Computing solubility parameters of phosphorous flame retardants by molecular dynamics and correlating their interactions with poly(ethylene terephthalate)

Abstract

The solubility parameter is a reliable way to study the adsorption phenomenon quantitatively for a wide range of systems. Herein, solubility parameters of five selected phosphorous flame retardants were computed by molecular dynamics (MD) simulations, whose phosphorous groups were not available in the group contribution method, with the aim to address the intermolecular interactions of flame retardants with poly(ethylene terephthalate) (PET) while transferring from an aqueous bath to PET textiles. To verify the reliability of the MD strategy, the solubility parameter of flame retardant 1,2,5,6,9,10-hexabromocyclododecane (HBCD) was computed by group contribution and MD as well. The obtained solubility parameters of the five phosphorous flame retardants were found to have a linear correlation with their thermodynamic parameters, which describes their adsorption on PET fibers and, cited from our previous publication, partition coefficient K and the change of standard Gibbs free energy of the transfer of flame retardants from water to PET fiber $\Delta G_t^0(\mathit{FR},H_{2}O\to \mathit{PET})$ , suggesting that flame retardants with lower solubility parameter in this study are more likely to adsorb on PET fibers. Compared with the polarity parameter E_T(30) which was determined in our previous publication, the solubility parameter behaved similarly in describing the interaction between flame retardants and PET fibers during the adsorption process.