Recycling of polyamides: Processes and conditions

Abstract

Polyamides (PA) are a family of engineering thermoplastics used in a wide range of applications including automotive, building, construction, separation processes, textiles, and so forth. This is related to their good properties (mechanical and thermal) which can also be modified by additives, other polymers (blends and multilayers) and fillers (composites). But these complex systems (several components) make the final materials more difficult to recycle. In this review, basic statistics on the production rate of polyamides are presented and the different recycling methods are reported to compare their advantages and limitations with respect to economics and technical analyses. The discussion includes biological, chemical, mechanical, physical, and thermal treatments to reintroduce, as much as possible, the parts after their end‐of‐service. Finally, a general conclusion on the current state of PA recycling is presented with several openings for future developments to satisfy the concept of circular economy and general sustainability.

Design of depolymerizable polymers toward a circular economy

“…Due to the popularity of polyamides in consumer products, it is pertinent to briefly discuss research into potential application of polyamides in a circular economy. However, since many other reviews have covered polyamide synthesis 122–124 and recyclability, 125 this section will be kept brief. In the realm of polyamides, the current research is heavily geared towards depolymerization of post-consumer nylon-6 through RCD and development of its replacement.…”

Electrochemical recycling of polymeric materials

“…17 They find a wide range of applications from rigid/flexible foams to coatings, fibers, adhesives, and elastomers. 64,65 In Europe in 2017, the end-of-life management of this class of polymeric materials principally consisted of landfilling (0.9 Mt per year), incinerating (0.6 Mt per year) and recycling (mechanical and chemical, 0.5 Mt per year). 66 The wide range of chemical structures, molecular weights, degrees of crystallinity, crosslinking densities, and hard-to-soft segment ratios make the chemical recycling of polymeric materials containing C–N groups particularly challenging.…”

“…65 Similar to PET, the principal chemical recycling technique is solvolysis to (partially) recover monomers from polyurethanes and polyamides. 64,67 For example, BASF, Maincoop and Polytecna, among others, have implemented this technique at the industrial scale to recover the polyol fractions from flexible polyurethane foams. 67…”

Accessing Chemically Recyclable Polyamides with Tunable Properties via Geminal Dimethyl Substitution

“…Polyamide 6 (PA6) also known as nylon 6 which was synthesized by ring-opening polymerization (ROP) of ε-caprolactam (CL) has emerged as a robust and versatile thermoplastic with widespread applications. 5,6 Chemical recycling of PA6 to its monomer CL via ring-closing depolymerization (RCD) has been considered as an effective method to address the pollution of PA6 end-life. In fact, representative catalytic systems including 4-dimethylaminopyridine (DMAP), mixed alkali bases NaOH/KOH, La1 (La[N(SiMe3)2)]3), and metallocene complex La2 have been established to enable an efficient depolymerization of PA6 to CL (Figure 1a).…”

“…In fact, representative catalytic systems including 4-dimethylaminopyridine (DMAP), mixed alkali bases NaOH/KOH, La1 (La[N(SiMe3)2)]3), and metallocene complex La2 have been established to enable an efficient depolymerization of PA6 to CL (Figure 1a). [6][7][8][9][10][11] Despite the success of depolymerization, it required high temperature (>200 °C) due to the high melting processing temperature of PA6.…”