Effect of the CNFs and CNCs based-flame retardants on the fire retardancy of the hand-made coated paperboard

The destructive effects of heat increasing in cellulose substrates, which are the basic materials for the packaging industries, high-quality hygiene packaging, and ammunition packaging, are obvious and inevitable. Therefore, it is essential to modify the structure of these bio-based products with green and environmentally friendly materials, to increase their durability against heat.

In the current study, TEMPO-oxidized CNFs and CNCs, were initially and separately retarded using flame retardant mixtures, including dual “ammonium monophosphate+albumin”, “silica+methyltri-methoxysilane”, and quadruple “ammonium monophosphate+albumin+silica+methyltri-methoxysilane”. Using a rod coater, each combination was then coated individually on the produced cellulosic paperboards. Flame retardancy properties were evaluated by three thermal experiments, including a Mini Fire Tube, Limited Oxygen Index, and Mass Loss Calorimeter.

Based on the observed results, the role of mono-ammonium phosphate, due to the presence of phosphorus-containing groups as the driving force of the charring during combustion, was more prominent and significant in the dual coating mixture than the quadruple coating mixture, containing silica and phosphorus, both in the paperboards coated based on CNFs and paperboards coated based on CNCs. Comparison of the CNFs and CNCs based-flame retardant, as the main basis of the coating formulation, showed that paperboards coated with CNFs based-flame retardant, due to having amorphous and crystalline regions, had much lower amount of mass loss in the Mini Fire Tube test, almost similar Limited Oxygen Index, and Peak Heat Release Rate (PHRR) and Heat Release Rate (HRR) in the Mass Loss Calorimeter test, compared to those of the paperboard coated with CNCs based-flame retardant.

In general, CNFs and CNCs based-flame retardants with mono-ammonium phosphate and albumin, even in low concentrations, can be used as effective retardants and replacements for conventional flame retardants, in high-quality cellulose-based packaging production.