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Description
Blended nylon–cotton (NYCO) fabric combines the comfort of cotton with the strength of nylon, but its flammability limits its use in protective clothing. In this study, a sustainable, water-based coating composed of egg white proteins (EWP), pectin (P), and guanidine phosphate (GP), a phosphorus- and nitrogen-containing salt, was applied to NYCO fabric through a two-step process. The effects of salt addition, polyelectrolyte concentration, and pH on coating deposition, flame retardancy, and mechanical properties were investigated.
The EWP/P coating without GP produced only 1.8% weight gain and did not prevent complete burning. As a salt, GP induced charge screening along the pectin macromolecules, reducing electrostatic repulsion and increasing coating deposition. It also acted as an acid source and blowing agent within the intumescent system. This behavior agrees with the effects of ionic strength, pH, and charge density on weak-polyelectrolyte deposition.¹ Increasing the EWP, P, or GP concentration improved flame retardancy. The 4% EWP/(1% P–20% GP) formulation was subsequently deposited at pH 2, 3, and 4 to evaluate the influence of pH. Although all three coatings self-extinguished, pH 3 provided the best balance between flame retardancy and mechanical performance, producing 14.8% weight gain and the lowest char length of 127 mm. At pH 2, deposition was accompanied by reduced tensile strength due to cellulose hydrolysis, whereas pH 4 preserved tensile strength but resulted in lower deposition and a longer char length. The pH 3 treatment retained a tensile strength of 1333.5 N, comparable to 1345.5 N for uncoated NYCO, while the coating slightly increased stiffness and reduced elongation and air permeability.² These findings show that controlling GP addition, polyelectrolyte concentration, and pH enables effective flame retardancy while preserving NYCO mechanical performance.
Keywords: nylon–cotton fabric, flame retardancy, polyelectrolyte complex, pH
References
1. Shiratori, S. S.; Rubner, M. F. pH-Dependent Thickness Behavior of Sequentially Adsorbed Layers of Weak Polyelectrolytes. Macromolecules 2000, 33, 4213–4219. DOI: 10.1021/ma991645q.
2. Petkovska, J.; Radoičić, M.; Marković, D.; Rodriguez-Melendez, D.; Smith, D. L.; Iverson, E. T.; Dimova, V.; Radetić, M.; Grunlan, J. C.; Jordanov, I. Sustainable Two-Step Polyelectrolyte Complex for Flame Retardant