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Degradation Behavior (degradation + behavior)
Kinds of Degradation Behavior Selected AbstractsInfluence of Heat Treatments on In Vitro Degradation Behavior of Mg-6Zn Alloy Studied by Electrochemical Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Shaoxiang Zhang The influence of heat treatment on the in vitro degradation of Mg-6Zn alloy is studied by electrochemical measurements. After solid-solution treatment, the microstructure of the Mg-6Zn becomes more homogeneous, along with an elevated charge-transfer resistance in SBF and a reduced corrosion current density. After ageing treatment, the discrete intermetallic ,-MgZn phase enhances the cathodic hydrogen evolution and impairs the corrosion resistance of the alloy. Galvanic cells are expected on ageing, but the ageing process makes the microstructure of the alloy homogeneous. Heat treatment alters the in vitro degradation behavior of Mg-6Zn alloy and is applicable in adjusting the biodegradation rate. [source] Influence of Different Surface Machining Treatments of Magnesium-based Resorbable Implants on the Degradation Behavior in Rabbits,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Nina Von Der Höh The surface of magnesium,calcium implants (MgCa0.8) was differently treated which resulted in cylinders with smooth, sand-blasted, or threaded surface. These cylinders were implanted into the medial femoral condyle of New Zealand White rabbits. The degradation behavior and the reaction of the organism were assessed by clinical compatibility, radiographs, and µ -computed tomography. [source] Thermal and Photooxidative Degradation Behaviors of Poly(propylene)/SiO2 Nanocomposites with Various Polymer MorphologiesMACROMOLECULAR REACTION ENGINEERING, Issue 2 2008Ken-Ichi Sumino Abstract Photo- and thermal stabilities of poly(propylene) (PP)/SiO2 nanocomposites were studied by varying the particle size of the SiO2 nanoparticles. It was found that smaller SiO2 nanoparticles improved the stabilities of the nanocomposites by depressing the size of spherulites. The phenomenon was successfully explained within the infectious spreading model, where the spatial spreading of oxidation was delayed at the interfacial region between the spherulites. [source] Electrospun PEG,PLA nanofibrous membrane for sustained release of hydrophilic antibioticsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Xiuling Xu Abstract Reported in this study is the successful incorporation of a hydrophilic antibiotic drug, tetracycline hydrochloride (TCH), into electrospun PEG,PLA nanofibrous membrane without loss of its bioactivity. Degradation behavior of the copolymer was studied in vitro. Release behavior of TCH from the electrospun membrane and antimicrobial effects of the TCH-loaded membrane against Staphylococcus aureus culture were investigated. The medicated nanofibrous membrane demonstrated sustained release of TCH over 6 days and was found to be effective in inhibiting growth of S. aureus. In addition, increasing the antibiotic drug content in the electrospun membranes was found to enhance the anti-bacterial effectiveness of the medicated fiber mats. And the combination of mechanical barriers provided by the electrospun biodegradable nanofibrous membranes and their capability of local sustained delivery of antibiotics made these membranes more useful in biomedical applications, particularly as new wound dressings for ulcers caused by diabetes or other diseases, and to provide a better means of treatment for these malignant wounds and ulcers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Degradation behavior of nanoreinforced epoxy systems under pulse laserJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009M. Calhoun Abstract Nanocomposites using EPON 824 as their matrix were exposed to pulse laser at 532 nm for various time intervals. The developed nanomaterials used for this study were manufactured using EPON 824 with multiwalled carbon nanotubes (MWCNTs) at a loading rate of 0.15% by weight and nanoclays at a loading rate of 2% by weight as reinforcements. The effect of laser irradiation on polymer composites has been investigated. The degradation mechanism for the epoxy was of a laser induced burning nature. Of all specimens tested, the ultimate strength of the MWCNT-reinforced specimens decreased the most as a function of radiation time; the nanoclay-reinforced epoxy retained the most strength after 2 min of laser radiation. In addition, the threshold fluence for decomposition indicated that less energy was required to initiate decomposition in the MWCNT-reinforced epoxy than in the nanoclay-reinforced epoxy. This can be attributed to the high thermal conductivity of the carbon nanotubes. Measurement of surface damage in the material was observed via electron microscopy. Fourier transform infrared spectroscopy was used to investigate changes to the molecular structure as a function of exposure time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Peptide-doxorubicin conjugates specifically degraded by matrix metalloproteinases