# Circularity in Polyamide Textiles: Enhancing Recycled Polymer Molar Mass with Carbodiimide Linear Coupling

## TL;DR

This paper introduces a new recycling method for polyamide 6 textiles using carbodiimide to increase polymer molar mass and improve circularity.

## Contribution

A novel carbodiimide-based recycling method is proposed to recover PA6 molar mass and enable cradle-to-cradle textile recycling.

## Key findings

- CDI increased molar mass of dry and wet PA6 by 40% and 75%, respectively.
- CDI promotes linear chain extension rather than branching, confirmed by DFT calculations.
- CDI-treated PA6 showed higher glass transition temperature and no tertiary carbon formation.

## Abstract

Textile waste from
clothing production poses growing environmental
and economic challenges with global fabric disposal expected to reach
148 million tons by 2030. Polyamide 6 (PA6), commonly used in fabrics,
degrades during recycling due to hydrolysis, lowering its molar mass
and limiting its reuse. This study presents a method to recycle PA6
fabrics using a carbodiimide (CDI) additive, which acts as an antihydrolysis
agent and chain extender, aiming for cradle-to-cradle recycling. Controlling
physicochemical properties, especially molar mass, is crucial; yet,
the mechanisms of molar mass recovery are not well-understood and
can be affected by humidity. This work showed that CDI reduced degradation
in both dry and wet PA6, increasing molar mass by 40% and 75%, respectively,
as confirmed by rheological analysis. Molecular investigation through 13C NMR showed no tertiary carbon signals, and Time Domain
NMR indicated a higher glass transition temperature with CDI. These
findings, supported by Density Functional Theory (DFT) calculations,
suggest that CDI promotes linear chain extension over branching. This
approach supports closed-loop recycling of PA6 fabrics, enhancing
textile circularity and minimizing environmental impact.