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Polymer Type (polymer + type)
Selected AbstractsCone calorimeter testing of S2 glass reinforced polymer compositesFIRE AND MATERIALS, Issue 7 2009Alexander B. Morgan Abstract With the ever increasing demand for fuel savings on vehicles, there is a strong push to replace metal with polymeric + fiber (carbon/glass) composites. However, the replacement of metal with polymeric composites can lead to additional fire risk. Our study focused on glass fiber reinforced polymer composites meant for vehicular structural applications, and flammability performance of these composites was studied by cone calorimetery. The effects of fiberglass loading, nanocomposite use (clay, carbon nanofiber) and polymer type (epoxy, phenolic) were studied under a heat flux of 50kW/m2 to better understand the potential effects that these variables would have on material flammability. It was found that as fiberglass loading increased, flammability decreased, but at a cost to structural integrity of the residual polymer + fiber char. The use of nanocomposites has little effect on reducing flammability in this set of samples, but the use of phenolic resins in comparison with epoxy resins was found to yield the greatest improvements in flammability performance. Further, the phenolic system yielded a higher level of structural integrity to the final polymer + fiberglass char when compared with the other polymer systems of low heat release. Copyright © 2009 John Wiley & Sons, Ltd. [source] Online temperature measurement and simultaneous diameter estimation of fibers by thermography of the spinline in the melt spinning processADVANCES IN POLYMER TECHNOLOGY, Issue 3 2004M. Golzar Abstract Online measurements of the temperature and the diameter of fibers in the melt spinning process of thermoplastics are discussed. The temperature and the diameter of fibers can be applied in many fields such as fiber formation modelling, cooling rate behavior (Nusselt number), and rheological investigations (apparent extensional viscosity) of polymers. The online measurements along the spinline were carried out with an infrared camera during the melt spinning process. Two different experiments were designed and carried out to find the correction factor, i.e., the emissivity. The results show that the emissivity correction factor depends on the polymer type and the fiber diameter. Usually the diameter of the fibers is measured by an instrument or by direct velocity measurements invoking the continuity equation. In this new approach the diameter is found directly by the evaluation of the measured temperature. Therefore only one apparatus, namely an infrared camera taking snapshots, is required to find the fiber diameter. The key of this method can be seen in the temperature difference between the fiber and the environment. A mathematical procedure was developed to estimate the diameter of the fiber from the distribution curve. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 176,185, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20008 [source] Drug,polymer solubility and miscibility: Stability consideration and practical challenges in amorphous solid dispersion developmentJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2010Feng Qian Abstract Drug,polymer solid dispersion has been demonstrated as a feasible approach to formulate poorly water-soluble drugs in the amorphous form, for the enhancement of dissolution rate and bioperformance. The solubility (for crystalline drug) and miscibility (for amorphous drug) in the polymer are directly related to the stabilization of amorphous drug against crystallization. Therefore, it is important for pharmaceutical scientists to rationally assess solubility and miscibility in order to select the optimal formulation (e.g., polymer type, drug loading, etc.) and recommend storage conditions, with respect to maximizing the physical stability. This commentary attempts to discuss the concepts and implications of the drug,polymer solubility and miscibility on the stabilization of solid dispersions, review recent literatures, and propose some practical strategies for the evaluation and development of such systems utilizing a working diagram. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:2941,2947, 2010 [source] Zidovudine-loaded PLA and PLA,PEG blend nanoparticles: Influence of polymer type on phagocytic uptake by polymorphonuclear cellsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2009Rubiana Mara Mainardes Abstract Mononuclear (macrophages) and polymorphonuclear leucocytes cells play an important role in the immunopathogenesis of acquired immunodeficiency syndrome. Zidovudine is a broad-spectrum drug used in current antiretroviral therapy. The development of controlled drug delivery systems for the treatment of chronic diseases is of great interest since these systems can act as vectors, carrying the drug only to the target, and the adverse effects can be reduced. In this study, PLA and PLA/PEG blend nanoparticles containing zidovudine were developed and their uptake by polymorphonuclear leucocytes were studied in vitro. The influence of polymer type on particle size, Zeta potential and particle uptake by polymorphonuclear leucocytes was investigated. The cells were isolated from rat peritoneal exudate and their activation by nanoparticles was measured by luminol-dependent chemiluminescence and microscopical analysis. The PEG in the blend modified the Zeta potential suggested the formation of a PEG coat on the particle surface. The phagocytosis depended on the PEG and its ratio in the blend, the results showed that the PLA nanoparticles were more efficiently phagocytosed than PLA/PEG blends. The blend with the highest PEG proportion did not prevent phagocytosis, indicating that the steric effect of PEG was concentration dependent. