Structure Development (structure + development)

Distribution by Scientific Domains


Selected Abstracts


Evolution of structure in the softening/melting regime of miscible polymer mixing

POLYMER ENGINEERING & SCIENCE, Issue 6 2001
Heidi E. Burch
Structure development in the softening/melting processing regime is investigated using the model miscible blend poly(styrene-co-acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fourier-transform infrared spectroscopy is used to help determine the normalized sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale(s) present in the blend at short mixing times. Results of these experiments indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that this multimodality is due to the operation of the Scott/Macosko sheeting mechanism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixing model, which postulates the formation of a striated mixture while ignoring the softening/melting regime. [source]


The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009
V. Brucato
Abstract An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000°C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100,200 ,m thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1,2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting structure, using techniques such as density measurements and wide-angle x-ray diffraction (WAXD) patterns. The cooling mechanism and temperature distribution across the sample thickness were analyzed. Results show that the final structure is determined only by the imposed thermal history and pressure. Experimental results for isotactic polypropylene (iPP), poly(ethylene terephthalate) (PET), polyamide 6 (PA6), and syndiotactic polystyrene (sPS) are reported, showing the reliability of this experimental approach to assess not only quantitative information but also a qualitative description of the crystallization behavior of different classes of semicrystalline polymers. The present study gives an opportunity to evaluate how the combined effect of the cooling rate and pressure influences the crystallization kinetics for various classes of polymer of commercial interest. An increase in the cooling rate translates into a decrease in crystallinity and density, which both experience a sudden drop around the specific "crystallizability" (or "critical cooling rate") of the material examined. The exception is sPS where competition among the various crystalline modifications determines a minimum in the plot of density vs. cooling rate. As for the effect of pressure, iPP exhibits a "negative dependence" of crystallization kinetics upon pressure, with a decrease of density and degree of crystallinity with increasing pressure, owing to kinetic constraints. PA6 and PET, on the other hand, due to thermodynamic factors resulting in an increase in Tm with pressure, exhibits a "positive dependence" of crystallization kinetics upon pressure. Finally, recent original results concerning sPS have shown that the minimum in the density vs. cooling rate curve shifts toward larger cooling rates upon increasing pressure. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:86,119, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20151 [source]


RHEOLOGY AND MICROSTRUCTURE OF WHEAT DOUGH DEVELOPED WITH CONTROLLED DEFORMATION

JOURNAL OF TEXTURE STUDIES, Issue 1 2000
EMILY J. SCHLUENTZ
ABSTRACT Undeveloped wheat dough samples were strained in shear and extensional flow between parallel plates to produce a controlled level of development. Dough made in a standard Farinograph, considered developed dough, was used for comparison. Scanning electron microscopy images of deformed dough were subjected to numerical image processing to characterize the protein matrix present. Results were compared to dynamic rheological properties to evaluate the influence of strain deformation on the formation of microstructure. Viscoelastic moduli of wheat dough showed that developed dough had the greatest amount of structure formation, followed by extensionally-strained and shear-strained samples, respectively. Undeveloped dough showed the lowest levels of structure development. Image analysis indicated statistically significant differences between protein matrices in developed and undeveloped samples; however, results were not significantly different between shear- and extension-ally-strained samples. [source]


Cultivation of low-temperature (15°C), anaerobic, wastewater treatment granules

LETTERS IN APPLIED MICROBIOLOGY, Issue 4 2009
J. O'Reilly
Abstract Aims:, Anaerobic sludge granules underpin high-rate waste-to-energy bioreactors. Granulation is a microbiological phenomenon involving the self-immobilization of several trophic groups. Low-temperature anaerobic digestion of wastes is of intense interest because of the economic advantages of unheated bioenergy production technologies. However, low-temperature granulation of anaerobic sludge has not yet been demonstrated. The aims of this study were to (i) investigate the feasibility of anaerobic sludge granulation in cold (15°C) bioreactors and (ii) observe the development of methanogenic activity and microbial community structure in developing cold granules. Methods and Results:, One mesophilic (R1; 37°C) and two low-temperature (R2 and R3, 15°C) laboratory-scale, expanded granular sludge bed bioreactors were seeded with crushed (diameter <0·4 mm) granules and were fed a glucose-based wastewater for 194 days. Bioreactor performance was assessed by chemical oxygen demand removal, biogas production, granule growth and temporal methanogenic activity. Granulation was observed in R2 and R3 (up to 33% of the sludge). Elevated hydrogenotrophic methanogenesis was observed in psychrophilically cultivated biomass, but acetoclastic methanogenic activity was also retained. Denaturing gradient gel electrophoresis of archaeal 16S rRNA gene fragments indicated that a distinct community was associated with developing and mature granules in the low-temperature (LT) bioreactors. Conclusions:, Granulation was observed at 15°C in anaerobic bioreactors and was associated with H2/CO2 -mediated methanogenesis and distinct community structure development. Significance and Impact of the Study:, Granulation underpins high-rate anaerobic waste treatment bioreactors. Most LT bioreactor trials have employed mesophilic seed sludge, and granulation <20°C was not previously documented. [source]


