Glycolysis of semi-interpenetrated polymer network foam based on poly(vinyl chloride) for recovery and reuse of the individual components. (November 2022)

• Record Type: Journal Article
• Authors: Calosi, Matteo; Renon, Marco; Belletti, Giada; Mazzanti, Valentina; Mollica, Francesco; Massi, Alessandro; Bertoldo, Monica
• Is Part Of: Waste management. Volume 153(2022)
• Page Start: 229
• Page End: 239
• Publication Date: 2022-11
• Subjects: PVC foam -- Semi-IPN -- Recycling -- Glycolysis; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2022.09.001
• Languages: English
• ISSNs: 0956-053X

Abstract

Graphical abstract: Highlights: A process to recycle rigid semi-IPN foams based on PVC has been developed. The isocyanate-derived portion of the semi-IPN was depolymerized by glycolysis. Thermal stabilizers were used to avoid PVC degradation during glycolysis. After separation of the depolymerized fraction thermoplastic PVC was recovered. The other fraction consisted in difunctional OH- or NH2 -terminated oligomers. Abstract: Rigid semi-Interpenetrated Polymer Network (semi-IPN) foam based on poly(vinyl chloride) (PVC) and crosslinked polyurea/isocyanurate are complex materials that at present are not recyclable. They are used in many fields, including wind blade cores. In this work we studied the depolymerization of the crosslinked portion of the foam under glycolysis conditions for the separation and reuse of the individual components. Reaction products were characterized by FT-IR, NMR, solvent solubility, DSC, elemental analysis, titration of amine and hydroxyl groups and rheology measurements. Triisocyanurates and urea moieties were synthesized and used as model compounds. Glycolysis conditions were optimized to maximize depolymerization while minimizing PVC degradation. The parameters studied were reaction time (8 min to 3 h), temperature (155 to 200 °C), catalyst (potassium acetate or dibutyl tin dilaurate (DBTL)), glycol (ethylene glycol, 1, 4 butanediol, diethylene glycol, dipropylene glycol, polyethylene glycol), as well as the effect of PVC thermal stabilizers such as hindered phenols and organo-phosphites. The results showed that the optimal reaction condition for foam glycolysis is 165–175 °C for 20–30 min, using DBTL as catalyst and including thermal stabilizers. No drastic difference was noticed by the kind of glycol used, except for PEG that led to greater PVC degradation. The greatest part of the crosslinked portion (≥90 %) was depolymerized and the result were mainly hydroxyl- and in minor amount amine- terminated oligomers. The recovered PVC (purity roughly 90 %) had a low degree of degradation and a viscosity suitable for its processing as thermoplastic material, i.e. by injection moulding.