Effectiveness of phosphinates and radiation crosslinking on fire-retardancy of unfilled and wood-filled bio-based polyamides

Bio-based polyamides (PA 6.10, PA 10.10 and PA 11) were combined with three different phosphinates based on aluminum diethyl phosphinate (AlPi) to produce fire-retarded compounds. In case of PA 10.10 and PA 11, compounds including wood particles were also prepared. V-0 classification at 1.6 mm thickness was obtained for all formulations in UL94-tests, except for the compound based on PA 6.10 (V-1). After radiation-crosslinking, UL94 performance worsened due to asymmetric heat impact which led to sample warpage, unless wood particles were included and melt stability was improved. Cone calorimeter investigations showed that the addition of wood particles reduced the peak heat release rate of fire-retarded PA 10.10 and PA 11 by 69 % and 77 %, respectively, and contributed to an increase in the CO2/CO ratio and residue due to char formation. Glow wire ignition temperature reached 960 ◦C and was maintained after cross-linking only when wood particles were present. A high comparative tracking index (CTI) of up to 600 V was determined for formulations with and without wood particles. Dynamic mechanical analysis showed that the stiffness (storage modulus G´) of radiation-crosslinked, fire-retarded PA was significantly increased in the high-temperature region beyond 200 ◦C compared to non-crosslinked PA.Tensile strength was improved by up to 18 % after cross-linking while notched impact strength was reduced by up to 41 % which was consistent with an increase in modulus of elasticity since the materials became more brittle.