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:257,267, 2009 [source] Controlled and complete release of a model poorly water-soluble drug, prednisolone, from hydroxypropyl methylcellulose matrix tablets using (SBE)7m -,-cyclodextrin as a solubilizing agentJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2001Venkatramana M. Rao Abstract Sustained-release formulations such as hydroxypropyl methylcellulose (HPMC)-based hydrophilic matrix tablets of poorly water-soluble drugs often result in incomplete release because of the poor solubility and dissolution rate of the drug in the hydrophilic matrix. Sulfobutylether-,-cyclodextrins ((SBE)7M -,-CDs) have been known to improve the solubility of such drugs by forming inclusion complexes. The present paper deals with the modification of drug release from an HPMC-based matrix tablet of a sparingly water-soluble drug, prednisolone (PDL), using (SBE)7M -,-CD as a solubilizing agent. Tablets were prepared by direct compression of a physically mixed PDL, (SBE)7M -,-CD, and polymer. On exposure to water, an in situ PDL:(SBE)7M -,-CD complex was formed in the gel layer, and enhanced drug release relative to a control formulation was observed (lactose used as the excipient instead of (SBE)7M -,-CD ). Other possible changes due to the incorporation of (SBE)7M -,-CD in the formulation were also probed. Incorporation of (SBE)7M -,-CD lead to a higher water uptake relative to the control (lactose) formulation. For a fixed total tablet weight, polymer type, and loading, the drug release rate appeared to depend on the molar ratio of (SBE)7M -,-CD to PDL and not the absolute amount of (SBE)7M -,-CD present in the matrix tablet. This work shows that incorporation of (SBE)7M -,-CD into the matrix tablets could be considered in designing a sustained-release tablet of poorly water-soluble drugs. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:807,816, 2001 [source] Prediction of Chain Length Distribution of Polystyrene Made in Batch Reactors with Bifunctional Free-Radical Initiators Using Dynamic Monte Carlo SimulationMACROMOLECULAR REACTION ENGINEERING, Issue 3 2007Ibrahim M. Maafa Abstract The objective of this paper is to present a dynamic Monte Carlo model that is able to simulate the polymerization of styrene with bifunctional free-radical initiators in a batch reactor. The model can predict the dynamic evolution of the chain length distribution of polystyrene in the reactor. The model includes all relevant polymerization mechanistic steps, including chemical and thermal radical generation, and diffusion-controlled termination. The model was applied to styrene polymerization and the Monte Carlo estimates for chain length averages were compared to those obtained with the method of moments. Excellent agreement was obtained between the two methods. Although styrene polymerization was used as a case study, the proposed methodology can be easily extended to any other polymer type made by free-radical polymerization. [source] The Characteristics of Polyethylene Film for Stretch and Cling Film ApplicationsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2004C.M. Small Part I. A range of polyethylene films were prepared from metallocene linear low density polyethylene (m-LLDPE), linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) resins, containing 0 and 8% polyisobutylene (PIB). FTIR, DSC and mechanical analysis techniques were used to investigate the effect of co-monomer type, density and melt flow index (MFI) on the mechanical performance, orientation and crystallinity of these films. The study established that co-monomer type and MFI were the greatest factors influencing mechanical performance and crystallinity. Crystallinity was found to be the most influential factor governing PIB migration in these films and this in turn was related to polymer type, density and MFI, High MFI, octene co-monomer films exhibited the highest orientation, tear resistance and tack strength and would therefore be suitable for stretch film applications. Ultra low-density polymers gave relatively low tack strength and poor overall mechanical performance. Part II. A range of ethyl vinyl acetate (EVA)/m-LLDPE/EVA co-extruded films was manufactured, with vinyl acetate (VA) co-monomer content of 6, 12 and 18% and PIB content from 0,20%. The films were aged at 45d,C for up to 28 days, to enable tack (cling) development. The results show that film tack strength improved significantly with ageing. Increased VA concentration in the surface layer also showed significant improvement in film tack strength. The film tensile strength, elongation and tear properties in both machine direction (MD) and transverse direction (TD) were not significantly affected by increase in PIB concentration. However, increased VA content showed slight improvement in MD mechanical performance of the films, TD properties were relatively unaffected. Films with 12 to 18% VA in the surface layers produced high surface tack film and the mechanical performance of these films were comparable to mono-layer polyethylenes. These films are suitable for stretch wrap applications and have reduced the overall concentrations of tack additives, though high VA films were more difficult to process. [source] Synthesis and characterization of semifluorinated polymers and block copolymersMACROMOLECULAR SYMPOSIA, Issue 1 2003Doris Pospiech Abstract The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains. [source] A simple model for the interaction between water vapour and oxygen transmission in multilayer barrier materials intended for food packaging applicationsPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2008Marianne Jakobsen Abstract The low oxygen permeability of the ethylene-vinyl alcohol copolymer, EVOH, is outstanding, but is also known to be very sensitive to moisture uptake and cannot be used as a monolayer packaging material. In this paper, theory is presented in order to calculate the average water activity of the EVOH layer at steady state and the corresponding oxygen barrier for different multilayer structures using various polymer types and layer thicknesses. Multilayer materials can be designed for different food packaging applications and storage conditions, in order to keep the relative humidity of the barrier below recommended 75%, by varying the thickness of the outside versus the inside protective layers and/or varying the water vapour transmission rate of the outside versus the inside layer. The conclusion reached is that to retain the optimal barrier properties and thereby the optimal protection of the food, asymmetric multilayer structures are necessary. Copyright ©2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||