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This study investigates the thermal decomposition and fire behavior of zinc phosphinate (ZnP) in combination with low sulphonate content alkali lignin (LS) in a polyamide 11 (PA11) matrix. The influence of ZnP with LS on PA11 was assessed by using thermogravimetric analysis coupled with FTIR spectroscopy (TG-FTIR). Such decomposition products as hydrocarbons, amide and carbonyl units, phenolic and phosphinate compounds control the decomposition. The chemical structure of the condensed phase was evaluated by FTIR measurements carried out on the residues. The fire behavior was investigated using UL 94 vertical flame spread tests and cone calorimetry tests. In the ternary blends, the addition of LS promotes char formation as assessed by TG analyses; furthermore, ZnP contributes to flame inhibition mainly by radical trapping and partially by dilution of fuel, due to phosphinate ions and a small amount of phosphinic acid released in the gas phase. Besides, phosphate compounds are formed in the condensed phase. The combination of LS and ZnP enhanced flame-retardant properties due to the formation of a stable char layer with barrier features. [ABSTRACT FROM AUTHOR]

Biobased lignin represents one of the possible materials for next-generation flame retardant additives due to its sustainability, environmental benefits and comparable efficiency to other flame retardant (FR) additives. In this context, this study presents the development of FR polyamide 11 (PA11) multifilament yarns and fabric structures containing different industrial lignins (i.e., lignosulfonate lignin (LL), and Kraft lignin (KL)) and zinc phosphinate (ZnP). The combination of ZnP and lignin (KL or LL) at different weight ratios were used to prepare flame retarded PA11 blends by melt mixing using a twin-screw extruder. These blends were transformed into continuous multifilament yarns by the melt-spinning process even at a high concentration of additives as 20 wt%. The mechanical test results showed that the combination of KL and ZnP achieved higher strength and filaments showed regularity in structure as compared to the LL and ZnP filaments. Thermogravimetric (TG) analysis showed the incorporation of lignin induces the initial decomposition (T5%) at a lower temperature; at the same time, maximum decomposition (Tmax) shifts to a higher temperature region and a higher amount of char residue is reported at the end of the test. Further, the TGA-FTIR study revealed that the ternary blends (i.e., the combination of LL or KL, ZnP, and PA11) released mainly the phosphinate compound, hydrocarbon species, and a small amount of phosphinic acid during the initial decomposition stage (T5%), while hydrocarbons, carbonyls, and phenolic compounds along with CO2 are released during main decomposition stage (Tmax). The analysis of decomposition products suggests the stronger bonds formation in the condensed phase and the obtainment of a stable char layer. Cone calorimetry exploited to study the fire behavior on sheet samples (polymer bulk) showed an improvement in flame retardant properties with increasing lignin content in blends and most enhanced results were found when 10 wt% of LL and ZnP were combined such as a reduction in heat release rate (HRR) up to 64% and total heat release (THR) up to 22%. Besides, tests carried out on knitted fabric structure showed less influence on HRR and THR but the noticeable effect on postponing the time to ignition (TTI) and reduction in the maximum average rate of heat emission (MARHE) value during combustion. [ABSTRACT FROM AUTHOR]