Tailoring the structure and mechanical properties of casein biodegradable films with decanoic acid

Petroleum-based plastics are causing considerable negative environmental impacts. This study presents a clean-label approach to develop casein-based biodegradable films exhibiting enhanced mechanical properties. The impacts of ethanol (EtOH, 0–50 %) and decanoic acid (DA, 0–20 %) at different pH levels on the structure and mechanical properties of casein-based films were evaluated. Casein films prepared with 50 % EtOH exhibited improved mechanical properties compared to those made without EtOH. The elongation at break (EAB) increased by >33 %, and tensile strength (TS) increased by > 63 %. Moreover, adding 10 % DA to the 50 % EtOH film forming dispersions significantly enhanced EAB, increasing it from 39 % (in films with 50 % EtOH and 0 % DA) to 100 %. As confirmed by X-ray diffraction (XRD) spectra and differential scanning calorimetry (DSC) thermograms, adjusting the pH of dispersions in the presence of DA resulted in the formation of sodium decanoate crystals, weakening the flexibility of casein films. Fourier transform infrared (FTIR) spectra confirmed the interaction between DA and casein as well as the formation of sodium decanoate in pH-adjusted samples. These findings confirm that EtOH and DA under controlled pH conditions can be used as a promising strategy to tailor the structure and enhance the mechanical properties of protein-based clean-label biodegradable films.