Silk Sericin Films from Concentrated Aqueous Solutions: Processing Routes, Structure, and Properties

Abstract: This study aimed to understand the impact of different concentration routes on the structure and properties of silk sericin (SS) films. Sericin was extracted from defective cocoons (DC), at high temperature and pressure (HTHP) using an autoclave. The obtained aqueous solution was concentrated using three different routes until a final concentration of 2% (w/v) was reached. These routes include freeze-thawing (SS_FT), rotary evaporation (SS_E), and the dissolution of spray-dried SS in distilled water (SS_SD). Films were formed from the three solutions obtained, which were characterized by Fourier transform infrared spectro-metry (ATR-FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), and their water absorption capacity and non-soluble fraction were evaluated. According to the FTIR and TGA results, the samples concentrated by evaporation or using spray-dried SS exhibited a more amorphous and lighter structural conformation than those found in F-SS_FT. This finding suggests that the use of high temperatures for SS concentration promotes protein degradation and the formation of less ordered structures in SS films. The structural properties of the SS films were confirmed by the water absorption results. In particular, the major presence of crystalline structures in F‑SS_FT seems to limit their affinity for water, favoring the non-soluble fraction in this sample. The marked effect of the concentration method on the structure and properties of SS films highlights the potential of this process in the design of more efficient manufacturing routes for SS-based materials that exhibit a distinctive performance.