Data-Assisted Mechanical Balance Screening of and Candidate Window Identification for Starch/Halloysite Nanotube-Modified Cow Dung-Based Biodegradable Films

Agricultural waste-based biodegradable films are promising alternatives to polyethylene mulch films, but their use is limited by insufficient mechanical stability and the difficulty of balancing strength, ductility, and stiffness. In this study, cow dung-based biodegradable films were modified with cationic starch and halloysite nanotubes (HNTs) through a brush-coating process. SEM observations of pristine HNTs, the uncoated substrate, the starch-coated control, and the representative starch/HNT composite film provided morphological evidence for starch coating formation and HNT incorporation into the surface layer. Fifteen initial formulations were evaluated using tensile strength, elongation at break, apparent tensile modulus, a normalized mechanical balance score, and weighting sensitivity analysis. The highest values of the three mechanical indicators occurred at different formulations, indicating that formulation selection should be treated as a mechanical balance problem rather than a single-property maximization task. F14 showed the most stable overall mechanical balance among the tested formulations. SVR and GBR models were then used as bounded auxiliary tools for local trend mapping, with LOOCV R2 values of 0.679, 0.855, and 0.856 for tensile strength, elongation at break, and apparent tensile modulus, respectively. A desirability-based consensus analysis identified a high-potential window at approximately 2.30–2.50 wt% starch and 1.25–1.75 wt% HNT. Four previously untested formulations selected from this frozen model-defined region were independently prepared and experimentally validated, showing good prediction–experiment consistency within the candidate window. Preliminary soil burial observation further indicated progressive macroscopic structural deterioration of F14 during prolonged soil exposure, although this result was interpreted only as qualitative appearance evidence. Overall, the proposed workflow provides an experimentally bounded decision-support strategy for prioritizing mechanically balanced starch/HNT-modified cow dung-based biodegradable film formulations.