expressed from tumorDRUG DEVELOPMENT RESEARCH, Issue 5 2006Gee Young Lee Abstract Specific peptide-doxorubicin conjugates were developed for targeting matrix metalloproteinases (MMPs) expressed from tumors. The peptide-doxorubicin conjugates were designed to be cleaved by MMP-2 and MMP-9 in order that doxorubicin or the active form that acts as an anticancer agent was released free from the peptide fragment at the tumor site. Three types of peptide-doxorubicin conjugates were synthesized using the peptides: GPLG (Gly-Pro-Leu-Gly), GPLGV (Gly-Pro-Leu-Gly-Val), and GPLGPAG (Gly-Pro-Leu-Gly-Pro-Ala-Gly). The synthesized peptide-doxorubicin conjugates were characterized for their degradation behavior and bioactivity in vitro, and their antitumoral activity was assessed using the Lewis lung carcinoma (LLC) model, which expresses MMP-2 and MMP-9. After incubation with active MMP-2 for 24,h, GPLG-doxorubicin was barely degraded, whereas GPLGV-doxorubicin and GPLGPAG-doxorubicin were considerably degraded by active MMP-2. Consequently, all peptide-doxorubicin conjugates had significantly low cytotoxicity compared to doxorubicin, but tumor growth suppression was exhibited only by GPLGV-doxorubicin and GPLGPAG-doxorubicin. The tumor growth suppression by the two conjugates was higher compared to control, although it did not exceed the suppression level shown by doxorubicin. The low toxicity exhibited by peptide-doxorubicin conjugates resulted in only slight body weight loss in mice, whereas doxorubicin greatly reduced body weight and induced severe side effects. Therefore, we propose MMPs-specific peptide-doxorubicin conjugates in targeting anti-cancer drug delivery that could reduce systemic toxicities. Drug Dev. Res. 67:438,447, 2006. © 2006 Wiley-Liss, Inc. [source] Factors affecting the degradation of pharmaceuticals in agricultural soils,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2009Sara C. Monteiro Abstract Pharmaceuticals may be released to the soil environment through the application of biosolids to land. To understand those factors affecting the persistence of pharmaceuticals in the soil environment, the present study was performed to assess the effects of soil type, the presence of biosolids, and the impact of chemical mixture interactions on the degradation of three pharmaceuticals: naproxen, carbamazepine, and fluoxetine. Single-compound studies showed that naproxen degraded in a range of soils with half-lives ranging from 3.1 to 6.9 d and in biosolids with a half-life of 10.2 d. No relationships were observed between degradation rate and soil physicochemical properties and soil bioactivity. For naproxen, addition of biosolids to soils reduced the degradation rate observed in the soil-only studies, with half-lives in the soil-biosolid systems ranging from 3.9 to 15.1 d. Carbamazepine and fluoxetine were found to be persistent in soils, biosolids, and soil-biosolid mixtures. When degradation was assessed using a mixture of the three study compounds and the sulfonamide antibiotic sulfamethazine, the degradation behavior of fluoxetine and carbamazepine was similar to that observed in the single compound studies (i.e., no degradation). However, the degradation rate of naproxen in soils, biosolids, and soil-biosolid systems spiked with the mixture was significantly slower than in the single-compound studies. As degradation studies for risk assessment purposes are performed using single substances in soil-only studies, it is possible that current risk assessment procedures will underestimate environmental impacts. Further work is therefore warranted on a larger range of substances, soils, biosolid types, and chemical mixtures to better understand the fate of pharmaceuticals in terrestrial systems. [source] Influence of Heat Treatments on In Vitro Degradation Behavior of Mg-6Zn Alloy Studied by Electrochemical Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Shaoxiang Zhang The influence of heat treatment on the in vitro degradation of Mg-6Zn alloy is studied by electrochemical measurements. After solid-solution treatment, the microstructure of the Mg-6Zn becomes more homogeneous, along with an elevated charge-transfer resistance in SBF and a reduced corrosion current density. After ageing treatment, the discrete intermetallic ,-MgZn phase enhances the cathodic hydrogen evolution and impairs the corrosion resistance of the alloy. Galvanic cells are expected on ageing, but the ageing process makes the microstructure of the alloy homogeneous. Heat treatment alters the in vitro degradation behavior of Mg-6Zn alloy and is applicable in adjusting the biodegradation rate. [source] In Vitro Characteristics of Surface-Modified Biphasic Calcium Phosphate/Poly(L -Lactide) BiocompositeADVANCED ENGINEERING MATERIALS, Issue 4 2010Weizhong Yang Abstract Surface-modified biphasic calcium phosphate (BCP)/poly(L -lactide) (PLLA) biocomposite is shown to have improved microstructure and mechanical properties compared to the unmodified system. In vitro biodegradation and bioactivity of the composite are investigated in simulate body