Effect of Keratin Hydrolysis Conditions on the Physicochemical Properties of Biodegradable Films

This study aimed to optimize the composition of a keratin–polyvinyl alcohol–glycerol composite, and alternative processing conditions were identified. Films prepared from keratin hydrolysate obtained under three different hydrolysis conditions were tested and compared for their morphological, chemical, thermal, mechanical, and biodegradation properties. The presence of Amide I (1648.84, 1647.45, and 1642.60 cm -1 ), Amide II (1545.22, 1558.31, and 1542.51 cm -1 ), and Amide III (1243.69, 1239.47, and 1240.06 cm -1 ) bands in the infrared spectra of the keratin hydrolysate-containing film samples indicated that the overall protein structure was preserved. Thermogravimetric analysis revealed that the total mass loss was 84.39–95.85% in the temperature range of 30–600°C, indicating extensive thermal degradation of the keratin–polyvinyl alcohol–glycerol composite films. At higher temperatures, the samples decomposed almost completely, confirming that they are predominantly organic and biodegradable materials. All samples were identified as organic C–O-based composite films (C: 48.49–52.96%; O: 41.66–51.33%). Sulfur detected in the keratin hydrolysate-containing samples was attributed to disulfide (–S–S–) bonds derived from cysteine residues in keratin. In addition, the films exhibited mechanical strength, elasticity, and measurable Young’s modulus values. The films showed 67.5–92.4% mass loss within 90 days, confirming their biodegradability.

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