The chances of thermooxidation stabilization of poly(3‐hydroxybutyrate) during processing–A critical evaluation

• Published in: Journal of applied polymer science 2021-07, Vol.138 (27), p.n/a
• Main Authors: Tocháček, Jiří, Přikryl, Radek, Menčík, Přemysl, Melčová, Veronika, Figalla, Silvestr
• Format: Article
• Language: English
• Subjects: Atomic properties; biopolymers and renewable polymers; Chain scission; Degradation; Extrusion; Free electrons; Inorganic salts; Materials science; Performance evaluation; Phenols; polyesters; Polyhydroxybutyrate; Polymers; stabilization; Steric hindrance
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.50647

The performance of a series of thermooxidation stabilizers was investigated in poly(3‐hydroxybutyrate) (PHB) during processing by multiple extrusion at 190°C. The issue was to find out if PHB may be processing stabilized or not. Phenols of different steric hindrance, phosphites, amine oxide, hydroxylamine, lactone, hindered amine and carbodiimide were tested as potential stabilizers and their efficiencies compared with non‐stabilized polymer as a reference. Multiple extrusion data was evaluated using the processing degradation index (PDI) formerly designed for polypropylene. Changes in molecular weight were monitored as well. The results have shown that none of the stabilizing structures, currently successfully used in other polymers, have the ability to protect PHB. This indirectly implies that no radical chain scission takes place during PHB processing, i.e. no thermooxidation takes place. Moreover, nearly all of the tested structures act as prodegradants in PHB, some of them very strong. The strongest ones contain P or N atoms with asymmetrical free electron pairs in their molecules that evidently accelerate the main degradation mechanism of PHB—thermally induced cis‐elimination.