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121.
122.
Thermoplasticization of High Amylose Starch by Chemical Modification Using Reactive Extrusion 总被引:2,自引:0,他引:2
Jacqueline Stagner Vanessa Dias Alves Ramani Narayan Adelaide Beleia 《Journal of Polymers and the Environment》2011,19(3):589-597
Modified thermoplastic high amylose starch (MTPS) was synthesized by reactive extrusion in the presence of maleic anhydride
(MA) as an esterification agent in a twin-screw extruder. The objective of this work was the preparation of reactive thermoplastic
starch in the presence of glycerol and with different amounts of maleic anhydride (MA) and free-radical initiator, in order
to improve processability and reactivity. The concentration of MA added varied from 2 to 6 wt% (of starch + glycerol), and
the free-radical initiator, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, also called Luperox 101, varied from 0.1 to 0.5
wt% (of starch + glycerol). Characterization of maleated thermoplastic starch was performed using dynamic light scattering
and thermal analysis. Further, proof of chemically modified extrudate was determined by Fourier transform infrared spectroscopy
and by soxhlet extraction with acetone. The modified high amylose corn starch (20 or 30% glycerol) could be pelletized and
gave pellets that were more transparent than thermoplastic starches not modified with maleic anhydride. There was negligible
change in hydrodynamic radius as the percentage of maleic anhydride increased. However, as the percentage of Luperox 101 increased,
the hydrodynamic radius decreased. It could be inferred that the molecular weight decreased as the percentage of free-radical
initiator increased. Using the maximum temperature in the extrusion process of 165 °C instead of 135 °C caused a decrease
in the hydrodynamic radius, due to the high influence of the temperature profile on the molecular weight of the thermoplastic
starch. The MTPS samples presented higher melting temperatures compared to TPS samples. The soxhlet studies indicated that
the plasticizer, glycerol, was chemically linked to the starch. Using the maximum temperature of 165 °C versus 135 °C in the
extrusion temperature profile resulted in more interaction between glycerol and starch. 相似文献
123.
124.
Investigation of heavy metal accumulation in Polygonum thunbergii for phytoextraction 总被引:5,自引:0,他引:5
Kim IS Kang KH Johnson-Green P Lee EJ 《Environmental pollution (Barking, Essex : 1987)》2003,126(2):235-243
In this study, cadmium (II), lead (II), copper (II) and zinc (II) were determined in Polygonum thunbergii and soil from the Mankyung River watershed, Korea. Soil samples contained detectable lead (<17.5 g g(-1)), copper (<8.4 g g(-1)) and zinc (<24.5 g g(-1)), whereas cadmium was undetectable. Whole plants of P. thunbergii contained detectable lead (<320.8 g g(-1)), copper (<863.2 g g(-1)) and zinc (<2427.3 g g(-1)), whereas cadmium was detectable only in the stem (<7.4 g g(-1)) and root (<10.1 g g(-1)). Whole plant concentrations were very different for each metal, particularly in the case of zinc. The mean content of heavy metal in the whole plants increased in the order of cadmium (8.5 g g(-1))相似文献
125.
John M. Cheeseman Steven C. Lund Coleman A. Doggett Thomas O. Perry 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1213-1216
Meteorological dispersion modeling and pine trees used as "integrating monitors" were used to consider the probable source of a phytotoxic pollutant producing symptoms previously un-reported in the literature. Two sources, a chemical plant (A) and a fabric finishing plant (B) north of Raleigh, NC, were considered using the Air Quality Display Model (AQDM). Using the ability of this model to accommodate extra receptors corresponding to "monitoring" sites, we found good correlation between observed injury and predicted relative concentrations due to assumed emissions from source A. The poor agreement between predicted and observed injury if source B alone were modeled (or both sources together) suggested that source A alone emitted the causal agent. 相似文献
126.
127.
A. I. Clark A. E. McIntyre J. N. Lester R. Perry 《Environmental monitoring and assessment》1984,4(3):205-232
Air quality impact assessment (AQIA) is an important technique for determining the relative contribution to ground level pollutant concentrations of specific current or future source emissions at receptor sites. The principal activities in AQIA are air quality modelling and monitoring techniques. The choice of techniques which are applicable to a particular situation is intimately related to the problem to be assessed. A review of relevant modelling techniques has been presented, with emphasis placed on Gaussian plume models because of their ease of use and broad applicability. Alternative modelling techniques have been suggested when departures from the Gaussian form in the atmosphere occurs or when more detailed information on atmospheric chemistry, deposition or long range transport is required. The objectives and techniques of ambient air quality monitoring have been examined and the siting of instruments, duration and frequency of sampling, choice of monitoring rationale (fixed or mobile), minimization of sampling errors, data storage and analysis are discussed. Modelling and monitoring are essential to successful AQIA. An orderly approach to the principles and procedures involved in performing AQIA studies, using these two techniques in conjunction, has been presented. 相似文献
128.
Diurnal variability in chlorophyll fluorescence caused by dynamic irradiance conditions is an important issue when using pulse amplitude modulation fluorometry to measure physiological conditions of plants at the landscape scale. We examined the use of slopes and y-intercepts of diurnal effective photochemical efficiency of photosystem II (PSII) (ΔF/F m′) versus photosynthetically active radiation (PAR) regressions in addition to direct measurements of maximum photochemical efficiencies of PSII (F v/F m) values to assess physiological status of Thalassia testudinum seedlings in a controlled mesocosm study. Seedlings were exposed to two light treatments (full sun and 50–70 % light reduction) and three salinity treatments (20, 35, and 50). Measurements were taken at 0600, 0900, 1200, 1500, 1800, and 2100 hours in order to assess the diurnal variation in photochemical efficiency of PSII and PAR, with measurements at 2100 providing F v/F m. Results indicated significant effects of light and salinity on regression y-intercepts and measured F v/F m values. Shaded seedlings had higher values for both parameters, suggesting low-light acclimation. The highest salinity treatment resulted in significant reductions for both parameters, suggesting stress. Stress was also indicated by significant reductions in both seedling leaf growth and mean differences between seedling leaves and media osmolalities in the hypersaline treatments (152.0 ± 26.4 vs. 630 ± 40.2 mmol kg?1 for the control treatments). Slopes of ΔF/F m′ versus PAR significantly differed with varying light treatments, with full sun seedlings exhibiting shallower slopes than shaded seedlings, indicating higher efficiency of dissipation of excess energy (photoprotection). These experimental results confirm field data suggesting that diurnal ΔF/F m′ versus PAR regressions are responsive to changes in the physiological status of T. testudinum and that the y-intercepts of diurnal regressions may be used as a proxy for F v/F m. 相似文献
129.
Chemical extractions have been shown to measure the biodegradable fraction of aromatic contaminants in soil; however, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for cyclodextrin extractions to predict hexadecane biodegradation in soil. Soils were amended with 10 or 100 mg kg−1 of a model alkane n-hexadecane and 100 Bq g−114C-n-hexadecane. Correlations between the extents of mineralisation and extractions of the 14C-contaminant were determined. Solvent shake extractions and aqueous CaCl2 extractions were poor predictors of hexadecane bioaccessibility. However, the novel HP-α-CD shake extraction showed close correlation (r2 = 0.90, n = 36, p < 0.05) to the mineralisation data. This novel extraction technique has the potential to be used to assess the biodegradable aliphatic hydrocarbon fraction in contaminated soils. 相似文献
130.