With the mandatory separation of bio-waste at source compostable packaging could be treated in industrial composting stations be get out of their waste status and be converted in a valuable product, a compost used as soil fertilizer. However, compost can be considered as a potential source of soil contamination with nano and microplastics. To date, there is no standardized method for detecting and quantifying nano and microplastics in compost. The objective is to develop an efficient and non- destructive extraction protocol to identify and quantify biodegradable and conventional nano and microplastics present in compost by FTIR and Raman microspectroscopies, and thermal analysis (Pyr‐ GC-MS).The micro and nanoplastics were first extracted from the inorganic compounds present in the Compost complex matrix using the density difference using CaCl2 (d=1.4). The organic compounds present in the compost were eliminated by oxidative digestion using hydrogen peroxide H2O2 at 30%. Depending on their chemical fingerprint and after optimization microplastics were identified and quantified by number and mass (estimation by calculation using area, volume and density) by FTIR microspectroscopy and nanoplastics by Raman microspectroscopy. Pyr-GC-MS was used to quantify the polymer type in plastic.A method to extract microplastics from compost was optimized and validated with a recovery rate greater than 92% which proves extraction efficiency without significantly affecting the physical and chemical integrity of microplastics. Biodegradable nano and microplastics were analyzed well identified from a compost sample with a correlation coefficient at least greater than 70% compared to the internal library containing reference spectra of known materials and the analysis time is relatively short (4 hours per sample for FTIR) similar to that found by other authors and much longer for Raman.In this study, for the first time, a simple and efficient method for extracting biodegradable microplastics from compost was optimized and validated. Comparison of several analytical approaches using IR and Raman micro spectroscopy and thermal analysis was also proposed for identification and quantification.

With the compulsory separation of biowaste at source from January 2024 (in France and Europe), some compostable packaging could be processed in industrial composting plants in association with food waste. In line with the circular economy strategy, they could thus be transformed from waste into compost, a soil improver. In this context, an exhaustive experimental analysis of the transient and persistent degradation products generated by conventional and biodegradable plastics in this complex organic matrix is essential. Used as an organic soil improver in the agricultural sector, biowaste compost is a lignin-rich organic waste product that can be considered a potential source of microplastic soil contamination. To date, there is no standardized method for detecting and quantifying microplastics in compost. This study led to the development of an efficient, non-destructive preparation protocol for quantitatively extracting biodegradable and conventional nano and microplastics from compost. To identify and quantify the microplastics obtained, FTIR and Raman microspectroscopies were used alongside thermal analysis (Pyr-GC-MS). A critical comparison of these different methodologies is proposed.

We investigate the spreading of falling ambient-temperature Newtonian drops after their normal impact on a quartz plate covered with a thin layer of liquid nitrogen. As a drop expands, liquid nitrogen evaporates, generating a vapour film that maintains the drop in levitation. Consequently, the latter spreads in inverse Leidenfrost conditions. Three drop-spreading regimes are observed: (i) inertio-capillary, (ii) inertio-viscous, and (iii) inertio-viscous-capillary. In the first regime, although the drop expansion is essentially driven by a competition between inertial and capillary stresses, it is also affected by viscous effects emerging from the vapour film, which ultimately favours the development of a shear flow within the drop. Interestingly, vapour film effects become marginal in both the second and third regimes, allowing the drop to undergo biaxial extension primarily. More specifically, in the inertio-viscous scenario, the expansion is driven by the balance between inertial and biaxial extensional viscous stresses in the drop. Finally, inertia, capillarity and drop viscosity are all relevant in the third regime. These physical mechanisms are underlined through a mixed approach combining experiments with multiphase three-dimensional numerical simulations in light of spreading dynamics analyses, energy transfer and scaling laws. Our results are rationalized in a two-dimensional diagram linking the drops’ maximum expansion and spreading time with the observed spreading regimes through a single dimensionless parameter given by the square root of the capillary number (the ratio of the viscous stress to the capillary stress).

We present a dynamic light scattering setup to probe, with time and space resolution, the microscopic dynamics of soft matter systems confined within millimeter-sized spherical drops. By using an ad hoc optical layout, we tackle the challenges raised by refraction effects due to the unconventional shape of the samples. We first validate the setup by investigating the dynamics of a suspension of Brownian particles. The dynamics measured at different positions in the drop, and hence different scattering angles, are found to be in excellent agreement with those obtained for the same sample in a conventional light scattering setup. We then demonstrate the setup capabilities by investigating a bead made of a polymer hydrogel undergoing swelling. The gel microscopic dynamics exhibit a space dependence that strongly varies with time elapsed since the beginning of swelling. Initially, the dynamics in the periphery of the bead are much faster than in the core, indicative of nonuniform swelling. As the swelling proceeds, the dynamics slow down and become more spatially homogeneous. By comparing the experimental results to numerical and analytical calculations for the dynamics of a homogeneous, purely elastic sphere undergoing swelling, we establish that the mean square displacement of the gel strands deviates from the affine motion inferred from the macroscopic deformation, evolving from fast diffusivelike dynamics at the onset of swelling to slower, yet supradiffusive, rearrangements at later stages.