Photooxidation of dyed styrene-butadiene and natural rubbers

Dyed natural rubber (NR) and styrene-butadiene rubber (SBR) designed for outdoor applications were exposed to accelerated artificial aging in xenon light. The aging results in the deterioration of the properties of the exposed surface material. The ability of dyed polymers to withstand prolonged sunlight exposure without fading or undergoing any physical deterioration is largely determined not only by the photochemical characteristics of the absorbing dyestuff itself but also by the polymer structure and fillers. Results indicate that dyed filled NR and SBR samples behave differently during photooxidation. The photodegradation products were observed by Fourier transform infrared spectroscopy (FTIR) to characterize the changes occurring in the polymer matrix during UV aging. The fading of the dyed polymers was found to be promoted in the NR sample. Moreover, the effects of photooxidation on the dyed SBR and NR materials were assessed by the formation of cracks and the thickness of the degraded area. The degradation thickness is more important for the NR sample than for the SBR one according to environmental scanning electron microscopy (ESEM) observations. For the NR sample, cracks appear initially at the surface and then grow through the thickness of the specimen, while for the SBR sample cracks are small and discontinuous. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1081–1085. This article was submitted by the authors in English.     

Optimization of preparation conditions of Fe-Co nanoparticles in low-temperature CO oxidation reaction by taguchi design method

Mixed iron-cobalt oxide(Co/Fe molar ratio=1/5) are prepared using a simple co-precipitation procedure and studied for the catalytic oxidation of carbon monoxide.In particular,the effects of a range of preparation variables such as pH value when precipitation,aging temperature,precipitation agent type and aging time are investigated on the catalytic performance of synthesized Fe-Co oxides in CO oxidation reaction.In addition,the preparation factors were optimized by Taguchi design method.The optimized sample was characterized by XRD,N2 adsorption/desorption,TEM and TGA/DTA techniques.The results reveal that the optimized sample shows a mesoporous structure with a narrow pore size distribution centered in the range of 2-7nm.The sample prepared under optimized conditions has high activity and stability toward removal of carbon monoxide at lower temperatures.It is shown that different preparation variables influence the catalytic performance of Fe-Co oxide in CO oxidation reaction.     

On-line introduction of high-pressure gas-liquid sample for capillary gas chromatographic analysis

An on-line sample introduction technique in capillary gas chromatograph (CGC) for the analysis of high-pressure gas-liquid mixtures has been designed and evaluated. A sample loop of 0.05 microL and a washing solvent loop of 0.5 microL are mounted on a 10-port switching valve, which serves as the injection valve. A capillary resistor was connected to the vent of sample loop in order to maintain the pressure of the sample. Both the sample and the washing solvent are transferred into the split-injection port through a narrow bore fused silica capillary inserted into the injection liner through a septum. The volume of the liner is used both as the pressure-release damper and evaporation chamber of the sample. On-line analysis of both reactants and resultants in ethylene olimer reaction mixture at 5 MPa was carried out, which demonstrated the applicability of the technique.     

Stability of polydimethylsiloxane-magnetite nanoparticle dispersions against flocculation: interparticle interactions of polydisperse materials

The colloidal stability of dispersions comprised of magnetite nanoparticles coated with polydimethylsiloxane (PDMS) oligomers was investigated theoretically and experimentally. Particle-particle interaction potentials in a theta solvent and in a good solvent for the PDMS were predicted by calculating van der Waals, electrostatic, steric, and magnetic forces as functions of interparticle separation distances. A variety of nanoparticle sizes and size distributions were considered. Calculations of the interparticle potential in dilute suspensions indicated that flocculation was likely for the largest 1% of the population of particles. Finally, the rheology of these complexes over time in the absence of a solvent was measured to probe their stabilities against flocculation as neat fluids. An increase in viscosity was observed upon aging, suggesting that some agglomeration occurs with time. However, the effects of aging could be removed by exposing the sample to high shear, indicating that the magnetic fluids were not irreversibly flocculated.     

Matrimid®5218/PSf双层非对称中空纤维膜的制备及其气体分离性能研究

以商业化聚酰亚胺Matrimid®5218作为功能层材料, 聚砜作为支撑层材料, 采用共挤出法制备双层非对称中空纤维气体分离膜. 所制备的双层非对称中空纤维膜具有致密无缺陷的超薄皮层, 致密皮层厚度约为0.21 μm. 在25 ℃, 0.5 MPa下, CO2/CH4的选择性系数达51.39, CO2的渗透系数为46.29 GPU, O2/N2的选择性系数达到7.13, O2的渗透速率为6.38 GPU. 考察了温度和压力对膜的渗透系数和选择性系数的影响, 并考察了物理老化对膜性能的影响.     

