Polyamide recycling economics

Economic and ecological aspects of chemical recycling are examined, and the application of such processes to the recovery of monomers and intermediates from PETP, polyamides, polyurethanes, polycarbonates, unsaturated polyesters, polyacetals, PMMA and PS is discussed. 17 refs. SNIA... 

Suitably recycled plastics can have properties that are good enough for many applications, with a noticeable economic advantage. Table 3.22 compares properties of virgin and recycled polyamides. These data are examples only and cannot be considered as representative. 

Polyamide 6 is among the most used polyamides, due to the good availability of the raw material (caprolactam), to the wide range of applications and to the production, transformation and recycling of polyamide 6 being easy and economically viable. 

There are recycling opportunities for other plastics beyond the few recognized by SPI RICs. The automobile industry, for instance, utilizes a series of engineering thermoplastics that have a built-in market if they can be recovered and reprocessed. These high value plastics include polyamides (Nylon 6, Nylon 6,6, etc.), polycarbonates (PC), acrylics (PMMA), styrenics (ABS), and blends (TPO, PC/PBT, PC/ ABS, etc.). Their higher value and demand allow recyclers the opportunity to practice more exotic recovery procedures and still have an economically viable product. 

Unlike commodity plastics, the upgrading and recycling of TPEs e.g., poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), polyamides (PA), polyurethanes (PUR), as well as the copolymers with ester, amide and urethane blocks) or polycarbonates is economically attractive. A reason for this is the beneficial relationship between material costs and the retained performance value after recycling (Figure 1). 

There are forms of recycling that are less familiar —in that they do not directly recycle the materials into new artifacts. Tertiary recycling breaks down the plastic to its component monomers, which can be repolymerized. This requires pyrolysis of the materials, sometimes called thermal cracking, and is most easily accomplished with step growth polymers such as polyamides and polyesters but is also possible for poly(methyl methacrylate). The processes require specialized plant, so are capital intensive, and a large-scale operation is necessary for economic viability. 

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