Investigation of the decomplexation of polyamide/CaCl₂ complex toward a green, nondestructive recovery of polyamide from textile waste

Abstract

The 'circular economy' concept envisages deriving the maximum value out of resources and reducing waste to a minimum. In textiles, that includes the recovery of fiber materials out of used clothing and reusing them in the construction of new clothes. Processes such as mechanical separation, depolymerization treatment, and selective dissolutions of individual polymers are applied. We investigate the approach of selective nondestructive dissolution and recovery of polyamide fiber from mixed textile waste by using the solvent system CaCl 2 /ethanol/water (CEW) based on complexation and decomplexation of polyamide (PA). The results show that PA is precipitated and decomplexed by simple addition of water and a substantial amount of previously incorporated calcium by complexation, is removed. The recovered polyamide shows properties similar to pristine polyamide. Investigation on a mixed textile waste model of polyamide/wool demonstrates that CEW treatment can successfully separate different fiber materials. The nondestructive approach in dissolving PA using CEW, clearly shows the benefit, that PA fiber can be separated by controlled complexation/decomplexation without degradation, thus avoiding the repolymerization step. Furthermore, the solvent system is made of abundantly available materials that are inexpensive and used widely in industrial-scale operations. Thus, the concept will make significant contribution to a green textile recycling approach.

Separation of polyamide 66 from mixtures with cellulose fibers by selective dissolution in calcium chloride‐ethanol‐water solvent

“…Calcium contents in PA 66 and cellulose were determined by extraction of about 0.1 g specimens in 0.1 M HCl followed by complexometric titration of the extracts with EDTA, as described previously 10 . The nitrogen contents were determined on ca.…”

“…Calcium contents in PA 66 and cellulose were determined by extraction of about 0.1 g specimens in 0.1 M HCl followed by complexometric titration of the extracts with EDTA, as described previously. 10 The nitrogen contents were determined on ca. 0.15 g specimens by the Dumas method on a rapid N III nitrogen analyzer (Elementar Analysensysteme GmbH, Germany).…”

“…The complex can be disrupted to precipitate the dissolved polymer by changing the solvent composition, for example by addition of water. The previous work was focused on disruption of the complex and precipitation of the polymer, the washing off of calcium residues, and determining that the recovered precipitates exhibit no degradation of viscometric molecular weight 10,12 …”

“…The work presented here is a continuation of previous investigations on the use of calcium chloride-ethanol-water (CEW) mixtures as solvent for the selective dissolution of polyamide 66 (PA 66). 10,11 The mixture, in a certain range of proportions of the individual components, dissolves the polymer through Lewis acid-base complexation of the PA 66 carbonyl groups with Ca 2+ ions. The complex can be disrupted to precipitate the dissolved polymer by changing the solvent composition, for example by addition of water.…”

“…The previous work was focused on disruption of the complex and precipitation of the polymer, the washing off of calcium residues, and determining that the recovered precipitates exhibit no degradation of viscometric molecular weight. 10,12 In this work, the focus was on the use of CEW in the separation of PA 66 from mixtures with cellulose (viscose) fibers. Three compositions of the CEW solvent, varying in the relative proportion of ethanol to calcium chloride, were employed to investigate the following:…”