# Poly(o‑phenylenediamine) as an Organic Filler for Enhancing the Mechanical and Antibacterial Performance of Chitosan Films

## TL;DR

This paper shows how adding a small amount of poly(o-phenylenediamine) to chitosan improves its strength, moisture resistance, and antibacterial properties for sustainable packaging.

## Contribution

A low concentration of poly(o-phenylenediamine) significantly enhances chitosan's mechanical and antibacterial performance without petroleum-based additives.

## Key findings

- Adding 0.15 wt% PoPD increased chitosan's tensile strength from 9.28 MPa to 27.98 MPa.
- PoPD reduced moisture absorption and improved antibacterial activity against Bacillus subtilis.
- Molecular interactions like π–π-stacking and hydrogen bonding explain the antibacterial effects.

## Abstract

Understanding structure–property
relationships is essential
for designing multifunctional biopolymer composites that integrate
mechanical robustness, barrier performance, and antimicrobial activity
in sustainable materials. Chitosan (CS) exhibits excessive hydrophilicity,
limited mechanical strength, and poor moisture stability, which restrict
its long-term performance in packaging applications. With the aim
to enhance the mechanical strength, moisture absorption, and overall
performance of CS, an organic aromatic polymer, poly­(o-phenylenediamine) (PoPD), was introduced into the matrix through
in situ oxidative polymerization. Incorporation of PoPD improved the
properties of CS by introducing aromaticity and electron delocalization,
thereby limiting water uptake and molecular diffusion without relying
on petroleum-derived additives. Remarkably, a low filler concentration
(0.15 wt % of PoPD) produced drastic enhancement, in a tensile strength
of 27.98 ± 1.40 MPa (as compared to 9.28 ± 0.46 MPa in neat
CS) and an elongation at break value of 5.44 ± 0.27%. Moisture
absorption studies confirmed a marked reduction at low filler levels,
whereas higher PoPD contents generated compact morphologies that further
restricted diffusion. Antibacterial evaluations revealed pronounced
inhibition of Bacillus subtilis across
all filler concentrations. Molecular docking analyses attributed this
behavior to π–π-stacking, hydrogen bonding, and
electrostatic interactions between PoPD and bacterial residues. The
properties can be tuned by adjusting the filler content, producing
multifunctional composites suitable for smart, sustainable packaging
applications.