fluid for up to four weeks. Weight changes of the samples and the pH changes of the SBF are recorded. Surface properties of the composite after immersion are characterized by XRD, SEM and EDX analyses. Cyto-compatibility was determined by MTT assay with L929 mouse fibroblasts. The difference of the degradation behavior between modified BCP/PLLA and the reference unmodified composite are investigated, and mBCP/PLLA composite is proved to be a better as a scaffold material. The surface formed bio-apatite layer after immersion shows the excellent bioactivity of the mBCP/PLLA composite. L929 cells show a high growth rate and proliferation, demonstrating the good cytocompatibility of mBCP/PLLA composite. [source] Different Calcium Phosphate Granules for 3-D Printing of Bone Tissue Engineering Scaffolds,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Hermann Seitz The 3-D printing technique was used for the fabrication of HA, TCP and BCP ceramics and the influence of the granulate composition on the 3-D printed scaffolds was investigated. An optimal composition for 3-D printing granulates was found. Thus, individual implants can be manufactured via 3-D printing from different CaP phase compositions to tailor their degradation behavior and osteoconductivity for enhanced bone healing. [source] Modeling multi-stage decomposition of cotton fabrics considering char oxidation in the presence of oxygenFIRE AND MATERIALS, Issue 8 2009F. L. Zhu Abstract A theoretical model, describing thermal degradation behavior of cotton fabrics that exposed to a constant radiant heat flux, is proposed in the paper. The model describes thermal and oxidative degradation of cotton fabric under the oxygen-containing atmosphere and considers pseudo-bi-component separate-stage kinetic process. Both exothermic and endothermic reactions are included in the decomposition process. At present, gas phase oxidation reactions are not included. Comparison with experimental results demonstrates that the predictions of the mass loss rate and temperature profile with these cotton fabrics are in agreement with the experiment. Effects of thermal radiation and ambient oxygen concentration on decomposition have also been investigated. The gas phase temperature is also predicted by the present numerical model. Results from numerical model will help contribute to a better understanding of the ignition mechanism of flame-resistant cotton fabrics used for fire safety garments. Copyright © 2009 John Wiley & Sons, Ltd. [source] The Influence of , -Tricalcium Phosphate Nanoparticles and Microparticles on the Degradation of Poly(D,L -lactide-co-glycolide)ADVANCED MATERIALS, Issue 38-39 2009Zhijie Yang The in vitro degradation behavior of a series of resorbable, bioactive nano- and microcomposites designed for orthopaedic application is explored. Nanoparticles of , -tricalcium phosphate are significantly more effective than the equivalent microparticles in reducing heterogeneity of the poly(D,L -lactide-co-glycolide) degradation. More uniform degradation, reduced acid release, and less swelling of polymer were observed. [source] Knowledge-Based Approach towards Hydrolytic Degradation of Polymer-Based BiomaterialsADVANCED MATERIALS, Issue 32-33 2009Dieter Hofmann Abstract The concept of hydrolytically degradable biomaterials was developed to enable the design of temporary implants that substitute or fulfill a certain function as long as required to support (wound) healing processes or to control the release of drugs. Examples are surgical implants, e.g., sutures, or implantable drug depots for treatment of cancer. In both cases degradability can help to avoid a second surgical procedure for explanation. Although degradable surgical sutures are established in the clinical practice for more than 30 years, still more than 40% of surgical sutures applied in clinics today are nondegradable.1 A major limitation of the established degradable suture materials is the fact that their degradation behavior cannot reliably be predicted by applying existing experimental methodologies. Similar concerns also apply to other degradable implants. Therefore, a knowledge-based approach is clearly needed to overcome the described problems and to enable the tailored design of biodegradable polymer materials. In this Progress Report we describe two methods (as examples for tools for this fundamental approach): molecular modeling combining atomistic bulk interface models with quantum chemical studies and experimental investigations of macromolecule degradation in monolayers on Langmuir,Blodgett (LB) troughs. Finally, an outlook on related future research strategies is provided. [source] Thermal degradation behavior of poly(vinyl chloride) in the presence of poly(glycidyl methacrylate)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Magdy W. Sabaa Abstract The thermal degradation behavior of poly(vinyl chloride) (PVC) in presence of poly(glycidyl methacrylate) (PGMA) has been studied using continuous potentiometric determination of the evolved HCl gas from the degradation process from one hand and by evaluating the extent of discoloration of the degraded samples from the other. The efficiency of blending PGMA with dibasic lead carbonate (DBLC) conventional thermal stabilizer has also been investigated. A probable radical mechanism for the effect of PGMA on the thermal stabilization of PVC has been suggested based on data reported by FTIR and elemental analyses. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of chemical modifications on the thermal stability and degradation of banana fiber and banana fiber-reinforced phenol formaldehyde compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Seena Joseph Abstract Banana fiber has been modified by treatments with sodium hydroxide, silanes, cyanoethylation, heat treatment, and latex treatment and the thermal degradation behavior of the fiber was analyzed by thermogravimetry and derivative thermogravimetry analysis. Both treated and untreated fibers showed two-stage decomposition. All the treatments were found to increase the thermal stability of the fiber due to the physical and chemical changes induced by the treatments. The thermal degradation of treated and untreated banana fiber-reinforced phenol formaldehyde composites has also been analyzed. It was found that the thermal stability of the composites was much higher than that of fibers but they are less stable compared to neat PF resin matrix. Composite samples were found to have four-stage degradation. The NaOH treated fiber-reinforced composites have very good fiber/matrix adhesion and hence improvement in thermal stability is observed. Though both silane treatments increased the thermal stability of the composite the vinyl silane is found to be more effective. Heat treatment improves the crystallinity of the fiber and decreases the moisture content, hence an improved thermal stability. The latex treatment and cyanoethylation make the fiber surface hydrophobic, here also the composite is thermally more stable than untreated one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Electrospinning of degradable elastomeric nanofibers with various morphology and their interaction with human fibroblastsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Erik Borg Abstract Artelon® (degradable poly(urethane urea) elastomer) was electrospun into scaffolds for tissue engineering. The diameter of the electrospun fibers, studied by scanning electron microscopy, ranged from 100 nm to a few ,m, with an average diameter of 750 nm. The molar mass of the polymer had a major influence on the morphology of the scaffold. Furthermore, aging of the polymer solution caused changes in viscosity, as measured by stress sweeps between 13.5,942 Pa that affected the morphology. The electrospun Artelon mats exhibited about the same elongations to break, both exceeding 200%, measured by tensile tests. The degradation study showed similar degradation behavior in electrospun mats and solids. In vitro study showed that human fibroblasts not only adhere to the surface but also migrate, proliferate, and produce components of an extracellular matrix. These results strongly support the use of electrospun Artelon as a scaffold in tissue engineering. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis of a magnesium/aluminum/iron layered double hydroxide and its flammability characteristics in halogen-free, flame-retardant ethylene/vinyl acetate copolymer compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Chuan-Mei Jiao Abstract Mg,Al,Fe ternary hydrotalcites were synthesized by a coprecipitation method and characterized with powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The flame-retardant effects of Mg/Al,CO3 layered double hydroxides (LDHs) and Mg/Al/Fe,CO3 LDHs in an ethylene/vinyl acetate copolymer (EVA) were studied with the limited oxygen index (LOI), the UL-94 test, and the cone calorimeter test (CCT), and the thermal degradation behavior of the composites was examined by thermogravimetric analysis. The results showed that the LOI values of the EVA/(Mg/Al/Fe,CO3 LDH) composites were basically higher than those of the EVA/(Mg/Al,CO3 LDH) composites at the same additive level. In the UL-94 test, there was no rating for the EVA/(Mg/Al,CO3 LDH) composite at the 50% additive level, and a dripping phenomenon occurred. However, the EVA/(Mg/Al/Fe,CO3 LDH) composites at the same loading level of LDHs containing a suitable amount of Fe3+ ion reached the V-0 rating, the dripping phenomenon disappearing. The CCTs indicated that the heat release rate (HRR) of the EVA composites with Mg/Al/Fe,CO3 LDHs containing a suitable amount of Fe3+ decreased greatly in comparison with that of the composites with Mg/Al,CO3 LDHs. The introduction of a given amount of Fe3+ ion into Mg/Al,CO3 LDHs resulted in an increase in the LOI, a decrease in the HRR, and the achievement of the UL-94 V-0 rating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of filler content and size on the properties of ethylene vinyl acetate copolymer,wood fiber compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007D. G. Dikobe Abstract In this study, the main focus was on