Investigation of the processes of atmospheric destruction of flame-retardant coating by IR spectrometry methods

Introduction . The durability and retention of fire-retardant properties of thin-film intumescent coatings are largely determined by the resistance of their chemical composition to atmospheric influences, primarily moisture. Direct in-situ observations of degradation processes require extensive time, making the use of instrumental analytical methods, such as infrared spectroscopy, essential for rapid diagnostics and identification of degradation mechanisms. This article discusses the application of Fourier-transform IR spectroscopy for comparative analysis of the chemical state of fire-retardant coatings after operation in various climatic conditions. Aim . To conduct a comparative identification of functional groups and assess the degree of chemical degradation of an epoxy-acrylate-based fire-retardant coating after prolonged (2 years) exposure to atmospheric moisture during operation in an open industrial atmosphere in a cold climate (open circuit) compared to protected operating conditions (closed circuit). Materials and methods. This study analyzed fire-retardant coating samples collected from operational sites. Infrared absorption spectra were recorded on a Fourier spectrometer in the range of 4000–400 cm -1 using KBr pellets in accordance with State Standard R 57941-2017. Qualitative interpretation of the spectra was based on an analysis of the characteristic absorption bands of the functional groups of the polymer matrix, organophosphorus flame retardant, and mineral filler. Results . IR spectroscopy revealed significant differences in the chemical state of the samples. The open-loop sample showed the almost complete disappearance of bands in the range of 1240–980 cm -1 , characteristic of the stretching vibrations of the P=O and P–O–P bonds of the polyphosphate flame retardant, indicating its profound hydrolytic degradation and leaching. Concurrently, a significant strengthening of the broad band of bound OH groups (3600–3200 cm -1 ) and a weakening of the epoxy matrix signatures were observed. In the closed-loop sample, the key bands of the flame retardant and polymer are preserved, but the presence of the OH band indicates the initial stages of hydrolysis. Conclusions . It was established that the dominant degradation mechanism of the fire-retardant coating is hydrolytic degradation, the intensity of which directly depends on the level of moisture load. The results confirm the high sensitivity of the organophosphorus flame retardant and the polymer matrix of the epoxy-acrylate-based fire-retardant coating to long-term exposure to moisture.