Effect of Confinement on Gas Barrier and Mechanical Properties of Rheologically Mismatched Multilayer TPU Films

ABSTRACT Multilayer thermoplastic polyurethanes (TPUs) and polyethylene terephthalate glycol (PETG) films are fabricated using layer‐multiplying coextrusion with high‐aspect‐ratio (HAR) dies to explore the effects of high viscosity mismatch on gas barrier and mechanical properties. Three 50:50 polymer combinations spanning soft and rigid TPUs and PETG are studied. Despite viscosity ratios up to 24:1 and elasticity ratios up to 80:1, scanning electron microscopy (SEM) confirms successful multilayer structures up to 129 layers. Rheological analysis guides optimization of processing temperatures. Differential scanning calorimetry (DSC) reveals that spatial confinement enhances molecular packing and reduces diffusion pathways, lowering oxygen permeability by over 30% in some cases. Mechanical testing shows significant increases in modulus and puncture resistance as the number of layers increases, with the modulus of 129‐layer films approaching 80% of the rigid TPU control. Among the compositions studied, the multilayer films combining rigid and soft TPUs exhibit the greatest enhancement in barrier and mechanical performance, attributed to effective confinement, strong intermolecular hydrogen bonding, and refinement of hard segment domains (HSDs). This study demonstrates the feasibility of coextruding TPUs with extreme viscosity mismatch and establishes a processability benchmark, enabling the design of advanced multilayer films with improved performance for packaging and protective applications.