Researchers at the National Center of Excellence for Functional Materials (FUNMAT) in Finland tested nitrogen containing organic chemicals (azoalkanes, AZO and BIZASO) for processing compatibility and fire performance in a low density polyethylene (LDPE) extrusion coating of Kraft paper. Comparison was made to a brominated and a mineral flame retardant. The new products achieved low flammability (self-extinguishing) and good finished paper coating quality at loadings of 0.5 – 1% and processing temperatures up to 260°C.
The azoalkanes are considered to inhibit fire by releasing radicals. The deterioration of fire performance at higher processing temperatures is probably the result of radical release during processing, modifying the polymer structure, and should be addressed by developing azoalkanes which are stable at higher temperatures. The authors conclude that this type of nitrogen azoalkane product can be an effective flame retardant for such paper coatings, confirming previous work which shows self-extinguishing of other polymers treated with azoalkanes (polypropylenes, polyurethanes, polystyrenes) offering advantages of low toxicity, necessary for food contact papers.
“Toward halogen-free flame resistant polyethylene extrusion coated paper facings”, W. Pawelec et al., Progress in Organic Coatings, in press 2014 www.elsevier.com/locate/porgcoat