Green and facile preparation of hydrophobic bioplastics from tea waste

Abstract

In this work, we report a green, waste-free method of synthesizing hydrophobic bioplastic films from tea waste, an industrial byproduct of tea brewing. Utilizing only spent tea leaves, citric acid, and water—all of which can be sustainably sourced—this facile technique is completely non-toxic, generates zero waste, and requires mild conditions and short processing times. The resultant bioplastics were chemically characterized by XPS and HPLC-MS, mechanically characterized by uniaxial tensile tests, and surface characterized by contact angle, SEM, and confocal microscopy. Citric acid did not fully react with the tea waste matrix (53.6% reaction efficiency), yet it is hypothesized that unreacted citric acid acts as a hygroscopic plasticizer in the bioplastic films, which exhibited an ultimate tensile strength of 6.16 MPa and an elongation at break of 13.33%. The tea waste bioplastics demonstrated strong hydrophobic character with a water contact angle of up to 117°, which we attempted to explain by quantifying the surface roughness of the films. Mechanical and hydrophobic characteristics were also found to be dependent on relative humidity. Biodegradable and sustainably sourced, these tea waste bioplastics and the findings herein represent a step towards more sustainable packaging solutions.