Effects of the green cross-linking agent tannic acid and its oxidation on the properties of porcine plasma protein superabsorbent materials

Tannic acid is a natural polyphenol capable of strongly interacting with proteins, with good antioxidant and antibacterial properties. Thus, tannic acid (TA) or oxidized tannic acid (oxTA) may be used as cross-linking agents in the development of reinforced and fully protein-based superabsorbent materials (SAMs). oxTA was produced so that reactive quinone groups were generated, which are expected to increase its reactivity. In this study, porcine plasma protein (PPP) and glycerol (gly) were used in a 50/50 PPP/gly ratio to obtain SAMs through twin screw mixing and injection molding. The results showed that both TA and oxTA increased the storage modulus and the loss tangent of blends and bioplastics due to the physical interactions established between TA or oxTA and PPP. The mechanical properties, particularly the Young's modulus and tensile strength, were generally enhanced as well. Water absorption was strongly influenced by the addition of TA, resulting in a decrease in the amount of water absorbed. However, samples containing oxTA resulted in a greater water absorption capacity, retaining a higher proportion of the superabsorbent properties of the reference composition. Moreover, systems containing oxTA generally possess better mechanical properties than those of equivalent TA formulations, especially those containing 5 % and 10 % oxTA.