Influence of phospho-halogenated flame retardant on the chemical recycling of polyisocyanurate foams

The purpose of this work is to find a way to recycle a polyurethane foam containing TCPP as flame retardant. This foam is used at industrial level as thermal and acoustic insulator. The issue is that it is used in large quantities, making it essential to explore a method for recycling it. In the first part of the study, the foam without flame retardant is analyzed to establish the optimal working conditions that allow for the best properties of the final recycled polyols. Specifically, the type and amount of catalyst, the type of glycol, and the operating temperature are examined. From them result that potassium acetate is the best catalyst, with a concentration of 30mmol/100g waste. Without the TCPP the product obtained with the mixture DEG/PEG400 as glycol is the best, with a hydroxyl number of 276 and a viscosity of 6599cP. Working at the highest possible temperature facilitates the process. Following this, the analysis shifted to the foam containing the flame retardant, using the conditions established in the first part as a starting point and adjusting them based on the influence of TCPP. In particular, from NMR analysis is obtained that the TCPP reacts with the catalyst, for that reason a higher amount of it is required. The flame retardant reacts also with other compounds, as the amines, reducing their amount in the final product. A test was also conducted in which part of the PU foam was replaced with PETG, in order to reduce the amount of catalyst required and the viscosity of the product. In the final phase, a deamination step is necessary to reduce the 4,4’-methylenedianiline concentration below the legal limit of 0.1% by weight. During this part, various deaminating agents are tested to determine the most effective one for the analyzed product; PLA glycolyzate results to be the best, also if an increase in viscosity is observed. Finally, new foams are produced using the best glycolysis products; they are made using different amounts of recycled polyol, 0%, 25%, 50%, 75% and 100%. Tests are conducted on these foams to analyze their mechanical and thermal properties. The results yielded to increasing the amount of recycled polyol leads to worst mechanical resistance and thermal conductivity. Thermal degradability tests are done on the produced foams, from which is noticed an increase of the thermal resistance of the foam with the increase of the percentage of the recycled polyol. Using SEM images is analyzed the molecular structure of the foams; the reference foam shows an optimal closed cell, while the other foams show increasing deformations as the amount of recycled polyol increases.