# Tracking the Progress of Biocomposites Based on Poly(3-hydroxybutyrate) with Hypromellose Additives via Thermal Analysis, Mechanical Properties, and Biological Studies

## TL;DR

This paper studies how adding hypromellose to P3HB biocomposites affects their thermal, mechanical, and biological properties.

## Contribution

The novel contribution is the detailed analysis of structural and thermal changes in P3HB composites with hypromellose additives.

## Key findings

- Adding hypromellose reduces crystallinity and increases the amorphous phase in P3HB biocomposites.
- Thermal stability of biocomposites increases with higher hypromellose content.
- Biocomposites with 2% filler contain a rigid amorphous fraction not seen in others.

## Abstract

Poly(3-hydroxybutyrate) (P3HB) was used to produce biocompatible composites with hypromellose as an additive. The study aimed to assess their biological and mechanical properties, as well as specific thermal parameters and phase content. Differential scanning calorimetry was applied to analyze the phase transitions of both biocomposites and the polymer matrix. Furthermore, the thermal parameters—encompassing both non-equilibrium and equilibrium states—of the biocomposites and unfilled P3HB were evaluated according to their thermal history. Using equilibrium parameters such as the heat of fusion for fully crystalline materials and the heat capacity change at the glass transition for fully amorphous composites, we estimated the degrees of crystallinity as well as the mobile and rigid amorphous fractions. Adding hypromellose to the P3HB matrix reduced crystallinity compared to the unfilled material. At the same time, an increase in the amorphous phase was observed. It was also discovered that the rigid amorphous fraction exists solely in biocomposites containing 2% by mass of filler. Thermogravimetric analysis showed that the thermal stability of all biocomposites surpasses that of unfilled P3HB. Adding an extra 1% filler by mass raises the degradation temperature by about 37 °C compared to unfilled P3HB. The immunosafety of the tested biocomposites, with very low or no endotoxin contamination, was confirmed in accordance with Food and Drug Administration and European Medicines Agency guidelines. The study clearly demonstrates the influence of the filler in the P3HB matrix on various structural, thermal, mechanical, and biological properties of the prepared biocomposites.