Thermal analysis of light-curing composites

The aim of this study has been to evaluate light-curing composites polymerization quality (monomer/polymer) with an halogen and diode lamp through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 50 s through a constant and a soft start polymerization and, subsequently, analyzed by TG-DTA. The TG/DTA analysis shows that different light-curing times affect the degree of conversion of the composite, since by increasing the curing time the quantity of the monomer that has not reacted (residual) decreases. The halogen lamp, compared to the diode lamp, produces a lower mass loss at 20 s, while for 40 and 50 s the results are overlapping. The soft start polymerization (20 s) initially produces a higher mass loss, if compared to the constant intensity, but, by performing a polymerization for at least 40 s, the results can be overlapped.     

Evaluation of composites light-curing at different times and distances of irradiation

The aim of this study is to evaluate light-curing composites polymerization quality (monomer/polymer) carried out at different times and distances of irradiation through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 60 s (0-2-4-6-8 mm) through a constant polymerization and subsequently analysed by TG-DTA. The TG/DTA analysis shows that different light-curing times and different distance of irradiation affect the quality of polymerization; it is necessary to increase the curing time when the irradiation distance is longer than 2 mm.     

Thermal studies on different classes of clinical dental composites

Various classes of dental composites have evolved over the years for various clinical applications, differing mainly in the relative proportions of their individual components (BisGMA, TEGDMA, UDMA, fillers, etc.). Four classes of composites have been investigated here via DSC and TG (after curing with blue light from a halogen light-curing unit): a ‘microhybrid’, a ‘nanocomposite’, a ‘flowable’ and a ‘fluoride-releasing’ variety. The aims were to compare various thermal properties amongst the four classes and also to compare the quality of polymerization of halogen light cure. We concluded that the DSC scans of all the polymers showed no exotherms, signifying the absence of any residual reactivity. However, the scans showed onset of endothermic regions before glass transition temperature (GTT), which may signify structural rearrangements within the polymers. The overall enthalpy ranged from ?1.4 to ?50 J g^?1, with significant differences between the ‘fluoride-releasing’ variety and the rest. The ‘fluoride-releasing’ variety showed the largest endotherm, signifying greater mass loss than the rest. The GTT (129 °C) did not differ significantly amongst the composite types. These same parameters, on a second DSC run of the same samples, followed a pattern similar to the first run, albeit to a lesser degree in magnitude. Hence, no benefit was gained by heating after the initial ‘light’ cure. The initial and total mass losses were higher for ‘fluoride-releasing’ (19 and 46%) and ‘flowable’ (12 and 38%) types compared to ‘microhybrid’ (3 and 24%) and ‘nanocomposite’ (4 and 20%). In a clinical scenario, the ‘fluoride-releasing’ composite may adequately photopolymerize, given its use in thin layers. The microhybrid and nanocomposites might also polymerize well in thinner layers without the need for a secondary heat treatment. The ‘flowable’ variety on the other hand, is not recommended to be subjected to a secondary heat treatment, due to its inferior thermal stability.     

Application of a xenon arc lamp as a light source for evaporative light scattering detection

The standard tungsten-halogen light source used in a commercial evaporative light scattering detector (ELSD) was replaced with a 180 W xenon arc lamp. The xenon arc lamp possesses a broader spectrum in the UV region than the halogen source. The influence of the UV transmittance of five selected solvents was studied with a size-exclusion chromatography column. This solvent parameter was not observed to influence the ELSD response between the two light source settings. With the solvents studied, better sensitivity was obtained with the xenon arc lamp than the halogen lamp. This high-energy source was applied to ceramide III analysis with an octadecyl-grafted silica column and methanol:tetrahydrofuran 97:3 as the mobile phase, and the sensitivity of the quantification of ceramide III increased 16-fold for injected amounts of 14∼140 ng. The molecular species in a sample of naturally occurring ceramides was analyzed using two C18 columns at 40 °C and gradient elution from 100% acetonitrile to 100% isopropanol in 30 min. The increased ELSD sensitivity achieved when using the xenon arc lamp allowed both the minor and major ceramide species to be observed, in contrast to the results achieved when the halogen lamp was used, where the increased photomultiplier voltage needed to observed the signals from the minor species caused the signals from the major ceramide species to occur above the detector response window.     

Rapid Identification of Plastics from Electronic Devices With Nir-Spectroscopy

ABSTRACT

In this study, a NIR- based identification system for recycling purposes of plastics from electronic devices has been constructed and tested with 91 typical samples, such as computer housings. The system consisted of a robust NIR-monochromator with a fast InGaAs-diode array detector, a conventional halogen lamp as light source and a standard PC for signal processing. Spectra have been collected in the wavelength range between 800 and 1700 nm. Chemometric data analysis with appropriate data preprocessing (smoothing, differentiation) led to the desired distinction of the different plastic types. It was shown, that the presented system has, due to its speed, the potential of being applied to high throughput recycling streams.     

Ultrasound-assisted emulsification microextraction using low density solvent for analysis of toxic nitrophenols in natural waters

An ultrasound-assisted emulsification microextraction (USAEME) based on low-density solvents was successfully applied for the extraction and pre-concentration of four toxic nitrophenols in water samples. The extracted analytes were analyzed by high-performance liquid chromatography-UV detection. The important parameters influencing the extraction efficiency were studied and optimized utilizing two different optimization methods: one variable at a time (OVAT) and central composite design (CCD). The results showed that the emulsification process can be completed in a few seconds using low-density solvents, but almost 10–20?min is necessary for high-density solvents. Under the optimum conditions (extraction solvent, 1-octanol; extraction solvent volume, 40?µL; sample pH, 3.0; salt concentration, 20% (w/v) NaCl; extraction temperature, 40 (±3)°C), limits of detection of the method were in the range of 0.25 to 1?µg?L^?1 and the repeatability and reproducibility of the proposed method, expressed as relative deviation, varied in the range of 2.2–4.2% and 4.7–6.9%, respectively. Linearity was found to be in the range of 1 to 200?µg?L^?1 and the preconcentration factors (PFs) were between 77 and 175. The relative recoveries of the four nitrophenols from water samples at spiking level of 10.0?µg?L^?1 were in the range of 92.0 to 115.0%.     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Cr2O3/C@TiO2核壳型复合材料的设计合成及其光催化产氢性能

随着社会经济的快速发展,能源危机和环境污染问题成为世界各国关注的焦点.通过光催化剂将太阳能用于污染物降解、分解水产氢、CO2还原及有机物合成等领域,是解决上述问题的理想途径.过渡金属氧化物TiO2因其稳定性高、催化活性好、制备简单等优点,被认为是最理想的光催化材料.然而,TiO2带隙较宽、光响应范围窄、光量子效率低等缺点限制了其实际应用.将碳或Cr2O3与TiO2结合形成复合结构已被证明可以有效提升其光催化性能.另一方面,金属离子的掺杂可以有效提高氧化钛的可见光响应.本文利用具有高比表面积的金属有机骨架材料MIL-101(Cr)纳米材料作为模板、镉源和碳源,首先在MIL-101(Cr)表面可控生长TiO2纳米颗粒,获得MIL-101(Cr)@TiO2复合结构;然后在氮气保护下碳化形成Cr2O3/C@TiO2核壳型复合材料.碳化后,制备的复合材料具有模板的八面体形貌和高比表面积,MIL-101(Cr)中的Cr元素一部分会形成Cr2O3,一部分会掺杂到TiO2中,使得TiO2的吸收边红移.此外,Cr2O3/C@TiO2中的C有利于光的吸收和载流子的分离.这种独特的纳米结构赋予Cr2O3/C@TiO2复合材料优异的光催化性能.在300 W氙灯照射下,该复合材料光解水产氢的速率为446μmol h?1 g?1,约为纯TiO2的4倍.在可见光照射下,Cr2O3/C@TiO2分解水产氢的速率为25.5μmol h?1 g?1.将获得的粉体催化剂制备成光电极发现,Cr2O3/C@TiO2在全幅光照射下的光电流密度在0.4 V(vs.Ag/AgCl)下达到2.3 mA/cm2,约为纯TiO2的3.5倍.Cr2O3/C@TiO2光催化产氢活性的提高一方面是由于Cr掺杂到TiO2中使得其具有可见光响应,另一方面MIL-101碳化获得的Cr2O3/C有效促进了光生载流子的分离.     

