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Polyurethane waste utilization is gaining increasing priority
Global Polyurethane (PU) consumption is currently pegged at more than 10 million tons. PU waste constitutes about 5% of the municipal waste, mainly derived from post consumer products. Hence PU is increasingly becoming the target of regulators for clear understanding of regulations on its reuse and recycling as well as waste disposal. Which one of the waste generation systems will gain in PU is being discussed and debated by scientists.

The waste generation of PU waste can be done by one of the following methods:

Land filling

Mechanical recycling
Chemical recycling
Energy generation

Land filling is the most used methods so far, but with an increasing amount of PU waste it is not an ideal method of waste disposal.
Mechanical recycling essentially means converting waste into regrind and using it along with virgin material. Grinding PUR wastes into powders and then re-using these powders in various ways constitute the mechanical recycling approach. Wastes for this process can come from factory trim and scrap, as well as post-consumer products. The powdered PUR is available as filler in production of PUR foams or elastomers. When used as fillers, the powders are usually first added to the polyol component in a PUR production process. Molded PUR products, such as auto seat cushions can contain up to 20% regrind without any deterioration in properties or performance. Mechanical recyclers grind PUR into powders with various milling and knife-cutting processes. To be used as fillers, PUR particles should be less than 200 microns in size, and preferably under 100 microns. Shredded PUR foam wastes can be rebonded using heat, pressure and an adhesive binder. Rebonding is commonly used to make vibration sound dampening mats, flooring, sports mats, cushioning and carpet underlay. In a similar process, known as adhesive pressing, PUR granules are coated with a binder and cured under heat and pressure. Contoured products are made from adhesive pressing; they include automotive floor mats and tire covers.
RIM and reinforced-RIM parts can also be ground into small particles, which can be molded under high pressure and heat to form solid parts for the auto industry. These compression-molded solid parts - such as pump and motor housings, and catalytic converter shields, can contain up to 100% RIM regrind.

Chemical recycling is a solution that cannot be used for a larger proportion of PU products. Only moulded products can be used for this method.

Energy generation is possibly the best method and is increasingly getting popularity. There are essentially gasification and pyrolysis methods that are used for energy generation. Studies have found that PUR can be added to municipal solid waste in amounts up to 20% by weight without increasing levels of undesirable gas emissions or ash. Further PUR can be fed into advanced incinerators linked to thermal energy recovery units and flue-gas cleaning equipment. Such combination units are said to be capable of providing up to 10% of electricity requirements of local communities. PUR wastes have also been used as fuel for domestic heating and cement kilns.

Technologies for recycling polyurethane wastes have been under development for more than a decade, but the recycling issue has recently become more urgent. Reasons for this include the closing of landfill sites, rising waste disposal fees, and government regulations that mandate quotas for recycled plastics. The main technologies for PUR recycling are energy recovery, mechanical recycling and chemical recycling. Which of these methods is suitable depends on the product being recycled, the location, local energy costs, and intended end-use markets. Much of the PUR recycled today is industrial scrap. The lack of a collection, sorting and processing infrastructure has hindered recycling of post-consumer PUR wastes to some extent, although industry is addressing this issue through the efforts of various trade groups.

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