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  • Author or Editor: S. Wang x
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Abstract  

Dibutyl-and monobutylphosphoric acid in acidic toluene medium were determined by ion chromatography. The procedure involved stripping with dilute sodium hydroxide solution and used carbon tetrachloride as diluent, then detection with a conductivity meter. The effect of flow rate, eluent strength and stripping solution, the effect of chloride and nitrate ion on DBP, the effect on DBP in sodium hydroxide solution, and the effect of organic aliphatic acids were discussed. The detection limits of 0.19 ppm and 0.14 ppm were found for DBP and MBP, respectively.

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Abstract  

The recent progress of positron studies on polymers are briefly reviewed. The correlation between free-volume holes and mechanical properties are discussed. The results indicate that the positron spectroscopy is a potential tool to characterize the microstructure and mechanical properties of polymeric materials.

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Abstract  

We generalize classical results concerning L 1 integrability, and tell a somewhat different story for sine series.

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Summary

An ultrasensitive and rapid method for the determination of epicatechin, rutin, and quercetin was developed using capillary zone electrophoresis with on-line chemiluminescence detection. Under the optimal conditions, the analytes were baseline separated within 12 min. The limits of detection in turn were 0.60 pg mL−1 for epicatechin, 0.50 pg mL−1 for rutin, and 1.0 pg mL−1 for quercetin. The developed method was an easy and reliable method of determining these analytes concentrations in tea, extract Ginkgo biloba, and rutin tablet, demonstrating the feasibility and reliability of the proposed method.

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Artificial grassland plots with various degrees of diversity were established near Heishiding Nature Reserve, Guangdong Province, China. After an establishment phase of one year, one half of each plot was exposed to drought stress in order to explore the relationship between diversity and compositional stability of the grassland communities. The experiment showed that relationships between diversity and compositional stability varied with the diversity values in non-stressed control subplots and the duration of drought disturbance. When control subplots had higher evenness, species richness negatively affected compositional stability, which led to a negative relationship between diversity and compositional stability. When control subplots had lower evenness, compositional stability was determined by evenness or species identity (particular species) at different periods of drought disturbance. This resulted in negative, weakly positive or no relationships between diversity and compositional stability. Based on these results, we suggest that different relationships between diversity and compositional stability, and controversial data from such relationships in previous studies may reflect differences in environmental and experimental conditions.

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Abstract  

Positron annihilation lifetime spectra and ionic conductivity have been measured for poly(etherurethane)-LiClO4 as a function of temperature. The effects of Li salt on glas transition free volume and ionic conductivity have been discussed. A correlation between fractional free volume and ionic conductivity was first experimentally confirmed by using the free volume theory.

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Abstract  

The phase behaviour of thermoplastic polymer-dispersed liquid crystal system is studied with particular emphasis on the various transitions that occur within the system. The extent of plasticization of the polymer(polymethyl methacrylate) by the low molecular weight liquid crystal(E7) along with the several transitions of theLC(Liquid Crystal) are determined by modulated DSC. Optical microscopy was used to construct the temperature versus composition phase diagram. Our study indicates the existence of a limiting temperature of 40°C around which the PMMA matrix turns glassy irrespective of the initial composition within the phase separated region, suggesting the intersection of the glass transition curve with the coexistence curve. A slight depression of theN-I(Nematic to Isotropic) transition of theLC is observed with increasing composition of PMMA whereas theS-M(Smectic to Nematic) transition and theT g (Glass transition temperature) of theLC remain unaffected. The one phase mixture remains isotropic until phase separation at a lower temperature where theLC rich domains become nematic. The growth ofLC rich domains is studied as a function of temperature and time.

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Abstract  

The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine the activation energy (E a) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol −1) obtained was smaller slightly than the value of E a=96.82 kJ mol−1 found with the Barrett method.

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Abstract  

2,2-dinitropropyl acrylate (DNPA), 2,2-dinitrobutyl acrylate (DNBA) and 2,2-dinitrobutyl methacrylate (DNBMA) were synthesized and the kinetics of their free-radical polymerization in the presence of 2,2′-azobisisobutyronitrile (AIBN) were investigated by DSC in the non-isothermal mode. The kinetics of the free-radical polymerization as estimated by the Kissinger and Ozawa methods showed that the reaction is disfavoured by increasing steric hindrance around the acrylyl double bond. The rate constants calculated from the activation parameters showed the structural dependency. The polymerization kinetics revealed that the polymerizability of three monomers decreased due to the presence of substituent methyl groups on the acrylyl double bond and 2,2-dinitrobutyl on ester group. Thus, the polymerization tendency increased in the order DNPA>DNBA>DNBMA.

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Abstract  

Combustion experiments of three typical seaweeds (Gracilaria cacalia, Enteromorpha clathrata and Laminaria japonica) have been studied using a DTA-60H Thermal Analyzer and the combustion processes and characteristics are studied. Thermogravimetric experiments are carried out on the samples with 0.18 mm particle size at the heating rate of 20°C min−1. The results indicate that the ignition mode of seaweed is homogeneous and the combustion process is composed of dehydration, the pyrolysis and combustion of volatile, transition stage, the combustion of char as well as the reaction at high temperature. And the combustion characteristic parameters are obtained such as ignition temperature, maximum rate of combustion, burnout temperature etc. The combustion models of these seaweeds are also analyzed. The combustion characteristics and model differences between the seaweed and woody biomass are caused by the differences of volatile components. The combustibility indexes of seaweeds calculated are better than that of woody biomass, and the index of Gracilaria cacalia is the best. At last, activation energies are determined using Arrhenius model that is solved by binary linear regression method.

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