Upcycling spent coffee grounds as a sustainable additive for superior impact-resistant and flame-retardant polylactide biocomposite films

In polymer engineering applications, it has been a challenge to improve the mechanical performances and flame retardancy of polylactide (PLA) biodegradable materials to expand their uses. In this study, spent coffee grounds (SCG) were upcycled as a sustainable and multifunctional additive and successfully used to fabricate impact-resistant and flame-retardant PLA biocomposite films. The mechanical performances, thermal behaviors, crystallization process, flame retardant properties, and morphological characteristics of PLA biocomposite films were investigated. The results revealed that tributyl phosphate (TBP) acted as an excellent plasticizer for PLA, improving the flexibility and toughness of the film, especially at 20 phr. Notably, when TBP and SCG were incorporated, the PLA/TBP/SCG biocomposite film achieved the VTM-0 UL-94 rating and its impact tension resistance was greatly improved from 68.55 kJ/m 2 of neat PLA to 586.91 kJ/m 2 . Combining TBP and SCG prevented combustion and even caused self-extinguishing, while also promoting carbonization. Furthermore, as demonstrated by thermal and morphological analyses, the addition of TBP and SCG improved the flexibility and toughness of the film significantly compared with pure PLA. The Sustainable Development Goals (SDGs) and bio-circular-green (BCG) economic model were supported by this work effort, which also allowed for their broader application. • Spent coffee grounds achieved as sustainable additive for PLA. • Synergistic combination of SCG and TBP on the PLA was reported. • PCG10B20 film got the VTM-0 rating. • This film balanced in toughness and remained excellent flame retardant. • This work permitted their wider application and supported the 12th SDGs.