigated as a function of time, temperature, and consolidation pressure. Experiments using a prepreg stack demonstrated that the material exhibited a linear viscoelastic bulk deformation under vacuum/autoclave pressure and furthermore, the in-plane gas flow exhibited non-Darcian flow behavior with a permeation hysteresis. This behavior was viewed and analyzed by two viscoelastic relaxation processes: (1) bulk dimensional relaxation, and (2) microscopic pore structure rearrangement. A modified standard linear solid (SLS) viscoelastic model was used to interpret the creep compliance and dynamic gas permeability utilizing two independent relaxation parameters. By visual investigation of pore sizes and their distribution, air permeation was found to take place mostly through the interlaminar porosity network for the prepreg system examined.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750160505
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