Self sTratifying Intumescent Coatings – STIC

The first main objective is to identify and analyze a panel of incompatible resins showing a self-stratifying effect when their mixture are considered. This system should fit the basic requirements needed to obtain (i) adhesion to Polycarbonate or steel and (ii) UV and moisture barrier effects. The choice of the adequate resins depends on their intrinsic characteristics as well as on the behavior of the resin mixtures. The influence of the substrate on the behavior of the film formation has also to be considered, as one of the resins must be able to wet the substrate spontaneously.
In a second step, the objective of the project will consist in managing to incorporate one or more specific FR fillers in one of the “successful” self-stratifying coatings developed for each substrate in order to provide (i) a fire retardant effect on the PC substrate and (ii) a fire protective effect on the steel substrate without affecting the self-stratifying process. Several approaches will be investigated such as the use of liquid flame retardant and the use of FR solid fillers .

The major identified scientific issues are:
- To determine the good combination of resins and curing agents that will permit the formation of a self-stratifying coating, To do this Hansen and surface energy theoretical approaches have been chosen.
Stratification was investigated by SEM cross section analyses
- To determine the right fire retardant filler that enables to obtain good flame retardant properties without modifying the self-stratifying process,
- The control of the dispersion and distribution of the FR fillers in the coating during the self-stratifying process: this has been done by SEM-EDS and EPMA cross section analyses
- The development of techniques permitting to fully characterize the materials during each steps. Ionic polishing, and specific fire tests (UL94, LOI, cone calorimeter) as well as aging experiments will be considered.

The work carried out these last 18 months allowed answering most of the objectives detailed in the workplan. Type I self-stratifying coatings were obtained on Polycarbonate, fitting the specification in term of appearance and adhesion. Moreover, effective flame retardant (FR) self stratifying coatings, containing one FR filler have been formulated.

To summarize
(i) A new type I self-stratifying coating, based on a silicon resin and an epoxy resin, has been developed and applied on polycarbonate. A paper is being written on that subject. Another type I system, based on fluoropolymer and epoxy resins, less innovative but perfectly characterized, was also obtained

(ii) Contrary to what is reported in litterature, pigments/fillers do not necessarily remain in the phase they have been dispersed in, but migrate in the phase they have the more affinity to. This is for example the case with the epoxy/silicon/iron oxide system studied in this project; a paper is being written on that subject.

(iii) An interesting result for the next step of the study has been obtained. The incorporation of a pigment (red iron oxide) at low loading shows good fire retardant properties in both self-stratifying epoxy/silicon and epoxy/ fluoropolymer systems. This pigment, as well as another filler having FR properties have shown no negative effect on the stratification process, contrary to some literature data, which report that most of the commonly additives used in a coating influence negatively the stratification. One paper is being written on that subject.

The incoming work is mainly based on the study of fire retardant properties and aging of the filled epoxy/silicon system on polycarbonate.
Some other flame retardants or combinations of these agents will be studied.One step will also consist in elucidating the FR mechanism of action of the most effective formulations.
The epoxy/silicon self-stratifying system is the most promising one for this project, and in particular as it is an innovative system. Indeed, such coating has never been reported yet. An ageing study in accelerated conditions of the most promising systems will be carried out without and with FR agents.
The development of a self-stratifying coating on steel remains however currently one of the main objectives : an issue is to obtain a type I system on steel. To reach this objective, surface energy modifications on steel will be done (by plasma, phosphatation, etc.) to influence the stratification process. If an efficient system is developed, same study as in the case of PC will be carried out , i.e. incorporation of FR fillers and ageing study of the formulations.

3 papers for peer-reviewed international journals are currently under writing, as well as a review on self stratifying coatings.
One paper describing the project has been published in the International Innovation Journal:
Research media : « Fire fighters », International Innovation, www.internationalinnovation.com/fire-fighters/

Three oral communications in international conferences have been given:

1. Communication orale: COSI 2016 « Epoxy-Silicone self-stratifying coatings », 27 juin-1er juillet 2016, Pays-Bas

2. Communication orale: EUROCOAT 2016 : « Self-stratifying coatings »22-24 mars 2016, Paris, France

3. Communication orale : ISPAC 2016 “Solutions against weathering of intumescent fire resistant coatings”, 12-15 juin 2016, Singapour

Two seminars allowed presenting the project:

Journée des doctorants 2015 et 2016, Ecole doctorale ED SMRE, Université de Lille 1

2. Colloque Franco-Allemand avec l’institut fédéral pour la recherche et les essais de matériaux (BAM : Bundesanstalt für Materialforschung und –prüfung), 13-16 mars 2016, Germany

And finally the PhD student on the project (Agnes Beaugendre) has candidated to the «Bourse Loreal-UNESCO« allowing promoting women in science

Flame retardant coatings constitute one growing branch of the coating industry, with the increasing trend of more stringent fire safety regulations and demands for reduction of fire hazard posed by several combustible materials. To provide durable fire retardancy to a material through its surface, three different coatings with different functional properties (e.g. adhesive, fire retardant and hydrophobic properties) are needed. These multilayered systems usually require complex application and curing procedures. Multiple formulation, application and processing steps not only contribute to environmental waste generation and pollution, they also use excessive amount of energy until a solid film has been produced. It would thus be highly desirable to reduce the number of layers to a minimum, providing the equivalent or better overall performance of the current systems, forming multilayered paint films from a single coat system. The self-stratifying approach allows a one-step formation of complex multi-layer or gradient coating structures directly to plastics and steel, combining optimized top and adhesion properties in one coating composition. These coatings are developing mainly for automotive, self-healing and weather-resistant applications, but the self-stratifying approach has never been considered in the fire retardant and fire protection fields, whatever the substrate involved. This concept thus constitutes a great possible versatile process for a broad range of fire retardant applications and could thus favor an industrial eco-efficient development of products, taking into account the reduction of solvents and labor cost. Flame-retardant self-stratifying coatings thus completely fit the needs of both the finishing industry in general and the flame retardant coating industry in particular, and also perfectly fit the project call orientations, as the aim is to develop an innovative eco-friendly process to stimulate the fire retardant coating industry development. As no academic paper or patent has been written on that specific subject, it opens the door to a real breakthrough and challenge in this industry. The goal of this project is thus to establish a proof-of-concept on formulating a model self-stratifying fire retardant coating showing (i) adhesive properties to a substrate, (ii) intumescent properties when submitted to a fire and (iii) good durability when submitted to accelerated aging tests. Two substrates will be considered: a plastic one (polycarbonate) usually fire retarded in the bulk (addition of additives in the polymeric matrix during its extrusion process), and a steel substrate, usually protected by a three-layers system.
The objective is to obtain a type I coating, corresponding to a perfect stratification giving rise to two well distinct and homogeneous layers, or at least a type II coating, in which the phase separation leads to a stratification characterized by an homogeneous concentration gradient more or less pronounced in the film thickness. We aim at designing one thin (< 150µm) self-stratifying system showing good adhesion to PC and resistant to UV and moisture and one thick (1-2 mm) self-stratifying system showing good adhesion to steel and resistant to UV, moisture, water and salted water. In this part of the work, an optimization of the resins composing the formulation will be carried out. In a second step, we will investigate the effect of the incorporation of one or more specific intumescent fillers in one of the “successful” self-stratifying systems developed for each substrate in order to provide (i) a fire retardant effect on the PC substrate and (ii) a fire protective effect on the steel substrate without affecting the self-stratifying process, the adhesive properties and the surface barrier properties. The final goal is to reach better or at least equivalent FR properties than a bulk treated PC or than a commercial thick coating applied on steel.