The effect of Brazilian organic-modified montmorillonites on the thermal stability and fire performance of organoclay-filled PLA nanocomposites

Abstract

To investigate the influence of chemical compositions of organoclays on the thermal stability and fire behavior of PLA nanocomposites, 2, 6 and 8 wt% of single and hybrid Brazilian organically-modified montmorillonites (OMt), containing ammonium and phosphonium based surfactant - di-(hydrogenated tallow) dimethyl ammonium chloride (HTA), trihexyl tetradecyl phosphonium chloride (TDP), di(alkyl ester) dimethyl ammonium chloride (EA) and ethoxylated tallow amine (ETA) - were added to PLA using a melt-compounding process. It was noticed that the addition of OMt and melt-compounding contributed to a decrease of the initial decomposition temperature and average molecular mass of PLA, assessed by thermogravimetric analysis (TGA) and gel permeation chromatography (GPC), respectively. Moreover, PLA nanocomposites with single OMt (TDP and HTA) showed lower thermal stability than those with hybrid OMt. PLA nanocomposites with hybrid OMt containing EA and ETA displayed higher fire-reaction performance under cone calorimeter test. Comparing with neat PLA, these nanocomposites registered a peak heat release rate (pHRR) reduction of 29% and 38%, and a fire index grow rate (FIGRA) reduction of 32% and 37%, respectively, as well as the absence of melt dripping during combustion. The enhancement of the fire-reaction behavior was related to the nanoparticles high degree of dispersion and compatibility between PLA and nanoparticles, characterized in a previous work (Alves et al., 2019), which contributed to the formation of an effective protective layer on the condensed phase during combustion.