Different Rheological Properties (different + rheological_property)

Distribution by Scientific Domains


Selected Abstracts


Protein-Release Behavior of Self-Assembled PEG,, -Cyclodextrin/PEG,Cholesterol Hydrogels

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Frank van de Manakker
Abstract This paper reports on the degradation and protein release behavior of a self-assembled hydrogel system composed of , -cyclodextrin- (,CD) and cholesterol-derivatized 8-arm star-shaped poly(ethylene glycol) (PEG8). By mixing ,CD- and cholesterol-derivatized PEG8 (molecular weights 10, 20 and 40 kDa) in aqueous solution, hydrogels with different rheological properties are formed. It is shown that hydrogel degradation is mainly the result of surface erosion, which depends on the network swelling stresses and initial crosslink density of the gels. This degradation mechanism, which is hardly observed for other water-absorbing polymer networks, leads to a quantitative and nearly zero-order release of entrapped proteins. This system therefore offers great potential for protein delivery. [source]


A comprehensive 3-D analysis of polymer melt flow in slit extrusion dies

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2004
Yihan Huang
Abstract An understanding of flow behaviour of polymer melts through a slit die is extremely important for optimizing die design and, consequently, for die performance in processing polymer sheets and films. In view of the complex nature and the physical properties of polymer melts as well as of die geometries, such as coat-hanger dies, no simple mathematical formulae can be used to compute the flow regimes within dies. This paper illustrates the development of a three-dimensional (3-D) computer model of an example of a coat-hanger die design using the computational fluid dynamics package, FIDAP, based on the finite element method. A difference of only 3.7% was found when comparing the velocity distribution at the die exit obtained from the 3-D simulation with that calculated using a two-dimensional analytical design procedure, indicating that full 3-D analysis seems to be unnecessary. However it has been shown that unwanted flow phenomena and production problems can be ameliorated by means of visualization and the detailed information obtained from computer simulations. Comparative simulation results with polymers of different rheological properties in the same die are also described. The comprehensive analyses provide a means of interpretation for flow behavior, which allows modification of the die geometry for optimal design. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 111,124, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20002 [source]


Design of optimal extrusion die for a range of different materials

POLYMER ENGINEERING & SCIENCE, Issue 3 2009
Nadhir Lebaal
THE coat-hanger melt distributor is a device commonly used in the wire coating process. Its task is to distribute the melt around the conductor uniformly. It is quite common that materials and flow rates differ from what had been specified during the design procedure. This may lead to bad performance with materials of very different rheological properties from the design material. In this article, we present an optimal design approach to avoid this loss of performances. This approach involves coupling a three-dimensional finite element simulation software with an optimization strategy based on a response surface method. The objective is to determine a coat-hanger melt distributor geometry that ensures a homogeneous exit velocity distribution that will best accommodate for a different range of materials. A coat-hanger melt distributor with a manifold of constant width is designed, and a set of flow distribution measurements is established for two different materials. The results of numerical simulation are then validated by comparison with experimental measurements. The effect of material change is also investigated. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source]


Thickness uniformity of HDPE blown film: Relation to rheological properties and density

POLYMER ENGINEERING & SCIENCE, Issue 5 2004
Hiroyuki Higuchi
Previous work has elucidated that the wall slip velocity and viscosity of polymer melts influence the thickness uniformity of blown film. The present study investigates the effects of the stress dependence of wall slip, the shear thinning and the density on the uniformity. We have prepared high-density polyethylenes with a variety of molecular weight distributions, which have different rheological properties. Examination of the thickness uniformity of their blown film has shown that the uniformity is correlated with wall slip velocity, the stress dependence of the velocity, melt viscosity, shear thinning and density; the coefficient of the correlation is determined to be 0.990. The reason why the stress dependence of wall slip and the shear thinning affect the uniformity is explained in terms of polymer melt flow behavior in a die, while the effect of density is interpreted considering bubble fluctuation in the blow-up process. Polym. Eng. Sci. 44:965,972, 2004. © 2004 Society of Plastics Engineers. [source]


CASA Assessment of Kinematic Parameters of Ram Spermatozoa and their Relationship to Migration Efficiency in Ruminant Cervical Mucus

REPRODUCTION IN DOMESTIC ANIMALS, Issue 4 2008
I Robayo
Contents Sperm motility is an indicator of male fertility because of its importance for sperm migration through the female genital tract and for gamete interaction at fertilization. This study analyses the relationship between computer assisted semen analysis (CASA) motility patterns and sperm migration of rams in ruminant cervical mucus. In experiment 1, spermatozoa extended with sperm analysis medium (SAM) and seminal plasma were compared in terms of motility. In experiment 2, 56 semen samples were collected either with artificial vagina (AV) or electroejaculator to be compared in terms of motility performance. In experiment 3, 104 ejaculates collected by AV from 26 males were analysed via the CASA system to characterize their motility patterns. In experiment 4, ejaculates from pairs of rams (20 rams in total) were simultaneously assessed for mucus migration (ovine, caprine, bovine) and motility patterns to evaluate the correlations between both parameters. Semen collected by AV and extended in SAM allows the most reliable assessment for sperm motility. Ram spermatozoa move fast and follow a linear trajectory compared with other ruminants. Continuous line velocity (VCL) and average path velocity (VAP) are the only sperm kinematic parameters that presented significant positive correlations with the ability to migrate in sheep cervical mucus (p < 0.05). Continuous line velocity, VAP, straight line velocity and linearity are highly significantly related with migration efficiency in goat cervical mucus (p < 0.01) and only lateral head displacement is negatively related to sperm migration in bovine cervical mucus (p < 0.05). These results suggest that specific kinematic parameters confer the ability of spermatozoa to colonize and migrate through epithelial mucus with different rheological properties. [source]