Valorization of biopolymers waste through chemical recycling

The purpose of this work is to evaluate the chemical recycling of poly(butylene adipate terephthalate) (PBAT) by alcoholysis or better glycolysis. We tried to use 1,4-butanediol as both solvent and co-reactant to produce bio-based polyols. However, this glycol was proved to be not suitable for our purpose as it tends to polymerize with the polymer. Dipropylene glycol (DPG) instead was proved to be a suitable solvent. We studied the effect of different catalysts and for all of them we measured properties of interest such as dynamic viscosity, hydroxyl value, and acid value. We found that the depolymerization in absence of catalyst was the most efficient way to recover a liquid product suitable to produce new polyurethane products. This product had very low acid value. The conditions for this process were 200°C and a polymer/glycol ratio of 2 kg/kg. Glycolysis experiments were conducted using a polymer-to-glycol mass ratio of 2 kg/kg, employing both PBAT and PLA polymers in a mass ratio of 9:1. The tests were carried out at temperatures of 190°C, 200°C, and 210°C. The mixture of oligomers formed during the alcoholysis are hydroxy-terminated and we used them for the production of polyisocyanurate foams with an isocyanate index of 2.5 and an apparent density of 41 kg/m3. We prepared 2 series foams with different percentages of the recycled polyol (one using only PBAT and one with both PLA and PBAT) in particular 25, 50, 75 and 100%. We measured apparent density, thermal conductivity and compression resistance and we also did thermogravimetric analysis (TGA). We compared these proprieties with a reference foam formed with an industrial formulation employing two virgin polyols. Results showed that compression resistance is consistently higher in most cases compared to the reference. The thermal conductivity, even in the least favorable scenario, only marginally exceeds the one of the reference foam, being lower in half of the cases. We confirmed also that the thermal stability is maintained in all foams through the TGA.