# Modeling and Experiments on Multilayered Barrier Coatings Containing Water-Sorbent Biopolymers

## TL;DR

This paper explores using biopolymer layers in packaging to reduce water loss, offering a sustainable alternative to petroleum-based plastics.

## Contribution

A novel theoretical model and design concept for multilayered barrier coatings with water-absorbent biopolymers.

## Key findings

- Increasing the thickness and water-holding capacity of absorbent layers reduces water mass loss rate.
- Dried absorbent layers (initial water activity of 0) provide the greatest reduction in water flux.
- Thicker barrier layers on the low-activity side are most effective in reducing water permeability.

## Abstract

Environmental regulations and consumer demand are driving
the need
for packaging materials to reduce or eliminate the use of petroleum-based
plastics by replacing them with natural and degradable alternatives.
Water flux through a barrier layer is governed by the differential
in water activity between a high side (e.g., an aqueous solution)
and a low side, such as humid air. We propose that a water-absorbent
layer sandwiched between two barrier layers will act as a sponge and
locally raise the water activity. It will thereby lower the activity
differential across the first barrier layer and, hence, reduce the
water flux through the multilayer for a set time period. We present
a theoretical model that predicts the water flux through a multilayered
structure of two or more barrier layers sandwiching hydrophilic layers
that hold water according to an absorption isotherm. We use this model
to evaluate the effects of layer thicknesses and distributions, the
barrier permeability, the water-holding capacity, and initial water
activity of the absorbent layers. We found that the water mass loss
rate decreases when the thickness and water-holding capacity of the
absorbent layer increase. The greatest reduction in the mass loss
through a multilayer was achieved when the absorbent layer had an
initial water activity of 0 (fully dried). The relative thicknesses
of the barrier layers in the multilayer also have an impact on the
water loss rate; thicker barrier layers on the low-activity side of
the multilayer are the most effective in reducing the water flux.
We have verified the model in an ideal system. We also investigated
a multilayer structure of a waterborne emulsion polymer barrier coating
and water-absorbing chitosan, which is a deacetylated form of chitin.
Here, the chitosan layer offered little benefit in decreasing the
water permeability because the layers were not thick enough and the
permeability of the waterborne coating on its own is not sufficiently
low. With our design concept for multilayer barriers containing absorbent
layers and the underpinning theoretical model, we envisage materials
systems with enhanced barrier properties while also using less petrochemically
derived plastic.