A new version of differential flow heat capacity calorimeter; tests of heat loss corrections and heat capacities of aqueous NaCl from T = 300 K to T = 623 K

A new differential flow heat capacity calorimeter was constructed. It is designed to operate at temperatures up to 700 K and pressures up to 35 MPa and its primary use is for determining the massic heat capacities at constant pressure of dilute aqueous solutions. The instrument works in the so-called isoperibol regime, where the fluid sample flowing through the cell is heated by an electrical heater and the power necessary to provide a constant temperature rise is measured relative to that for a reference fluid (water). From the two values of power for sample and water the ratio of massic heat capacities of the sample to that of water can be calculated. A thorough investigation of calibration techniques showed that the calorimetric performance is very sensitive to the thermal conductivities of the sample and reference fluids. Measurements under turbulent flow conditions are questionable since there is no guarantee that by changing the flow rate the experiments and the calibrations would be performed at the same flow conditions. The procedure is very accurate and sensitive when measuring the difference in heat capacity between a solvent and a dilute solution of solute in the same solvent. The calorimeter was used to measure heat capacities of aqueous solutions of NaCl at eight temperatures up to 623 K and pressures to 30 MPa. The newly obtained values show consistency with previously published results and enlarge the database of experimental values aboveT =  573 K, where experimental data are rare.     

Mechanical strengthening of TMOS-based alcogels by aging in silane solutions

It has been shown that aging of tetramethoxysilane (TMOS)-based alcogels in solutions of tetraethoxysilane (TEOS)/methanol (MeOH) provides new monomers to the alcogel and favorably increases the strength and stiffness of the alcogel and hence reduces the shrinkage during the subsequent drying. Load relaxation experiments have been performed to determine the shear modulus (G), Poisson's ratio (), and the permeability of wet gel rods as a function of aging time in the TEOS/MeOH solution. The modulus of rupture (MOR) and G have also been obtained from 3-point bending tests. Aging the gels in 70 vol% TEOS/MeOH causes an increase in G from 0.48 MPa to 1.8 MPa and 7.4 MPa after aging for 24 hours and 144 hours, respectively.It is shown that the drying stress is actually increased by the aging treatment, but the increase in strength of the gel is even greater; hence, strengthening of the alcogels dramatically reduces the probability of cracking during drying. Unaged gels with higher TMOS concentrations corresponding to the silica content of gels aged in TEOS solution, however, showed large shrinkage and severe cracking.     

Metastable effects on martensitic transformation in SMA

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.     

BDIE·[Zn-Al]催化二氧化碳与氧化环己烯共聚

在α-二亚胺型催化剂BDIE.[Zn-Al]催化下采用新的工艺进行CO2与氧化环己烯共聚反应,催化效率得到较大地提高.这些新的工艺包括在反应前用与催化剂摩尔比为1.5∶1的氧化环已烯进行数小时陈化;采用二氧化碳与氧化环已烯分批加料的聚合工艺.在25℃温度下陈化4 h,采用分批加料的方式反应,BDIE.[Zn-Al]的催化效率提高到69.9 g/g.     

The influence of physical aging on the creep rupture behavior of polystyrene

The effects of postannealing aging time on the brittle fracture behavior of polystyrene were studied. A combination of mechanical properties, including creep and creep rupture under constant load and the behavior under constant extension rate deformation were examined for polystyrene samples of different prior aging times (from 1h to 2 months). The specimens and fracture surfaces were examined by optical microscopy and SEM to observe any change in the fracture behavior. It was found that longer aging times caused not only a change in the time-dependent modulus of the material but also a significant decrease in the creep rupture life and a decrease in strain to failure. It was found that the reasons for this are that although aging delays craze formation, craze breakdown and ultimate failure are accelerated by aging. The importance of these findings are discussed, particularly in relation to failure criteria involving the use of critical strains. © 1993 John Wiley & Sons, Inc.     

