I think they're called thermosetting plastics and can only be heated and shaped once.....
I was watching Bang goes the theory recently, a television programme run by the Open University. Some plastics are not biodegradable and they can't be broken down naturally through the chemical or weathering process or even the decomposition process, and most plastics take many years to degrade. However, scientists have recently found a way to combat this problem. They have found an organism that eats the plastic that doesn't degrade naturally. These bacteria eat the plastic and pass a by product of biodegradable plastic. Thus, scientists have found a way to recycle even the toughest plastic.
Yet, thermosetting plastics are one example, although they can be recycled...to some limited extent...by grinding and using as inert filler in some other plastic. Another example is fiberglass-reinforced printed circuit boards. William Gibson has made the comment, in one of his novels, that they were using them...after scraping off the solder and electronics...as materials to laminate for handles of knives, because there was so much of it.
