Spatially Programmed Water Access Reconciles Service Stability with Triggered Post-Use Degradation in Biobased Multilayer

Sustainable packaging plastics often face a fundamental paradox: the material must resist moisture and remain stable during service, yet undergo controlled disassembly after disposal. Therefore, sustainable materials should not be evaluated solely based on their service performance or degradation rate, but rather on their ability to undergo effective functional transitions at critical stages throughout the lifecycle. Here, we developed a spatially programmed design strategy that addresses these conflicting requirements by regulating not only when and where water enters the material, but also how the degradation proceeds. The film consists of a hydrophilic, pectin-based inner layer, a hydrophobic polylactic acid (PLA) outer layer, and a hydrogen-bonded interface formed via hydrogen bonding. During packaging service, the PLA layer acts as a moisture-shielding skin, maintaining wet stability, barrier performance, and mechanical integrity. A key conceptual advance of this work lies in turning an inherent weakness into a lifecycle-regulating function, where water sensitivity serves as a trigger rather than a limitation. After use, assisted by mechanical damage, water activates the pectin/deep eutectic solvent (DES) phase. The acidic, water-rich microenvironment generated by the pectin/DES supports preferential cleavage near the PLA chain ends, promoting progressive molecular weight reduction while preventing premature failure that could compromise service performance. Density functional theory (DFT) calculations further establish a molecular-level structure-function relationship within the architecture. The calculated interfacial binding energies and molecular interactions elucidate the origin of structural stability during service, while comparative analysis of PLA ester bond cleavage pathways demonstrates a more favorable energetic pathway for terminal ester cleavage after activation, supporting the chain-end-preferential degradation tendency. In contrast to conventional multilayer materials that mainly improve individual properties, this work provides insights into biopolymer design, moving beyond the long-standing trade-off paradigm of stability and degradability by spatially programming these functions as complementary components within a lifecycle-balanced architecture.