Polyester scrap

Deiringer, G Process for reclaiming thermally strained polyester scrap material, US Patent 5 225 130, Claim 12, 1991. 

Because all depolymerization processes will generate waste that may be classified as hazardous waste or at least chemical waste, it will always be economically preferable to separate as much non-PET material from the PET material as is practical. Traditional bottle washing procedures can produce used bottle flake that is clean enough to be used to make more bottles or somewhat less clean and less expensive material. Technologies have been proposed to dissolve the polyester scrap in appropriate solvents to separate PET from other materials such as cotton fiber or magnetic tape components [19]. 

Efforts to recover plasticizers or their main structural units are reported in litera-ture. " ° In one potential solution, transesterification of terephthalate polyester scrap was proposed. This results in degradative synthesis of terephthalate plasticizer. In another development, PVC containing phthalates are exposed to catalyzed cracking process in which phthalic anhydride is produced and isolated. " Many processes of synthesis of phthalates and their substrates are known from patent literature and these are discussed in Section 2.3. 

R.E. Michel, Recovery of methyl esters of aromic acids and glycols from thermoplastic polyester scrap using methanol vapor, Eur. Patent, 484, 963, May 13, 1992 ... 

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam appHcations. These are obtained from residues of terephthaHc acid production or by transesterification of dimethyl terephthalate (DMT) or poly(ethylene terephthalate) (PET) scrap with glycols. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Multiblock Copolymers. Replacement of conventional vulcanized mbber is the main appHcation for the polar polyurethane, polyester, and polyamide block copolymers. Like styrenic block copolymers, they can be molded or extmded using equipment designed for processing thermoplastics. Melt temperatures during processing are between 175 and 225°C, and predrying is requited scrap is reusable. They are mostiy used as essentially pure materials, although some work on blends with various thermoplastics such as plasticized and unplasticized PVC and also ABS and polycarbonate (14,18,67—69) has been reported. Plasticizers intended for use with PVC have also been blended with polyester block copolymers (67). 

A process for depolymerizing nylon-6 and polyester-nylon-6 mixed scrap was patented by Allied Chemical Corporation in 19656 and 1967.7 Ground scrap was dissolved with high-pressure steam at 125-130 psig (963-997 kPa) pressure and 175-180°C for 0.5 h in a batch process and then continuously hydrolyzed with superheated steam at 350°C and 100 psig (790 kPa) to form -caprolactam at an overall recovery efficiency of 98%. The recovered monomer could be repolymerized without additional purification. 

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. 

Dicarboxylic acids or esters thereof are recovered from solid phase polyester materials, such as post-consumer products and factory scrap, by subjecting the polyester to at least two hydrolysis stages in at least the first of which the amount of water used is substantially less than needed to effect total conversion of the polyester to the dicarboxylic acid. Also the diol content is controlled in the course of carrying out the hydrolysis. The hydrolysis reactions may be preceded by reaction of the polyester with a diol, the resulting depolymerisation products then being hydrolysed. 

RECYCLING OF INJECTION-MOULDED POLYURETHANE SCRAP IN THE PRODUCTION OF SATURATED POLYESTER RESINS... 

Superior Environmental Products, Inc. introduced a product based on liquid poly sulfide containing 40% of a surface-modified scrap tire mbber. The product, ER-IOOR, is a coating that can temporarily contain chemical, oil, and gasoline spills. Rodriguez [97] reported that an unsaturated polyester resin containing silane-treated CGR showed better mechanical properties than that containing untreated CGR. 

When the new product to be manufactured is the same as what it started as, for example a new bottle made from bottle scrap, the recycling is referred to as closed-loop. When the new application is different from the starting one, the process is referred to as open-loop recycling, as is the case when the polyethylene terephthalate bottle is used to produce polyester fiber for carpeting. 

The methanolysis begins with reasonably clean PET scrap to which a catalyst and methanol are added. This mixture is heated under pressure to force the PET to depolym-erize. The end products are ethylene glycol and dimethyl terephthalate (DMT). Pure DMT and ethylene glycol are obtained through reciystallization and distillation, respectively. These pure materials can be used as feedstocks for the synthesis of new polyesters. 

In the Tirecycle process, first developed in 1982, finely ground scrap rubber is treated with a liquid polymer to form a reclaimed rubber product. RRE literature claims superior bonding properties and suggests use in tread rubber and other products including washers, mats, car parts, and tiedowns. The Tirecycle product is claimed to be useful with thermoplastics such as polypropylene, polyethylene, and polystyrene, as well as polyvinyl chloride, polyesters, and urethanes. 

Injection molding can be used with some thermosets in addition to thermoplastics, as long as the process can be controlled such that the crosslinking or curing takes place in the mold and not in the extruder barrel. It has been used effectively, for example, with thermosetting polyester resins. Scrap runners or defective parts must be discarded, however, as they cannot be remelted. 

One of the cheapest biopolymers is Solanyl, produced by Rodenburg Biopolymers, which costs between 0.8-1.5 per kg. Solanyl prices are so low because it uses scrap potato peel, a very cheap source of raw material. FkuR s PLA/polyester blends, on the other hand, cost between 2.85-3.70 per kg. 

This process can achieve a recovery of scrap foam into a polyol mixture, which can be used to produce polyurethane without the need for purification. This method requires low capital investment and is simple enough to cope with variations in the mix scrap foam. The resulting recycled polyol can be incorporated with polyisocyanate to produce recycled polyurethane which can be used to modify recycled polyester mortar made with either virgin or recycled resins. 

In this work, polyurethane was made from recycled polyol obtained from rigid foam and polyisocyanate. The raw material for the polyester resin was recovered from scrap PET [5], then depolymerized using different amounts of ethylene, propylene glycol into glycolized monomer and oligomer. These glycolized products were reacted with maleic or terephthalic acid to obtained recycled polyester. The proportion of recycled polyurethane to recycled polyester was varied ranging from 1 1, 1 2, 1 2.5, and 0 1. The combined resins were then mixed with initiator,... 

The experience that the manufacturing equipment is less stressed when the polyester is formed first, and the availability of cheap polyfethylene terephtha-late) scrap, led to patents where all kind of processes were claimed to make po-ly(ester-imide) wire enamels from this polyester [97-101]. The problem is that clean, unpigmented and granulated poly(ethylene terephthalate) is needed for profitable production. There are some indications that this process is used today for industrial productions of wire enamels. Polyethylene terephthalate) is not only used as a raw material for the synthesis, but it can also be blended with a poly(ester-imide) to give a useful wire enamel [102]. 

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