How might we address in the field polyethylene (PE) wrinkling and/or tenting in different climates?
- Polyethylene is an excellent liner for many applications – both covered and uncovered. Because PE expands and contracts up to 2% over width and length, expect it to shift in the course of installation [LLDPE and HDPE slightly more than RPE (reinforced) membranes]. Polyethylene sheets expand or contract within hours of deployment. Overnight, movement follows temperature changes. Remember to focus on anchor trench back-fill at the best time & temperature. If uncovered (no water, dirt or ballast anchors on the liner), shifts can stress the membrane at pipe boots and attachment to structures. Installers typically leave enough liner in anchor trenches so inches (or feet) can shift out of trench into the cell as temperatures fluctuate. Beware “locking in” that anchor trench in a hurry — only to find the next morning the membrane tightened up and toes of slope lifting off the subgrade. Weight at slope bottoms minimize the effect (sandbags, ballast bags or tubes). Filling with liquid is the best way to assure PE membranes stay in contact with subgrade at all points within a cell (even a foot or two depth).
- Welding PE membranes at relatively cold times – followed by hot stretches – may lead to wrinkling throughout a cell. That doesn’t mean “too much liner” was installed: only that it expanded (and will continue to do so in cycles until covered or filled). As with back-fill of an anchor trench, keep that in mind for determining safest times to cover a PE liner with soils or gravel.
Is it possible to weld flexible (plasticized) PVC to rigid PVC pipe by hot air welding?
- The difficulty with hot air welding is that the melting point of the rigid and flexible PVC may not match up well enough to make welding in this method easy.However, this problem has an easy solution. You can solvent bond flexible PVC to rigid PVC pipe quite easily. Normally, PVC pipe cement is a mixture of THF (tetrahydrofuran) mixed with dissolved PVC pipe resin (and a few other chemicals to slow the reaction). The main ingredient is THF. That is the same solvent used to weld flexible PVC liner materials. Using THF to weld rigid to flexible PVC is a fairly common procedure. Make sure all the pieces are pre-cut and fit together. Slide a THF laden brush between the surface of the liner and the pipe you want to weld. A little roller pressure and it should set up nicely.
What design features are essential for baffle curtains?
- Curtains are effective ways to maximize the flow and settling processes in waste-water, sedimentation and various industrial lagoons. Baffle curtains are often made of reinforced Polypropylene (RPP). More corrosive fluids may require use of Cool-Guard, XR-5 or reinforced PVC products.. Flexible and durable, any material needs proper hardware and attention (e.g. never leave it flapping in the wind) to assure long-term service. Floats can be built into the top edge and often weights hold the curtain bottom where it can best function. Never assume the liner material can handle the stresses (without reinforcement) around cables, chains, anchor points and flow through windows.
Is chlorine, the raw material used to make PVC toxic – since “natural” organochlorides are not known to exist?
- Numerous instances of natural organochlorides exist. In fact, life itself could not exist without chlorine chemistry.
Is smoke from the wedge welding process hazardous?
- The concentration is non-toxic and wedge welding outdoors poses no risk.
Does PVC decompose and create groundwater hazard when it is subjected to landfill leachate?
- PVC is a highly stable material that is extremely resistant to the aggressive chemical environment found in landfills. Any plasticizers released when PVC is buried under these conditions would constitute minuscule amounts over an extended period of time and thus present no threat to human health or the environment. Forensic studies show the liner to be in excellent condition after 30 years of burial.
Do rats and rodents eat the PVC geomembrane?
- It is only possible to eat the geomembrane at an edge, fold, or seam onto which the animal can grip. Since PVC geomembranes have 80% less field seams than polyethylene geomembranes, the likelihood of having an edge, fold, or seam is significantly less. However, it is important to note the following information about PVC geomembranes:
- (1) they possess no compounds that have any food or nutritional value to rats and rodents,
- (2) the materials are not addictive, and
- (3) the reason for an animal eating through a geomembrane is probably to obtain access to the other side for food, warmth, or some other reason.
Is PVC environmentally “friendly”?
- Not only does PVC outlast and outperform many competitive materials, but because 50 percent of its base polymer comes from common salt, an inexpensive, renewable resource, it is also much preferred to materials that rely 100 percent on petrochemical feedstocks and those that deplete forests or ore reserves.
* Information provided by the Vinyl Institute, A Division of The Society of the Plastics Industry, Inc.