Solvent-free polyurethane pastes are often used for manufacturing synthetics which find application as surface goods in the shoe and leather goods industries, for example, handbags, luggage, and upper materials for shoes.
Solvent-free polyurethane pastes are typically composed polyol and isocyanate prepoloymers and may also include fillers, pigments and flow-control agents.
Waste paste containing polyurethane is sometimes produced due to mistakes, for example, defective batches, and when processing equipment such as pumps and lines are cleaned with solvents, e.g., methyl-ethyl ketone, to remove residues. Thus, polyurethane waste pastes may be either solvent-free or contain solvent.
Plants typically process solvent containing polyurethane waste pastes by expelling solvent. Depending on the residual solvent content, the expelling processes may produce a highly viscous or heavily encrusted non-flowing residue which must be disposed of as special waste material. Special disposal requirements may also apply to many solvent-free waste pastes because they can rarely be used or reprocessed.
The possibilities for modifying or reprocessing polyurethane paste wastage to enable reuse or simplify disposal are limited.