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991.
The synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present,but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas-phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V-1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties. 相似文献
992.
The presence of cocaine on US paper currency has been known for a long time. Banknotes become contaminated during the exchange, storage, and abuse of cocaine. The analysis of cocaine on various denominations of US banknotes in the general circulation can provide law enforcement circles and forensic epidemiologists objective and timely information on epidemiology of illicit drug use and on how to differentiate money contaminated in the general circulation from banknotes used in drug transaction. A simple, nondestructive, and accurate capillary gas chromatographic method has been developed for the determination of cocaine on various denominations of US banknotes in this study. The method comprises a fast ultrasonic extraction using water as a solvent followed by a SPE cleanup process with a C(18) cartridge and capillary GC separation, identification, and quantification. This nondestructive analytical method has been successfully applied to determine the cocaine contamination in US paper currency of all denominations. Standard calibration curve was linear over the concentration range from the LOQ (2.00 ng/mL) to 100 microg/mL and the RSD less than 2.0%. Cocaine was detected in 67% of the circulated banknotes collected in Southeastern Massachusetts in amounts ranging from approximately 2 ng to 49.4 microg per note. On average, $5, 10, 20, and 50 denominations contain higher amounts of cocaine than $1 and 100 denominations of US banknotes. 相似文献
993.
R. M. Laine M. Roll M. Asuncion S. Sulaiman V. Popova D. Bartz D. J. Krug P. H. Mutin 《Journal of Sol-Gel Science and Technology》2008,46(3):335-347
Cubic silsesquioxanes (SQs) offer perfect and nearly perfect 3-D symmetry with eight functional groups with each functional
group occupying a different octant in Cartesian space. This paper is concerned with the synthesis of both highly symmetrical
octa-monofunctional SQs and statistically bifunctional SQs wherein because of similar properties each functionality separates
to one side of the cubically symmetric SQ giving Janus-like behavior. In the latter case we find these materials to offer
novel properties of use in making both coatings with controlled contact angles ranging from 50–120 °C, with hardnesses (pencil)
as high as 6H and the opportunity to make layer-by-layer coatings. 相似文献
994.
Chang Sool Kim Eun Kyung Park Sun-Geon Kim 《Journal of Sol-Gel Science and Technology》2008,47(1):7-15
Silver–silica nanostructured composites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing
silver nitrate. The physical and chemical characteristics of the composites prepared at different Ag/Si atomic ratio in the
sols and temperatures of pyrolysis were examined by TEM, SEM, XRD, FT-IR and UV-visible spectra. For the low silver ratios
up to 0.2, well-dispersed silver particles were produced in the pore of the silica agglomerates with their size and surface
plasmon resonance depending on the pore size and silver mobility, in addition to the loading and temperature. The formation
of silver silicate and new-phase silica as well as crystallinity of the silver prepared was discussed. There was also explained
how the temperature of preparation affected the morphologies of the composites produced with higher Ag/Si ratios greater than
1. Mechanism on the formation of silver–silica composites was proposed for the wide range of the ratios from 0.01 to 3. 相似文献
995.
Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system 总被引:4,自引:0,他引:4
The effects of lanthanum oxide (La2O3) as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (IFR-PP) were studied, and the new IFR system mainly consisted of the charring-foaming agent (CFA) and ammonium polyphosphate (APP). The limiting oxygen index (LOI), UL-94 test, thermogravimetric analysis (TGA), cone calorimeter (CONE) and scanning electron microscopy (SEM) were used to evaluate the synergistic effects of La2O3. It was found that when IFR was fixed at 20 wt% in IFR-PP composites, only a little amount of La2O3 could enhance LOI value and pass the UL-94 V0 rating test (1.6 mm). The TGA data showed that La2O3 could enhance the thermal stability of the IFR-PP systems at high temperature and effectively increase the char residue formation. The CONE results revealed that La2O3 and IFR could clearly change the decomposition behavior of PP and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSP), ignition time (IT) and so on. The morphological structures observed by SEM demonstrated that La2O3 could promote to form the homogenous and compact intumescent char layer. Thus, a suitable amount of La2O3 plays a synergistic effect in the flame retardancy and smoke suppression of IFR composites. 相似文献
996.
