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Polymer Content (polymer + content)
Selected AbstractsLow Temperature Fabrication of ,-TCP,PCL Nanocomposites for Bone Implants,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Michael Bernstein Abstract A method to fabricate strong bioresorbable calcium phosphate,polymer nanocomposites with low polymer content without exposing the material to excessively high-processing temperatures is reported. Dense ,-TCP-based nanocomposites containing 5 or 15,vol% of uniformly distributed polycaprolactone (PCL) polymer were obtained by mixing ,-TCP nanopowder with PCL dissolved in chloroform followed by room temperature consolidation at the high pressure of 2.5,GPa (cold sintering). The composites had an attractive combination of compressive strength and ductility, and their dissolution behavior was similar to that of pure cold sintered ,-TCP. The immersion of ,-TCP,PCL composites in simulated body fluid (SBF) yielded in vitro deposition of a bone-like apatite layer suggesting the ability of these materials to bind to native bone tissue upon implantation. [source] High-Nanofiller-Content Graphene Oxide,Polymer Nanocomposites via Vacuum-Assisted Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Karl W. Putz Abstract Highly ordered, homogeneous polymer nanocomposites of layered graphene oxide are prepared using a vacuum-assisted self-assembly (VASA) technique. In VASA, all components (nanofiller and polymer) are pre-mixed prior to assembly under a flow, making it compatible with either hydrophilic poly(vinyl alcohol) (PVA) or hydrophobic poly(methyl methacrylate) (PMMA) for the preparation of composites with over 50 wt% filler. This process is complimentary to layer-by-layer assembly, where the assembling components are required to interact strongly (e.g., via Coulombic attraction). The nanosheets within the VASA-assembled composites exhibit a high degree of order with tunable intersheet spacing, depending on the polymer content. Graphene oxide,PVA nanocomposites, prepared from water, exhibit greatly improved modulus values in comparison to films of either pure PVA or pure graphene oxide. Modulus values for graphene oxide,PMMA nanocomposites, prepared from dimethylformamide, are intermediate to those of the pure components. The differences in structure, modulus, and strength can be attributed to the gallery composition, specifically the hydrogen bonding ability of the intercalating species [source] Use of sunflower oil mixed with jojoba and paraffin oils in deep-fat frying processINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2008Radwan S. Farag Summary The aim of the present study was to increase the stability of sunflower oil during frying process and to obtain low-calorie fried foods. Therefore, sunflower oil was mixed separately with jojoba oil and paraffin oil at ratios of 9:1 and 8:2 (v/v). The frying process was conducted at 180 ° ± 5 °C for 12 h continuous heating time. Some physico-chemical properties (refractive index, viscosity, colour, acid value, peroxide value, thiobarbituric acid test, iodine value and polymer content) of non-fried and binary fried oil systems were measured at various heating periods. The results demonstrated that mixing sunflower oil with jojoba oil or paraffin oil increased the stability and hence improved the quality of sunflower oil during frying process. [source] Electrosprayed polymer particles: Effect of the solvent propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Chul Ho Park Abstract Electrospraying technology has been studied in many fields to produce particles of various substances from nanoscale to microscale sizes. Unlike pure liquids, droplets formed by electrospraying that are comprised of polymer solutions undergo additional solidification processes involving solvent evaporation, which primarily determine the particle size and morphology. Herein, the effects of the solvent properties on the morphology and dimensions of solidified particles were systematically studied. In general, the size of the solidified spherical particles with smooth surfaces reflected that of the initially formed liquid droplets, which could partially be estimated by theoretical equations developed for pure liquids. Particle sizes increased with an increase in polymer content and a decrease in the boiling point of the volatile solvent. Inhomogeneous drying processes related to phase separation or skin formation resulted in hollow, cuplike, and porous particle structures, with particle sizes and morphologies that were outside of the scope of the theoretical treatments. The selection of a proper solvent or solvent mixture seemed to be a convenient way to control the particle morphologies, such as hollow, cuplike, or porous structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Storage of biodegradable polymers by an enriched microbial community in a sequencing batch reactor operated at high