DFT-informed molecular vulnerability and fragment-water interaction mechanisms of microplastic-relevant polymer fragments from bottled drinking water packaging

Plastic packaging used for bottled drinking water can release microplastic or nanoplastic precursors through mechanical abrasion, thermal exposure, ultraviolet irradiation, oxidation, hydrolytic aging, and processing-related residual stress. However, the molecular-level factors that make specific packaging-derived fragments more vulnerable to water-assisted release remain insufficiently resolved. This study developed a descriptor-guided computational framework to evaluate representative PET/rPET, HDPE, PP, and PE seal-derived molecular fragments using DFT-derived electronic descriptors, predicted active-site reactivity, water-accessibility mapping, bond-scission vulnerability, and fragment–water contact visualization. Global descriptor analysis showed that oxidized PET/rPET and oxidized cap fragments were more polar than non-oxidized aliphatic fragments, while atom-level mapping localized predicted reactivity around ester-, carbonyl-, and carboxyl-associated sites. Water-accessibility and contact analyses showed that hydration relevance emerged when polar active sites overlapped with exposed oxygenated regions, and bond-scission mapping identified C–O linkages near oxidized PET/rPET motifs as the most vulnerable local sites. A literature-constrained scenario analysis distinguished early, episodic cap/neck abrasion from progressive release associated with residual stress, photothermal oxidation, and hydrolysis. The molecular models are oligomeric defect motifs rather than whole micro- or nanoplastic particles; they identify local chemistries that may initiate fragmentation but do not predict release rates or particle concentrations. The framework provides a mechanistic screening basis for prioritizing packaging materials, stress scenarios, and molecular sites for experimental validation.