PubMed · 15398098
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H J TRURNIT. 1950-01-06. Protein permeability through thin organic layers.. https://doi.org/10.1126/science.111.2871.1
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Percolate production and precipitation data for a full-scale landfill in operation measured over a 13-year period were used to evaluate the impact and importance of the hydrological conditions of landfill sections on the percolate production rates. Both active (open) and closed landfill sections were included in the evaluation. A simple top cover model requiring a minimum of input data was used to simulate the percolate production as a function of precipitation and landfill section hydrology. The results showed that changes over time in the hydrology of individual landfill sections (such as section closure or plantation of trees on top of closed sections) can change total landfill percolate production by more than 100%; thus, percolate production at an active landfill can be very different from percolate production at the same landfill after closure. Furthermore, plantation of willow on top of closed sections can increase the evapotranspiration rate thereby reducing percolate production rates by up to 47% compared to a grass cover. This process, however, depends upon the availability of water in the top layer, and so the evaporation rate will be less than optimal during the summer where soil-water contents in the top cover are low.
A new active material for the treatment of uranium-contaminated groundwater using permeable reactive barriers has been developed. This material, called PANSIL, is an example of a tailored ligand system that selectively removes a contaminant from solution. The active medium in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating. PANSIL is highly effective at sequestering UO2(2+) from solution when the pH is between about 5 and 8 and can preferentially sequester UO2(2+) from solutions that are typical of the groundwater from a mine tailings site, due to the stability of the polyacryloamidoxime uranyl complex formed. Uranium sequestration capacity will depend on the surface area of the sand that is resin coated, but in the batch of PANSIL tested (<2% resin by weight), it exceeds 4000 mg of UO2 per kg of PANSIL at pH 4.5 when the dissolved UO2(2+) concentration is greaterthan 300 mg/L. PANSIL largely retains the permeability and strength of the sand employed and therefore has suitable engineering properties for permeable reactive barrier applications.
Starch acetates (SA) have been investigated as novel, multifunctional excipients for the direct compression tableting process. In this study, the film-forming ability of SA (DS 2.8) and the effect of commonly used plasticizers on the physical properties of SA films were evaluated. The results were compared with the properties of ethylcellulose (EC). Free films were prepared by a solvent-cast method. Mechanical studies, water vapor and drug permeability tests, and thermal analysis (DSC) were used to characterize the film-forming ability of SA and efficiency of tested plasticizers. SA films were tougher and stronger than EC films at the same plasticizer concentration. Also, in most cases, the water vapor permeability of SA films was lower than that of EC films. DSC thermograms supported the findings of the tensile test: plasticizers with several small ester groups (e.g., triacetin and triethyl citrate) were the most compatible with SA. Due to the good mechanical properties, low water vapor, and drug permeabilities of the films, SA seems to be a promising film-former for pharmaceutical coatings. The toughness of SA films may result from their dense film structure, which is due to strong interaction forces between adjacent SA molecular chains.