Eva Rodriguez Hortelano

Blending poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with thermoplastic polyurethane (TPU) improves toughness but compromises compostability above a critical TPU content. To our knowledge, this is the first three-dimensional, voxel-based Monte Carlo (MC) framework for simulating the disintegration of PHBV/TPU blends under ISO 20200 composting conditions. It couples Monod-type microbial growth, a cardinal-temperature correction, biomass and moisture transport, and a blend morphology generated by random sequential adsorption (RSA) and calibrated against scanning electron microscopy (SEM) data. The transition between complete and incomplete disintegration is described by partitioning the TPU phase into reachable and trapped fractions derived from the connectivity of the generated TPU network. Calibrated against eight compositions (100/0 to 0/100; 58 °C; 41 days) with 22 adjusted parameters, the model yields a root-mean-square error (RMSE) of 3.97% over all 40 fitted points and reproduces complete disintegration up to 40 wt% TPU, the incomplete disintegration of the 50/50 blend and the minimal degradation of neat TPU. In a hold-out test, the compositions withheld from calibration (90/10 and 70/30) were predicted with an RMSE of 3.23%. Sensitivity and identifiability analyses reveal a composition-dependent parameter hierarchy, and virtual temperature experiments illustrate the thermal behaviour implied by the model assumptions.

The disintegration time of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in compost varies by more than an order of magnitude for the same polymer, and standardised tests quantify this variability without explaining it. Here we present a three-dimensional, spatially resolved Monte Carlo model of PHBV film disintegration, in which the polymer is discretised into a voxel lattice derived from the specimen geometry and eroded via local Monod kinetics. A single reference kinetic set is calibrated once against a benchmark dataset (RMSE = 2.27 pp) and held fixed; each compost is then described by one physically interpretable parameter, the initial density of degrading inoculum, whose fitted range quantifies the microbial-activity variability the standards leave unexplained. With the kinetics fixed, the model reproduces an independent thermophilic dataset by varying only this parameter and the geometry (RMSE = 3.05 pp), and passes two a priori tests with the parameter transferred, not fitted: a 400 µm film from the literature (RMSE = 14.1 pp) and a 50 µm film characterised here (RMSE = 7.01 pp). Together these span two ISO standards and an eightfold range of thickness (50–400 µm), bracketing the 200 µm calibration point. A further dataset, obtained in undiluted real compost rather than a diluted synthetic substrate, is reported as a documented exception requiring its own kinetic set (RMSE = 5.24 pp). Because geometry is an explicit input, the model predicts how thickness sets the disintegration window and resolves the spatial fragmentation pattern, beyond the reach of empirical fits.