# Process-Controlled Functional Polymer Films on Paper: Oxygen Barrier and Antimicrobial Performance of PVA–Amylose Coatings

## TL;DR

This study shows how to create continuous, oxygen-blocking, and antimicrobial polymer coatings on paper by controlling the coating process and thickness.

## Contribution

The study identifies a critical film thickness for eliminating defects and achieving high-performance coatings on paper.

## Key findings

- Multi-layer deposition enabled continuous polymer films with significantly reduced oxygen transmission rates.
- ZnO NP-loaded coatings showed strong antimicrobial activity against E. coli and S. aureus.
- Coatings maintained mechanical flexibility and repulpability, making them suitable for sustainable packaging.

## Abstract

The development of functional polymer films on porous paper substrates is inherently constrained by substrate-induced defects that hinder film continuity and barrier performance. In this study, process-controlled amylose–Poly(Vinyl alcohol) (PVA) coatings incorporating ZnO nanoparticles (ZnO NPs) were fabricated via aqueous deposition to investigate the process-structure-property relationship governing oxygen barrier behavior on paper. The moisture resistance of the coating was also evaluated. Single-layer coatings exhibited severe barrier failure due to insufficient film formation and pervasive pinhole defects. In contrast, systematic multi-layer deposition enabled the formation of continuous polymer films. A pronounced non-linear reduction in oxygen transmission rate was observed once the dry coating thickness exceeded approximately 5 µm. Under these conditions, the oxygen transmission rate decreased to approximately 15 cc/m2·day·atm at 20 °C and 65% relative humidity. This transition was correlated with the elimination of substrate-induced defects, as confirmed by morphological analysis. In addition to enhanced barrier performance, ZnO NP-loaded coatings demonstrated strong and broad-spectrum antimicrobial activity against both Escherichia coli and Staphylococcus aureus, indicating their multifunctional potential for active packaging applications. Supporting evaluations further indicated adequate mechanical flexibility and high repulpability, highlighting the suitability of the coating for sustainable paper-based packaging. Overall, this work identifies a quantitative critical film thickness that serves as process-specific design guideline for engineering high-performance functional polymer coatings on porous paper substrates.