黄芩中黄芩苷的亚临界水提取及高效液相色谱分析

建立了黄芩药材中黄芩苷的亚临界水提取 高效液相色谱测定方法。分别考察了温度、压力、提取时间、提取物颗粒度、溶剂比等因素对提取量的影响,并与有机溶剂提取法比较。结果表明,当两者具有相同的提取效果时,亚临界水提取法的提取时间及提取溶剂的消耗量大大减少,避免了使用有机溶剂造成的污染。黄芩苷提取最佳条件为:样品颗粒度80～100目,溶剂比0.2 mL/mg ,5 MPa,130 ℃保持10 min。并通过提取 高效液相色谱联机分析实现了对提取物的实时监测。该技术有望成为从中药材中提取脂溶性成分的有效方法。     

Optimization of sample packing in diffuse reflectance infrared spectroscopy

Parameters of sample packing in diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) have been investigated and optimized. One MPa pressure applied for 1 min was found to provide simultaneously at least ±3% reproducibility and appropriate band intensity. It has been also demonstrated that this precision can be obtained if the sample mass is controlled to ±2% and the sample is dry. A simple sample packing accessory was designed and constructed for reproducible sample preparation. Quartz concentration of dust samples has been determined and good agreement has been found with the results of the conventional pellet technique.     

Comparison of antioxidants for combined radiation and thermal aging and superposition of radiation and thermal aging for EPR and XLPE

Thermal and combined thermal and radiation aging of low voltage EPR and XLPE cable insulation with Agerite MA antioxidant and with the ZMTI/Aminox antioxidant system was examined to compare the relative effectiveness of the antioxidant and polymer systems. All provided significant stability with no clear choice of any particular combination being superior to the others. A comparison of degradation from thermal and radiation aging with degradation from combined thermal/radiation aging showed that the damage from the individual aging effects was superposable. This indicates that synergistic effects have little importance for the EPRs and XLPEs tested under the aging conditions observed.     

Reduction of Breakdown Pressure by Filter Cake Removal Using Thermochemical Fluids and Solvents: Experimental and Numerical Studies

The process of well cleanup involves the removal of an impermeable layer of filter cake from the face of the formation. The inefficient removal of the filter cake imposes difficulty on fracturing operations. Filter cake’s impermeable features increase the required pressure to fracture the formation. In this study, a novel method is introduced to reduce the required breakdown pressure to fracture the formation containing the water-based drilling fluid filter cake. The breakdown pressure was tested for five samples of similar properties using different solutions. A simulated borehole was drilled in the core samples. An impermeable filter cake using barite-weighted drilling fluid was built on the face of the drilled hole of each sample. The breakdown pressure for the virgin sample without damage (filter cake) was 6.9 MPa. The breakdown pressure increased to 26.7 MPa after the formation of an impermeable filter cake. Partial removal of filter cake by chelating agent reduced the breakdown pressure to 17.9 MPa. Complete dissolution of the filter cake with chelating agents resulted in the breakdown pressure approximately equivalent to the virgin rock breakdown pressure, i.e., 6.8 MPa. The combined thermochemical and chelating agent solution removed the filter cake and reduced the breakdown pressure to 3.8 MPa. Post-treatment analysis was carried out using nuclear magnetic resonance (NMR) and scratch test. NMR showed the pore size redistributions with good communication between different pores after the thermochemical removal of filter cake. At the same time, there was no communication between the different pores due to permeability impairment after filter cake formation. The diffusion coupling through NMR scans confirmed the higher interconnectivity between different pores systems after the combined thermochemical and chelating agent treatment. Compressive strength was measured from the scratch test, confirming that filter cake formation caused added strength to the rock that impacts the rock breakdown pressure. The average compressive strength of the original specimen was 44.5 MPa that increased to 73.5 MPa after the formation of filter cake. When the filter cake was partially removed, the strength was reduced to 61.7 MPa. Complete removal with chelating agents removed the extra strength that was added due to the filter cake presence. Thermochemical and chelating agents resulted in a significantly lower compressive strength of 25.3 MPa. A numerical model was created to observe the reduction in breakdown pressure due to the thermochemical treatment of the filter cake. The result presented in this study showed the engineering applications of thermochemical treatment for filter cake removal.     

