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Crystalline Content (crystalline + content)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Experimental Study of the Aging and Self-Healing of the Glass/Ceramic Sealant Used in SOFCs

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010
Wenning N. Liu
High operating temperatures of solid oxide fuel cells (SOFCs) require that the sealant must function at a high temperature between 600°C and 900°C and in the oxidizing and reducing environments of fuel and air. This paper describes tests to investigate the temporal evolution of the volume fraction of ceramic phases, the evolution of micro-damage, and the self-healing behavior of the glass,ceramic sealant used in SOFCs. It was found that after the initial sintering process, further crystallization of the glass,ceramic sealant does not stop, but slows down and reduces the residual glass content while boosting the ceramic crystalline content. Under a long-term operating environment, distinct fibrous and needle-like crystals in the amorphous phase disappeared, and smeared/diffused phase boundaries between the glass phase and ceramic phase were observed. Meanwhile, the micro-damage was induced by the cooling down process from the operating temperature to room temperature, which can potentially degrade the mechanical properties of the glass/ceramic sealant. The glass/ceramic sealant exhibited self-healing upon reheating to the SOFC operating temperature, which can restore the mechanical performance of the glass/ceramic sealant. [source]

Improving mechanical performance of injection molded PLA by controlling crystallinity

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008
Angela M. Harris
Abstract Currently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis-stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half-times were found to decrease nearly 65-fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effect of morphology on barrier properties of poly(ethylene terephthalate),

POLYMER ENGINEERING & SCIENCE, Issue 3 2005
A.A. Natu
The effects of morphology on the barrier properties of poly(ethylene terephthalate) (PET) have been investigated. Various levels of crystallinity can be developed in PET as a result of thermal exposure, orientation, and heat setting. The morphologies of the crystalline phase are affected by the conditions of their formation. As a result of morphological differences, samples with equivalent levels of crystallinity have been found to exhibit different oxygen barrier properties. These differences are most apparent at low and intermediate levels of crystallinity. For thermally crystallized systems, at the same crystalline content, increasing superstructure size in the crystalline phase leads to greater tortuosity for the permeant molecules, resulting in lower permeability. For stretched and heat set PET, transport properties can be correlated with birefringence as well as overall orientation, measured in terms of fraction of molecules in the trans or extended chain conformation. At high levels of crystallinity, where the spherulites become volume filling, permeation takes place primarily through the interlamellar regions of the crystalline phase and is controlled by level of crystallinity, independent of the mode of crystallization. The barrier properties of PET, before spherulitic impingement occurs, are governed by the size and number of spherulites as well as by the amorphous orientation present in non-crystalline regions. POLYM. ENG. SCI., 45:400,409, 2005. © 2005 Society of Plastics Engineers [source]

A lithium ionomer of poly(ethylene-co-methacrylic acid) copolymer as compatibilizer for blends of poly(ethylene terephthalate) and high density polyethylene

POLYMER ENGINEERING & SCIENCE, Issue 11 2002
A. Retolaza
Blends of 75/25 poly(ethylene terephthalate) (PET)/high density polyethylene (HDPE) containing poly(ethylene-co-methacrylic acid) partially neutralized with lithium (PEMA-Li) were obtained by direct injection molding in an attempt (i) to ameliorate the poor performance of the binary blend and (ii) to find the best compatibilizer content. The presence of PEMA-Li caused a nucleation effect on PET, and a decrease in the crystalline content of HDPE. The compatibilizing effect of PEMA-Li was due to the combined effects of interaction at the interface and chemical reactions. The ternary blends showed a complex morphology, with two dispersed HDPE and PEMA-Li phases that contained a small internal dispersed phase, probably of PET. The compatibilizing effect of PEMA-Li was clearly shown by means of an impressive increase in the ductility and to a minor extent in the impact strength. The highest property improvement (ductility increase 1450%) appeared upon the addition of 45% PEMA-Li with respect to the HDPE phase, but taking into account the recycling interest, the ternary blend with the addition of roughly 22.5% PEMA-Li appears to be the most attractive. [source]

Comparative Crystallization Study of Several Linear Dinitramines in Nitrocellulose-Based Gels

PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 2 2003
Denis Spitzer
Abstract This study deals with the crystallization behaviour of several dinitramines with plasticizing abilities in a nitrocellulose-based gel. The tendency of these compounds to interact with nitrocellulose is an important parameter for the development of new propellants, especially for those which should have a temperature-independent combustion. It is shown that, on the basis of their crystallization behaviour, the nine studied dinitramines form three different groups. Whereas the first one (large symmetrical molecules) exhibits a strong crystallization tendency, the second group (asymmetric compounds) has low crystalline contents and shows a good interaction capacity with nitrocellulose. At last, DNDA6 (2,4-dinitro-2,4-diazahexane) with 3.3 noncrystallizing molecules per anhydroglucosidic unit of nitrocellulose, presents the most pronounced interaction with nitrocellulose, due to its lowest content of crystalline plasticizer. [source]