# The Influence of Small Amounts of the Biobased Polyester PEF on the Mechanical Recycling of PET

## TL;DR

This study explores how adding small amounts of a biobased polyester (PEF) affects the recycling of PET, finding that up to 10% PEF does not hinder the process but changes material properties like transparency and color.

## Contribution

The study provides new insights into the compatibility of PEF with PET recycling at industrial scales and identifies effects on crystallization and coloration.

## Key findings

- PEF content up to 10% does not negatively impact the mechanical recycling of PET.
- Higher PEF content reduces crystallization rate and increases bottle transparency.
- Yellowness increases with PEF content, prompting further research to mitigate this effect.

## Abstract

Reducing dependence on fossil-based feedstocks for packaging can be achieved through three complementary strategies: minimizing packaging use, increasing closed-loop recycling rates, and expanding the adoption of renewable (e.g., biobased) packaging materials. To ensure these defossilization pathways reinforce rather than hinder one another, it is essential to understand how new biobased materials interact with existing recycling streams. With the market introduction of packaging containing the biobased polyester poly(ethylene 2,5-furandicarboxylate) (PEF) approaching, several studies have investigated blends and copolyesters of poly(ethylene terephthalate) (PET) and PEF. This study expands current knowledge of thermomechanical and crystallization behavior by examining the influence of PEF on the mechanical recycling process of bottle-grade PET. Processing behavior was assessed at various PEF contents at both laboratory and industrial scales, and the resulting recycled resin and bottles were analyzed for color, crystallization behavior, and bottle performance. Although the melting temperature decreased with rising PEF content, no negative impact on the industrial recycling process investigated was observed for PEF levels up to 10 wt%. Two notable trends emerged: increasing PEF content reduced crystallization rate, yielding bottles with higher transparency, while yellowness also increased. Ongoing research aims to understand and mitigate this rise in yellowness.