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Title: The Chemical Mechanism of Thermolytic Synthesis in Charring Intumescent Coatings for Passive Fire Protection // Proceedings of the Ninth International Seminar on Fire and Explosion Hazards. Vol. 2: 21-26 April 2019, Saint Petersburg, Russia
Creators: Ustinov A.; Zybina O.; Tanklevsky L.
Organization: Peter the Great St. Petersburg Polytechnic University; “Gefest” Enterprise Group
Imprint: Saint Petersburg, 2019
Collection: Общая коллекция
Document type: Article, report
File type: PDF
Language: English
DOI: 10.18720/SPBPU/2/k19-78
Rights: Свободный доступ из сети Интернет (чтение, печать, копирование)

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Fireproofing properties of charring intumescent materials are determined by the formation of the carbonaceous porous layer, which is generated as a result of thermolytic synthesis. The layer has low thermal conductivity, and it shields the construction from the external heat flux. Char-forming coatings have been used for passive fire protection for more than 50 years. However, the existing technologies of creating new intumescent compositions are still fully empirical, and the problem of ensuring optimal combination of material properties has not been resolved yet. This implies the need in an in-depth understanding of the thermolysis mechanism that controls the performance of the coating in fire conditions. The primary objective of this work is to identify the main chemical reactions occurring in the thermolytic synthesis of the intumescent carbonaceous layer. The intumescent coatings were exposed to annealing in a furnace and thereby produced carbonaceous samples were studied by chromatography-mass spectrometry and IR spectroscopy. TGA-DSC thermal analysis of the virgin samples of the intumescent coatings has also been undertaken. It has been established that in the thermolytic synthesis the melamine forms three-dimensional polymer-oligomeric structures with aldehydes. In its turn, the aldehydes are produced by the pentaerythritol decomposition catalyzed by ammonium polyphosphate and titanium dioxide. It is also shown that the role of the ammonium polyphosphate is two-fold. First, it generates ammonia gas, which facilitates swelling. Second, it serves as a blocking catalyst in hardening of the ammonia-aldehyde porous char produced by the resin. As a result, the heat-resistant layer of graphite-like carbon nitride (g-C3N4) forms. It consists of condensed nitrogenous fragments incorporated into a graphene π-linking system inlaid with refractory inorganic compounds such as titanium pyrophosphate. The above mechanism is expected to be useful to enhance the efficiency of porous char formation by new intumescent coatings.

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