Influences of binder on fire protection and anticorrosion properties of intumescent fire resistive coating for steel structure

Abstract

The combination of epoxy emulsion and self-crosslinked silicone acrylate (SSA) emulsion was used as mixed binder for preparing water-borne intumescent fire resistive coating. The influences of binders on the properties and char formation of the coatings were investigated in detail by using thermogravimetry (TG), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), rheological measurement, fire protection test and anticorrosion property test. It was found that the fire protection and foam structure of the coating was significantly improved by adding 14% SSA (by mass). The TG results showed that adding SSA increased the residue weights of the coatings. The XRF results demonstrated that anti-oxidation of the coatings was improved by adding SSA into the mixed binders. The results of anticorrosion property test indicated that the anticorrosion property of the coatings was enhanced with increase of content of SSA.

Introduction

Intumescent fire resistive coatings have been found widespread used as passive fire protection for steel structure which applied in civil buildings, chemical plants and other facilities [1], [2]. Intumescent coatings were composed of three fire retardant additives: an acid source (such as ammonium polyphosphate, APP), a carbon source (such as pentaerythritol, PER) and a blowing agent (such as melamine, MEL) bound together by a binder. During the intumescent process, the binder became important due to two effects: it contributed to the char layer expansion and ensured the formation of uniform foam structure [3], [4], [5]. However, hydrophilic fire retardant additives (APP and PER) in the coatings were very sensitive to corrosive substances, such as water, acid and alkali [6]. They could easily migrate to the surface of the coatings in corrosive environment [7]. This would significantly depress the expected effect of intumescent coatings. The binder as a film-forming component could prevent or remarkably reduce migration of fire retardant additives and access of the corrosive substances [8], [9]. However, some polymer binders, such as acrylic resin, were not efficient enough to provide good corrosion resistance [10].

The objective of this work was to develop a highly protective intumescent coating, which not only had advantages of good fireproof performance, but also showed great anticorrosion property. To achieve this objective, epoxy emulsion and self-crosslinked silicone acrylate (SSA) were selected as mixed binders. Epoxy was used to bind fire retardant additives and provided a carbon source of the intumescent system. Moreover, the chemical structure of epoxy imparted them high chemical resistance against severe corrosive conditions [11]. The crosslinking structure of SSA could increase intumescent rate of coating and improve the foam structure of char layer. Furthermore, when SSA was mixed with epoxy emulsion, the reaction might occur between the two resins, which could enhance crosslinking degree of the mixed resin and lead to an increase of corrosion resistance of the coatings [12], [13].

The influences of the mixed binder on the fire protection and anticorrosion properties of intumescent coating were analyzed. Based on the obtained results, the effects of mixed binder on the coatings were evaluated.