Endothermic salt-hydrogel cooling complex for diaper applications

Overview

This early-stage materials technology introduces a swollen salt-hydrogel complex designed to deliver temporary skin cooling within absorbent hygiene products such as diapers. The approach combines a superabsorbent polymer matrix with salts that dissolve endothermically: when the diaper becomes wet, potassium chloride and sodium sulfate decahydrate melt or dissolve and absorb heat from the surrounding moisture and skin, while the polymer network remains stable and swollen. The technology aims to provide passive, chemical-based cooling without active electronics or refrigeration, offering a practical path to improved comfort in disposable hygiene products.

The value proposition is a tunable absorbent-core formulation that can be adjusted for cooling intensity and duration. By selecting polymers that remain swollen in saline and sulfate solutions, the system is intended to maintain absorbency while generating a temporary cooling effect that diffuses through the diaper toward the skin.

Technical specifications

Core mechanism:

• Endothermic dissolution of potassium chloride absorbs approximately 235 joules per gram of energy; a typical diaper load of around 1,000 joules could dissipate roughly 1 watt from the skin over several minutes.
• Sodium sulfate decahydrate melting provides an additional enthalpy-of-hydration cooling pathway alongside the polymer swelling process.

Materials under investigation:

• Sodium polyacrylate hydrogels are evaluated for stability in potassium chloride and saline solutions.
• Sodium alginate and potassium polyacrylate formulations are considered for stability in sodium sulfate and potassium chloride environments.
• Encapsulation of salts in a thin wax sheet is proposed as a controllable release option if cooling kinetics need to be slowed or triggered on demand.

Validation plan:

• Synthesis and swelling tests on hydrogel samples exposed to saline and solid salts.
• Thermal measurements using a sheathed thermometer to confirm heat absorption.
• Custom calorimetry inside a benchtop environmental chamber to measure cooling duration.
• Whole-diaper testing on a dummy model: loading the core with KCl, wetting with saline, and measuring skin-surface temperature and enthalpy of solution.

Technology readiness level

The project is at an early stage, targeting proof of concept (TRL 3) by the first quarter of 2027 and progressing to calorimetry-based validation (TRL 4) by the second quarter of 2027. The proposed work will establish polymer-salt compatibility, confirm endothermic cooling behavior, and measure skin-level temperature reduction in a representative diaper format. Current uncertainties include the kinetics of cooling, polymer stability at high salt concentrations, and the need to optimize salt-to-polymer ratios for both absorbency and cooling performance.