organic load rateJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2005Davide Dionisi Abstract The production of polyhydroxyalkanoates (PHAs) from organic acids by mixed bacterial cultures using a process based on aerobic enrichment of activated sludge, that selects for mixed microbial cultures able to store PHAs at high rates and yields, is described. Enrichment resulted from the selective pressure established by periodic feeding the carbon source in a sequencing batch reactor (SBR); a mixture of acetic, lactic and propionic acids was fed at high frequency (2 hourly), high dilution rate (1 d,1), and at high organic load rate (12.75 g chemical oxygen demand (COD) L,1 d,1). The performance of the SBR was assessed by microbial biomass and PHA production as well as the composition and polymer content of the biomass. A final batch stage was used to increase the polymer concentration of the excess sludge produced in the SBR and in which the behaviour of the biomass was investigated by determining PHA production rates and yields. The microbial biomass selected in the SBR produced PHAs at high rate [278 mg PHAs (as COD) g biomass (as COD),1 h,1, with a yield of 0.39 mg PHAs (as COD) mg removed substrates (as COD),1], reaching a polymer content higher than 50% (on a COD basis). The stored polymer was the copolymer poly(3-hydroxybutyrate/3-hydroxyvalerate) [P(HB/HV)], with an HV fraction of 18% mol mol,1. The microbial community selected in the SBR was analysed by DGGE (denaturing gradient gel electrophoresis). The operating conditions of the SBR were shown to select for a restricted microbial population which appeared quite different in terms of composition with respect to the initial microbial cenosis in the activated sludge used as inoculum. On the basis of the sequencing of the major bands in the DGGE profiles, four main genera were identified: a Methylobacteriaceae bacterium, Flavobacterium sp, Candidatus Meganema perideroedes, and Thauera sp. The effects of nitrogen depletion (ie absence of growth) and pH variation were also investigated in the batch stage and compared with the SBR operative mode. Absence of growth did not stimulate higher PHA production, so indicating that the periodic feed regime fully exploited the storage potential of the enriched culture. Polymer production rates remained high between pH 6.5 and 9.5, whereas the HV content in the stored polymer strongly increased as the pH value increased. This study shows that polymer composition in the final batch stage can readily be controlled independently from the feed composition in the SBR. Copyright © 2005 Society of Chemical Industry [source] Kinetics of styrene emulsion polymerization above the critical micelle concentration: Effect of the initial monomer concentration on the molecular weightJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005Jorge Herrera-Ordonez Abstract The emulsion polymerization of styrene above the critical micelle concentration has been experimentally studied from a low final polymer content up to a high polymer content (,50%). A maximum in the molecular weight (M) evolution has been observed in all cases. The presence or absence of such a maximum depends on the relative values of the rate of free-radical entry (,) and the rate of chain transfer to the monomer (KtrCMp, where Ktr is the chain transfer to monomer rate coefficient and CMp is the monomer concentration in particles). If , , KtrCMp, M is constant and equal to Kp/Ktr (where Kp is the propagation rate coefficient), except at very low particles sizes typical of the early stages of the reaction, in which the chain length is limited by the particle size. On the other hand, if , , KtrCMp, M is determined by both CMp and ,. It is proposed that , is determined by the sum of the entry of the oligomeric radicals formed in the aqueous phase and those contained in particles that undergo limited coagulation. This coagulative entry can become very significant; therefore, reactor hydrodynamics can play a major role in the kinetic behavior observed. Disagreement between Clay and Gilbert's model and molecular weight distribution data can be ascribed, to a lesser or greater extent, to the degree of correctness of the quasi-steady-state and instantaneous-termination approaches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1963,1972, 2005 [source] Surface Functionalization of Silica with 2-Vinylfuran by Cationic PolymerizationMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5-6 2003Susanne Höhne Abstract Cationic surface polymerization of 2-vinylfuran with chlorotriphenylmethane as initiator has been used for the functionalization of silica particles. The influence of monomer/initiator ratio and temperature on grafting efficiency, yield, and degree of grafting has been investigated. Grafting efficiency is a significant function of temperature and monomer/initiator ratio, because crosslinking reactions between cationically