the effect of wood fiber (WF) content and particle size on the morphology and mechanical, thermal, and water-absorption properties of uncompatibilized and ethylene glycidyl methacrylate copolymer (EGMA) compatibilized ethylene vinyl acetate copolymer,WF composites. For uncompatibilized composites, the tensile strength decreased with increasing WF content, whereas for compatibilized composites, the tensile strength initially decreased, but it increased for composites containing more than 5% WF. Small-WF-particle-containing composites had higher tensile strengths than composites containing larger WF particles, both in the presence and absence of EGMA. WF particle size did not seem to have much influence on the degradation behavior of the composites, whereas water absorption by the composites seemed to be higher in composites with smaller particle sizes for both compatibilized and uncompatibilized composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3645,3654, 2007 [source] Synthesis and evaluation of novel injectable and biodegradable polyglycolide-based compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007Dong Xie Abstract Novel 3-arm methacrylate-endcapped biodegradable polyglycolide prepolymer was synthesized and characterized. Injectable and in situ curable composites formulated with the liquid prepolymer and bioabsorbable ,-tricalcium phosphate were prepared. The pastelike composites were cured at room temperature using a redox-initiation system. The initial compressive strengths (CSs), curing time, exotherm, and degree of conversion of the cured composites were determined. The composites showed initial yield CS ranging from 20.1 to 92.3 MPa, modulus from 0.73 to 5.65GPa, ultimate strength from 119.9 to 310.5 MPa, and toughness from 630 to 3930 N mm. Increasing filler content increased yield strength and modulus but decreased ultimate strength and toughness. Diametral tensile strength test showed the same trend as did CS test. Increasing filler content also increased curing time but decreased exotherm and degree of conversion. During the course of degradation, all the materials showed a significant burst degradation behavior within 24 h, followed by a significant increase in strength between Day 1 and Day 3, and then continuous degradation until no strength was detected. The composites with higher filler content retained their strengths longer but those with lower filler contents lost their strengths in 45 or 60 days. The degradation rate is filler-content dependent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2977,2984, 2007 [source] Control of surface free energy in titanium doped phosphate based glasses by co-doping with zincJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Ensanya Ali Abou Neel Abstract To significantly improve the biocompatibility of titanium doped phosphate based glasses, codoping with zinc has been attempted. This study investigated the effect of doping a quaternary 15Na2O:30CaO:5TiO2:50P2O5 glass with zinc oxide (1, 3, and 5 mol %) on bulk, structural, surface, and biological properties; the results were compared with glasses free from ZnO and/or TiO2. ZnO as adjunct to TiO2 was effective in changing density, interchain bond forces, degradation behavior, and ions released from the degrading glasses. Incorporation of both TiO2 and ZnO in T5Z1, T5Z3, and T5Z5 glasses reduced the level of Zn2+ release by two to three orders of magnitude compared with glasses containing ZnO only (Z5). 31P NMR results for T5Z1, T5Z3, and T5Z5 glasses showed the presence of Q3 species suggesting that the TiO2 is acting as a network former, and the phosphate network becomes slightly more connected with increasing ZnO incorporation. Regardless of their relative lower hydrophilicity and surface reactivity compared with the control glass free from TiO2 and ZnO (T0Z0), these glasses have significantly higher surface reactivity compared with Thermanox®. This has been also reflected in the maintenance of >98% viable Osteoblasts, proliferation rate, and expression level of osteoblastic marker genes in a comparable manner to Thermanox® and T5 glasses, particularly T5Z1 and T5Z3 glasses. However, T0Z0 and Z5 glasses showed significantly reduced viability compared to Thermanox®. Therefore, it can be concluded that ZnO doped titanium phosphate glasses, T5Z1 and T5Z3 in particular, can be promising substrates for bone tissue engineering applications. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Synthesis, characterization, and in vitro degradation of liquid-crystalline terpolyesters of 4-hydroxyphenylacetic acid/3-(4-hydroxyphenyl)propionic acid with terephthalic acid and 2,6-naphthalene diolJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2002V. S. Prasad Abstract Melt-processable liquid-crystalline terpolyesters of 4-hydroxyphenylacetic acid (HPAA) and 3-(4-hydroxyphenyl)propionic acid (HPPA) with terephthalic acid and 2,6-naphthalene diol were synthesized by one-step acidolysis melt polycondensation followed by postpolymerization and were characterized with viscosity studies, Fourier transform infrared (FTIR) and NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarized light microscopy, and wide-angle X-ray diffraction. The melting behaviors and liquid-crystalline transition temperatures of the terpolyesters were dependent on the composition of the HPAA/HPPA content. The transition temperatures of the polyesters could be effectively reduced by the introduction of an even number of built-in short methylene spacers in combination with the 2,6-naphthalene offset structure. A terpolyester with an HPPA content of 33% (NTP33) showed optimum properties for the glass-transition temperature, around 71 °C, and the melting temperature, near 240 °C, with a Schlieren nematic texture. The polymer showed excellent flow behavior in a Brabender plasticorder. It was also thermally stable up to 400 °C. NTP33 showed 2.5% in vitro hydrolytic degradation in buffer solutions of pH 10 at 60 °C after 540 h. Considerable enzymatic degradation was also observed with porcine pancreas lipase/buffer solutions in comparison with Candida rugosa lipase after 60 days. The degradation was also followed with FTIR, DSC, and TGA. Apart from the temperature and pH of the buffer solution, several structural parameters, such as the aromatic content, crystallinity percentage, and composition of the polymer, affected the degradation behavior. FTIR studies indicated the involvement of chain scission during degradation. Scanning electron microscopy studies further showed that surface erosion also played a major role in the degradation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1845,1857, 2002 [source] Electrode,Ceramic Inter-Diffusion of Ba(Ti,Zr)O3 -Based Y5V MLCCs with Ni ElectrodesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Lei Chen The Ba(Ti,Zr)O3 -based multilayer ceramic capacitors (MLCCs) with Ni electrodes, which meet the Electronic Industry Association Y5V standard (from ,30° to 85°C, at a temperature capacitance coefficient between ,82% and 22%), have been studied in view of the electrode-ceramic inter-diffusion by several microstructual techniques (scanning electron microscopy/transmission electron microscopy/high-resolution transmission electron microscopy (HRTEM)) with an energy-dispersive X-ray spectrometer (EDS). The EDS analysis shows that the elements' inter-diffusion took place along the metal,dielectric interface and the migration of Ni toward the dielectric layers dominated this process. The incorporation of Ni did not transform the crystal structure but introduced lattice distortions, which were characterized by HRTEM, X-ray diffraction, and EDS. The degree of Ni diffusion in the sample with the thinner dielectric layer was more severe. It was concluded from the results that the Ni diffusion is related to the formation of oxygen vacancies after the annealing process, which should be a noticeable factor in the degradation behavior and reliability of base metal electrode MLCCs. The factors influencing the inter-diffusion are also discussed. [source] AB-polymer Networks with Cooligoester and Poly(n -butyl acrylate) Segments as a Multifunctional Matrix for Controlled Drug ReleaseMACROMOLECULAR BIOSCIENCE, Issue 9 2010Christian Wischke Abstract Semi-crystalline AB-copolymer networks from oligo[(, -caprolactone)- co -glycolide]dimethacrylates and n -butylacrylate have recently been shown to exhibit a shape-memory functionality, which may be used for self-deploying and anchoring of implants. In this study, a family of such materials differing in their molar glycolide contents ,G was investigated to determine structure,property functional relationships of unloaded and drug loaded specimens. Drug loading and release were evaluated, as well as their degradation behavior in vitro and in vivo. Higher ,G resulted in higher loading levels by swelling and a faster release of ethacridine lactate, lower melting temperature of polymer crystallites, and a decrease in shape fixity ratio of the programmed temporary shape. For unloaded networks, the material behavior in vivo was independent of the mechanical load associated with different implantation sites and agreed well with data from in vitro degradation studies. Thus, AB networks could be used as novel matrices for biofunctional implants, e.g., for urogenital applications, which can self-anchor in vivo and provide mechanical support, release drugs, and finally degrade in the body to excretable fragments. [source] in vitro Evaluation of Biodegradable Poly(butylene succinate) as a Novel BiomaterialMACROMOLECULAR BIOSCIENCE, Issue 5 2005Haiyan Li Abstract Summary: Poly(butylene succinate) (PBSU) can be easily synthesized by condensation polymerization of the starting materials of succinic acid and butan-1,4-diol. It has good degradability and possesses excellent processability. Due to these advantages, PBSU was first evaluated in the present study for its potential application as a novel biomaterial. The in vitro biocompatibility of the PBSU was evaluated by monitoring proliferation and differentiation of osteoblasts cultured on the PBSU film substrates for different periods. The results showed