Development of antioxidant and self-healable gelatin-polyaniline films extracted from red tilapia fish scale

Gelatin is promising biomass for developing active biofilm due to its good film-forming properties and compatibility with active substances such as solid polyaniline (PANI). In addition, interestingly, the damaged gelatin-based film has the potential to self-heal the damaged zone by physical interaction in the presence of moisture. Nevertheless, the potential of this active film properties in the current research has not been explored in-depth. Hence, the aim of this research is to develop a self-healable active film from gelatin extracted from red tilapia’s fish scale incorporated with polyaniline (PANI). 4.34% dry weight basis of snowy white, crystal and light textured of gelatin was extracted from red tilapia’s fish scale. The extracted gelatin also has high amounts of glycine (20.79g/100g) and hydroproline (14.38g/100g), contributing to the filmogenic properties. Several chemical interactions on the peptide bonds are indicated as amide A, amide I, amide II, and amide III. Then, the good film-forming gelatin was further developed into gelatin-based film with the incorporation of 25% (w/w of gelatin) of glycerol using the solution casting method. The mechanically significant variations altered the G-Gly (with glycerol) film flexibility by more than 90% and decreased the tensile strength (TS) to 14.83 MPa. From the investigation via color, morphology, addition of functional group in Fourier transform infrared spectroscopy (FTIR), moisture content, mechanical, thermal, water vapor permeability (WVP) analysis, it was conclusive that G-Gly film was effectively developed with the addition of glycerol as plasticizer. The gelatin-based film was further explored with the incorporation PANI (G-Gly-PANI) in various sizes (x) (50µm ≤x≤ 100µm, 100µm ≤x≤ 125µm, 125µm ≤x≤ 250µm) and concentrations (0.5, 1 and 2 g/L) with feature characteristics of the films were further explored as active film. PANI dispersion inside the film was seen clearly as the green spots and the moisture content of G-Gly-PANI film decreased due to the hydrophobic properties of PANI. Based on the different Tg values obtained, G-Gly-PANI composite film was heterogenous and immiscible. Additionally, G-Gly-PANI films show differences in thermal degradation temperature and weight loss. From the mechanical aspects, the TS of the films increased and decreased in elongation at break (EAB) with the addition of small size of PANI due to the rigidity properties of PANI. Meanwhile, it contradicted with the larger size of PANI where the arrangements of PANI were more spacious, reducing the effect on the flexibility. The G-Gly-PANI film exhibited more than 40% in antioxidant activity. Out of the analyses subjected, it is noteworthy that the small size (50µm ≤x≤ 100µm, 100µm ≤x≤ 125µm) and high concentration of PANI can transition gelatin as the active film, which denoted its high capability as antioxidant. Next, G-Gly-PANI film was further investigated the ability and behaviour of self-healing properties of the film. The G-Gly-PANI film can repair the scratches that reach the underlying substrate by utilizing water stimuli. The absorbed water disrupted the intermolecular hydrogen bonds, allowing the polymer chains to move around and begin the self-healing process. Nevertheless, the mechanical properties of the self-healed film showed a significant decrement in flexibility compared to the non-damage films. From the sorption analysis of the films, based on R2 values (more than 0.95), Peleg and Guggenheim Anderson de Boer (GAB) models were respectively found to be the best-fitted model for representing the experimental data within the RH (23%, 33%, 57%, 75%) and temperature (5, 30, 40 °C) studied. Additionally, high relative humidity (75%) and low temperature (5 °C) does trigger the healing progress in a more incorporating way. After 7 days stored the films, the scratched film only nearly self-healed. The moisture was absorbed on the whole film and not only at the scratched area. Thus, when the films reach equilibrium, they will stop absorbing moisture and the healing process. In conclusion, this study revealed the feasibility of developing a self-healable active gelatin-based film incorporating with PANI as an active substance. Therefore, the complement of this study shows that the developed G-Gly-PANI film shows excellent potential as an active and self-healing film with potential applications in the food packaging industry, especially perishable fruit and vegetable.

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