Biodegradable, UV-blocking, and antioxidant films from lignocellulosic fibers of spent coffee grounds

Abstract

Plastics are strong, flexible, and inexpensive and hence desirable for packaging. However, as they biodegrade very slowly, their waste remains a global burden and pollution, warranting a search for safer alternatives. Towards this end, residual fibers from biowaste, such as spent coffee grounds (SCGs), stand out for creating biodegradable packaging materials. Herein, lignocellulosic fibers from SCG were extracted, and various amounts (0.6, 0.8, 1.0, and 1.2 g) were solubilized using 68 % ZnCl₂ and crosslinked with salt (CaCl₂) amounts 0.1, 0.2, 0.3 and 0.4 g and prepared biodegradable films. The films were characterized for their color, thickness, moisture content, tensile strength, elongation at break, water vapor permeability, transmittance of electromagnetic radiation, biodegradability, and antioxidant properties. The results reveal that the films possess the highest tensile strength of 26.8 MPa. The tensile strengths are positively correlated to salt and SCG extract amounts. The percentage of elongation decreased with an increase in the calcium ions but increased with SCG residue increment. The films biodegraded in the soil, and most lost >80 % of their initial weight in 45 and 100 days, respectively, at 30 % and 12 % soil moisture. Biodegradability and water vapor permeability decreased with an increase in salt content. Films also showed antioxidant properties and blocked UV and IR radiation significantly. Overall, this research involving green and recyclable chemicals in preparation of SCG residue fibers is a promising, economical, and sustainable route to produce strong biodegradable films to replace petrochemical plastics and thus is an attractive contribution to the circular bioeconomy.

Keywords: Bioplastics; Green process; Plastic replacement; Valorization of agricultural biomass; Value-addition.