The difference between PVC and polythene was a subtlety that had escaped me - how do you tell the difference?...
Yikes! This is important stuff. The most important bit being the 'C' in PVC.
One way to tell the difference is to burn a sample, but there may be better ways. Polythene burns in air with a blue-tinged but sooty flame, producing only carbon monoxide, carbon dioxide and water. Burning PVC in air produces horrendously sooty smoke, lots of hydrochloric acid which is a gas that you won't see, and other compounds that we'll get to later. Both polythene and PVC melt when they burn and you don't want the molten, burning stuff anywhere near your skin, but that isn't the half of it.
The simplest way to tell is usually to look at it. You'll very often find it's written on it.
The recycling symbol (a sort of curvy-pointed triangle made from arrows) on most plastic things thesedays tells you without much doubt.
http://www.earthodyssey.com/symbols.html
Polythene is made from ethylene gas (which usually comes from oil fractionation). It is available in several forms which differ primarily, but not by much, in density. All are less dense than water so they float. PVC is around 30% to 40% denser than water so it sinks, obviously for example unless it's a football.
Polythene is used primarily for packaging, things like freezer bags, carrier bags and bin liners. It's also used for pipes and electrical insulation in things like your TV aerial cable. It's 'floppier' than PVC so you can tell the difference by feel when you're used to it. When we talk about a "poly bag" it's usually polythene. Dyneema is polythene.
http://en.wikipedia.org/wiki/Polyethylene
PVC is used for a much wider range of things like stationery products, upholstery, furniture, floor tiles, pipes (less flexible than polythene pipes), window frames, and things like those cheap air beds that people take to the pool... a very very long list indeed. Toys used to account for a lot of PVC usage but nowadays there's a tendency to move away from it for that sort of thing on health grounds.
Both making and burning PVC can produce some extremely dangerous very long-lived toxins. The 'C' in PVC is from chlorine. Burning PVC, especially at low temperatures such as in a stove or camp fire, can produce dioxins and organic chlorine compounds. Some of these compounds have been infamous since for example being used as pesticides, found in our food, then in ourselves, then in our offspring (through mothers' milk) and eventually banned world-wide.
http://en.wikipedia.org/wiki/Hexachlorobenzene
http://en.wikipedia.org/wiki/Dioxin
http://en.wikipedia.org/wiki/Polychlorinated_dibenzodioxins
The Union Carbide disaster in Bhopal in 1984 produced large quantities of such toxins which to this day pollute the environment and are found in the human and animal populations.
http://en.wikipedia.org/wiki/Bhopal_disaster
Burning PVC in landfill and other waste sites is responsible for serious pollution and damage to the environment in many other parts of the world.
http://en.wikipedia.org/wiki/Pvc
The only responsible way to dispose of PVC is to get it to professional recyclers. Local governments are the unsung heroes of this story, they can burn it safely in high-temperature incinerators and the heat produced is often used e.g. for local heating schemes. Such installations are common in some parts of the world but we haven't exactly been are the forefront of development in the UK. There's one under construction in Derby at the moment, and about 200 metres from where I'm sitting there's a feedstock plant for it, which will collect local refuse, sort it, and send appropriate materials to the Derby plant for incineration. I have a stack of PVC waste to take round there once it starts operating.
