There is a patent document which claims that the denim fabric can be produced from waste denim yarn. In this fabric 40%-100% of waste fiber is used. To reclaim the waste fiber, the fabric is subjected to garnetting and low tension carding, before spinning it in the form of yarn and using it to weave fabric.
The only thing remains to be seen is the techno-commercial viability of such product. Garnetted fibers produce problems in carding, drawframe and posisbly in high speed weaving. Though it is claimed that such a denim will have adequate strength, it will remain a challange. It is suggested that some virgin fiber should be added in the garnetted fiber or it is subjected to some lubrication before spinning. All this will lead to increase in process cost.
Neverthless, this is a good news for your torn denim jeans which can now be recycled into a new one without damaging the environment. Just give your jeans to the local rag picker and it will eventually find itself into a new jeans. However, if you don't want to part away with your jeans, here are the instructions what you can do with them. Of course, there are 25 other ways to make use of your old jeans.
Worldwise, concerns are growing reagarding using the denim waste. A project making the use of denim shoddy is one of such cases. It is being used in myriad ways including its use in oil filters. Successful attempts have been made to make paper out of denim wastes.
Note: Garnetting is a process by which material such as threads, rags, woven cloth scraps, and the like are broken up and returned to a substantial fluffy, fibrous condition simulating the original condition of the fiber. This is done by first chopping the material to small pieces (e.g. two to six inches) and then running the pieces through a series of high speed cylinders which can be covered with wire (e.g. saw wire), steel spikes, or the like. The treatment breaks up the material into individual fibers typically having a length of one and one-eighth inches or less.