High Level Of Orientation Research Articles

EFFECTIVENESS OF HOME ENVIRONMENT MODIFICATIONS FOR ELDERLY WITH DEMENTIA CORRESPONDING TO ELDERLY PEOPLE'S CONDITIONS BASED ON SURVEY WITH CARE MANAGERS

This study aims to clarify home environment modifications corresponding to the conditions of elderly people with dementia. A mail survey to 2000 cares managers. We investigated the present situations of home environmental modification in the questionnaires the mail survey which had twenty-five items. 254 elderly people were classified into four groups based on the eight items, adapting SOM. The four groups were “High-walking and high-orientation level”, “Middle-walking and middle-orientation level”, “High-walking and low-orientation level”, and “Low-walking and low-orientation level”. We found the characteristics of effectiveness of home modifications.

Modification of orientation birefringence of cellulose ester by addition of poly(lactic acid)

Effect of the addition of poly(lactic acid) (PLA) to cellulose acetate propionate (CAP) on the optical anisotropy is studied considering the morphology and molecular orientation. It is found that PLA is miscible with CAP when the amount of PLA is less than 3 wt.%. The dissolution of PLA chains having large intrinsic birefringence into CAP phase enhances the orientation birefringence of a stretched film, although the viscosity and thus the relaxation time of PLA is significantly shorter than those of CAP. The high level of orientation of PLA chains without relaxation is attained by the cooperative alignment with CAP chains. As a result, a retardation film having appropriate birefringence can be designed by polymer blends composed of biomass-based materials. When the amount of PLA is more than 3 wt.%, however, phase separation occurs. In the case of the blends with phase-separated morphology, the orientation birefringence is not greatly enhanced by blending PLA, because the molecular orientation of PLA in PLA phase relaxes immediately as compared with that of CAP.

Hierarchical structure of injection-molded bars of HDPE/MWCNTs composites with novel nanohybrid shish–kebab

Injection-molded products usually show hierarchical structure from skin to core due to the existence of shear gradient and temperature gradient. Investigating the hierarchical structure is helpful to better understand the structure-property relationship of injection-molded sample, which is important for design and preparation of polymer products with high performance. In this work, the hierarchical structures of injection-molded bars of high-density polyethylene (HDPE)/multi-walled carbon nanotubes (MWCNTs) composite were explored by examining the microstructure and crystal morphology, layer by layer, along the sample thickness, using SEM, DSC and 2D-WAXS. To enhance the shear effect, a so-called dynamic packing injection molding (DPIM) technique was used to prepare the molded bar with high orientation level. Interestingly, SEM revealed that in the skin and core zones, the lamellae of PE anchored randomly on the surface of MWCNTs, while well-defined nanohybrid shish–kebab (NHSK) entities, in which fibrillous carbon nanotubes (CNTs) act as shish while HDPE lamellae act as kebab, exist in the oriented zone. The changed NHSK crystal structure along the thickness direction of molded bar is considered as due to the shear gradient and thermal gradient in injection molding. And the underlying origin of in situ formation of NHSK under shear effects is discussed based on experimental observations.

A Mechanical Model for Stress Developmentin PA12 Tube Extrusion

Abstract In polyamide 12 tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In the present paper we develop a thermomechanical model which consists of two parts: a viscoelastic mechanical model for the calculation of stresses and a thermal model for the determination of the temperature field. Three types of inputs are necessary: processing parameters, material data (e. g., crystallization kinetics and rheology in the melt, the solid state and the transition zone) and heat transfer coefficients to describe the heat exchanges along the extrusion line. The model allows us to propose a physical interpretation of the oriented layer. During cooling high axial stresses are frozen in the first solidified layers. They induce a plastic deformation of the polymer leading to a high level of orientation in the outer zones.