active chains increases the amount of the immobilized polyvinylfuran fraction. Thus, larger initiator concentrations on the silica cause higher polymer content on the surface. Polymer structure elucidation and surface properties are analyzed by means of solid-state NMR spectroscopy, UV-vis spectroscopy, BET , measurements, and scanning electron microscopy. [source] Prediction of Polymer Properties in LDPE ReactorsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2005Gary J. Wells Abstract Summary: A new analysis tool is presented that uses the governing kinetic scheme to predict properties of low-density polyethylene (LDPE) such as the detailed shape of the molecular weight distribution (MWD). A model that captures mixing details of autoclave reactor operation is used to provide a new criterion for the onset of MWD shouldering. Kinetic effects are shown to govern the existence of MWD shoulders in LDPE reactors, even when operation is far from perfectly-mixed. MWD shoulders occur when the mean reaction environment has a relatively high radical concentration and has a high polymer content, and is at a low temperature. Such conditions maximize long chain formation by polymer transfer and combination-termination, while limiting chain scission. For imperfectly-mixed reactors, the blending of polymer-distributions produced in different spatial locations has a small effect on the composite MWD. However, for adiabatic LDPE autoclaves, imperfect mixing broadens the stable range of mean reactor conditions, and thereby increases the possibility for MWD shouldering. Polymer MWD produced in an LDPE autoclave reactor by various kinetic mechanisms. [source] Studies on nylon-6/EVOH/clay ternary compositesPOLYMER COMPOSITES, Issue 1 2006N. Artzi Nylon-6 (Ny-6)/EVOH blends are interesting host multiphase systems for incorporation of low clay contents. The Ny-6/EVOH blend is a unique system, which tends to chemically react during melt-mixing, affecting thermal, morphological and mechanical properties of the ternary systems containing clay. The addition of clay seems to interrupt the chemical reaction between the host polymers at certain compositions, leading to lower blending torque levels when clay is added. A competition between Ny-6 and EVOH regarding the intercalation process takes place. Ny-6 seems to lead to exfoliated structure, whereas EVOH forms intercalated structure, as revealed from XRD and TEM analyses, owing to thermodynamic considerations and preferential localization of the clay in Ny-6. Hence, the ternary systems have combined intercalated and delaminated morphology or complete exfoliated morphology depending on blend composition and clay content. Selective extraction experiments (gel content) indicate the formation of chemical reaction between the Ny-6 and EVOH, and give an indirect indication of the polymer content residing in the galleries. The thermal properties of the polymers were found to be affected by the occurrence of chemical reaction, the level of intercalation and exfoliation and plasticizing effect of the low molecular weight onium ions treating the clay. Of special interest is the increased storage modulus attained upon the addition of only 1.5 wt% clay. POLYM. COMPOS. 27:15,23, 2006. © 2005 Society of Plastics Engineers [source] Thermally oxidized palm olein exposure increases triglyceride polymer levels in rat small intestineEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 9 2010Raul Olivero David Abstract The origin and presence of triglyceride polymers in small intestine have been poorly studied. The present study combined a short in vivo absorption experiment and high-performance size-exclusion chromatography determination. Groups of six male Wistar rats were administered by esophageal probe 1,g/100,g body weight unused palm olein and palm oleins used in 40 and 90 potato frying operations. Small intestines were dissected, cleaned of luminal fat, and analyzed for the presence of triglyceride polymers (oligomers and/or dimers) after 4,h oil administration. The intestinal fat content did not change but the polymers content was positively and significantly correlated (r,=,0.5983; p<0.01) with the amount of polymers present in the oil tested. The small intestine contained 5.05,mg [median and percentile 25 (1.57,mg),percentile 75 (10.40,mg)] of polymers after 4-h exposure to palm olein used for frying 90 times. The results suggested that 2.7,4.9% of the triglyceride polymers administered were present in the small intestine 4,h after ingestion. TBARS levels (p<0.05) and the redox index (oxidized glutathione/total glutathione) (p<0.01) in the small intestine increased significantly after exposure to the palm olein used in 90 frying operations. In conclusion, administration of altered oil increased the presence of resynthesized polymers in the small intestine, thus contributing to small intestine oxidative stress. [source] | |||||||||||||||||||||||||