Hard Segment Engineering in Thermoplastic Polyurethane Directs Interfacial Microphase Separation for Moisture Management in Polymer Composites

To protect humidity-sensitive products such as pharmaceuticals, food, and precision electronics, packaging materials must combine high moisture adsorption with good processability. Conventional desiccants (e.g., silica gel or molecular sieves) are typically enclosed in sachets, which occupy space and pose safety risks. Incorporating desiccants directly into polymer matrices provides an attractive alternative, yet the performance of such composites is often limited by poor filler dispersion and discontinuous moisture transport pathways. In this study, a polypropylene/polyethylene glycol/thermoplastic polyurethane/molecular sieve (PP/PEG/TPU/MS) multiphase composite was designed by controlling the hard segment (HS) ratio of TPU. The mechanism through which the HS ratio regulates the composite microstructure, interfacial interactions, and moisture absorption behavior was systematically investigated. The results show that at a TPU HS ratio of 42%, the composite forms a continuous interpenetrating hydrophilic network, along with the largest mesopore size and the lowest density. Fourier transform infrared spectroscopy confirms that strong hydrogen-bond networks form among the TPU HS, PEG, and MS at this ratio, serving as molecular bridges that promote uniform dispersion and strong interfacial adhesion of the MS. Consequently, the PP/42-TPU/PEG/MS composite exhibits the highest equilibrium moisture capacity and the fastest adsorption kinetics while maintaining good processability. Analysis of the adsorption mechanism indicates that moisture transport follows a diffusion process consistent with the Fickian model and the diffusion coefficient increases with relative humidity, revealing a moisture-induced plasticization effect in the polymer. Practical packaging tests further verify the effective protective performance of the composite for moisture-sensitive products under high-humidity conditions.