Characterization by Raman Microspectroscopy of the Strain-Induced Conformational Transition in Fibroin Fibers from the Silkworm Samia cynthia ricini

Raman microspectroscopy has been used to quantitatively study the effect of a mechanical deformation on the conformation and orientation of Samia cynthia ricini (S. c. ricini) silk fibroin. Samples were obtained from the aqueous solution stored in the silk gland and stretched at draw ratios (lambda) ranging from 0 to 11. Using an appropriate band decomposition procedure, polarized and orientation-insensitive spectra have been analyzed to determine order parameters and the content of secondary structures, respectively. The data unambiguously show that, in response to mechanical deformation, S. c. ricini fibroin undergoes a cooperative alpha-helix to beta-sheet conformational transition above a critical draw ratio of 4. The alpha-helix content decreases from 33 to 13% when lambda increases from 0 to 11, while the amount of beta-sheets increases from 15 to 37%. In comparison, cocoon silk is devoid of alpha-helical structure and always contains a larger amount of beta-sheets. Although the presence of isosbestic points in different spectral regions reveals that the conformational change induced by mechanical deformation is a two-state process, our results suggest that part of the glycine residues might be incorporated into beta-poly(alanine) structures. The beta-sheets are initially isotropically distributed and orient along the fiber axis as lambda increases, but do not reach the high level of orientation found in the cocoon fiber. The increase in the orientation level of the beta-sheets is found to be concomitant with the alpha --> beta conformational conversion, whereas alpha-helices do not orient under the applied strain but are rather readily converted into beta-sheets. The components assigned to turns exhibit a small orientation perpendicular to the fiber axis in stretched samples, showing that, overall, the polypeptide chains are aligned along the stretching direction. Our results suggest that, in nature, factors other than stretching contribute to the optimization of the amount of beta-sheets and the high degree of orientation found in natural cocoon silk.

Enhancing effects of nicotine and impairing effects of scopolamine on distinct aspects of performance in computerized attention and working memory tasks in marmoset monkeys

With the CAmbridge Neuropsychological Test Automated Battery (CANTAB), computerized neuropsychological tasks can be presented on a touch-sensitive computer screen, and this system has been used to assess cognitive processes in neuropsychiatric patients, healthy volunteers, and species of non-human primate, primarily the rhesus macaque and common marmoset. Recently, we reported that the common marmoset, a small-bodied primate, can be trained to a high and stable level of performance on the CANTAB five-choice serial reaction time (5-CSRT) task of attention, and a novel task of working memory, the concurrent delayed match-to-position (CDMP) task. Here, in order to increase understanding of the specific cognitive demands of these tasks and the importance of acetylcholine to their performance, the effects of systemic delivery of the muscarinic receptor antagonist scopolamine and the nicotinic receptor agonist nicotine were studied. In the 5-CSRT task, nicotine enhanced performance in terms of increased sustained attention, whilst scopolamine led to increased omissions despite a high level of orientation to the correct stimulus location. In the CDMP task, scopolamine impaired performance at two stages of the task that differ moderately in terms of memory retention load but both of which are likely to require working memory, including interference-coping, abilities. Nicotine tended to enhance performance at the long-delay stage specifically but only against a background of relatively low baseline performance. These data are consistent with a dissociation of the roles of muscarinic and nicotinic cholinergic receptors in the regulation of both sustained attention and working memory in primates.

Evaluation of the microstructure and melting behavior of drawn polypropylene fibers with a microthermal analyzer

The strong correlation of melting behavior with the microstructure of original and zone-drawn isotactic polypropylene fibers was evaluated by microthermal analysis (micro-TA) combined with wide-angle X-ray diffraction analysis. The crystal structure of both the original and zone-drawn fibers was a monoclinic α-form with a ∼ 0.64 nm, b ∼ 2.03 nm, and c ∼ 0.65 nm. In contrast to the absence of any oriented polymer molecules in the original fiber, the polymer molecules in the zone-drawn fiber were extended and highly oriented in at least two different states; one arranged along the drawn axis and the other at 40° to the drawn axis. The micro-TA-derived melting points corresponded to these microstructural changes caused by the zone-drawing process and differed from the melting points obtained by differential scanning calorimetery. The micro-TA melting point of 140°C corresponded to the z-e-p melting point of the original fiber, being much lower than the conventional differential scanning calorimetery melting point of 163°C. As for the zone-drawn fiber, an increase of 19°C in the melting temperature revealed its high orientation level, and the appearance of three elevated melting peaks (161, 167, and 178°C) at the highest heating rate (1500°C/min) coincided with its several oriented states. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1306–1311, 2006