Nylon 66/clay nanocomposite structure development in a twin screw extruder,

POLYMER ENGINEERING & SCIENCE, Issue 4 2009
Bin Lin
Nylon 66/clay nanocomposites were prepared in a Berstorff ZE25A UTX Ultra-glide corotating twin screw extruder at 270°C. Two types of extruder configurations with different mixing sections were used. One comprised two kneading block sections in the screws (KB only) and the other had a combination of a multi-process-element (MPE) section and a kneading block section. Samples at eight different locations along the extruder screw were obtained and analyzed using scanning electron microscope and transmission electron microscope to examine the morphology development of clay inside nylon down the length of the extruder. It is found that the clay aggregates are quickly broken into smaller tactoids (micron size) and then even much smaller clay bundles (nanometer size) and single clay platelets in the first mixing section. The structure changes in the second mixing section are much less significant. X-ray diffraction (XRD) analysis of the nanocomposite products showed small, or disappearance of, characteristic XRD (001) peaks, which indicates partial exfoliation, or complete exfoliation, respectively, of clay inside nylon matrix. Differential scanning calorimetry nonisothermal study shows that the crystallization temperature of the nanocomposites has increased around 17°C when compared with neat nylon 66. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]


Nonuniformity of phase structure in immiscible polymer blends

POLYMER ENGINEERING & SCIENCE, Issue 3 2008
Ivan Fortelný
This article is focused on the phase structure development in immiscible polymer blends during melt mixing. Nonuniformity of the phase structure, i.e., the coexistence of areas containing particles with markedly different size distribution, was detected in quenched and compression molded samples of a number of various blends prepared by long and intensive mixing in the chamber of a Plasticorder. The same effect was found also for polystyrene/polyamide blends prepared in a twin-screw extruder. It was shown that neglecting nonuniformity of the phase structure can lead to considerable error in evaluation of the effect of system parameters on the blend morphology. The reasons for the effect were discussed and it was found that inhomogeneous flow field in mixers is a plausible explanation of the nonuniform phase structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]


Comparison of structure development in injection molding of isotactic and syndiotactic polypropylenes

POLYMER ENGINEERING & SCIENCE, Issue 8 2002
Dongman Choi
A comparative study of the crystallization and orientation development in injection molding isotactic and syndiotactic polypropylenes was made. The injection molded samples were characterized using wide angle X-ray diffraction (WAXD) techniques and birefringence. The injection molded isotactic polypropylene samples formed well-defined sublayers (skin, shear and core zones) and exhibited polymorphic crystal structures of the monoclinic ,-form and the hexagonal ,-form. Considerable amounts of ,-form crystal were formed in the shear and core zones, depending on the injection pressure or on the packing pressure. The isotactic polypropylene samples had relatively high frozen-in orientations in the skin layer and the shear zone. The injection molded syndiotactic polypropylene exhibited the disordered Form I structure, but it did not appear to crystallize during the mold-filling stage because of its slow crystallization rate and to develop a distinct shear zone. The core zone orientation was greatly increased by application of high packing pressure. The isotactic polypropylene samples exhibited much higher birefringence than the syndiotactic polypropylene samples at the skin and shear layers, whereas both materials exhibited similar levels of crystalline orientation in these layers. [source]


Evolution of structure in the softening/melting regime of miscible polymer mixing

POLYMER ENGINEERING & SCIENCE, Issue 6 2001
Heidi E. Burch
Structure development in the softening/melting processing regime is investigated using the model miscible blend poly(styrene-co-acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fourier-transform infrared spectroscopy is used to help determine the normalized sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale(s) present in the blend at short mixing times. Results of these experiments indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that this multimodality is due to the operation of the Scott/Macosko sheeting mechanism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixing model, which postulates the formation of a striated mixture while ignoring the softening/melting regime. [source]


Geomechanical simulation to predict open subsurface fractures

GEOPHYSICAL PROSPECTING, Issue 2 2009
Helen Lewis
ABSTRACT Geomechanical simulation of the evolution of a geological structure can play an important role in predicting open fracture development for all stages in that structure's development. In this work, three such geomechanical simulations are used to predict the evolving stress and strain fields, including dilational and compactional changes in the rock fabric in developing fault and fold systems. Their consequences for open fracture development and flow are addressed. These simulated stress and strain fields show considerable spatial and temporal heterogeneity that is consistent with deformation patterns observed in both natural examples and in laboratory-deformed analogues. But the stress and strain states that develop are neither co-axial nor do they bear a simple relationship to one another. The dilational and compactional strains, manifest as open fracturing or sealing, represent some significantly increased or significantly decreased flow rates. However, open-fracture predictions based on such geomechanical simulations are extremely difficult to validate with any degree of confidence as there is little direct evidence of sub-surface fracture distributions. In this context we also discuss possible integration of seismic anisotropy measurements, as an independent measure of open fracture alignment, to support the geomechanically derived fracture predictions. The focus of this work is on volumetric strains in fault zone evolution, though folding is also addressed. [source]