Smart and Sustainable Sizing: Investigating the Sensing Behavior of Glass Fabrics Coated With Waterborne Polyurethane/Graphene Dispersions

The study focuses on developing smart, sustainable sizing agents that impart functional properties to glass fabrics (GFs). A series of graphene/waterborne polyurethane (WPU) dispersions is formulated and optimised to transform insulative GFs into electrically conductive ‘smart’ fabrics with strain-sensing capabilities. The novelty of this work lies in a stable, waterborne graphene sizing formulation that enables direct, single-step dip-coating of GFs, eliminating the need for multi-layer deposition, post-processing, or hazardous chemicals. Dispersion stability is assessed using T2 relaxation time measurements on a nuclear magnetic resonance (NMR) spectrometer. The optimised formulation used to coat the GFs in this study exhibits good dispersion stability (T2 value of 822.7 ms), higher than that of the other formulations developed. This enhanced stability directly contributed to uniform coating morphology and effective electrical conductivity across the GFs. Additionally, comprehensive material characterisation is conducted to analyse the structural, morphological, and chemical properties of the advanced graphene/WPU formulations. Electromechanical testing demonstrates reproducible piezoresistive behavior under cyclic compressive loading, with force estimation accuracy remaining below 10% (RMSE) for loads exceeding 1000 N and improving to below 4% for loads within 1.2–5 kN. The force–conductance calibration shows strong reproducibility (R2 ≈ 1), supporting reliable sensing performance under medium-to-high load regimes relevant to structural health monitoring (SHM). The findings of the study offer a sustainable and scalable alternative to traditional solvent-based systems, addressing environmental concerns while enabling high-performance applications in composite manufacturing.