Thermal Degradation Analysis of Sustainable Recycled Saudi Coffee/PLA Bio-nanocomposites

The global surge in plastic production has led to significant environmental challenges, particularly with the accumulation of non-biodegradable waste in marine and terrestrial ecosystems.Conventional disposal methods like combustion often result in harmful greenhouse gas emissions, while landfilling contributes to long-term pollution [1].Consequently, there is an urgent need for sustainable alternatives, such as biopolymers like polylactic acid (PLA) and the incorporation of agricultural waste (biomass) to create eco-friendly composites [2].This study investigates the thermal behavior of biocomposites composed of Recycled Saudi Coffee (RSC) and PLA.Saudi Arabia's high coffee consumption generates substantial spent grounds (RSC), which can serve as a sustainable feedstock to potentially accelerate plastic degradation and support circular economy initiatives.The materials used included Ingeo Biopolymer 3251D (PLA) and RSC prepared from boiled and dried Arabica coffee grounds.Both materials were processed into powdered forms (sieve sizes 100-200 m) to ensure uniform thermal contact.This specific particle size range was chosen to mitigate alterations in the thermograms that could arise from variations in the thermal contact surface of the materials.Biocomposites were synthesized at varying weight ratios: 0, 25, 50, and 100 wt% RSC.Thermogravimetric analysis (TGA) was conducted using a Mettler Toledo system at heating rates of 20, 40, and 60 oC/min under a nitrogen atmosphere (40 mL/min) within a temperature range of 25 to 600 oC.Fourier Transform Infrared (FTIR) spectroscopy was also employed to identify functional groups, such as cellulose, hemicellulose, and lignin in the RSC.The TGA and derivative thermogravimetric (DTG) analysis revealed distinct degradation stages for both pure materials and their blends.Pure RSC exhibited an initiation stage 25-275 oC with approximately 10.2 wt% loss attributed to moisture and oil retention.In contrast, pure PLA showed high thermal stability, with its primary degradation occurring between 345-440 oC, resulting in a massive 97 wt% weight loss [3].A critical observation was the synergistic interaction between RSC and PLA.Increasing the concentration of RSC biomass in the blends noticeably reduced the thermal stability of the composite compared to pure PLA.For example, the peak degradation temperatures for pure PLA shifted from 382.6 to 413.2 oC as the heating rate increased from 20 to 60 oC/min, demonstrating the influence of residence time [4].When blended, the RSC acted as a "biocatalyst accelerator," modifying the weight loss profile during the propagation stage.Furthermore, the presence of lignin in the RSC was found to impede degradation at elevated temperatures (above 450 oC), whereas pure PLA was completely decomposed by this point.This indicates that while RSC promotes initial breakdown, its complex lignocellulosic structure provides a residual char that persists at higher temperatures.This research highlights that RSC can be effectively utilized as a sustainable filler in PLA biocomposites.TGA analysis confirmed that blending RSC with PLA reduces the overall thermal stability of the plastic, which may facilitate faster degradation after end-of-life disposal.The study provides valuable insights for environmental engineers and plastic manufacturers looking to optimize biopolymer processing while reducing energy requirements for thermal treatment.