SYNTHESIS AND PROPERTIES OF HIGH MOLECULAR WEIGHT POLY(LACTIC ACID) AND ITS RESULTANT FIBERS

Direct melt/solid polycondensation of lactic acid(LA)was carried out to obtain high molecular weight poly(lactic acid)(PLA)by a process using various catalysts in the first-step melt polycondensation,and followed solid polycondensation by using p-toulenesulfonic acid monohydrate(TSA)as the catalyst in the second step.Effects of various catalysts and reaction temperature on the molecular weight and crystallinity of resulting PLA polymers were examined.It was shown that SnCl_2·2H_2O/TSA,SnCl_2·2H_2O/succinic ...

Pollutants removal and simulation model of combined membrane process for wastewater treatment and reuse in submarine cabin for long voyage

A laboratory scale test was conducted in a combined membrane process （CMP） with a capacity of 2.91 m3/d for 240 d to treat the mixed wastewater of humidity condensate, hygiene wastewater and urine in submarine cabin during prolonged voyage. Removal performance of chemical oxygen demand （COD）, ammonia nitrogen （NH4^＋-N）, turbidity and anionic surfactants （LAS） was investigated under different conditions. It was observed that the effluent COD, NH4^＋-N, turbidity and LAS flocculated in ranges of 0.19-0.85 mg/L, 0.03-0.18 mg/L, 0.0-0.15 NTU and 0.0-0.05 mg/L, respectively in spite of considerable fluctuation in corresponding influent of 2120-5350 mg/L, 79.5-129.3 mg/L, 110-181.1NTU and 4.9-5.4 mg/L. The effluent quality of the CMP could meet the requirements of mechanical water and hygiene water according to the class I water quality standards in China （GB3838-2002）. The removal rates of COD, NH4^＋-N, turbidity and LAS removed in the MBR were more than 90%, which indicated that biodegradation is indispensable and plays a major role in the wastewater treatment and reuse. A model, built on the back propagation neural network （BPNN） theory, was developed for the simulation of CMP and produced high reliability. The average error of COD and NH4^＋-N was 5.14% and 6.20%, respectively, and the root mean squared error of turbidity and LAS was 2.76% and 1.41%, respectively. The results indicated that the model well fitted the laboratory data, and was able to simulate the removal of COD, NH4^＋-N, turbidity and LAS. It also suggested that the model proposed could reflect and manage the operation of CMP for the treatment of the mixed wastewaters in submarine.

Crystallization mechanism of CeAlFeCo bulk metallic glasses

Crystallization behaviors of Ce60Al15Fe5+xCo20-x(x=0,5,10) bulk metallic glasses(BMGs) were studied by means of differential scanning calorimeter(DSC) and X-ray diffraction(XRD).The crystallization processes of different samples were simulated by JMA equation.Experimental results demonstrated that incubation and crystallization time increased with decreasing isothermal temperature for the same sample.The crystallization mechanism of CeAlFeCo BMGs was discussed.

Effect of Aluminium Addition on Glass Forming Ability of Nd_(55-x)Al_(10+x)Fe_(15)Co_(20)(x=0,5,10)Alloys

Nd55-x Al10＋x Fe15 （x =0, 5, 10） bulk glass-forming alloys with distinct glass transition in differential scanning calorimetry （DSC） traces were obtained by suction casting, The glass forming ability （GFA） of the alloys was investigated. It was found that the reduced glass transition temperature （Trg） and the parameter γ of the alloys increased with the increasing concentration of Al. The glass formation enthalpy of the alloys was calculated based on Miedema＇s model, and it was suggested that the GFA of the alloys could be enhanced by the decrease of the glass formation enthalpy with Al additions.

