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Mechanical Shearing (mechanical + shearing)
Selected AbstractsA Stimuli-Responsive, Photoluminescent, Anthracene-Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical ProcessesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Yoshimitsu Sagara Abstract Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable,stable phase transition induced by external stimuli is prepared. A 2,6-diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6-diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid-crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic-columnar phase transition induced by heating or mechanical shearing for this 2,6-diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable,stable LC phase transition. [source] Physical characterization of starch extrudates as a function of melting transitions and extrusion conditionsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2004Stéphanie Blanche Abstract The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin-screw extruder at varying moisture content, medium/high screw configuration, and 300/400-rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (,T) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. ,T was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose,lipid complex formation during extrusion increased as ,T increased and leveled off at ,T of about 20°C. Pasting peak viscosity of the starch extrudates decreased as ,T increased and leveled off at ,T of about 15°C. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as ,T increased. Extrudate expansion was negatively correlated to bulk density. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 277,290, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20017 [source] Facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration treatmentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Min Lang Tsai Abstract The objective of this study was to propose a facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration (UF) treatment. The proposed method was based on the degradation rate and rate constant of various process variables, such as: solution temperature, reaction time, concentration of chitosan solution, with or without concurrent removal of degraded fragments during mechanical shearing. The result obtained was that the degradation rate constant was 1.8,6.0 times higher for those using UF to remove smaller degraded molecules concurrently during treatment, than that without UF treatment. The degradation rate constant increased with increasing solution temperature; however, the solution temperature should not exceed than 50°C to prevent the undesired color changes of the resulting product. A method combining mechanical shearing/UF treatment at 50°C and ultrasonic radiation or microfluidization/UF treatment at 30°C is proposed here for a facile method to manipulate the molecular weight of the resultant chitosan with an energy saving, efficient and practical mass production. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Fabrication and electrical properties of CNT/PP conductive composites with low percolation threshold by solid state alloyingPOLYMER COMPOSITES, Issue 6 2010D.L. Gao The carbon nanotube/polypropylene conductive composites with a percolation threshold as low as 0.25 wt% were fabricated by solid state alloying. This solid state alloying method uses the super-high speed mechanical shearing (at 10,000 rpm) to process the entangled catalytically grown carbon nanotubes (CNTs) and the polymer matrix in solid state. The electrical properties of the nanocomposites and the structure and distribution of CNTs were investigated. The results indicated that via the shear-intensive process, CNTs were truncated and dispersed effectively, and their length could be controlled properly to fully exert the advantage of high aspect ratios (length-to-diameter ratios). At the same time, a linear structure conductive network which may considerably lower the percolation threshold was also formed by this method. Moreover, the CNTs could be further dispersed under the action of thermo energy provided by increasing the processing temperature. The super-high speed solid state alloying method is a favorable approach for the production of low percolation threshold conductive composites of CNTs filled high viscosity resins. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Biocomposites based on Alfa fibers and starch-based biopolymerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2009R. Belhassen Abstract Biocomposite materials based on Alfa cellulose fibers (esparto grass plant) as reinforcing element and starch-based biopolymer matrix were prepared and characterized in terms of mechanical performance, thermal properties, and water absorbance behavior. The fibers and the matrix were first mixed in the melted state under mechanical shearing using a plastograph and the obtained composites were molded by injection process. The tensile mechanical analysis showed a linear increase of the composite flexural and tensile modulus upon increasing the fiber content, together with a sharp decrease of the elongation at break. The fibers, incorporation into the biopolymer matrix brings about an enhancement in the mechanical strength and the impact strength of the composite. Dynamic mechanical thermal analysis (DMTA) investigation showed two relaxations occurring at about ,30 and 35°C. The addition of Alfa fibers enhanced the storage modulus E, before and after T,, which is consistent with the reinforcing effect of Alfa cellulose fibers. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||