The usefulness of the secondary line at 252.744 nm and the approach of side pixel registration were evaluated for the development of a method for sequential multi-element determination of Cu, Fe, Mn and Zn in soil extracts by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). The influence of side pixel registration on the sensitivity and linearity was investigated by measuring at wings (248.325, 248.323, 248.321, 248.329, and 248.332 nm) of the main line for Fe at 248.327 nm. For the secondary line at 252.744 nm or side pixel registration at 248.325 nm, main lines for Cu (324.754 nm), Mn (279.482 nm) and Zn (213.875 nm), sample flow-rate of 5.0 mL min−1 and calibration by matrix matching, analytical curves in the 0.2-1.0 mg L−1 Cu, 1.0-20.0 mg L−1 Fe, 0.2-2.0 mg L−1 Mn, 0.1-1.0 mg L−1 Zn ranges were obtained with linear correlations better than 0.998. The proposed method was applied to seven soil samples and two soil reference materials (IAC 277; IAC 280). Results were in agreement at a 95% confidence level (paired t-test) with reference values. Recoveries of analytes added to soil extracts containing 0.15 and 0.30 mg L−1 Cu, 7.0 and 14 mg L−1 Fe, 0.60 and 1.20 mg L−1 Mn, 0.07 and 0.15 mg L−1 Zn, varied within the 94-99, 92-98, 93-101, and 93-103% intervals, respectively. The relative standard deviations (n = 12) were 2.7% (Cu), 1.4% (Fe - 252.744 nm), 5.7% (Fe - 248.325 nm), 3.2% (Mn) and 2.8% (Zn) for an extract containing 0.35 mg L−1 Cu, 14 mg L−1 Fe, 1.1 mg L−1 Mn and 0.12 mg L−1 Zn. Detection limits were 5.4 μg L−1 Cu, 55 μg L−1 Fe (252.744 nm), 147 μg L−1 Fe (248.325 nm), 3.0 μg L−1 Mn and 4.2 μg L−1 Zn. 相似文献
997.
Solà Vázquez A Costa-Fernandez JM Ruiz Encinar J Pereiro R Sanz-Medel A 《Analytica chimica acta》2008,623(2):140-145
The impact of brominated flame retardants (BFRs) on the environment and their potential risk in animal and human health is a present concern. Therefore, existing legislation in the European Union demands that polymers with BFRs are identified and eliminated from the recycling process due to their potential health hazard.In this work, a flow-injection (FI) system coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was optimized for the detection of traces of bromine in polymers, plastic paints and enamels containing BFRs. Sample preparation requires a microwave-assisted digestion in order to transfer bromine in polymeric samples to solution. After appropriate optimization of the digestion procedure and the ICP-MS detection, a detection limit (DL) of 4.2 mg kg−1 was obtained for synthesized polyurethane standards containing known concentrations of bromine. The precision of the proposed method, evaluated as the R.S.D. of signals obtained for three replicates of polymeric standard BFRs at the normative EU level, was as low as 3.6%.This simple developed methodology was characterized for the screening of bromine in polymeric matrices. The proposed system provides rapid binary yes/no overall responses, being appropriate for the screening of bromine above a pre-set concentration threshold. The unreliability region (UR), given by the probability of false positives and false negatives (set at 5% in both cases), was in the range between 442 and 678 mg kg−1 of bromine (at a cut-off level of 0.1% in BFRs by weight of homogeneous material fixed by the EU normative). Finally, the applicability of the proposed screening system was tested for the reliable control of bromine in different commercial samples including flame-retardant paints and enamels. 相似文献
998.
In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol−1 scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol−1. 相似文献
999.
The flammability behavior of the system polyamide 6 (PA 6) + melamine cyanurate (MC) with or without organically modified layered montmorillonite (OMMT) or sodium montmorillonite (Na+MMT) was studied. The high degree of flame retardancy (FR) obtained with 13 wt% MC is maintained upon adding up to 0.2 wt% OMMT or Na+MMT. Increase mass % of OMMT is antagonistic to the MC effect. The rate of dripping decreases while the size and mass of drops in the UL‐94 tests increases with increasing wt% OMMT indicating increase in viscosity of the melt and decrease in the rate of sublimation of melamine. Addition of poly vinyl pyrrolidone (PVP) decreases the viscosity and partially restores the FR rating. Na+MMT does not increase the viscosity and the FR ratings are partially preserved. The peak of heat release rate (PHRR) in the cone calorimeter decreases with increased loading of OMMT. Addition of Na+MMT or PVP has little influence on the PHRR. The time of ignition decreases with increase in OMMT, but is not affected when Na+MMT is used. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. Mechanistic considerations are presented. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
1000.
Melamine salt of tripentaerythriol phosphate (MTP), as a new intumescent flame‐retardant, was prepared from tripentaerythritol (TPE), polyphosphoric acid, phosphoric pentoxide, and melamine, and then incorporated into polypropylene (PP) to obtain flame‐retarded PP‐MTP. FT‐IR analysis showed that MTP was in the form of cage structure. The flammability, combustion behavior, and thermal degradation and stability of flame‐retarded PP were characterized by using LOI, UL‐94 test, cone calorimetry, and TGA, respectively. By SEM, the char structure of PP‐MTP was analyzed. XRD diffraction tests showed that PP‐matrix of PP‐MTP presented better crystallized phases, when MTP was modified by methyl hydrogen siloxane. The relations of the dispersion of MTP in PP matrix to the compatibility between PP and MTP, and to the flame retardancy were discussed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献