Soil burial degradation of bio-composite films from poly(lactic acid), natural rubber, and rice straw

Agricultural activities contribute to numerous waste problems and have emerged as a significant environmental concern. Nondegradable plastic residues decompose, releasing microplastics and affecting ecosystems and the environment. Consequently, biodegradable bio-composite films consisting of polylactic acid (PLA), natural rubber (NR), and rice straw (RS) have been developed with the aim of using them in agricultural applications. In this study, the PLA/NR blend, at a fixed ratio of 60/40 wt%, was filled with 3 and 5 wt% RS powder and extruded through a slit die into films. The biodegradability of all films was examined after being buried for 90 days in soil with a moisture content of 30% by weight. The neat PLA film showed the lowest weight loss percentage, 3.33%, suggesting a comparatively slower degradation rate in comparison to the PLA/NR(60:40) blend and all bio-composite films. The presence of 40 wt% NR in the film helped accelerate the biodegradation process during soil burial. The film produced from PLA/NR 60:40 wt% matrix filled with RS at 5 wt% led to rapid degradation, leading to a weight loss of 8.30%. From SEM micrographs, the morphology of all polymers after burial in soil showed fractures, the formation of pores, and obvious surface indications of fungi growing. The content of carbon decreased after soil burial, while oxygen content increased, and nitrogen was detected. The XRD analysis revealed low crystallinity in the neat PLA, consistent with the DSC analysis. The addition of NR and RS to the composites led to an increase in the crystallinity of PLA phase. All investigated materials exhibited an increase in crystallinity after being buried in soil. This research demonstrates that bio-composite films manufactured from the PLA/NR(60:40) blend filled with RS degrade more easily than unmodified PLA film.