# Different Crystalline Populations for Biopolyesters within Graphene-Based Nanopapers

## TL;DR

This paper explores how biopolyesters form different crystal structures when embedded in graphene-based nanopapers, affecting their thermal and mechanical properties.

## Contribution

The study reveals unique high-temperature stable crystals formed at the interface between biopolyesters and graphene-related materials.

## Key findings

- High melting point crystals were observed due to strong interactions with graphene-related materials.
- Crystals showed thermal stability beyond the equilibrium melting points of PCL and P4HB.
- WAXS results suggest interfacial stabilization of crystals by adsorption onto GRM.

## Abstract

The control and design of the semicrystalline structure
of polymer
binders within nanopapers based on graphene-related materials (GRM)
may have a significant impact on the nanopapers’ physical properties,
including thermomechanical resistance and thermal conductivity. In
this article, biopolyesters differing in methylene chain length between
ester groups were studied, specifically using poly­(ε-caprolactone)
(PCL) and poly-4-hydroxybutyrate (P4HB), with additional comparisons
to polyglycolide (PGA). The crystallization behavior and crystalline
structure of the polymers embedded in GRM nanopapers were studied
by differential scanning calorimetry (DSC) and wide-angle X-ray scattering
(WAXS). In particular, high melting point crystals originating from
strong nucleation and strong molecular interactions with the GRM were
observed with thermal stability dependent on the chemical structure
of the polymer. The crystals having the highest melting temperatures,
well above the equilibrium melting points of PCL and P4HB, are of
particular interest. Besides their high thermal stability, these crystals
cannot be fractionated through successive self-nucleation and annealing.
At the same time, WAXS revealed distinct crystal diffraction reflections
and relatively broad rings, suggesting the formation of crystals stabilized
up to high temperatures by their interfacial adsorption onto GRM.
These findings offer new insights into the mechanism of polymer crystallization
at the interface with nanoparticles and may have implications for
the development and application of hybrid organic/inorganic flexible
nanopapers in electronic devices.