Roll-drawing and die-drawing of toughened poly(ethylene terephthalate). Part 1. Structure and mechanical characterization

In this work, two solid-state forming processes, namely roll-drawing and die-drawing, were evaluated for inducing high levels of orientation in toughened semicrystalline poly(ethylene terephthalate) (PET), modified with a metallocene ethylene-octene copolymer. In order to study the role of adhesion at the particle/matrix interface, the elastomer was grafted with glycidyl methacrylate (GMA). The GMA functional groups, which can graft to PET to form a copolymer, induced a reduction in the size of the elastomeric phase. The oriented toughened sheets from roll-drawing and die-drawing processes were characterized in terms of processing conditions (process and draw ratio), interfacial modification (GMA grafting), morphology (particle size and shape) and tensile mechanical properties (modulus, yield stress and toughness).

Fibre reinforcement of elastomers: nanocomposites based on sepiolite and poly(hydroxyethyl acrylate)

AbstractThe reinforcement of poly(hydroxyethyl acrylate) provided by sepiolite particles has been analysed. Stress–strain measurements at equilibrium, as well as swelling experiments, were carried out on the unfilled and filled polymers. The state of dispersion of the filler was characterized by transmission electron microscopy. Moreover, an evaluation of chain orientation by infrared dichroism reveals a high orientation level in the filled system. The strong interaction between the two phases, combined with a good dispersion and a high shape factor of these clay particles, explain the improvement of the mechanical properties of the composites with respect to the pure polymer. Copyright © 2004 Society of Chemical Industry

Amplification effect of platelet type nanoparticles on the orientation behavior of injection molded nylon 6 composites

The effect of platelet type nanoparticles and processing conditions; mold temperature and injection speed, on the development of local microstructure in injection molded nylon 6 parts was investigated. The molded parts exhibit two crystal forms (α and γ) of nylon 6 in varying proportions from skin to core. The γ crystals preferentially grow near the surface regions and α crystal fraction increases with distance from the surface in all molded parts. However, the spatial variation of crystal phases across the thickness in nanocomposites differs from that of unfilled nylon 6. Nanoplatelets induce high levels of orientation of the polymer matrix throughout the thickness of the molded part even at high mold temperatures where nonisothermal effects are highly suppressed and confined to very close proximity of surfaces. These high chain orientation levels observed in nanoparticle filled systems is a result of the shear amplification effect that occurs in small spaces between adjacent nanoparticles of differing velocity. The local preferential crystalline orientation of nylon 6 resin and nanoparticles across the thickness of the molded parts are investigated using a series of structure characterization techniques including microbeam wide angle X-ray, SAXS and TEM.

Comparison of statistical and blocky copolymers of ethylene terephthalate and ethylene 4,4′‐bibenzoate based on thermal behavior and oxygen transport properties

AbstractPoly(ethylene terephthalate) (PET) was blended with a frustrated liquid‐crystalline polymer, poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) (PETBB55), in the weight ratio 70:30. Under the melt conditions used for blending, NMR analysis showed that some transesterification had occurred. Accordingly, the blended product resembled a blocky copolymer more closely than it did a physical blend. A random copolymer with the same composition was synthesized for comparison. The study examined the effect of the comonomer distribution (blocky vs random) on the thermal behavior and oxygen transport properties of the glassy and cold‐drawn polymers. The glass‐transition temperatures and the crystallization behavior suggested that the PETBB55 blocks phase‐separated as very small domains. Higher levels of orientation, as indicated by higher densities and higher trans glycol fractions, were achieved by the cold drawing of the blocky copolymer. It was speculated that the cold drawing of the blocky copolymer at temperatures up to the glass‐transition temperature of the PETBB55 blocks produced highly oriented PETBB55 domains. Constraints imposed by connections between PET and the PETBB55 blocks prevented the relaxation of the continuous PET phase, even at temperatures well above the glass‐transition temperature of the PET blocks. In this sense, the blocky copolymer embodied the concept of a self‐reinforcing polymer. As a result, an improved oxygen barrier was obtained over a wider range of cold‐draw temperatures with the blocky copolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 289–307, 2003

