Theoretical And Experimental Study On Dissolving And Recycling Nylon6in Ionic Liquids

With the development of nylon industry, nylon products are widely used in humanlife.Because of the stable chemical properties and difficulty to degradate under naturalcircumstance, large number of waste nylon products have caused serious environmentalpollution. The traditional recycling ways of nylon still directly or indirectly bring problems ofsecondary pollution. Thence, research on more efficient and environmental recyclingtechnology of nylon has essential significance. Nylon6is one of the most important productsof nylon industry and its production and consumption ranks in the first position in the nylonindustry. In this paper, our study focused on the the theoretical and experimental study ofdissolution and recovery of nylon6using ionic liquids.Density functional theory （DFT） with B3LYP/6-31+G*theoretical level was used tostudy the interactions of nylon6segments, nylon6-1-ethyl-3-methylimidazolium bromide（[Emim]Br）,[Emim]Br-water, nylon6-[Emim]Br-water at molecular level. And at the sametheoretical level Atoms in Molecules theory （AIM） was used to analyze the hydrogen bonds（HBs） of the four systems. The binding energy of nylon6segments was smaller than that ofnylon6-[Emim]Br and the binding energy of nylon6-[Emim]Br was smaller than that of[Emim]Br-water. With more water molecules, the binding energy of [Emim]Br-waterincreased. In addition, the binding energy of nylon6-[Emim]Br decreased after adding waterto the system and it meant the stable structure of nylon6-[Emim]Br could be damaged bywater molecules. It was found that N H···O=C and C₂H···O were the main HBs in thenylon6segments and nylon6-[Emim]Br, respectively. Furthermore, the bond length ofcarbonyl bond elongated and the vibration frequency decreased, then redshift of carbonylbond occurred. The larger binding energy of nylon6-[Emim]Br was, the greater of distance ofredshift was. Due to the intervention of water molecule, C₂H···O was weakened evencompletely destroyed and the vibration frequency of carbonyl bond increased, then blueshiftoccurred. Moreover, the thermodynamics of nylon6-[Emim]Br was researched and it foundthat the dissolution process may happen.Experimental researches were taken to investigate the dissolution of nylon6in [Emim]Br.IR, TG, DSC, XRD and SEM were used to characterize the structure, properties andmorphology of regenerated nylon6. In addition, material ratio, temperature and time wereoptimized and the optimum reaction condition was that the largest dissolving recovery was95.18%when the temperature was175℃, the reaction time was1.5h and the mass ratio of[Emim]Br was6.25%.The same experimental method was used to study the dissolution of nylon6in differentionic liquids. It was found that nylon6could not dissolve in [Emim]Br and [NMP]CH3SO₃at140℃, but could dissolve in [Emim]Ac,[C₄mimSO₃H]HSO₄and [NMP]HSO₄. The order ofdissolving recovery of regenerated nylon6was [Emim]Ac>[NMP]HSO₄>[C₄mimSO₃H]HSO₄.And the order of thermal stability was [Emim]Ac>[NMP]HSO₄>[C₄mimSO₃H]HSO₄.