a disposable diaper can be almost completely degradable when each of its diaper closure tapes has as its backing a polyolefin film containing a chemical prodegradant such as a metal salt together with an unsaturated elastomer such as a block copolymer of styrene and isoprene of butadiene . preferably , the polyolefin of each of those backings is a copolymer of polypropylene and polyethylene or a blend of crystalline isotatic polypropylene and a compatible ethylene - based polymer .