Biodegradation behavior of waste cotton fiber-reinforced polylactic acid composites under soil-burial conditions

Abstract

This study investigates the effect of biodegradation on the mechanical and thermal properties of waste cotton fiber-reinforced polylactic acid (PLA) biocomposites with varying fiber-to-matrix ratios (30/70, 40/60, 50/50, 60/40, and 70/30 cotton/PLA) under soil burial conditions for 15, 30, and 45 days. The mechanical, thermal, and morphological properties were analyzed to evaluate the influence of fiber content on composite performance during degradation. Tensile and flexural properties gradually decreased with increasing exposure time, primarily due to the hydrolytic degradation of PLA and fiber-matrix debonding. The 70/30 (cotton/PLA) composite exhibited the most significant reduction in mechanical strength, confirming accelerated degradation with higher cotton content, whereas the 50/50 (cotton/PLA) ratio retained a favorable balance between strength and biodegradability. Fourier Transform Infrared Spectroscopy (FTIR) revealed the attenuation of characteristic PLA peaks and the appearance of hydroxyl groups, indicating ester bond hydrolysis. Scanning Electron Microscopy (SEM) micrographs demonstrated surface erosion, fiber pull-out, and microcrack formation, further validating microbial and hydrolytic attack on the composite surfaces. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) analyses confirmed a gradual reduction in thermal stability and crystallinity after biodegradation. Overall, the results highlight that waste cotton fiber is a viable reinforcement for developing eco-friendly, biodegradable PLA composites, where the 50/50 (cotton/PLA) ratio offers the best compromise between structural integrity and environmental degradability.