Recovery of Green Polyols from Rigid Polyurethane Waste by Catalytic Depolymerization

Abstract

Polyurethane (PU) is one of the most versatile polymers available and can be found in an infinite number of formats ranging from rigid or flexible foams to elastomers. Currently, most Rigid PU Foam (RPUF) waste is landfilled, even though a small amount is mechanically recycled, in which the material is conditioned in size to a very fine powder, which is introduced as a filler. In this work, chemical recycling of two types of rigid PU foams is studied, the major difference being the aliphatic or aromatic nature of the isocyanate used in the synthesis. A solvolysis process is developed, a chemical depolymerization that breaks the chains by means of a chemical agent, a solvent, in the presence of a catalyst and under controlled process conditions. The glycolysis products are purified by vacuum distillation, centrifugation, and acid water treatment, depending on the most suitable process for each waste type. Optimal process conditions are established to obtain high-purity green polyols by performing a set of catalytic glycolysis reactions at laboratory scale with the previously conditioned RPUF waste samples. The physicochemical properties of the polyols, such as hydroxyl value, acid value, average molecular weight (Mn), and viscosity, are analyzed. The chemical structure and thermal stability of the polyols are studied by means of FTIR and TGA, respectively. Partial substitution of the commercial polyol (up to 15 wt.%) by the recycled polyols for RPUF synthesis is studied and characterized.

Opportunities in Closed-Loop Molecular Recycling of End-of-Life Polyurethane

“…Alkali metal hydroxides and organic/inorganic metal salts are common catalysts for glycolysis. For example, addition of sodium hydroxide (NaOH), sodium acetate (NaOAc), or iron chloride (FeCl 3 ) improved both rate and conversion of glycolysis with EG. ,− With the addition of a catalyst, glycolysis with EG reached 90% conversion within 1 h, while without a catalyst glycolysis was limited to 80% overall conversion after 5 h. The addition of a potassium octoate catalyst to the glycolysis of PU with DEG expedited the kinetics to a rate comparable to that observed with EG which increased the yield of repolyol to 80%, compared to 40% without a catalyst . Furthermore, Maioli et al demonstrated glycolysis of PU assisted by ionic liquids, giving 70% yield of repolyol in DEG or glycerol medium with 1-butyl-3-methylimidazole trichloromanganate or 1-butyl-3-methylimidazole trichlorozincate catalysts .…”

Recycling of polyurethanes: where we are and where we are going

“…Pursuing this research, the same group 134 employed a glycolysis process for the recovery of polyols from rigid polyurethane foams either aromatic or aliphatic. Ethylene glycol or diethylene glycol was employed as a glycolysis reagent; sodium hydroxide, sodium acetate or diethanolamine was utilized as a catalyst.…”

Accelerated Aging on the Compression Properties of a Green Polyurethane Foam: Experimental and Numerical Analysis

“…However, there is a lack of scientific publications regarding the lifespan of PUFs where their mechanical properties are relevant, such as sandwich panels [ 6 ]. Many studies regarding the synthesis, characterizations and applications of bio-based PUFs are being carried out every year due to its pairing characteristics with oil-based foams as well as its relative low cost and eco-friendly origin [ 7 , 8 , 9 , 10 ]. PUF is a two-phase material composed of a continuous polymer matrix and the gas in the discretely distributed cells.…”