229,677 research outputs found

    A novel profluorescent dinitroxide for imaging polypropylene degradation

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    Free-radical processes underpin the thermo-oxidative degradation of polyolefins. Thus, to extend the lifetime of these polymers, stabilizers are generally added during processing to scavenge the free radicals formed as the polymer degrades. Nitroxide radical precursors, such as hindered amine stabilizers (HAS),1,2 are common polypropylene additives as the nitroxide moiety is a potent scavenger of polymer alkyl radicals (R¥). Oxidation of HAS by radicals formed during polypropylene degradation yields nitroxide radicals (RRNO¥), which rapidly trap the polymer degradation species to produce alkoxyamines, thus retarding oxidative polymer degradation. This increase in polymer stability is demonstrated by a lengthening of the “induction period” of the polymer (the time prior to a sharp rise in the oxidation of the polymer). Instrumental techniques such as chemiluminescence or infrared spectroscopy are somewhat limited in detecting changes in the polymer during the initial stages of degradation. Therefore, other methods for observing polymer degradation have been sought as the useful life of a polymer does not extend far beyond its “induction period

    TGA/FTIR Studies on the Thermal Degradation of some Polymeric Sulfonic and Phosphonic Acids and Their Sodium Salts

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    The thermal degradation of poly(vinyl sulfonic acid) and its sodium salt, poly(4-styrenesulfonic acid) and its sodium salt, and poly(vinylphosphonic acid) was studied by a combination of techniques, including TGA/FTIR, to identify the volatile products which were evolved during the degradation as well as analysis of the residues which were obtained in order to propose a mechanism for the degradation. The motivation for the work was to attempt to identify new monomers which could be graft copolymerized onto a polymer in order to improve the thermal stability of that polymer

    Dielectric films improve life of polymeric insulators

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    Degradation of polymeric insulators may be significantly reduced when polymer surfaces are coated with film having gradation of dielectric constants, larger where it is in contact with polymer and smaller at its exposed surface

    Quasi-melt Processes For Single Polymer Composites And Products Thereof

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    Processes and compounds are described herein for single polymer composites based on a process for making the single polymer composites that includes the steps of heating a matrix material to create polymer melt, cooling the polymer melt to below its Tm to create an undercooled polymer melt, or quasi-melt, and combining the melt with an enhancing or reinforcing material to produce a single polymer composite. The process can produce materials that do not have any degradation of the polymer characteristic of the enhancing material due to melting of the polymer in the enhancing material.Georgia Tech Research Corporatio

    Kinetics and the Theoretical Aspects of Drug Release from PLA/HAp Thin Films

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    Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The theory of dissolution kinetics of gentamicin from polylactic acid-hydroxyapatite thin film composites is spotlighted with the combination of diffusion and polymer degradation modeling. The use of various mathematical models, characterizing diffusion, dissolution or/and erosion prevalence as well as a mix of dissolution-diffusion rate processes were employed in order to compare theory with experimental data. A number of factors influence the release kinetics of gentamicin from medical drug release systems and devices. It is difficult to have a single mathematical model that takes all these factors into account. It is shown that the degradation of the polymer matrix plays the biggest role in the release kinetics of polymer-ceramics thin film composites. It was also observed that multistage drug release form these devices depends also on the degradation kinetics of the polymer matrix. The effect of pH and device sizes were not studied but could also be of interest in future studies

    A CubeSAT payload for in-situ monitoring of pentacene degradation due to atomic oxygen etching in LEO

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    This paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.Peer ReviewedPostprint (author's final draft

    Photopolymerized thermosensitive poly(HPMAlactate)-PEG-based hydrogels : effect of network design on mechanical properties, degradation, and release behavior

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    Photopolymerized thermosensitive A-B-A triblock copolymer hydrogels composed of poly(N-(2-hydroxypropyl)-methacrylamide lactate) A-blocks, partly derivatizal with methacrylate groups to different extents (10, 20, and 30%) and hydrophilic poly(ethylene glycol) B-blocks of different molecular weights (4, 10, and 20 kDa) were synthesized. The aim of the present study was to correlate the polymer architecture with the hydrogel properties, particularly rheological, swelling, degradation properties and release behavior. It was found that an increasing methacrylation extent and a decreasing PEG molecular weight resulted in increasing gel strength and cross-link density, which tailored the degradation profiles from 25 to more than 300 days. Polymers having small PEG blocks showed a remarkable phase separation into polymer- and water-rich domains, as demonstrated by confocal microscopy. Depending on the hydrophobic domain density, the loaded protein resides in the hydrophilic pores or is partitioned into hydrophilic and hydrophobic domains, and its release from these compartments is tailored by the extent of methacrylation and by PEG length, respectively. As the mechanical properties, degradation, and release profiles can be fully controlled by polymer design and concentration, these hydrogels are suitable for controlled protein release

    A statistical theory of polymer network degradation

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    A statistical theory was proposed for the degradation (random scission of chains) of a network having f-functional nodes in the case where all chains contain equireactive groups and a chain scission event does not create new groups or suppress more than one group. Closedform relations were established between the conversion ratio of the degradation process and the crosslink density. Emphasis was put on the value of the conversion ratio for which the gel disappears. Some limited cases already considered in the literature were recovered, but a general solution was proposed for networks having any number of reactive groups per chain, be it uniform or not, and for conversion ratios up to the degelation point. The results were applied successfully to recent experiments regarding the hydrolysis of a polyester

    Shearing stability of lubricants

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    Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound

    Fire retardant polyisocyanurate foam

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    Fire retardant properties of low density polymer foam are increased. Foam has pendant nitrile groups which form thermally-stable heterocyclic structures at temperature below degradation temperature of urethane linkages
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