# Preparation, Reaction Kinetics, and Properties of Polyester Foams Using Water Produced by the Reaction as a Foaming Agent

## TL;DR

This study creates sustainable polyester foams using bio-based materials, showing they have good thermal stability and flame resistance, making them a promising eco-friendly alternative to traditional petrochemical foams.

## Contribution

The paper introduces a modular system for producing bio-based polyester foams with tunable properties and minimal hygroscopicity.

## Key findings

- Foaming occurs in a narrow time window with first-order kinetic behavior observed in water formation.
- The foams exhibit thermal stability up to ~400 °C and burn 40 times slower than conventional foams in flammability tests.
- Scanning electron microscopy shows a homogeneous polymer matrix with dense, microporosity-free cell walls.

## Abstract

This study explores sustainable foamed polyester materials derived from natural or bio-based building blocks, including succinic, glutaric, and adipic acids, combined with trimethylolpropane and pentaerythritol. By precisely tuning the ratio of functional groups, the resulting polymers contain minimal free functionalities, leading to lower hygroscopicity and enhanced stability. The reaction is monitored by tracking the mass loss associated with water formation, the primary condensation by-product, which reveals a first-order kinetic behaviour. Infrared spectroscopy indicates that foaming occurs in a narrow time window, while esterification begins earlier and continues afterwards. Thermogravimetric analysis confirms thermal stability up to ~400 °C, with complete decomposition at 500 °C and no residue. Scanning electron microscopy images of test specimens with varying densities reveal dense, microporosity-free cell walls in both materials, indicating a homogeneous polymer matrix that contributes to the overall stabilisation of the foam structure. In flammability tests, the foams resist ignition during two 10 s methane flame exposures and, under prolonged flame, burn 40 times more slowly than conventional foams. These results demonstrate a modular system for creating bio-based foams with tunable properties—from soft and elastic to rigid—suitable for diverse applications. The materials offer a sustainable alternative to petrochemical foams while retaining excellent mechanical and thermal properties.