Simultaneous measurement of NAD metabolome in aged mice tissue using liquid chromatography tandem‐mass spectrometry

Nicotinamide adenine dinucleotide (NAD) is a major co‐factor that mediates multiple biological processes including redox reaction and gene expression. Recently, NAD metabolism has received considerable attention because administration of NAD precursors exhibited beneficial effects against aging‐related metabolic disorders in animals. Although numerous studies have reported that NAD levels decline with aging in multiple animal tissues, the pathway and kinetics of NAD metabolism in aged organs are not completely understood. To determine the NAD metabolism upon aging, we developed targeted metabolomics based on an LC/MS/MS system. Our method is simple and applicable to crude biological samples, including culture cells and animal tissues. Unlike a conventional enzymatic cycling assay, our approach can determine NAD and NADH (reduced form of NAD) by performing a single sample preparation. Further, we validated our method using biological samples and investigated the alteration of the NAD metabolome during aging. Consistent with previous reports, the NAD levels in the liver and skeletal muscle decreased with aging. Further, we detected a significant increase in nicotinamide mononucleotide and nicotinamide riboside in the kidney upon aging. The LC/MS/MS‐based NAD metabolomics that we have developed is extensively applicable to biomedical studies, and the results will present innovative ideas for the aging studies, especially for that of NAD metabolism.     

Direct evaluation of meat spoilage and the progress of aging using biosensors

A direct sensing method for monitoring meat quality was developed. The sensor is composed of an Ag/AgCl electrode and a platinum electrode on which putrescine oxidase or xanthine oxidase were immobilized to estimate bacterial spoilage or the progress of aging, respectively. A potential-step chronoamperometric method was applied in which the potential was stepped from 300 mV to 600 mV. A linear relationship was obtained between 5 and 60 nmol g⁻¹ for putrescine (Put) and 0.05 and 1.0 μmol g⁻¹ for hypoxanthine (Hx). The coefficient of variation was 0.75% for 20 nmol ml⁻¹ Put solution and 2.2 for a meat sample using the putrescine sensor, and 1.09% for 0.25 μmol ml⁻¹ Hx solution and 2.6% for a meat sample using the xanthine sensor. The pH requirements and substrate selectivity were suitable for the direct measurement of substrates on the surface of meat. From the results of practical experiments, the direct sensing method was indicated to be useful with some modifications for the estimation of meat quality during aging.     

The pressure tolerance of different poly-l-lysine conformers in aqueous solution: Infrared spectroscopy and two-dimensional correlation analysis

Poly-l-lysine can form either of three different conformers as α-helix, anti-parallel β-sheet and random coil stably under appropriate conditions. In buffer solution poly-l-lysine exists in a random coil at about pH 4, an α-helix above pH 12, and transforms from α-helix to β-sheet when the sample is heated to 46 °C for 30 min. The effects of elevated hydrostatic pressure on three different initial conformers of poly-l-lysine are investigated with Fourier transform infrared spectroscopy and two-dimensional correlation analysis. Changes observed in the amide I′ band indicate that the α-helix conformer undergo hydration enhancement at low pressure (<400 MPa), then gradually transition into an α′-helix. Two initial conformers, the β-sheet and random coiled polypeptide, undergo conformational changes to an α-helix at low pressure and to an α′-helix at high pressure. Moreover, the conversion occurred at a lower pressure for the β-sheet (∼250 MPa) than for the α-helix (∼300 MPa) and the random coil (∼850 MPa).     

Uniaxial ratcheting behavior of hygrothermal aging anisotropic conductive adhesive film

A series of uniaxial ratcheting experiments on anisotropic conductive adhesive film (ACF) were conducted under stress-control at elevated temperature using a DMA-Q800. The ratcheting behavior of ACF specimens with different hygrothermal aging times was investigated at room temperature and 120 °C. The effects of loading rate, mean stress and stress amplitude on the ratcheting behavior of unaged and aged specimens were compared. The results show that the ratcheting strains of aged specimens are smaller than those of unaged specimens under the same experimental conditions. The cycling stability of aged specimens is increased by hygrothermal aging. At room temperature, with the increase of aging time, the ratcheting strains of aged specimens increase with hygrothermal aging time when it is less than or equal to 96 h but, however, decrease when it exceeds 96 h. At 120 °C the ratcheting strains of ACF only decrease with the increase of hygrothermal aging time. Additionally, the effects of loading rate, mean stress and stress amplitude on the ratcheting behavior of unaged and aged ACF are different and their effects are weakened by hygrothermal aging.     

环氧树脂的物理老化

本工作发展了补偿式示差扫描量热(CDSC)法,用于环氧树脂热焓松弛研究,实验结果证明CDSC法较DSC法灵敏并能提供更多的信息。用CDSC法研究了交联度对环氧树脂热焓松弛动力学的影响,计算了活化能,对结果进行了讨论。