Recycling Process	Description	Process Yield
Mechanical recycling	Covers recycling routes to reuse PU without chemical decomposition.	The process reduces the waste into small particles of up to few millimeters in diameter to fine powders which can be used as inert fillers.
Chemical recycling	Chemical recycling includes glycolysis, hydrolysis, aminolysis, and thermo-chemical and biodegradation processes.	Chemical recycling is done to recover the initial raw materials, especially to produce high-quality recycled monomers of polyol to include in a new polymer.
Chemolysis	PU foam waste can be gradually de polymerized to form various organic compounds, original reactants, or other low molecular weight oligomers.	The properties of products formed by chemolysis of PU depend greatly on the type of degradation reagents used during the chemolysis process.
Hydrolysis	Hydrolysis of PU is based on the chemolysis of waste PU foam with water vapor and alkali metal hydroxide as a catalyst at high temperature under high pressures.	Hydrolysis of PU foam has many side reactions which are responsible for undesired by-products such as 4,4’-diaminodiphenylmethane (MDA), 2,4-toluylene diamines, and 2,6-toluylene diamines.
Alcoholysis	Alcoholysis reaction is carried out using a series of alcohols and metal hydroxide such as sodium hydroxides or potassium hydroxides at high temperature under high pressure.	This process produces the original reactants, i.e., polyols and urethane products.
Acidolysis	Acidolysis reactions were carried out by various types of inorganic and organic acids.	This process leads to a series of products such as amides, polyols, amine salts, and oligo ureas.
Aminolysis	Aminolysis method was carried out by the amine method which generally used hydroxyl and amino-derived compounds.	Aminolysis methods of PU foams generated various degraded product such as substituted polyol and polyamines compound.
Glycolysis	Glycolysis carried out through trans esterification reaction by reacting PU foam with various diol compounds at elevated temperatures.	The main objective of glycolysis of PU foam is the effective recovery and reuse of polyols.
Combined Chemolysis	The combined chemolysis methods comprise multiple stages and include processing with different chemical treatment such as hydroglycolysis, glycolysis-aminolysis, and aminolysis-hydrolysis.	The process not only uses a different chemical agent but also consists of two or more steps which combine totally distinct chemical treatment.
Hydroglycolysis	PU foam is degraded by a combination of various chemicals such as water, diethylene glycol, and alkali metal hydroxides such as lithium hydroxides (LiOH), sodium hydroxides, and potassium hydroxides at elevated temperature.	This process produces higher quality product mixture against simple glycolysis process.
Glycolysis-Aminolysis	The decomposition of PU by ethylene glycol and ethanolamine mixtures at elevated temperatures.	The resulting product being can be used to produce rigid PU foams.
Aminolysis-Hydrolysis	Chemolysis of PU foam through an aminolytic chain cleavage followed by hydrolysis.	This process yields original polyols and amines.