PUR is widely used as flexible, semi-rigid, rigid and reinforced rigid PUR foams in furniture and bedding, cushioning materials in the automotive industry, as thermal insulation in the construction or the refrigeration industry and also as PUR elastomers in shoe soles, as coatings, adhesives or sealants. Every year, more than 30 million mattresses reach their end of life, as well as more than 1500 kton of upholstered furniture in the EU. This represents more than 600 kton of PUR foam. The main waste processing technologies for this EoL PUR foam include incineration and landfill.
Problem
This scrap PUR material may be reused by grinding it to PUR powder and adding this powder as a filler in the PUR formulation, or in a rebonding process whereby the waste foam fragments are bonded to each other by means of a binder to produce carpet underlays, pillow fillings or athletic mats.
Besides representing an environmental pollution problem, these disposal techniques have an economic loss associated with both the land required for landfill and the permanent loss of costly materials as used in the preparation of PUR materials. Therefore, the main interest is to consider their recovery and reuse.
Chemical depolymerisation of PUR materials may be achieved by hydrolysis, hydroalcoholysis, alcoholysis and aminolysis.The most commonly used method in chemical depolymerisation of PUR materials is the alcoholysis method. Alcoholising methods for PUR materials are either mono-phase methods or split-phase methods that induce additional steps including evaporation or distillation, and extra purification.
Solution
An improved split-phase method for alcoholising and hydrolysing PUR materials which is economically advantageous to operate and which yields at least two phases would allow to recycle and recover both the polyol compound from one phase and the diamine compounds from the other phase and to reuse said polyol compound and diamine compounds in a process for preparing new polyurethane materials (circular process).
Recticel’s invention provides a method for alcoholising and hydrolysing polyurethane (PUR) materials including the following steps:
- contacting the polyurethane material with at least one alcoholising compound, thereby forming a reaction mixture (M0) and allowing the polyurethane material and the alcoholising compound to react in said reaction mixture, thereby forming a mixture
- allowing the mixture to separate into at least an upper phase [phase (A)] and a lower phase [phase (B)], wherein phase (A) and phase (B) are two immiscible phases;
- subjecting phase (B) to at least one hydrolysis step, thereby forming a phase (B1); wherein the at least one alcoholising compound is characterized by a melting point of lower than 200 °C; wherein the at least one alcoholising compound is characterized by a hydroxyl functionality of at least 2; and with the proviso that the at least one alcoholising compound is not glycerol.
The method, wherein the mixture is allowed to separate into two immiscible phases, phase (A) and phase (B), wherein phase (B) comprises at least a toluene diamine compound [TDA compound] and a toluene dicarbamate compound.
The method, wherein the reaction mixture further comprises at least one alcoholysis accelerator selected from heterocyclic amines, straight or branched chain aliphatic amines, cycloalkylamines, aromatic amines or cyclic amides, preferably cyclic amides such as 2-pyrrolidone, valerolactam, caprolactam and mixtures of two or more thereof.
Advantages
Because it is beneficial to obtain a recovered polyol compound that is very similar in terms of molecular weight and in particular hydroxyl value to the polyol compound which was originally used to prepare the PUR material, it is highly desirable to use chemical depolymerisation to recover the chemical constituents of the PUR material, such as the polyol or polyisocyanate compound, to manufacture new PUR materials. The alcoholysis is carried out by reacting polyether polyurethane foams with saturated alcohols having a boiling point between 185-220 Ć. The hydroxyl functionality of this saturated alcohol causes dissolution of the polyurethane, thereby forming dissolution products which comprise polyol, ureas, and carbamates.
