Loading ratio is key for biodegradation PHBV-based materials in home- composting conditions

In the context of growing plastic pollution in the packaging sector, biodegradable polymer alternatives present viable solutions, necessitating comprehensive understanding of biodegradation in accessible systems such as home composting. This research aimed to clarify the little-studied impact of PHBV-based material loading ratios on biodegradation kinetics in home composting environments, examining both film and shredded materials shape.The materials were tested according to three usage scenarios (high, medium and low) corresponding to material-to-compost ratios of 1/3, 1/30 and 1/50, under home composting conditions using ISO 14855-1 respirometry protocols. For both material forms, loading ratios has a stronger influence on the maximum biodegradation rate rather than on the ultimate biodegradation percentage. For shredded materials, the biodegradation rate linearly decreases with the increase of the ratio, whereas no direct correlation was shown for the material in film form. This suggests a material form effect on the polymer biodegradation rate regarding its loading ratio in the compost. For films, material residue persisting after one year suggested priming effects and revealed that PHBV biodegradation in our home composting setup occurs over extended timeframes beyond those captured by standard respirometry measurements. The study revealed that high loading ratios (1/3) induced substrate inhibition across all tested materials—a previously unreported phenomenon in PHBV biodegradability research. This inhibition extended the PHBV biodegradation time required to achieve 90% ultimate biodegradation from a maximum of 365 days prescribed by the standard to 578–613 days. These results establish the existence of a maximum optimal material loading ratio, above which biodegradation becomes suboptimal. Thanks to such a threshold, a careful consideration of material introduction rates would significantly benefit to the current waste management strategies and regulatory frameworks.