# Characterization of Biobased Polymers at the Gas–Solid Interface—Analysis of Surface and Bulk Properties during Artificial Degradation

## TL;DR

This study examines how biobased polymers change at their surface and inside when exposed to artificial degradation, revealing how these changes affect their reactivity and environmental impact.

## Contribution

The study introduces a combined interfacial and bulk analysis approach to better understand early-stage polymer degradation and its environmental implications.

## Key findings

- Degradation can decrease specific surface area while reactivity varies depending on available reactive groups.
- UV exposure increases water affinity, acidification, and ozone reactivity in both polymers.
- Surface hydroxyl groups in PAXA reduced significantly under UV and ozone exposure.

## Abstract

Accurately assessing the interfacial composition and
reactivity
of (bio)polymers under controlled but environmentally relevant conditions
remains challenging. This study explores the evolution of surface
functionalities of novel polyesters Poly(Butylene Xylose) (PBX) and
Poly(Alkyl Xylose Amide) (PAXA) under artificial degradation conditions.
Employing a Knudsen Flow Reactor (KFR) and a gas-titration approach,
we systematically analyze the chemical transformations occurring at
the polymer’s solid–gas interface. Both polymers are
derived from the same functionalized lignocellulosic sugar building
block, Diglyoxylic Acid Xylose (DGAX). Virgin (V), long-term UV (UV),
and short-term Ozone (O3) exposures induce specific but
differing alterations in molecular integrity and surface reactivity,
resulting in notable shifts in material properties and polymer structure.
Contrary to the assumption that degradation increases specific surface
area (SSA) and reactivity, our results reveal cases where the SSA
decreases, with reactivity either increasing or decreasing based on
the reactive groups available at the interface. Both polymers exhibited
increased water affinity, acidification, and ozone reactivity following
UV exposure. Interfacial reactivity, assessed with trifluoroacetic
acid, hydroxylamine, and nitrogen dioxide, increased for PBXUV but decreased for PAXAUV. Surface hydroxyl groups in
PAXA reduced 5-fold under short-term ozone and long-term UV exposure,
while bulk transport kinetics of hydroxylamine altered with long-term
degradation, though ozone exposure left transport mechanisms unaffected.
This combined interfacial and bulk analysis approach advances our
understanding of (bio)plastic degradation. It examines the role of
degraded polymers as potentially more or less reactive vectors for
chemicals and organisms upon environmental release while also demonstrating
that polymer degradation initiates significantly earlier than previously
assumed.

Polymer particle degradation and induced
surface functionality
changes are crucial for predicting environmental impact, particularly
their role as reactive vectors and pollutant carriers.