The effects of roll drawing on the structure and properties of oriented poly(ethylene terephthalate)

The effect of processing conditions on the structure and properties of roll drawn poly(ethylene terephthalate) (PET) was examined. It was found that, when roll drawing amorphous PET at temperatures just above the glass transition, only very low draw ratios were obtained. This is probably because there were no crystallites to lock in the applied extension. Roll drawing at high temperatures, above 130°C, where there was significant thermal crystallization, produced film of high strength. At temperatures between 130°C and 190°C, the properties were almost independent of processing temperature. Mechanical tests performed on roll drawn samples, processed in this temperature range, showed that the initial modulus and the yield stress increased linearly with draw ratio. The yield strain decreased with draw ratio up to λ = 4.0, and then became almost constant. The processing temperature that produced samples with the greatest strength was 170°C. This was because the highest draw ratios were obtained at this temperature while maintaining constant width deformation. At low draw ratios, the crystallinity increased with the processing, whereas at higher draw ratios, it was independent of temperature. This constant level of crystalline fraction may have produced the constant failure strain that was observed at high draw ratios. The orientation functions were similarly unaffected by the processing temperature, although birefringence measurements did suggest that lower processing temperatures may have produced higher levels of orientation. The orientation of the trans conformers was independent of the temperature, but the overall content was increased at higher processing temperatures.

Shear-induced alignment and relaxation of orientation in smectic side-chain liquid-crystalline polymers

Infrared rheometry showed that the mesogenic groups of two smectic side-chain liquid-crystalline polymers were aligned by shear until a steady-state value was achieved after approximately 10 s. The shear experiments were carried out at temperatures 10–50°C below the isotropisation temperature. The alignment of the mesogenic groups was always perpendicular to the shear flow direction. The degree of orientation increased with increasing shear rate and the highest reported value for the Hermans orientation function was −0.35 (−0.5 corresponds to perfect perpendicular orientation; it was assumed that the mesogen-group-orientation was unixaial). The turbidity of the sheared smectic samples indicates the presence of small domains in spite of their high level of orientation. A gradual loss of mesogen group orientation occurred after cessation of shear, and full recovery of the original isotropic state was in no case achieved within 60 000 s.

Influence of Processing Temperature on the Morphological and Mechanical Properties of a PC/TLCP Blend

Abstract The influence of processing temperature on the morphological and mechanical properties of polycarbonate (PC) blended with a thermotropic liquid crystalline polymer (TLCP) has been studied. At a barrel temperature of 310°C, the TLCP of the blends exhibits the high orientation level and fiber alignment which correspond to maximum tensile strength. This indicates that the processing temperature might result in the change of the viscosity ratios of the dispersed and continuous phase and is one of the main processing parameters.

Structure‐property relationships in short‐fiber‐reinforced composites

AbstractA computer model is presented for the study of the effects of fiber characteristics on the mechanical properties of short‐fiber‐reinforced composites. Our model results indicate a very weak effect of fiber orientation on the modulus and tensile strength of the composite. Very high levels of orientation are required before a true reinforcement of the composite by the fiber can occur. For randomly dispersed fibers, our results point to the presence of an optimum fiber aspect ratio for effective reinforcement. They also indicate a microfailure mechanism which originates at the fiber ends and propagates along the fiber‐matrix interface, with no fiber breaking being involved. Our model results are compared with predictions from other theories and available experimental data. © 1994 John Wiley & Sons, Inc.

