Comparison of two flame-retardant treatment methods on bulk hemp fibers: Towards a large-scale viability as a raw material for building insulation

The high flammability of bio-based insulation materials derived from plant fibers is a major barrier to their widespread use, necessitating the development of effective flame-retardant treatments. This study aims to optimize the treatment of raw hemp fibers by comparing two environmentally-friendly application methods: immersion and spraying. The fibers are treated with a solution containing phytic acid and urea, as biobased sources of phosphorus and nitrogen. The efficiency of the treatments is assessed by characterizing the quantity of phosphorus grafted, the thermal degradation of the fibers by thermogravimetric analysis and their flammability using a mass loss calorimeter. Both application methods are effective, but the spraying method demonstrated superior performance, resulting in a higher level of phosphorus grafted to the fibers and a reduced heat release rate. Additionally, the formation of a protective char layer on the fiber surface helps to limit flame propagation. Notably, this method requires ten times less treatment product than immersion, making it a highly scalable and efficient solution for the industrial production of flame-retardant insulating materials. • Two flame-retardant treatment methods are tested on bulk hemp fibers. • Both treatment methods significantly reduce the flammability of the hemp fibers. • The spraying method results in a higher phosphorus content, and a lower flammability. • The quantity of treatment for the spraying method is lower than for immersion. • The pulverization method can be used to treat fibers on a large scale.