that the PBSU was biocompatible as the osteoblasts could proliferate and differentiate on the PBSU plates. In addition, the hydrolytic degradation behavior of the PBSU films in the phosphate-buffered saline (PBS) was also investigated and the results suggested that the PBSU degraded in the PBS solution with the same behavior as that of the degradable poly(, -hydroxyesters). In addition to the biocompatibility and hydrolytic degradation, some physical properties, including hydrophilicity, and mechanical and thermal properties of the PBSU substrates, were also determined and the results revealed that the PBSU was hydrophilic and ductile with excellent processability. The biocompatibility of the PBSU, together with the advantages of hydrolytic degradability, hydrophilicity, and excellent processability, indicated that PBSU has the potential to be used as a biomaterial for tissue repair. Alkaline phosphate activity of osteoblasts cultured on PBSU and TCPS substrates for different time periods. [source] Thermal Behavior of Isotactic Poly(propylene)/Maleated Poly(propylene) BlendsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2007Catalin Vîlcu Abstract This paper analyzes the thermal and thermo-oxidative degradation behavior, phase separation, melting, and crystallization of blends consisting of isotactic poly(propylene) (IPP) and poly(propylene) grafted with maleic anhydride (PP- g -MA). It has been established that, depending on the blend composition and crystallization/preparation procedure, the blends of IPP and PP- g -MA can either co-crystallize or evidence phase separation. This conclusion has been attained by comparing the DSC results of crystallization under dynamic and isothermal conditions with X-ray diffraction results. On the basis of the obtained results, the optimum mixing ratios have been established as 95,85 wt.-% IPP/5,15 wt.-% PP- g -MA. Thermo-oxidative behavior has been studied by thermogravimetry and differential thermal analysis. [source] A Kinetic Study on the Thermal Degradation of Multi-Walled Carbon Nanotubes-Reinforced Poly(propylene) CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2004Min-Kang Seo Abstract Summary: The influence of the multi-walled carbon nanotubes (MWNTs) content on the thermal degradation behavior of MWNTs-reinforced poly(propylene) (PP) composites was investigated by using non-isothermal thermogravimetric analysis (TGA). Kinetic parameters of degradation were evaluated by using the Flynn-Wall-Ozawa iso-conversional method and the pseudo first-order method. As a result, compared with pristine PP, MWNTs-PP nanocomposites have lower peak temperatures of degradation, narrower degradation temperature ranges and a higher amount of residual weight at the end of the degradation, which is likely to be a result of specific interactions between complimentary functional groups. The values of the reaction order of MWNTs-PP nanocomposites determined by the Kissinger method are close to 1 in the non-isothermal degradation process. There is a good correlation between the Ea in region II and the peak temperature of degradation for the composites. Activation energies for degradation of different contents of MWNTs-filled PP nanocomposites as a function of conversion. [source] Beurteilung von Loten und Lötverbindungen unter dem Einfluss steigender Kupfergehalte in verunreinigten bleifreien LotbädernMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 1 2008B. Wielage Lead-free solders; phase selection; deep-etching; intermetallic compounds Abstract Zuverlässigkeit und Degradationsverhalten bleifreier Lote sind aufgrund von Widersprüchlichkeiten und notwendiger Problemlösungen nach wie vor Aspekte weiterer Untersuchungen. Die vorliegende Arbeit zeigt anhand von Phasenselektion der intermetallischen Phasen Ag3Sn und Cu6Sn5 sowie (Cu,Ni)6Sn5 und (Ni,Cu)3Sn4 morphologisch-mikrostrukturelle Zusammenhänge in Verbindung mit mechanischen Eigenschaften auf. Dazu wurden insbesondere das metallografische Tiefätzen und die instrumentierte Eindringprüfung genutzt. Die Lotlegierungen SnAg3,8CuX und SnCuXNi0,07 und deren Lötverbindungen wurden durch verschiedene Methoden komplex evaluiert. Es konnte nachgewiesen werden, dass das Zulegieren von Nickel als degradationsvermindernde Maßnahme des Kupfer-Leachings zur Versprödung der Legierung durch das Wachstum der Phase (Cu,Ni)6Sn5 führen kann. Evaluation of solders and solder joints processed in lead free solder baths with increasing copper content Reliability and degradation behavior of lead-free solders are due to contradictions and necessary problem solving remaining aspects of further investigations. This paper shows morphologic and microstructural relationships in conjunction with mechanical properties on the intermetallic phases Ag3Sn and Cu6Sn5 as well as (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4. In particular, the methods of metallographic deep-etching and the instrumented indentation hardness test were applied. The solders SnAg3,8CuX and SnCuXNi0,07 and their solder joints were comprehensively evaluated by various methods. It has been shown that alloying with nickel as a method of decreasing copper-leaching can induce embrittlement by growth of the (Cu,Ni)6Sn5 phase. [source] Effects of synthesis conditions on crystal morphological structures and thermal degradation behavior of hydrotalcites and flame retardant and mechanical properties of EVA/hydrotalcite blendsPOLYMER COMPOSITES, Issue 2 2007Longchao Du The effects of synthesis methods and reaction conditions on the crystal morphological structures and thermal degradation behavior of hydrotalcites have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analysis (PSA), and differential thermal analysis (DTA). The flame retardant and mechanical properties of ethylene,vinyl acetate (EVA) blends with the corresponding hydrotalcites have been estimated by limiting oxygen index (LOI), UL-94, and mechanical measurements. The results from the XRD, TEM, and PSA demonstrate that the hydrotalcites synthesized by ultrasound method have larger crystal sizes and particle size distribution than those by mechanical stirring method. Higher reaction temperature, longer dripping time, and lower solution concentration can increase the crystal and particle sizes of ultrasound-synthesized hydrotalcites, whereas the longer ultrasound aging time can increase the crystal sizes and decrease the particle sizes of hydrotalcites because of the smashing conglomeration. The DTA data give a positive evidence that the hydrotalcite samples prepared by mechanical stirring method with longer alkaline dripping time have higher thermal degradation temperature than those by ultrasound method, since the ultrasound-synthesized hydrotalcites have more lattice defects than stirring-prepared hydrotalcites. The data from LOI, UL-94, and mechanical tests show that the ultrasonic-synthesized hydrotalcites have better flame retardant properties, whereas the stirring-synthesized hydrotalcites have better tensile strength in the EVA/hydrotalcite blends. POLYM. COMPOS., 28:131,138, 2007. © 2007 Society of Plastics Engineers [source] Relationship among drug delivery behavior, degradation behavior and morphology of copolylactones derived from glycolide, l -lactide and ,-caprolactonePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2002Qing Cai Abstract A series of copolylactones was synthesized by ring-opening copolymerization of glycolide, L -lactide and ,-caprolactone, using stannous octoate as catalyst. The in vitro degradation behaviors of them were studied and data demonstrated different degradation rates which mainly depended on the compositions. Investigation of the 5-fluorouracil (5-Fu) release from these copolylactones revealed that the composition, degradation rate and the morphology of the polymeric matrix played an important role on the drug release kinetics. A sustained 5-Fu release without initial time lag was obtained from random poly(lactide-co-glycolide-co-caprolactone) (r-PGLC) drug carrier, and it differed from the cases of polylactide (PLA) or random poly(lactide-co-glycolide) (PLGA), which usually showed an initial time lag or biphasic drug release behavior. It was due to the low glass transition temperature (Tg) of the r-PGLC and the drug would diffuse faster in rubbery state under the experimental temperature. Furthermore, a significant change in the drug release behavior of r-PGLC was observed when the temperatures were changed around the Tg of the drug carrier, which implied that the drug release behavior could be regulated by adjusting the morphology of the drug carrier. Copyright © 2002 John Wiley & Sons, Ltd. [source] Thermally induced intramolecular oxygen migration of N -oxides in atmospheric pressure chemical ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2010Xin Wang N -Oxides are known to undergo three main thermal degradation reactions, namely deoxygenation, Cope elimination (for N -oxides containing a ,-hydrogen) and Meisenheimer rearrangement, in atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The ions corresponding to these thermal degradants observed in the ensuing APCI mass spectra have been used to identify N -oxides as well as to determine the N -oxidation site when the analyte contains multiple tertiary amine groups. In this paper, we report a thermally induced oxygen migration from one N -oxide amine to another tert -amine group present in the same molecule through a six-membered ring transition state during APCI-MS analysis. The observed intramolecular oxygen migration resulted in the formation of a new isomeric N -oxide, rendering the results of the APCI-MS analysis more difficult to interpret and potentially misleading. In addition, we observed novel degradation behavior that happened after the Meisenheimer rearrangement of the newly formed N -oxide: a homolytic cleavage of the NO bond instead of elimination of an aldehyde or a ketone that usually follows the rearrangement. Understanding of these unusual degradation pathways, which have not been reported previously, should facilitate structural elucidation of N -oxides using APCI-MS analysis. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||