Polylactic acid represents one of the most widely commercialized biodegradable bioplastics, frequently utilized in agricultural films and single-use packaging applications. To tailor mechanical and processing characteristics, manufacturers incorporate functional biogenic fillers like biochar into biopolymer matrices. Biochar offers long-term environmental advantages by increasing soil nutrient retention, buffering acidity, and sequestering carbon. However, incorporating particulate carbon fillers alters internal polymer crystallization, water sorption, and microbial attachment, making it difficult to predict how composite bioplastics degrade in end-of-life composting environments. Understanding how thermal processing conditions during biochar production interact with filler concentration allows materials scientists to design bioplastics with optimized mechanical lifespans and accelerated post-consumer breakdown.

To evaluate these structural interactions, researchers synthesized biochar from waste walnut shells under low-temperature processing at four hundred degrees Celsius and high-temperature processing at seven hundred degrees Celsius. The team compounded these distinct biochars into polylactic acid films at two weight percent and ten weight percent loadings using a high-temperature extrusion process. Laboratory testing evaluated material wettability, surface pore architecture, melt flow behavior, mechanical tensile strength, and structural crystallization before placing the composite films in controlled thermophilic composting vessels at fifty-eight degrees Celsius for sixteen weeks.

The experimental results revealed that pyrolysis temperature fundamentally alters biochar surface chemistry, shifting low-temperature biochar from a water-repellent state into a highly porous, water-attracting material. When added at a low concentration of two percent, low-temperature biochar yielded the highest overall biodegradation rate of seventy-seven point two percent after sixteen weeks. This accelerated breakdown occurred because isolated biochar particles maintained a higher proportion of easily degradable amorphous polymer regions without creating severe transport barriers. Conversely, raising low-temperature biochar content to ten percent severely retarded composting kinetics because the hydrophobic particles restricted moisture access to the polymer chains. At ten percent loading, high-temperature biochar outperformed low-temperature biochar due to its enhanced water affinity, higher surface roughness, and increased processing-induced chain shortening. Mechanical analysis confirmed that ten percent loadings reduced overall tensile strength across all formulations due to particle clustering, whereas two percent high-temperature biochar retained strong mechanical performance. These findings demonstrate that biochar thermal history and loading proportions can be tailored to control bioplastic durability during use while ensuring rapid end-of-life composting.

Source: Brdlík, P., Gomez-Caturla, J., Borůvka, M., & Jaafar, M. (2026). Influence of biochar on the physico-mechanical properties and biodegradation of PLA films. npj Materials Degradation, 8, Article 138.