Simulation of diffusion-limited step-growth polymerization in 2D: Effect of shear flow and chain rigidity

Multimolecule Brownian dynamics simulation results for diffusion controlled polymerization of bead–rod chain molecules in 2D solution are presented. Reaction between any two molecules undergoing Brownian diffusion takes place if the reactive chain ends approach each other to within a certain reaction radius, and if the chain end carrying segments are collinear within certain specified limits. The second order reaction rate constant is found to decrease with time as the molecular lengths increase and the diffusivities decrease. Application of a shear flow is seen to result in alignment of the molecules along the flow direction, thereby enhancing the concentration of molecular pairs with parallel orientation of reactive-end carrying chain segments, and hence the overall reaction rate. This effect is found to be more pronounced in the case of long rigid molecules as compared to flexible molecules because of the slow rotation and high level of orientation under flow of the former. Even the molecular weight distribution (MWD) obtained during polymerization may be affected. For example, longer molecules have lower diffusivities and hence lower reactivities, resulting in a narrower MWD in the absence of flow, as compared to the results with the usual assumption of molecular reactivity being independent of chain length. Furthermore, in the presence of an external flow, the longer molecules orient to a higher degree and hence display a higher enhancement in reactivity. This results in a wider MWD of the polymer. The simulation results are in qualitative agreement with previous experimental data for solution polymerization of rod-like molecules.

Strain‐induced crystallization of poly(ethylene terephthalate)

AbstractThe fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress‐ or strain‐induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide‐angle X‐ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide‐angle X‐ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.

Conductivite ionique de composes de type hydrotalcite

Lamellar compounds Zn 2Cr(OH) 6Cl· nH 2O and Zn 2Al(OH) 6Cl· nH 2O exhibit an ionic conductivity upto 1.3×10 -3 ω -1 at 21°C. The conductivity, essentially intrinsic to the material is attributable in part to protonic exchange between hydroxylated sheets and inter-lamellar water molecules, and also in part to chloride ions which are also mobile. Evolution of conductivity of both materials was followed as a function of temperature in the range -32-+98°C and of degree of hydration determined by control of atmosphere relative humidity. Interlamellar water content is a parameter of great importance in conductivity of these materials. Zn 2Al(OH) 6Cl· nH 2O is a promising system for deposition of 20–50 μm layer on alumina substrates. The enhanced conductivity in such layers is attributed to a high level of orientation of cristallites in relation to the substrate.

Molecular Switching in Liquid Crystal Elastomers

Abstract The synthesis is described of some liquid crystal polymers containing various degrees of cross linking units. Such materials show properties over and above those observed either from low molecular weight liquid crystals, or from conventional rubbers. Thus, though these compounds show simple rubber like elasticity in the isotropic phase, on cooling to the liquid crystal region, more complex behavior is observed, an example being the high levels of orientation produced at relatively low strain. Such materials also show unusual properties in that, when swollen with a low molecular weight liquid crystal, they undergo macroscopic shape changes in the presence of applied electric fields, in addition to the more usual electro-optic effects.

Biaxially oriented polypropylene film in power capacitors

AbstractThe use of polymer dielectrics, particularly biaxially oriented polypropylene (BOPP), has revolutionized power distribution around the world. BOPP film of sub mil thickness has displaced impregnated Kraft paper because of superior dielectric performance, lower cost, and small volume. The polypropylene molecule has a unique set of properties which combine stable dielectric properties in the operating temperature and frequency range along with an adequate dielectric constant. High levels of orientation and a small unbalance of orientation are required to produce films of high dielectric strength over large areas of film. Control of thickness uniformities to approximately ± 5 percent are critical to the reliable operation of the capacitor under load and to control of capacitance in the product. A special fibrillated surface is required which promotes complete impregnation by the dielectric fluid.This surface is acquired by the development of a specific crystal morphology at one surface of the film. No additives are used to promote this crystalline structure since most additives effect dissipation factor and generate unwanted heat. Similarly, control of contamination (ppm and ppb) is a key factor in the manufacture of film power capacitors.