Abstract
Polyurethanes (PU) are a general class of polymers prepared by the polyaddition of isocyanates and hydroxyl group containing compounds. PU foams are formed via the reaction of poly-isocyanate and multi-functional hydroxyl compounds resulting in urethane linkages. The foams are formed in wide range of densities and maybe flexible, semi-flexible or rigid in structure. To control the foam structure, blowing agents are employed. These agents are introduced during foam formation through volatilization of low-boiling liquids or through the formation of gas due to chemical reaction. Additionally, surfactants, catalysts, etc. are used during the manufacturing of foams. PU, including PU foams, is one of the most important groups of materials today and hence, their recycling has been of great interest. Many methods of recycling PU are available and many more are being studied further. However, no method has seen large scale commercialization or is brought into regular practice. The objective of this review is to bring to light the various technologies available and their current status of development as well as newer upcoming methods that may be available in the future.
Highlights
The world polymer and plastic industry has produced about 322 million tons of materials in 2015, including thermoplastics and polyurethanes (PU)
PU foams are formed via the reaction of poly-isocyanate and multi-functional hydroxyl compounds resulting in urethane linkages
Polyurethanes have become an integral part of the human lifestyle today
Summary
The world polymer and plastic industry has produced about 322 million tons of materials in 2015, including thermoplastics and polyurethanes (PU). China is the largest producer with almost 90 million tons followed by Europe with 58 million tons [1]. The total annual production of PU-based products was nearly 11.5 million tons in the Asia Pacific region and it is projected to be over 15.5 million tons in 2019. PU is one of the most widely used polymer materials be-. PU foams may be classified into three types based on their densities: these are flexible, semiflexible, semirigid, and rigid foam. Because of this versatility, PU is widely used for a variety of applications such as furniture, insulation walls, roofs, coatings, adhesives, and automotive parts [2] [3] [4]
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