Process Newplast Holding N.V., Herengracht 320, NL-1016 CE Amsterdam, Holland
A new process for recycling mixed plastics waste is described. With this process mixed plastics waste can be recycled without any compatibilizer giving rise to secondary materials easily processable in conventional machinery and with good mechanical properties. The process is based on homomicronization, a process of deep microhomogenization which permits differing polymers to result in a solid amalgam with good physical properties.
Recycling of mixed plastics waste is very difficult, in particular because of the incompatibility of different polymers and danger of degradation of polymers, such as PVC,1'2 but also due to their different melting points.
Some industrial or laboratory attempts are based on reprocessing at low temperatures. In these attempts high melting polymers are used as solid fillers. Another useful method comprises the use of compatibilizers and stabilizers in the polymer blends.4-8 Mechanical properties of these recycled mixed plastics are generally inferior, the surface properties are poor, and in some cases the cost of compatibilizers and stabilizers is too high for recycled materials.
The possibility of recycling of mixed plastics waste without any compatibilizer and obtaining a recycled material which easily processed in conventional machinery add value to manufacture. The properties of resultant material are also essential.
Following is a description of a new process aiming at achieving this goal. The process is based on homomicronization, a process of deep microhomogenization which permits differing polymers to result in a solid amalgam with good physical properties without prior sorting of the different polymers and with a very attractive cost.
The NEWPLAST-PROCESS line consists of three modular zones. Each zone can be entirely automated to produce a compound made from mixed plastics waste from industrial and/or urban sources. In the first area (Zone I) (Figure 1), waste is prepared for processing. The equipment used depends on the contamination level of the feedstock materials.
In the first processing step, the material is shredded. Ferrous and non-ferrous materials and heavy elements are separated. This is followed by grinding, washing, paper separation, and drying. The prepared mixture is now clean, dry and of consistent size.
This material is conveyed to homogenization silos and its composition is validated by infrared spectrometry. If necessary, the mixture can be supplemented with materials which are at too low concentration than expected and/or additives for a specific application.
The resulting mixture is then pneumatically transported into the second area (Zone II) (Figure 2) and automatically transferred into the homomicronization chamber.
Intense mechanical shearing causes a rise in temperature (about 200-230oC depending on the polymer composition) and the molecular linking of various polymer chains. This produces a homogeneous dough. The dough is extruded to filtering and degasification and then processed into pellets. The resulting NewplastTM compound has chemical and mechanical properties that are comparable to certain virgin resins. The compound can be processed with standard plastics techniques.
A third area (Zone III) (Figure 3) receives the pellets for conditioning. The NewplastTM compound is automatically transferred to the integrated production equipment for continuous parts manufacture. The energy requirements of the NEWPLAST-PROCESS are comparable to those ofvirgin-resin installation of identical capacity. The various life cycles of the Newplast™ compound give a positive balance.
The NEWPLAST-PROCESS technology can be easily adapted to different plastic mixtures or and/or formulated for a specific application. Such flexibility is made possible because the elements required for the final application can be added during processing.
The Newplast recycling line is divided into several sections, each fulfilling a particular function within the process. It has been designed to manage to treat waste containing up to 30% of contamination by paper, wood, sand, and metallic parts.
Zone I. Reception and pretreatment of contaminated plastics waste
The main items of this zone are (see Figure 1):
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