Biodegradable plastics appear as one promising means to help solving the increasing issue of environmental pollution by plastics. The present study aims at comparing the biodegradation mechanisms of two promising biodegradable plastics, PHBV Poly(3hydroxybutyrate-co-3-hydroxyvalerate) and PBSA Poly(butylene succinate-co-adipate) with the objective to provide a better understanding of the mechanisms involved and identify the most relevant indicators to follow biodegradation. For this purpose, the progress of the biodegradation process was monitored under controlled composting conditions at the laboratory scale at 58°C using several methodological approaches for evaluating polymer degradation. Indicators of the extent of material disappearance based on respirometry and mass loss were combined to other indicators evidencing the morphological, structural and chemical modifications induced at the surface or in the bulk of the material as surface erosion by MEB and AFM, decrease of molecular weight by GPC, crystallinity changes by DSC and chemical changes by ATR-FTIR. As expected, both polymers were rapidly biodegraded in less than 80 days. However, in spite of its higher molecular weight and degree of crystallinity PHBV degraded faster than PBSA, which led to suggest that different biodegradation mechanisms would be involved. At this regard, a two-phase scenario was proposed for each polymer on the strength of all the degradation-induced changes observed at the polymer surface and in its bulk. Based on these two scenarios, the discrepancy in biodegradation rate between PHBV and PBSA would be essentially attributed to significant differences in crystals morphology and spatial organization of both polymers.Regarding the relevance of the different indicators studied, mass loss stood out as the most relevant and accurate indicator to assess the disappearance of material especially when combined with respirometry and mineralization kinetics assessment. Besides, indicators focusing on the surface changes as SEM, AFM and POM were emphasized since seen as powerful tools to evidence morphological changes at different scales. At last, changes in thermal properties as crystallinity rate and melting temperature, even if complex to interpret due to the wide range of interdependent mechanisms they bring into play 2 appeared as inescapable tools for improving the understanding of the underlying mechanisms involved in polymer biodegradation.

Nanocomposite materials based on bio-polyesters (PBSA and PHBV) have been evaluated for their suitability for food contact according to the recommendations defined for non-biodegradable plastic materials, and subsequently, according to accelerated aging treatment. On the basis of the limited number of material/migrant/food simulant combinations studied here, the test for migration, using food simulants, appeared directly applicable to testing such materials which are not considered humidity-sensitive materials. Considering the only compliance criterion that must be met by the materials in contact, the materials submitted to the aging processing are not of safety concern and the incorporation of nanoclays in aged biodegradable materials does not interfere with their inertial properties in a dramatic way. At the molecular scale, the UV irradiation proved to induce an increase in the degree of crystallinity, resulting in a modification of transport properties of both packaging materials. The values of overall migration and specific migration were reduced without decreasing the diffusion coefficients of the target additives. The UV treatment and the addition of nanoparticles, therefore, seem to jointly promote the retention of organic compounds in the materials by increasing their affinity for packaging material.

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