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Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

Thermoplastic matrix towpreg production

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010
J. F. Silva
Abstract This work was carried out to establish the processing window for the cost-efficient production of thermoplastic matrix towpregs with a recently developed powder-coating equipment. Three different fiber-reinforced thermoplastic matrix systems were studied: one for highly demanding markets (carbon fiber/PrimospireÔ) and other two for commercial applications (glass/polypropylene and glass/polyvinyl chloride). The mechanical properties determined on compression-molded composite components obtained from the produced towpregs were also evaluated. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:80,85, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20174 [source]

Preparation, characterization, and properties of fluorene-containing benzoxazine and its corresponding cross-linked polymer

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2010
Ying-Ling Liu
Abstract A benzoxazine compound (FDP-FBz), which possesses a fluorene group and two terminal furan groups, and its corresponding cross-linked polymer (CR-FDP-FBz) have been prepared using 4,4,-(9-fluorenylidene)diphenol (FDP), furfurylamine, and formaldehyde as precursors. The chemical structure of FDP-FBz has been characterized with Fourier-transform infrared and 1H nuclear magnetic resonance spectroscopies. FDP-FBz displays a melting point at about 173 °C and a processing window of 52 °C as well as good solubility in common organic solvents. As a result, FDP-FBz can be fabricated in both molten and solution processes. Under an excitation at 365 nm, FDP-FBz exhibits a photoluminescent (PL) emission at about 445 nm. The PL intensity of FDP-FBz is as high as sixfolds of the intensity recorded with FDP. CR-FDP-FBz displays a glass transition temperature of 215 °C, a high storage modulus of 3.1 GPa, a 10% weight loss at 384 °C, and a high char yield of 56 wt % (900 °C, in nitrogen). Moreover, CR-FDP-FBz has a high refractive index of about 1.65 as a result of incorporating fluorene groups to its structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4020,4026, 2010 [source]

Base-Metal-Electroded BaTiO3 Capacitor Materials with Duplex Microstructures

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004
I-Nan Lin
The effect of dopants and processing conditions on the dielectric properties of base-metal-electroded materials was investigated. BaTiO3 materials simultaneously doped with MgO and Y2O3 additives can achieve small capacitance variation (,C/C), which meets the X7R specification, when the proportion of additives is abundant enough and the materials are not over-fired. Presumably, small ,C/C values of thus obtained materials are the result of the formation of core,shell structure, which requires stringent control of material processing conditions. In contrast, X7R-type materials can be obtained in a much wider processing window, when prepared by mixing two BaTiO3 materials of suitable dielectric constant,temperature (K,T) characteristics. Duplexed materials prepared from these two end-point BaTiO3 materials with ratios ranging from 3:1 to 1:2 exhibit K,T behavior within the X7R specification, provided that one of the components possesses flat K,T behavior. Moreover, the dielectric properties of these materials were simulated using a simplified microstructural model. Simulation results indicate that the effective dielectric constant of core,shell materials, (Ke)CS, varies significantly not only with the dielectric properties of cores and shells, but also with the shell-to-core thickness ratio, whereas the effective dielectric constant of duplexed materials, (Ke)D, can be maintained at a very small ,C/C value for a wide range of end-point constituent ratios, which agrees very well with the measured K,T properties for the materials. [source]

Gettering in silicon photovoltaics: current state and future perspectives

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2006
M. Seibt
Abstract This paper summarizes current understanding and predictive simulations of gettering processes predominantly applied in silicon photovoltaics. Special emphasis is put on various processes limiting gettering efficiency and kinetics, i.e. the mobility of interstitially dissolved metal species, the formation of the gettering layer, and the effect of immobile metal species. The latter are substitutional metal species, precipitates, complexes with defects related to non-metallic impurities, and finally the interaction with extended defects, in particular dislocations. Finally, alternative annealing schemes involving high-temperature rapid thermal processing are explored by simulations. It is shown that a processing window exists for a two-step process efficient for the removal of precipitates even under the constraints of a fixed thermal budget for phosphorus diffusion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Time-cure-temperature superposition for the prediction of instantaneous viscoelastic properties during cure

POLYMER ENGINEERING & SCIENCE, Issue 6 2000
Yongsung Eom
The relative sequence of shrinkage and evolution of modulus of a thermoset resin during cure leads to the build-up of internal stresses, especially if the resin is constrained by the presence of other materials in the form of a substrate or reinforcing fibers. To enable prediction of the levels of internal stress generated during processing and to determine appropriate processing windows, the evolution of the modulus of an epoxy-amine system during cure has been characterized and described with a phenomenological model. A combined reaction kinetics model is used to determine the degree of conversion of the epoxy over any complete range of cure. The chemorheological properties of the resin are measured as a function of curing temperature with a torsional parallel plate rheometer. A new phenomenological approach for time-cure-temperature superposition is proposed for predicting the relaxation modulus at any moment during cure and at any cure temperature. The combination of these two models provides a full description of the instantaneous viscoelastic properties during cure. This approach, which can be adapted to any curing resin, provides suitable tools for the analysis of viscoelastic stress build-up following any industrially relevant cure cycle. [source]