Enzymatic Recycling

   Enzymatic recycling/processing is a biochemical process that depolymerises, or break down, long-chain polyamides (namely nylon 6,6 and nylon 6) into easy-to-process monomers so that they may be purified, repolymerized, and pelletized into fresh nylon ready for manufacturing uses. This is done by exposing the nylon scraps to specific enzymes (NylA, NylB, NylC), often in buffered aqueous systems at moderate temperatures (40°C–75°C, pH 7–8). These enzymes cleave at the amide bonds and oligomers present in the nylon polymer chains to break it down into monomers (hexamethylenediamine, adipic acid and caprolactam). These monomers are then recovered from the solution and purified using:

1. Filtration and Centrifugation: to remove residual solids, unreacted nylon, and enzymes.

2. pH Adjustment and Solvent Precipitation: to neutralise the solution and separate the solvent from the monomer.

3. Crystallization or Distillation: To isolate pure monomers

    The pure monomers can now undergo known industry standard processes, albeit with considerations to the different environmental conditions on Mars, for polymerisation back into nylon. Ring-opening polymerization is used to manufacture nylon 6 from ε-caprolactam, and condensation polymerization is used to manufacture nylon 6,6 (from adipic acid and hexamethylenediamine).

   Enzymatic recycling meets various criteria for in-situ resource utilisation on Mars. It allows for handling of complex, colored, and contaminated materials, namely nylon-blend textiles or nylon scraps with hard-to-separate adhesive traces. The process itself requires relatively minimal energy input, without a need for high pressures or high thermal temperatures. Furthermore, the end product of enzymatic recycling being virgin-quality nylon means that closed-loop recycling can be achieved, which is crucial to continuous utilisation of limited resources. Compared to other processes, enzymatic recycling provides many advantages: