Search results for " Plastics"
showing 10 items of 2628 documents
Behavior of Calcium Phosphate–Chitosan–Collagen Composite Coating on AISI 304 for Orthopedic Applications
2022
Calcium phosphate/chitosan/collagen composite coating on AISI 304 stainless steel was investigated. Coatings were realized by galvanic coupling that occurs without an external power supply because it begins with the coupling between two metals with different standard electrochemical potentials. The process consists of the co-deposition of the three components with the calcium phosphate crystals incorporated into the polymeric composite of chitosan and collagen. Physical-chemical characterizations of the samples were executed to evaluate morphology and chemical composition. Morphological analyses have shown that the surface of the stainless steel is covered by the deposit, which has a very r…
Increased conformational rigidity of humic substances by oxidative biomimetic catalysis
2005
A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed …
Copolymerization of Ethylene with Selected Vinyl Monomers Catalyzed by Group 4 Metal and Vanadium Complexes with Multidentate Ligands: A Short Review
2021
This paper gives a short overview of homogeneous post-metallocene catalysts based on group 4 metal and vanadium complexes bearing multidentate ligands. It summarizes the catalytic behavior of those catalysts in copolymerization of ethylene with 1-olefins, with styrenic monomers and with α,ω-alkenols. The review is focused on finding correlations between the structure of a complex, its catalyst activity and comonomer incorporation ability, as well as the microstructure of the copolymer chains.
Growing Like Germany: Local Public Debt, Local Banks, Low Private Investment
2021
The paper uses a panel of more than 1m German firms over 2010-2016, to provide the first firm-bank level evidence of local crowding out for a developed economy characterized by low interest rates and fiscal austerity. Our mechanism relies on two structural features of Germany's banking landscape: the local segmentation of credit markets for small and medium-sized firms (SME) and the role of local public banks in local public finance. Local public banks dominate lending to small and medium firms in Germany and also have an explicit mandate to lend to the local public sector. With spreads on local government debt at all-time lows, local public banks tried to break even, using their market pow…
Synthesis and characterization of ethylene-1-hexene copolymers prepared by using MgCl2(THF)2-supported Ziegler-Natta catalysts
2000
Ethylene was copolymerized with 1-hexene over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated with Et2AlCl. So far these catalyst systems have not been known as initiators of ethylene-1-hexene copolymerization. The vanadium catalysts were more active than the titanium catalyst and, at identical comonomer concentrations in the feed, gave rise to a greater incorporation of 1-hexene into the copolymer. Even at relatively low fractions of 1-hexene, the MgCl2(THF)2-supported catalysts affected much the copolymer properties like density, melting point and crystallinity.
Polytetrafluoroethylene Films in Rigid Polyurethane Foams' Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor.
2021
As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation…
Data from an international multi-centre Study of Statistics and Mathematics Anxieties and Related Variables in University Students (the SMARVUS Datas…
2023
This large, international dataset contains survey responses from N = 12,570 students from 100 universities in 35 countries, collected in 21 languages. We measured anxieties (statistics, mathematics, test, trait, social interaction, performance, creativity, intolerance of uncertainty, and fear of negative evaluation), self-efficacy, persistence, and the cognitive reflection test, and collected demographics, previous mathematics grades, self-reported and official statistics grades, and statistics module details. Data reuse potential is broad, including testing links between anxieties and statistics/mathematics education factors, and examining instruments’ psychometric properties across differ…
Toward Anticancer Immunotherapeutics: Well-Defined Polymer-Antibody Conjugates for Selective Dendritic Cell Targeting
2014
This paper describes the synthesis of semitelechelic maleimide-modified N-(2-hydroxypropyl)methacrylamid) (HPMA) based polymers of narrow dispersity that can be conjugated e.g. to anti-DEC-205 antibodies affording "star-like" topologies (one antibody decorated with several polymer chains). FCS revealed a hydrodynamic diameter of R(h) = 7.9 nm and SEC narrow dispersity (1.45). Primary in vitro studies with bone marrow derived dendritic cells (DC) show higher cellular binding and uptake rates compared to control samples. Moreover, incubating these conjugates to primary splenocytes demonstrates a much higher affinity to the primary DCs than to any other immune cell population within the splee…
Evaluation of radiation stability of electron beam irradiated Nafion® and sulfonated poly(ether ether ketone) membranes
2022
Proton exchange membranes (PEM), which have been commonly used in fuel cells have raised interest for the application in harsh environments involving ionizing radiation. Therefore, radiation stability and ability to sustain their functionality under the radiation environment are of great interest. Within this study, electron beam irradiation in dose range from 50 to 500kGy was used to evaluate the effects of radiation on the physico-chemical and mechanical properties of two types of PEM: commercial Nafion®117 and sulfonated poly(ether-ether-ketone) (SPEEK) with high degree of sulfonation (DS = 0.75±0.5). SPEEK membrane presented higher mechanical and thermal stability compared to that of Na…
Caffeine analysis and extraction from a topical cream intended for UV-skin protection
2020
Made available in DSpace on 2021-06-25T10:16:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 This study aimed to develop and validate a method for the analysis of caffeine in complex cosmetic samples, such as sunscreens. Besides, an extraction method of caffeine from coffee oil and from creams, which contains both lipophilic and hydrophilic components, has been developed. The method to analyze caffeine was developed using an isocratic pump, Waters 1515 and an automatic injector Perkin-Elmer Series 200 and an UV detector Perkin-Elmer. As stationary phase, Kromasil C-18 (150 × 4.6 mm ID with particle size of 5 µm) column was used and a mixture of water (pH 4.00)/acetonitrile (…