Waste PET plastic recycling

PET plastics have a wide range of applications in the packaging field. PET plastics are used for packaging films, webs, and beer bottles. However, when these materials are discarded, they face the problem of how to deal with them. Through special alloying process, waste PET can be well recycled and used to make alloy materials that are blended with other plastics.

At the SPE Global Plastic Environmental Conference (GPEC) held in Detroit, an alloy made of polyethylene and recycled PET was introduced. At present, three producers in Europe have successfully developed this new type of alloy material, which is hard, high-strength, easy to process, and inexpensive.

For decades, although there have been reports on such technologies in technical literature, the real commercialization of such technologies is only a matter of recent years. At present, Erema North America cooperates with three European manufacturers to use Ermar's Vacurelna continuous curing reactor to heat and dry PET under vacuum to recover its intrinsic viscosity, and then use a crystallization dryer. Exhaust twin-screw extruders are extruded and pelletized.

PET/PE Alloy Application Field

PET/PE alloys have very good properties. They are less brittle than pure PET and do not require drying before processing. In addition, PET/PE materials have high strength, good fluidity, and a faster cooling rate than HDPE. Therefore, this material has a short molding press time and high yield.

Spalex SA, which has been acquired by Spain's SP Berner Plason SL, used alloys of five- and seven-layer PE protective film chips and PET coils in an extruder. They squeezed this mixture into monofilaments and made bristles. It is said that the performance of this monofilament is comparable to that of nylon, but the price is much lower than that of nylon. Since the coextruded film fragments contain a large amount of EVA adhesive layer, it can be used as a compatibilizer for PET and LDPE.

The Innova Packagiy System NV (IPS) company in Belgium first mixes the recycled PET coil with HDPE (75/25) and various additives in an extruder to obtain an alloy material, and then molds the alloy material. Grey black shipping tray.

The PET/PE alloy molding line used by IPS includes Ereman's Vacurema unit, crystal dryer, extruder and injection molding machine. In this line, PET flows from the solidifier at a temperature of 392°F and then enters the extruder at a temperature of 450°F (the processing temperature of PET). At the same time, PE and compatibilizer are added to the extruder. Inside the machine, the molten material is finally fed into the injection machine to form a plastic tray. It is said that the price of this kind of plastic tray is similar to that of products made of wood. The company's PET/PE pallets sell for 6 to 8 euros each, while wooden pallets cost 5 euros.

At present, MBM Maschinenbau of Germany is selling this pallet molding line and exporting it to Japan.

Three years ago, the UK's Dellve Plastics produced a qualified PET/HDPE double-wall corrugated pipe material made of a PET/HDPE alloy and a compatibilizer and impact modifier. The PET/HDPE alloy technology enabled Delleva Plastics to make full use of its internal defective recycling materials.

It is said that the performance of the PET/PE alloy material exceeds the standard requirements of the HDPE road drain of the Agremen HAPAS Commission in the United Kingdom. Delleve Plastics claims that a single-walled PET/PE pipe with a diameter of 75mm has an average hardness of 5.678kN/m2 and is as good as a 100mm diameter HDPE pipe. This alloy material has good fluidity, fast cooling, and easy processing. According to Erema, PET/HDPE alloys do not need to be dried prior to molding, and their performance is good. The processing cycle is only half that of HDPE.

Compatibilization of PET/PE alloy materials

The blending of PET materials and PE materials requires compatibilization. Most compatibilizers (some patented) can meet the requirements. EVA is a typical adhesive layer of PET and PE multi-layer films. It can also be used as a compatibilizer for PET and PE alloys. It is cheaper than other compatibilizers, but it has a larger amount of added, more by weight. 5% to 10%.

Erema found that using a Vacurema system with a vacuum dryer requires less compatibilizer than a Vacurema system without a vacuum dryer because it absorbs 5% of the functional ethylene copolymer under vacuum, making the compatibilizer The amount of addition was reduced by 0.3% to 0.6%.

PET/Nylon Alloy

At the GPEC annual meeting, two companies said that PET/PA beer bottle waste can also be recycled through alloying technology. Clariant and Johnsor Polyker LLC are using a PET chain extender to extend the PET and nylon in beer bottles. This chain extender, trade name CESA-extend, whose active ingredient is an epoxy-functional styrene/acrylic acid copolymer, was jointly developed by the two companies.

Clariant originally sold the product to increase the intrinsic viscosity of PET. Later, the company discovered that CESA-extend has a compatibilizing effect on PET/nylon alloys. It has been reported that adding 1% of CESA-extend chain extender can increase the impact strength by 20% and the tensile strength by 30%, and the melt index can be increased by 100. However, when the CESA-extend is added to 2%, the above-mentioned properties are improved. There is no longer any significant improvement.

(author/Li Jianguo)
Source: Zhong Bao Bao