# Structure–Property Relationship in Composite Superabsorbents: How Butyl Succinate Architecture Affects Water Uptake and Phytotoxicity?

## TL;DR

This paper shows how modifying the structure of a plasticizer can improve the water absorption and safety of superabsorbent materials used in agriculture.

## Contribution

The study introduces a novel approach using branched succinic acid esters to enhance superabsorbent performance without compromising biodegradability.

## Key findings

- Branched plasticizers increased swelling capacity by up to 64% while maintaining elasticity.
- Plasticized materials retained over 80% of their swelling capacity after multiple cycles.
- No phytotoxicity was observed at relevant agricultural concentrations.

## Abstract

Composite superabsorbents (C-SAPs) that combine synthetic and polysaccharide components hold great promise for sustainable agriculture. They improve water management and enable the controlled release of agrochemicals. However, increasing the polysaccharide content to enhance biodegradability often reduces water absorption capacity. In this study, we explore plasticization with succinic acid esters as a strategy to overcome this limitation. Our goal is to establish structure–property relationships between plasticizer architecture and C-SAP performance. A series of carboxymethyl cellulose-based superabsorbents was synthesized via radical copolymerization. They were then plasticized with 5 wt.% of dibutyl succinate, di-sec-butyl succinate, or di-iso-butyl succinate. The resulting materials were characterized using FTIR spectroscopy, differential scanning calorimetry, rheological tests, swelling kinetics, and phytotoxicity assays against oilseed radish and common oat. Increased plasticizer branching and molecular volume enhanced polymer network elasticity, lowered the glass transition temperature (by up to 6 °C), and increased the equilibrium swelling ratio by up to 64% compared to the unplasticized C-SAP (661 ± 17 vs. 402 ± 10 g/g). All plasticized C-SAPs retained more than 80% of their initial swelling capacity over five swelling–deswelling cycles across pH 3.0–9.2. They also showed no phytotoxicity at agriculturally relevant concentrations. These findings demonstrate that molecular engineering of plasticizer architecture enables simultaneous optimization of water absorption and environmental safety in C-SAPs for agricultural use.