Wood needs fire retardant treatments or coatings due to its inherently flammable nature. Typically, the fire retardants are based on halogens, phosphorus, nitrogen, metal ions, or nanofillers. There are environmental and toxicity issues with some of these fire-retardant chemicals. For example, the halogen-based com-pounds can leach from the coating into the environment and can bioaccumulate. In addition, during combustion they release toxic gases. Phosphorus-containing flame retardants are more suitable than halogen-based compounds as they favour the formation of char instead of combustible volatile species. A bio-based re-source with high potential as a fire retardant is functionalized microfibrillated cellulose (MFC). Phosphorylation and amination of MFC have also been explored previously to prepare fire retardant MFC (Ghanadpour et al. 2018).
The production and functionalization of MFC has been explored only at low solids content so far. The excess amount of water in the formulations leads to coating application and drying challenges. The high consistency enzymatic fibrillation of cellulose (HefCel) tech-nology in which MFC is produced at high consistency with the aid of enzymes (Hiltunen et al. 2015) can potentially resolve this challenge. This technology has also proven to be cost-effective compared to many state-of-the art technologies for MFC production (Lehmonen et al. 2017). Furthermore, this technology allows functionalization of MFC at high solids making the functionalized MFC a competitive candidate in development of low-cost, environmentally friendly alternatives to synthetic components in wood coatings.
In this work performed under the FireCellCoat project, a phosphorylated MFC was produced using a novel concept at high solids content (25 t.%) with low energy consumption (0.6 MWh/t). The fire-retardant coating formulations based on phosphorylated MFC were prepared and applied to a wood substrate using spray coating process. The formulations were also optimized for their rheological performance using carboxymethyl cellulose (CMC) as a rheology modifier. The fire-retardant properties of phosphorylated MFC coated wood were improved compared to those of uncoated wood. The coated wood showed self-extinguishing behaviour during flammability tests and did not ignite quickly when subjected to the cone calorimeter heat flux.
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Authors
Vinay Kumar
VTT Technical Research Centre of Finland Ltd, VTT, Tietotie 4E, 02150 Espoo, Finland
Aayush Jaiswal
Alexey Khakalo
Marie Gestranius
Marie Kangas
Tekla Tammelin
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