Biodegradation and Mechanical Performance of Flax Fibers in Soil Burial Conditions

Biodegradable materials are part of promising strategies to reduce environmental impact and facilitate end-of-life waste management through biological recycling. Flax is considered a strong candidate for biodegradable applications (textiles, ropes, and composite reinforcement). This study investigates the mechanical limits of flax fibers under conditions conducive to microorganism growth by examining the effects of soil biodegradation on their tensile properties. Flax fibers are buried in an organic agricultural soil under controlled temperature and moisture conditions. First, respirometry tests confirm the biodegradation potential of flax fibers in the soil. Scanning electron microscopy reveals surface degradations, bundle separation, and fiber individualization, attributed to the rapid breakdown of middle lamellae. Tensile properties were assessed at two structural levels: fiber bundles and single fibers. Despite a relatively modest biodegradation rate (~5%), tensile strength declined rapidly – by 84% in bundles and 64% in elementary fibers after 15 days of burial. Beyond certain durations, mechanical testing was no longer feasible due to sample fragility - up to 31 days in budlles and up to 72 days in elementary fibers. These results show that while biodeterioration begins quickly in direct soil contact, flax fibers retain partial mechanical functionality over time, suggesting potential for controlled-life applications in severe environments.