# Highly Asymmetric Water Permeation in Dense Laminated Membranes

## TL;DR

This paper presents a new type of membrane with highly asymmetric water permeation, useful for separation and packaging applications.

## Contribution

A novel dense laminated membrane with high asymmetry factor is developed using PVA and PETG with an SEBS-MA adhesive layer.

## Key findings

- Membranes with optimized geometry show an asymmetry factor of up to 6.7.
- The SEBS-MA adhesive layer improves adhesion between hydrophilic and hydrophobic layers.
- Directional water transport is due to moisture-induced plasticization of the PVA layer.

## Abstract

Directional permeation through dense laminated membranes
is relevant
for applications in various fields, including separation processes,
wound care, and packaging. While theoretical models have been used
to describe the asymmetric permeation in heterogeneous dense membranes,
only a few systems have been experimentally explored. Here, we report
dense asymmetric laminated membranes based on hydrophilic poly­(vinyl
alcohol) (PVA) and hydrophobic glycol-modified poly­(ethylene terephtalate)
(PETG). Modeling the system allowed us to optimize the thickness of
the PVA and PETG layers. While bilayer membranes made from the two
components suffered from poor interfacial adhesion and delamination,
this problem is overcome by using a thin poly­sty­rene-block-poly­(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride
(SEBS-MA) adhesive layer. The maleic anhydride groups (MA) react with
the hydroxyl groups present in the two polymers, and this greatly
improves the adhesion between the hydrophilic and the hydrophobic
layers. Membranes with optimized geometry display an asymmetry factor
of up to 6.7, one of the highest values ever reported. The directional
water transport is caused by the moisture-induced plasticization of
the PVA layer at high relative humidity (RH), which occurs only when
the PVA side of the membrane is exposed to moisture.