Thermal behaviour and flame retardancy of monoethanolamine-doped sol-gel coatings of cotton fabric

Abstract

Recent studies have shown that the combustion behaviour of cellulose-based materials can be strongly affected by the presence of a protective phosphorus-rich silica coating obtained with a promising sol-gel approach. Thus, in the present work, monoethanolamine (MEA) was used in combination with diethylphosphatoethyltriethoxysilane sol-gel precursor (DPTES) to investigate both the ability of MEA to neutralize the acidic conditions of DPTES sol before cotton fabric treatment and the fire resistant properties of the obtained coating (COT-A). Moreover, to study the influence of an inorganic–organic silica matrix on the durability of the proposed flame retardant finishing, the DPTES-MEA sol was mixed with tetraethoxysilane (TEOS) and 3-glycidoxypropyltriethoxysilane (GPTES) precursors, to produce hybrid coatings on cotton fibres (COT-B). Scanning Electron Microscope (SEM) and Attenuated Total Reflection-Infrared (ATR-IR) spectroscopy were used to characterize the surface morphology, as well as the chemical structure of the treated and untreated fabrics. Furthermore, thermogravimetric Analysis (TGA), Microscale Combustion Calorimeter (MCC), and Limiting Oxygen Index (LOI) were performed on the treated cotton fabrics with a promising outcome. The results showed that DPTES-MEA sol is able to enhance the thermal and thermo-oxidative stability of cotton, exploiting the joint effect of thermal shielding (exerted by the silica phases) and char-forming (exerted both by the phosphoric acid source present in the alkoxysilane precursor and by the nitrogen content in MEA). Both proposed sol-gel treatments allow the cotton samples to achieve a LOI value of 29, classifying them as self-extinguishing materials.