Cr2O3/C@TiO2核壳型复合材料的设计合成及其光催化产氢性能

随着社会经济的快速发展,能源危机和环境污染问题成为世界各国关注的焦点.通过光催化剂将太阳能用于污染物降解、分解水产氢、CO2还原及有机物合成等领域,是解决上述问题的理想途径.过渡金属氧化物TiO2因其稳定性高、催化活性好、制备简单等优点,被认为是最理想的光催化材料.然而,TiO2带隙较宽、光响应范围窄、光量子效率低等缺点限制了其实际应用.将碳或Cr2O3与TiO2结合形成复合结构已被证明可以有效提升其光催化性能.另一方面,金属离子的掺杂可以有效提高氧化钛的可见光响应.本文利用具有高比表面积的金属有机骨架材料MIL-101(Cr)纳米材料作为模板、镉源和碳源,首先在MIL-101(Cr)表面可控生长TiO2纳米颗粒,获得MIL-101(Cr)@TiO2复合结构;然后在氮气保护下碳化形成Cr2O3/C@TiO2核壳型复合材料.碳化后,制备的复合材料具有模板的八面体形貌和高比表面积,MIL-101(Cr)中的Cr元素一部分会形成Cr2O3,一部分会掺杂到TiO2中,使得TiO2的吸收边红移.此外,Cr2O3/C@TiO2中的C有利于光的吸收和载流子的分离.这种独特的纳米结构赋予Cr2O3/C@TiO2复合材料优异的光催化性能.在300 W氙灯照射下,该复合材料光解水产氢的速率为446μmol h?1 g?1,约为纯TiO2的4倍.在可见光照射下,Cr2O3/C@TiO2分解水产氢的速率为25.5μmol h?1 g?1.将获得的粉体催化剂制备成光电极发现,Cr2O3/C@TiO2在全幅光照射下的光电流密度在0.4 V(vs.Ag/AgCl)下达到2.3 mA/cm2,约为纯TiO2的3.5倍.Cr2O3/C@TiO2光催化产氢活性的提高一方面是由于Cr掺杂到TiO2中使得其具有可见光响应,另一方面MIL-101碳化获得的Cr2O3/C有效促进了光生载流子的分离.     

A new unconventional halogen bond C?X···H?M between HCCX (X = Cl and Br) and HMH (M = Be and Mg): An ab initio study

In this article, a new type of halogen‐bonded complex YCCX···HMY (X = Cl, Br; M = Be, Mg; Y = H, F, CH₃) has been predicted and characterized at the MP2/aug‐cc‐pVTZ level. We named it as halogen‐hydride halogen bonding. In each YCCX···HMY complex, a halogen bond is formed between the positively charged X atom and the negatively charged H atom. This new kind of halogen bond has similar characteristics to the conventional halogen bond, such as the elongation of the C? X bond and the red shift of the C? X stretch frequency upon complexation. The interaction strength of this type of halogen bond is in a range of 3.34–10.52 kJ/mol, which is smaller than that of dihydrogen bond and conventional halogen bond. The nature of the electrostatic interaction in this type of halogen bond has also been unveiled by means of the natural bond orbital, atoms in molecules, and energy decomposition analyses. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Fibers and fiber cocktails to improve fire resistance of concrete

Hybrid organic–inorganic resin matrix, i.e., hexa[3,4-dicyano]-phenyl phosphonitrile trimer (HPPT) has been prepared by the reaction of hexachlorophosphonitrile and 4-hydroxyphthalonitrile in the presence of sodium hydride which on heating at 300 °C yielded a high-temperature-stable highly crosslinked hybrid resin (C-HPPT). The elemental analysis (C, H, and N), FTIR, and ¹H and ¹³C-NMR studies were used to characterize the synthesized hybrid resin. The thermal analysis studies viz. TG and DSC were also carried out to determine the thermal stability and glass transition temperature of the cured resin. The isothermal study of the cured resin after 300 h at 300 °C showed only a mass loss of 4.36%.     

Carboxylic Acids as Directing Groups for C−H Bond Functionalization

The selective transformation of C?H bonds is one of the most desirable approaches to creating complexity from simple building blocks. Several directing groups are efficient in controlling the regioselectivity of catalytic C?H bond functionalizations. Among them, carboxylic acids are particularly advantageous, since they are widely available in great structural diversity and at low cost. The carboxylate directing groups can be tracelessly cleaved or may serve as the anchor point for further functionalization through decarboxylative couplings. This Minireview summarizes the substantial progress made in the last few years in the development of reactions in which carboxylate groups direct C?H bond functionalizations with formation of C?C, C?O, C?N, or C?halogen bonds at specific positions. It is divided into sections on C?C, C?O, C?N, and C?halogen bond formation, each of which is subdivided by reactions and product classes. Particular emphasis is placed on methods that enable multiple derivatizations by combining carboxylate‐directed C?H functionalization with decarboxylative couplings.     

