*2.1. Materials*

Bacterial aliphatic homopolyester PHB was supplied by Biomer (Krailling, Germany) as P226F. According to the manufacturer, this is certified both as compostable and food contact grade, presenting a density of 1.25 g/cm<sup>3</sup> and a melt flow rate (MFR) of 10 g/10 min at 180 ◦C and 5 kg. The weight-average molecular weight (M w) estimated by the manufacturer was 500 kDa and the polydispersity index (PDI) was 2.

2,2,2-trifluoroethanol (TFE) with 99% purity and D-limonene with 98% purity were both purchased from Sigma-Aldrich S.A. (Madrid, Spain). The two tested surfactants, hexadecyltrimethylammonium bromide (CTAB), with 99% purity, and tetraethyl orthosilicate (TEOS), with 98% purity, as well as palladium (Pd) nano-powder, <25 nm particle size measured by transmission electronic microscopy (TEM) and ≥99.5% trace metals basis, were also purchased from Sigma-Aldrich S.A. All products were used as received without further purification.
