Characterizing direct vacuum metallized paper substrates for improving moisture barrier performance with paper packaging

Abstract

Growing concerns about non-recyclable packaging and their impact on the environment are driving preference to switch to recyclable packaging materials. Paper-based materials can be a promising alternative to non-recyclable moisture-sensitive food packaging provided it is re-engineered for high moisture barrier characteristics without compromising its recyclability. This work describes the characterization of two types of high barrier paper structures for primary food packaging that have the same multilayer composition, however, they differ in terms of the aluminum metal layers, which were prepared using two different metallizers via physical vacuum deposition (PVD). When exposed to high relative humidity (RH), these materials exhibited different water vapor transmission rates (WVTR). One sample maintained excellent moisture barrier properties with a WVTR of 0.06 ± 0.01 g/m²/day at 23°C and 85 % RH, while the other sample partially lost its moisture barrier and reached a WVTR of 1.0 ± 0.6 g/m²/day under the same conditions. Optical density (OD) measurements along with scanning electron microscopy (SEM) imaging revealed that the loss of water vapor barrier performance can be assigned to the discontinuity of metal layer after exposure to high humidity. By taking a step further and determining the thickness, nano-scale morphology and crystal structures of the metal layers, as well as their chemical compositions, valuable information was obtained regarding the factors contributing to the loss of WVTR. In both cases the metallized paper structures are considered recyclable within existing standard paper recycling stream, following the CEPI 4Evergreen recyclability evaluation protocol for recycling mills with conventional process.