3.12. In Vitro Biodegradability Tests

Biodegradability tests were performed in independent tests in triplicate following ASTM F1635-11. To remove uncross-linked chains and monomer residues, the PUs were washed with ethanol for two days, renewing the ethanol each day. The solvent was then replaced by deionized water for two more days. The materials were dried in a vacuum chamber at 37 °C for 24 h [54]. Samples of 5 mm × 5 mm × 3 mm were placed in the biodegradation media and incubated at 37 °C for three months, except for the enzyme medium (10 units mg⁻¹ solid), which was for 21 days. After this time, the samples were washed with distilled water, dried in a vacuum chamber, and weighed. The reagents used were: 0.1 M HCl medium, 0.1 M NaOH medium, and porcine liver esterase enzymatic medium. The biodegradation rate was calculated by comparing the dry weight (w_f) of the sample after degradation during the predetermined time with the initial dry weight (w_i) of the sample using Equation (3) [81,82]: