A ground rice hull ash prepared by a new burning process has been found to be a moderately reinforcing filler for rubber. This filler, 85-90% amorphous silica and 10-15% carbon, is made by a controlled incineration process in which the bulk of the organic components of the rice hulls is removed, leaving the skeletal silica structure of the hull intact and in the amorphous state. The resultant ash is easily ground to produce fine particles, generally in the range of 0.1-2.0 μm. This filler does not adversely affect either the vulcanization characteristics or the aging of SBR, natural rubber, nitrile rubber, butyl rubber, neoprene, EPDM, and propylene oxide rubber compounds. As it is predominantly silica, it responds effectively to silane coupling agents in improving properties of the rubber compounds. It is concluded that RHA filler is a satisfactory substitute for MT black and that, in blends with blacks, it can be effectively used as a partial replacement for finer and more reinforcing blacks.
The widely different uses of geomembranes as barriers to the transport and migration of different gases, vapors, and liquids under different service conditions require a determination of permeability by test methods appropriate to the service. Geomembranes are nonporous and homogeneous materials that permeate gases, vapors, and liquids on a molecular scale by dissolution in the geomembrane and diffusion through the geomembrane. The rate of transmission of a given species, whether as a single permeant or in mixtures, is driven by its chemical potential or concentration gradient. Various methods to assess the permeability of geomembranes to single component permeants, such as individual gases, vapors, and liquids are described and data are presented. In addition, various test methods for the measurement of permeation and transmission through geomembranes of individual species in complex mixtures such as waste liquids are described and data are presented.
A research project was undertaken to assess the relative effectiveness and durability of a wide variety of liner materials when exposed to hazardous wastes under conditions simulating various aspects of service in waste storage and disposal facilities. The materials studied included compacted soil, admixes, sprayed-on asphalt and 32 polymeric membranes. Four partially crystalline polymeric sheetings, though not compounded for use as liners, were included in the study because of their known chemical resistance and their use in applications requiring good chemical and ageing resistance.The lining materials were exposed in test cells to 10 hazardous wastes (two acidic, two alkaline, three oil, a blend of lead, a pesticide and a briny industrial waste) and three media of known composition—deionized water, 5% aqueous solution of salt and a saturated solution of low-concentration (0.1%) tributyl phosphate. The polymeric materials were also exposed to wastes or environmental conditions under a variety of conditions that included primary one-sided exposure, immersion testing, two types of outdoor exposure and a pouch test. Some of the exposures were as long as 2700 days. New methods for testing polymeric materials are presented. Results indicated that some of the liner materials performed satisfactorily in contact with certain wastes but, because waste combinations can be highly specific, compatibility testing is needed to select a liner for a given waste.
Soluble catalyst systems derived from alkyl aluminum halides in combination with vanadium oxytrichloride or tetrachloride produce highly random ethylene-propylene copolymers with high catalyst efficiency. By the choice of the alkyl aluminum halide and molar ratio of aluminum to vanadium, variations in polymerization efficiency and molecular weight are possible. The copolymers prepared with these soluble catalysts show advantages in both processing and physical properties over those prepared with heterogeneous catalysts. Vulcanizates of these copolymers show somewhat different accelerated aging properties depending on the additive used along with the peroxide. Low temperature properties of copolymers containing less than 70 weight % propylene show a tendency for crystallization which is not shown by X-ray diffraction. Overall physical properties and tire tests show some preference for the 65 weight % propylene copolymer over the 50% material.
The lining of waste disposal facilities with materials of low permeability is a feasible means of preventing potentially polluting constituents in wastes impounded on the land from seeping out of the impoundment and entering the groundwater. A great array of materials, including fine-grain soils and clays, asphaltic compositions, concretes, and polymeric membranes, are potential candidates for use as liners. The use of materials for lining waste impoundments and disposal facilities is comparatively new, and experience in their field performance is limited. Considering the variety of lining materials that are available and the vast number of compositions of the waste streams that must be impounded, a body of test methods is needed to: (1) guide the selection of liners for specific applications, (2) assure that the quality of the liner that has been selected is placed on the site, and (3) monitor the condition of the liner during service. This paper discusses the test methods that are currently available for use in liner technology, and describes an overall approach to the testing of liners, principally membrane liners. Emphasis is placed on tests needed for liner selection and impoundment design. Of particular interest are the descriptions of several tests designed to simulate the conditions of service of liners in actual waste impoundments. Data from two ongoing Environmental Protection Agency (EPA) liner research projects are presented to illustrate the tests that are described.
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