Thermoplastic polymers like polyolefins can be remelted and reformed into new items. This approach is referred to as mechanical recycling and is usually the simplest and most economical form of recovery.  Post-consumer plastic will usually already bare a degree of degradation. Another round of melt-processing will exacerbate this, with the result being that mechanically recycled plastic will usually have poorer mechanical properties than virgin plastic.  Degradation can be enhanced by high concentrations of hydroperoxides, cross-contamination between different types of plastic and by additives present within the plastic. Technologies developed to enhance the biodegradation of plastic can also conflict with its recycling, with oxo-biodegradable additives, consisting of metallic salts of iron, magnesium, nickel, and cobalt, increasing the rate of thermal degradation.  Depending on the polymer in question, an amount of virgin material may be added to maintain the quality of the product.