Elucidating long-term migration of cosmetic emulsions and its effect on deformation mechanisms in polymer containers

A cosmetic formulation can penetrate its polymer packaging material through direct contact, resulting in changes in the physical properties of the container and visible deformation, thereby incurring significant economic and industrial losses. Therefore, understanding the mechanisms underlying formulation-promoted container deformation is essential for the development of preventive material strategies. In this study, we investigated the effect of a water-in-oil (W/O) emulsion on three types of polymer containers: polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), under accelerated conditions (45 °C, 80% relative humidity). The physical properties and morphologies of each polymer container were analyzed following long-term storage, revealing that continuous infiltration of the emulsion resulted in the plasticization of the crystalline regions of the PE container, leading to volumetric expansion, whereas the PP container exhibited bending deformation owing to the plasticization of its amorphous regions. In contrast, the PET container exhibited no noticeable changes in either its physical properties or appearance, presumably because of the high chain rigidity conferred by the aromatic PET structure. Overall, this study reveals that the long-term migration of a cosmetic emulsion into a polymer container depends on its intrinsic material characteristics, thereby providing a systematic morphological mechanism for the deformation phenomena.