Stress and Strain During the Process of Thermal Stabilization of Modified Pan Precursors

Thermal mechanical analysis,FT-IR,WAXD and some conventional measurements,such as densities and mechanical properties,were used to characterize the effect of the modification using KMnO4 and SnCl4 on the thermal mechanical behaviors and structural changes during the process of thermal stabilization of modified PAN precursors.Compared to the unmodified original PAN precursors,some conclusions were drawn that the thermal stabilization starts at a lower temperature for modified PAN fibers,for example,the peak of thermal stress changes for modified PAN precursors using KMnO4 displays a decrease of 20℃ and a increase of 30% in the ultimate thermal stress,that chemical modification makes structural transformation perfect and increases by 25% of the thermal stress at the temperature range of 230℃-300℃,that the modified PAN fibers display an increase of 100% in the thermal strain,once after pre-oxidized,show an increase of 7.8% in orientation index,and a decrease of 9.9% in crystal size for identical preload in the region of 13.1-14.5MPa.It was also concluded that the modification using SnCl4 would alleviate the changes in physical and chemical stress regimes and result in improvement in structure and decrease in defects.

Effect of Post Spinning Modification on the PAN Precursors and Resulting Carbon Fibres

The impregnation of a special grade polyacrylonitrile （PAN） precursor fibres was carried out in a 8 wt. % KMnO4 aqueous solution to obtain modified PAN precursor fibres. The foctts is primarily on the effects of modification on the chemical structure and the physical mechanical properties of precursor ribres, them-aft stabilised and their resulting carbon fibres, which were characterized by the con-bination use of densities, wide-angle X-my diffraction （WAXD）, X-my photoelectron spectrosopy （XPS）, Elemental analysis （EA）, Fourier transform infrared （FT-IR） and scanning clectronmicroscope （SEM）, etc. KMnO4 as a strong oxidizer can swell, oxidize and corrode the skin of a precursor fibre, tin, form partly C≡N groups to C=N ones, decrcase the crystal size, increase the orientation index, increase the crystallinity index, furthermore increase the densities of modified PAN precursors and resulting thermal stabiliscd fibres. As a result, the carbonfibres developed from modified PAN fibres show an improvement in tensile strength of 31.25% and an improvement in elongation of 77.78%, but a decrease of 16.52% in Young＇s modulus.

A novel application of the SAWD-Sabatier-SPE integrated system for CO_2 removal and O_2 regeneration in submarine cabins during prolonged voyages

To improve the working and living environment of submarine crews, an integrated system of CO2 removal and O2 regeneration was designed to work under experimental conditions for 50 people in a submarine cabin during prolonged voyages. The integrated system comprises a solid amine water desorption （SAWD） unit for CO2 collection and concentration, a Sabatier reactor for CO2 reduction and a solid polymer electrolyte （SPE） unit for O2 regeneration by electrolysis. The performances of the SAWD-Sabatier-SPE integrated system were investigated. The experimental results from the SAWD unit showed that the average CO2 concentration in the CO2 storage tank was more than 96% and the outlet CO2 concentration was nearly zero in the first 45 min, and less than 1/10 of inlet CO2 after 60 min when input CO2 was 0.5% （1000 L）. About 950 L of CO2 was recovered with a recovery rate of 92%-97%. The output CO2 concentration was less than 0.2%, which showed that the adsorption-desorption performance of this unit was excellent. In the CO2 reduction unit we investigated mainly the start-up and reaction performance of the Sabatier reactor. The start-up time of the Sabatier reactor was 6, 8 and 10 rain when the start-up temperature was 187.3, 179.5 and 168 ℃, respectively. The product water was colorless, transparent, and had a pH of 6.9-7.5, and an electrical conductivity of 80μs/cm. The sum of the concentration of metal ions （Ru^3＋, Al^3＋, Pb^2＋） was 0.028% and that of nonmetal ions （Cl^-, SO4^2-） was 0.05%. In the O2 regeneration unit, the O2 generation rate was 0.48 m^3/d and the quantity was 2400 L, sufficient to meet the submariners＇ basic oxygen demands. These results may be useful as a basis for establishing CO2-1evel limits and O2 regeneration systems in submarines or similar enclosed compartments during prolonged voyages.