Low-temperature reaction of trialkoxysilanes on silica gel: a mild and controlled method for modifying silica surfaces

The room temperature reaction of 4-(triethoxysilyl)butyronitrile, 4-TBN ((C2H5O)3Si(CH2)3CN), on weakly hydrated silica samples pretreated at 393 K has been studied by desorption experiments and by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy at different aging times under various water partial pressures. The reaction is demonstrated by the decrease of desorption of 4-TBN with time and the simultaneous disappearance of the 2980 and 1394 cm(-1) signals in the DRIFT spectra, assigned to the CH3 moiety of the ethoxy functions. Water partial pressure is shown to have a crucial effect on the rate and efficiency of the process as, after 6 days, for samples kept at room temperature under vacuum, ca. 50% of the silane has reacted, while for those kept in a water-saturated atmosphere the silane reaction reaches 96%. Although the silane appears to be irreversibly bonded to the surface, no definite conclusion may be drawn from these preliminary results as to the nature of the bonding (grafting or coating). These samples are compared to modified silicas prepared according to conventional methods. The same extent of silane reaction (50%) is achieved for preadsorbed samples kept under vacuum and either cured at 473 K for 30 h or kept at room temperature for 6 days. A mild and controlled modification of silica by triethoxysilanes can thus be achieved by first physisorbing known amounts of the modifying silanes from an organic solvent on pretreated silica and then letting the samples mature for a few days at room temperature in a water-saturated atmosphere.     

Dynamic mechanical properties of epoxy‐phenolic mixtures

The dynamic‐mechanical properties of different mixtures formed by an epoxy resin (DGEBA type) and a phenolic resin (resole type) cured by trietylenetetramine and/or p‐toluensulphonic acid at different concentrations have been studied by means of dynamic mechanical thermal analysis (DMTA). All samples were cured by pressing at 90 °C during 6 h. The mechanical studies were performed between ?100 to 300 °C at a heating rate of 2 °C/min. This study was also carried out for the epoxy‐TETA and phenolic‐p‐toluensulphonic acid systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1548–1555, 2005     

Resistance of composite materials based on BaCeO3 against the corrosive effects of carbon dioxide and water vapour at intermediate fuel cell operating temperatures

The objective of this work is to analyse the chemical stability of BaCe_0.85Y_0.15O_3?δ –Ce_0.85Y_0.15O_2?δ (BCY15–YDC15) composite materials at 600 °C and to compare the aforementioned chemical stability with that of pure BCY15. The composite powders were obtained by mixing together powders of BCY15 and YDC15 in the following volume fractions: 90 % BCY15 + 10 % YDC15, 70 % BCY15 + 30 % YDC15, 30 % BCY15 + 70 % YDC15, 20 % BCY15 + 80 % YDC15 and 10 % BCY15 + 90 % YDC15. After that both powders and sintered samples of the BCY15 and the BCY15–YDC15 composites were saturated in two different atmospheres at 600 °C: CO₂/H₂O (3.1 mol% H₂O) and N₂/H₂O (46.8 mol% H₂O). The effects of the previously mentioned atmospheres on the physicochemical properties of the samples were investigated via differential thermal analysis (DTA) combined with thermogravimetric analysis (TG). Furthermore, mass spectrometry was used to analyse the chemical composition of the gases released from the samples during the DTA–TG heating process. The surface and cross-section morphology of the samples were examined by scanning electron microscopy. Moreover, the phase composition of each sample was studied via X-ray Diffraction. From the combined analysis, it can be concluded that the addition of YDC15 in the composite samples leads to an increase in resistance against the corrosive effects of CO₂. Furthermore, it was determined that all samples maintain stability in the presence of H₂O at 600 °C.     

Pulsed NMR study of molecular motion in the diglycidyl ether of bisphenol-A cured with 4,4′-methylenedianiline

The monomeric diglycidyl ether of bisphenol-A cured with methylenedianiline has been studied by pulsed NMR. Values of the proton relaxation times T₁, T_1p, and T₂ have been measured over the temperature range ?160 to 200°C. The system was studied after being fully postcured at 180°C and after being cured at 100°C and at 54°C. The relaxation times are interpreted in terms of molecular motion in the cured resins, i.e., methyl group reorientation, segmental motions, and general molecular motion. The results are compared with those obtained previously by us for the uncured resin. Correlation frequencies for the segmental motions are compared with those obtained from dielectric relaxation and mechanical loss studies. There are at least two principal segmental motions present in the cured system, and the nature of these motions is found to depend on the cure temperature. These effects are discussed in terms of crosslinking and annealing of the system.     

