Three-Dimensional Monte Carlo Simulation of PHBV/TPU Blend Biodisintegration Under Composting Conditions: Role of TPU Network Percolation

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.