Recycling depolymerization

There is also uncertainty in the regulatory status of tertiary recycling when it does not result in the direct production of monomers suitable for polymerization into new plastic. The European Commission has at times supported the chemical recycling (depolymerization) of condensation polymers such as polyethylene terephthalate back to monomer (e.g., dimethyl terephthalate) as recycling for the purpose of government-mandated plastics recycling rate calculations, but not the liquefaction of polyolefin plastics back to petrochemical feedstocks for reprocessing in a refinery. Discussions around these types of definitional issues, and their environmental and economic implications, are likely to continue for many years to come. 

The greatest problems during material recycling (depolymerization) arise from the existing additives, that is, antistatics, flame retardants, and dyes. The exact qualitative and quantitative composition of these additives is usually not known to the recycling company. 

BMI also reacts with dienes to form Diels-Alder adducts [12]. When BMI reacts with a a,(n-biscyclopentadienyl compound or other bis-diene resin, the bis-maleimide chain is extended by the Diels-Alder reaction. Bis-maleimide, chain extended with bis-diene, is not used in adhesives. However, as the Diels-Alder reaction is reversible, there may be a possibility of recyclability of the cured resin by depolymerization of the backbone (Fig. 6). 

The major PET manufacturers are depolymerizing scrap PET with glycols (glycolysis) or methanol (methanolysis) to form low-molecular-weight polyester diols (and BHET) and dimethyl terephthalate.3 The purified products are then used to make new products. Goodyear uses glycolysis to make REPETE, a new product which contains 10-20% recycled PET. Hoechst Celanese used methanolysis to produce DMT for repolymerization. Eastman Chemicals uses depolymerization of PET to recover used X-ray scrap. 

Chemical recycling of nylon-6 carpet face fibers has been developed into a closed-loop recycling process for waste nylon carpet.5 The recovered nylon-6 face fibers are sent to a depolymerization reactor and treated with superheated steam in the presence of a catalyst to produce a distillate containing caprolactam. The crude caprolactam is distilled and repolymerized to form nylon-6. The caprolactam... 

In recent months, three nylon producers (DMS, DuPont, and Honeywell) have developed closed-loop recycling processes for nylon carpet,15 thereby joining companies like BASF, Allied, and Rhodia, which have been recycling nylon on a modest level for years. DuPont is building a demonstration plant in Maitland, Ontario, which will be dedicated to the chemical recycling of nylon-6,6 and nylon-6. The newly developed ammonolysis process invented by DuPont can be used to depolymerize both nylon-6 and nylon-6,6. However, the cost of recycled nylon is estimated to exceed that of virgin nylon by ca. 25%. 

Glycolysis is the most promising approach for the chemical recycling of polyurethanes.1 The chemistry of PUR depolymerization is complicated by the presence of other chemical groups in the polymer, such as ureas, allophanates, and biurets. 

Important solvolysis reactions for nylons are hydrolysis, methanolysis, glycolysis, aminolysis, ammonolysis, transamidation, and acidolysis.17 Hydrolysis of nylon-6 with steam in the presence of an acid catalyst to form caprolactam is tlie preferred depolymerization approach. However, when recycling carpet face fibers, file fillers in the polymer may react with file acid catalyst and lower the efficiency of the catalyst. 

Nylon-6,6 monomers, recycling, 544 Nylon-6,6 products, depolymerized, 533 Nylons, 19, 135. See also Nylon PA entries Polyamides (PAs) depolymerization of, 566-571 solvolysis reactions for, 535... 

PET industrial synthesis, 70 PET monomers, recycling of, 539-541 PET products, recycled and depolymerized, 531-532 PETRA, 532... 

Polymer Degradation and Stability 75,No.l,2002,p.l85-91 STUDY ON METHANOLYTIC DEPOLYMERIZATION OF PET WITH SUPERCRITICAL METHANOL FOR CHEMICAL RECYCLING... 

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