# Superabsorbent Hydrogels Derived from Cellulose Obtained from Post-Consumer Denim

## TL;DR

This paper introduces a sustainable method to convert old denim into high-performance hydrogels for agricultural and environmental uses.

## Contribution

The novelty lies in directly converting post-consumer denim waste into functional hydrogels without purification steps.

## Key findings

- Denim-derived hydrogels achieved a swelling capacity of 1900%, among the highest reported.
- The process uses eco-friendly methods like mechanochemical pretreatment and citric acid crosslinking.
- Pore sizes in the hydrogels reached up to 147 µm with increased urea content.

## Abstract

This study presents a novel, circular-economy-driven strategy for valorizing post-consumer denim waste into high-performance hydrogels through a fully integrated and eco-friendly process. Unlike conventional approaches that rely on virgin cellulose or harsh chemical treatments, our method uniquely combines high-energy mechanochemical pretreatment, in situ carboxymethylation to produce carboxymethylcellulose (CMC), and citric acid/urea-based crosslinking, all using recycled denim as the sole cellulose source. High-energy milling effectively reduced particle size and lowered the crystallinity index (CI) from 75.7% to 66.1%, transforming the fibrous structure into a more reactive substrate for etherification. Successful CMC synthesis was confirmed by FTIR (COO− stretch at 1587 cm−1), while citric acid crosslinking generated ester bonds (C=O at ~1724 cm−1), forming a 3D network further tailored by urea, acting as a green porogen. The resulting hydrogels exhibited enhanced thermal stability (TGA) and a tunable porous morphology (SEM), with pore sizes reaching up to 147 µm as the urea content increased. Notably, the hydrogel Hy/CMC/U2/CA achieved an exceptional swelling capacity of 1900%, which is among the highest reported for denim-derived or citric acid-crosslinked systems. The objective of this work is to demonstrate, for the first time, the feasibility of converting waste denim directly into functional hydrogels without intermediate purification steps, offering a scalable and sustainable route for agricultural applications, such as soil water retention, controlled nutrient release, or environmental remediation, within a true circular economy framework.