Lignin is an abundant bio-sourced material which as PIN flame retardant properties by contributing to char formation. In this study, kraft lignin was supplied by the paper industry (UPM Finland). This lignin contained around 6.5 mmol/g of OH content (reactive groups). The lignin reacted with phosphorus pentoxide after solvent dissolution, resulting in phosphorylated lignin with just over 4% P (P-LIG). Pure lignin and P-LIG were tested at 30% loading in ABS polymer (acrylonitrile butadiene styrene). P-LIG showed better thermal stability than pure lignin, and good dispersion in the ABS. At 30% loading, P-LIG reduced peak heat release rate by 1/3 – 2/3*. P-LIG reduced by 25 – 50% peak emissions of carbon monoxide (CO), nitric oxide (NO) and hydrogen cyanide (HCN), however total emissions of these gases were unchanged for CO, decreased by 30% for NO but increased by nearly 20% for HCN. Analysis suggested that the P-LIG was mainly acting in the condensed phase, generating a protective char layer on the polymer, but also to a small extent in the gas phase.
* 1/3 reduction in PCFC = Pyrolysis Combustion Flow Calorimeter, 2/3 reduction in MLC = Mass Loss Calorimeter.
“Phosphorylation of lignin to flame retard acrylonitrile butadiene styrene (ABS)”, B. Prieur et al., Polymer Degradation and Stability 127 (2016) 32e43 http://dx.doi.org/10.1016/j.polymdegradstab.2016.01.015