The effects of plasticizers on the mechanical properties and chemical composition of a gelatin biopolymer

Every day, oil-based plastics are manufactured, consumed, and discarded without a second thought. To combat plastic pollution, we decided to investigate gelatin bioplastics. We analysed the effects of the increasing concentration of polyethylene glycol (PEG) and glycerol plasticizers on the mechanical properties and chemical composition of the gelatin bioplastic matrix through a series of experiments. In the first experiment, we determined their tensile strength (TS) and the elongation at break (EAB) through tensile testing. We hypothesised that increasing concentrations of the plasticizers would decrease TS and increase EAB. In the second experiment, we studied their O–H bonds by Fourier-transform infrared spectroscopy analysis (FTIR). Our second hypothesis maintained that the number of O–H bonds would increase because plasticizers disrupt polymer-polymer and polymer-water hydrogen bonds. For the mechanical properties, we observed that when the concentration of PEG and glycerol plasticizers increased so too did EAB. The rising concentrations of glycerol led to a decreasing trend with TS, whereas PEG showed an increasing trend. The FTIR spectrum revealed that a high abundance of O–H bonds was present at the strong and broad absorption peak of 3400 cm-1, with the pure gelatin films having the highest absorption, followed by glycerol-plasticized films and PEG-plasticized films having the least absorption. We concluded that 3% w/v PEG film outperformed other PEG films and 3% w/v glycerol films. The cytotoxicity results showed that all films had a cell viability above the threshold of 75% and hence food-safe.