Lignin is an abundant natural biological polyphenol polymer, found e.g. in wood and plant fibres. A number of studies have shown that the lignin’s aromatic chemical structure supports char development, including in polypropylene, polylactide, polybutylene succinate and epoxy. In this study, phosphorus was reacted into lignin (4.1 % P). ABS was tested with 30% pure lignin and with 30% phosphorylated lignin (P-lignin). The peak heat release rate (pHRR) of ABS was reduced respective 43% and 58%.
With both pure and P-lignin, however, time to ignition was reduced by nearly 40%. The flame retardancy effect of P-lignin was shown to be mainly by char generation and partly by gaseous phase action, probably of phosphorus species. The authors suggest that increasing the P content of the P-lignin could further improve its effectiveness as a biobased flame retardant.
“Phosphorylation of lignin to flame retard acrylonitrile butadiene styrene (ABS)”, B. Prieur et al., Polymer Degradation and Stability (2016), http://dx.doi.org/10.1016/j.polymdegradstab.2016.01.015