Polyethylene ponds

In the sheeting market, the low density polyethylenes are less important than the high density resins. The high density resins have excellent chemical resistance, stress-crack resistance, durabiUty, and low temperature properties which make them ideal for pond liners, waste treatment faciUties, and landfills. In thicker section, HMW-HDPE sheet makes good containers, trays, tmck-bed liners, disposable items, and concrete molds. The good durabiUty, abrasion resistance, and light weight are critical elements for its selection. 

Many polymers are used in barrier applications, either to keep contents in or contaminants out. Food packaging is an excellent example of such usage. Plastic films and containers of many types are used to package food. Blow moldedbottles often contain numerous layers, each of which provides specific benefits. Polyethylene layers are excellent water barriers, polyvinyl alcohol is a good oxygen barrier, and polyethylene terephthalate impedes the diffusion of carbon dioxide from carbonated drinks. Other barrier applications include toothpaste tubes, diaper backsheets, tarpaulins, and geomembranes, which are used to line containment ponds and landfill pits. 

It is fairly true to say that the use of chlorinated polyethylene has not been large, possibly due to the greater ease with which the chlorosulphonated polyethylene (Hypalon), a closely related competitor material, can be cured. When used, chlorinated polyethylene has found its major use in the wire and cable industry. It is also used in pond liners. 

The excellent UV stability of chlorosulphonated polyethylene has led to wide use as a roof sheeting material, the ability to compound this material to slowly cure at ambient temperatures being an added advantage another sheeting application is pond liners. Wire and cable applications, coated fabrics, and items made from them, hoses and moulded goods are other areas in which this material finds use. 

Polyethylene and VAE or EBA copolymers such as LED PE geomembrane pond liners, HD PE alloy geomembrane liners, lightweight tarps and containment liners. Beware of low elongations at yield and the stress cracking sensitivity of certain polyethylenes. 

Chlorinated poly (vinyl chloride) (CPVC) has increased Tg compared to PVC, and this increases its upper use temperature. Applications include hot- and cold-water pipe as well as pipe for the handling of industrial chemical liquids. Chlorinated polyethylene (CPE) finds use as roofing and other vapor barrier membranes, as pond liners, and as an additive to improve the impact strength of PVC. 

Polyethylene in solution is treated with chlorine and sulfur dioxide to introduce approximately 1.39k sulfur and 29% chlorine into the polymer. Most of the chlorine is attached directly to the carbon atoms in the backbone of the polymer, The remainder is in the form of sulfuryl chloride groups, SO CI, through which crosslinking occurs In the curing step with metal oxides. The material has good oxidation and ozone resistance and thus overall excellent weather resistance. Calendered stocks are used for lining ditches and ponds, for example. 

Air. Concentrations of fenitrothion in air sampled 10 cm above treated ponds were highest in the first 24 hours post-treatment (Table III). GLC analysis of the extracts from polyurethane foam traps indicated that only fenitrothion was present. The levels of fenitrothion were generally higher above shaded ponds. This was expected because the polyethylene shelter reduced wind movement over the water surface which would dilute the observed concentrations. Recently Mallet and Volpe (7) reported the detection of ng/L levels of AF as well as fenitrothion in air samples collected near treated areas in New Brunswick (Canada) however, the source of AF was not clear from their study. 

A salt-gradient solar pond was constructed in 1975 at the the Ohio Agricultural Research and Development Center in Wooster, Ohio ( ). The first liner, a chlorinated polyethylene liner, 50 mil in thickness, failed on filling of the pond. It was replaced by a second liner of the same material which failed two years later in 1977. The third liner, Shelter-Rite XR-5, has been in use since August 1977 and continues in service. 

In 1970, DuPont Introduced Hypalon A5, a thermoplastic grade of chlorosulfonated polyethylene synthetic rubber, for applications as a pond liner material. It was one of the first thermoplastic elastomers retaining easy seamablllty both in the fabrication plant and in the field, and possessing outstanding resistance to outdoor weathering. 

Limnocorral Study A limnocorral is an enclosed water column in a lake, pond, or marine environment that may or may not be in contact with the bottom sediments. Such a system has been used to study the effects of a wood preservative, tetrachlorophenol (Fig. 10.5). ° The water column (5 m x 5 m and 4.5 m deep) is enclosed by vinyl walls and a polyethylene liner was installed... 

Carbon black is used as a stabilizer in a limited number offormulations where color is not a criterioiL It not only absorbs light, but it can also react with free-radical species that might be formed. The weathering properties of polyethylene are improved by the incorporation of carbon blacks (at 2%-3% concentration). Weather-resistant wire and cable insulation, pipe for outdoor applications, films for mulching, and water conservation in ponds and canals may be made from polyethylene containing carbon black. 

The spent fuel neutron counter (SFNC) is a prototype neutron-detector system that verifies closely packed spent fuel assemblies stored in a spent fuel pond (Ham et al. 2002). The system contains a fission chamber moderated by a polyethylene cylinder housed in a watertight stainless steel enclosure. The SFNC measures total neutron signals from long-cooled spent fuel assemblies while in their storage position, without requiring them to be moved. The technique can detect a missing fuel assembly. These measurements are performed underwater in a gap between four assemblies. 

Similarly, thermoplastic grades of chlorosulfonated polyethylene (CSM), such as Hypalon 45 (DuPont), are sometimes reinforced with PVC in roofing and pond liners. Such blends are also most conveniently mixed in an internal mixer. Often, such blends are formulated to crosslink in service by the reaction of metal oxides with CSM aided by atmospheric moisture. Blends of both CSM and CPE with PVC have also been used in such applications. 

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