Evaluation of Mechanical Properties of Phase‐Separated Cellulose Filler/Poly(Lactic Acid)/Elastomer Composites via Microstructure‐Informed Physics Simulation and In Situ Synchrotron X‐Ray Micro‐ <scp>CT</scp>

ABSTRACT This study investigates phase‐separated cellulose filler/poly(lactic acid) (PLA)/elastomer ternary composites to enhance the mechanical performance of bioplastics. Atomic force microscopy (AFM) reveals morphological transitions from sea–island to co‐continuous structures depending on the elastomer type and content. Two‐dimensional fast Fourier transform (FFT) analysis quantifies these morphologies by extracting radial and angular spectral features. A gradient‐based texture‐synthesis framework using Adam optimization reconstructs statistically equivalent microstructures that match the FFT‐derived spectra. These synthetic microstructures serve as models for finite‐element analysis (FEA) of the three‐phase composite system. The FEA results show that high hydrostatic stress near rigid cellulose fillers causes brittle failure in PLA, while elastomer domains mitigate stress concentration and induce localized plastic deformation, leading to ductile behavior. In situ micro‐computed tomography observations confirm these fracture mechanisms, displaying behavior consistent with simulation predictions. This work demonstrates that integrating FFT‐based morphological quantification with synthetic structure generation enables predictive, microstructure‐informed mechanical analysis of complex composite systems. The proposed approach provides a powerful framework for designing sustainable, high‐performance biocomposites through virtual testing and structure–property correlation.