Biodegradable and non-retrogradable eco-films based on starch–glycerol with citric acid as crosslinking agent

• Starch–glycerol eco–films using citric acid (CA) as crosslinking were developed.
• CA first reacts with glycerol and then starch–glycerol–CA reaction occurs.
• Different temperatures, 75 °C and 85 °C, were used in gelatinization process.
• Biodegradable and non-retrograde starch–glycerol–CA films are obtained at 75 °C.
• Films heated at 75 °C show decreases in WVP and integrity after swelling in DMSO.

Biodegradable and non-retrogradable starch–glycerol based films were obtained using citric acid (CA) as crosslinking agent at 75 °C. This material allowed decreasing water vapor permeability (WVP) more than 35%, remained amorphous for at least 45 days as a result of the network formed by the CA that avoided starch retrogradation and maintained the degradability in compost, occurring only six days after the films without citric acid. A simulation of the gelatinization process of starch–glycerol with and without CA, using a differential thermal analysis device, showed that the system with CA completed the gelatinization 5 °C before than the other and, CA first reacted with glycerol and then starch–glycerol–CA reaction occurred. The temperature at which the gelatinization process was carried out was critical to obtain the best results. An increase of gelatinization process temperature at 85 °C in system with CA, led to a worsening on WVP and its integrity after a swelling process with dimethylsulphoxide (DMSO), compared to the films processed at 75 °C.