薄层原位荧光扫描测定锗-132制剂中倍半氧双羧乙基锗含量的研究

本文报道由作者建立的薄层色谱法,样品在硅胶薄层板上展开后,以苯芴酮显色,再在碘钨灯下照射可使锗-132衍生成荧光化合物,从而可用原位荧光扫描(外标法)定量,已用于倍半氧双羧乙基锗(锗-132)原料和制剂的含量测定及稳定性研究。经3批原料、9批注射液、3批口服液样品的222个测试数据统计,C.V.值为2.29%,同板的C.V.值为1.5%～2.7%(n=7～10);加样回收率101.5%,最低检出限为0.12μg。     

Thermal behavior analysis of kaolinite–dimethylsulfoxide intercalation complex

The thermal behavior of kaolinite?Cdimethylsulfoxide intercalation complex was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FT-IR) spectroscopic analysis. The samples gradually heated up to different temperatures were studied by XRD and FT-IR. The kaolinite?Cdimethylsulfoxide intercalation complex is stable below 130?°C. With the rise in the temperature, the relative intensity of the 1.124-nm peak gradually decreased and disappeared at 200?°C, however, the intensity of the 0.714?nm peak increased in the XRD patterns. In the infrared spectra, the appearance of methyl bands at 3018, 2934, 1428, and 1318?cm^?1 indicates the presence of intercalated dimethylsulfoxide, the intensities of these bands decreased with the temperature rising and remained until around 175?°C, which agree with the XRD and TG?CDSC data.     

Liquid crystalline epoxies bearing biphenyl ether and aromatic ester mesogenic units: Synthesis and thermal properties

Two liquid crystalline epoxies containing biphenyl ether and aromatic ester mesogenic units, oxybis(4,1-phenylene)bis(4-(oxiran-2-ylmethoxy)benzoate)(LCE1) and oxybis(4,1-phenylene) bis(4-(4-(oxiran-2-yl)butoxy)benzoate)(LCE2), were synthesized and characterized. Subsequently, the epoxy monomers were cured with diaminodiphenylsulfone (DDS). From DSC, XRD and POM results, monomers did not show liquid crystalline phase while the cured samples exhibited nematic phase. The cured samples showed good mechanical properties with strength of 99.1MPa and excellent thermal stabilities with high glass transition temperature up to 168.0?°C, 5% weight loss temperature at 343?°C and high char yield of 24.5% at 800?°C. The relationship between thermal conductivity and network structure was discussed in this work. Due to the introduction of mesogenic units into epoxy networks, the cured resins showed high thermal conductivity as high as 0.292?W/(m*K), more than 1.5times higher than conventional epoxy resins. By introducing alumina (Al₂O₃) into LCE1/DDS cured system, composites of LCE1/DDS/Al₂O₃ with the highest thermal conductivity of 1.61?W/(m*K) was obtained with the content of 80?wt% while that of diglycidyl ether of bisphenol A (DGEBA, E51) epoxy resin/DDS/Al₂O₃ was 1.10?W/(m*K). The as-prepared epoxy resins showed high glass transition temperature and excellent thermal stabilities, indicating the potential of application in microelectronics.     

Stability studies of testosterone and epitestosterone glucuronides in urine

The stability of testosterone glucuronide (TG), epitestosterone glucuronide (EG) and the T/E ratio in urine has been studied. Samples were analyzed by gas chromatography coupled to mass spectrometry (GC/MS). Urine samples were submitted to a solid-liquid cleanup followed by extraction of unconjugated testosterone (T) and epitestosterone (E) with tert-butyl methyl ether (free fraction). The remaining aqueous phase was hydrolyzed with beta-glucuronidase and extracted at alkaline pH with n-pentane. Analytes were analyzed by GC/MS as their enol-trimethylsilyl (TMS) derivatives. The urine for stability testing was obtained from an excretion study after the administration of T to healthy volunteers. The homogeneity of the sample was verified before starting the stability study. The stability of TG and EG was evaluated at different storage conditions. For long-term stability testing, analyte concentration in urine stored at 4 degrees C and -20 degrees C was determined at different time intervals for 22 months. For short-term stability testing, analyte concentration was evaluated in urine stored at 37 degrees C for 3 and 7 days. The effect of repeated freezing (at -20 degrees C) and thawing (at room temperature) was studied for up to three cycles. Data obtained in this work demonstrated the stability of TG, EG and the T/E ratio in sterilized urine samples stored at 4 and -20 degrees C for 22 months and after going through repeated freeze/thaw cycles. Decreases in concentration were observed after 7 days of storage at 37 degrees C due to the partial cleavage of the glucuronide conjugates; however, the T/E ratio was not affected. These results show the feasibility of preparing reference materials containing TG and EG to be used for quality control purposes.