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. |