What began with theoretical exploration in laboratory has led to a completely new approach in PET recycling: SSP-FREE technology that transforms post-consumer PET flakes into food & bottle grade resin.

The new benchmark for PET-recycling

What began with theoretical exploration in laboratory has led to a completely new approach in PET recycling: SSP-FREE technology that transforms post-consumer PET flakes into food & bottle grade resin.The core concept of this technology is not to separate the degraded short-chain polymers caused by thermal and mechanical stress during processing by mechanical methods, but to reintegrate them into polymers of higher molecular weight by an innovative method using chemical additives. The additives are silicone oils and related substances that are added directly into the extrusion stage of the process. The material has an average molecular weight similar to that of virgin PET. The Patent owner and licensor of this revolutionary technology is PTP Group Ltd. This technology is known as “PET-M Recycling Technology”. The US FDA and CFIA (Canada) have assessed in depth the decontamination efficiency of the technology and awarded it a Letter of no Objection (LNO). The rPET resin produced using this method has obtained from FDA a Food Contact Notification (FCN) approval as a safe substance for food contact. The dossier for the technological process has been submitted to EFSA for evaluation and EU approval is currently pending. A major production plant using the technology was put into operation by a California-based company Verdeco Recycling Inc. in September of 2012.The basic concepts for one of the most exiting innovations in PET recycling had been developed by a group of scientists under the guidance of Dr. Levan Dadiani. They were studying the interactions between plastic polymers and carbon-silicon polymers, specifically Polysiloxanes (silicon-oxygen polymers), Silazanes (silicon-nitrogen polymers), and Silanes (silicon-hydrogen polymers). One of the discoveries was, that silicon polymers can “dock” on unsaturated ends of plastic polymers, e.g. at break points of polymer chains. After the saturation of these active ends of polymer chains a decrease in their chemical activity that was triggering polymer degradation processes, was observed. The first practical tests were carried out with Polyolefins and were quite successful. But this innovation had low interest from an economic perspective because the vast number of Polyolefin types used in the industry requires the development of a correspondingly large variety of the effective modifying agents. The research team subsequently focused on the modification of polyester, especially on Polyethylene Terephthalate (PET). The team developed combinations of silicon based polymers including derivatives of Siloxanes and Disilazanes as the optimal modification agents. The special feature common for all of these compounds is that they have a central silicon molecule which can potentially generate up to four chain branches, to which other polymers can connect. This allows the re-attachment of up to four low-molecular-weight polyester fragments (Oligomers) and the formation of the high molecular weight polymer (Fig.1). That effect could be achieved using relatively small volumes of the modifying agent in the range of 1.5 to 5 percent by weight.

Phase 1: From the lab to the field

The concept and the technological process are defined in the European patent granted in December 2005. The method described in the patent included the introduction of the modifying agent into a blender-crystallizer together with the washed PET-flakes in order to provide a uniform distribution of the liquid modifier on the surface of the flakes. The initial migration of the modifier into the PET-flakes required a mixing and drying process for more than 100 minutes at a temperature of 130 ± 5 ° C. The treated flakes were extruded using a twin screw extruder with application of high vacuum onto the melt, then transformed into pellets and later crystallized to become a suitable product for further industrial processing. This innovation attracted the attention of the Ofer Brothers, known for their enthusiasm to support projects related to innovations. The initiative for this start-up came from Zeev and Alex Ofer, the well-established company owners, Hi-Tech entrepreneurs and process developers. This was the moment, when the theory left the lab and started making its way into the traditional SSP (Solid State Polymerization)-dominated world of post-consumer PET recycling. To test the efficiency the new technology as an industrially viable process a first functional production line with the capacity of only 400 kg/h had been established at PTP- Plastic Technologies & Products s.r.o. in Jilovè u Prahy (CZ). In a next step, both the new material and the recycling process were certified by local accreditation bodies and by the U.S. FDA (Food and Drug Association)

Phase 2: From a pilot project to mass production

With the theory of the polymer chain repair using a modifying agent acting as a "polymer glue" proven, it was time to optimize the process. The goal was, to find silicone polymers with a higher boiling point, which would allow application of the liquid modifier directly into the extruder. This change would solve several critical tasks: significant decrease of the amount of the modifier needed for the reaction, more efficient pre-extrusion drying of the PET flakes due to the higher process temperatures and reduction of the process time needed for the production of the final product. Under the management and supervision of Zeev Ofer and Dr. Levan Dadiani, the specialists of the PTP Group developed the new combination of high molecular weight silicones. These are derivatives of silicone oils which are also used as food additives or pharmaceutical components. Their boiling points are significantly higher and allow to achieve all critical goals like dosing the modifier directly into the extruder together with the PET flakes (Fig. 2), higher drying temperatures for the PET flakes in the range of 165 to 185 °C with a shorter process time, resulting in an overall shorter process time. The optimized process and the modifying agent are protected by the patent.

Processing technology optimized

PTP Group has optimized not only the composition of the modifying agent and flake drying conditions but also the extrusion stage of the production process. After numerous trials PTP Group became the first company utilizing the new and innovative conical twin screw extruder MAS 90 with co-rotating screws, developed and manufactured by the Austrian MAS-Maschinen und Anlagenbau Schulz Ltd in a PET recycling set-up (Fig. 3a + b). The design of the extruder enables, in contrary to parallel-screw extruder, a high output due to the unparalleled difference of intake and discharge volume, without the need for high rotation speeds and shear rates. The shorter length of the plasticizing unit provides the shorter residence time of the material in the cylinder and contributes significantly to prevent the degradation of the material. In addition, the MAS extruder allows more efficient degassing of the PET melt with its larger ports compared to a parallel extruder with the same throughput. Larger surface of the melt treated by vacuum is crucial for the decontamination and for the prevention of the viscosity drop in the final product.

Material characteristics at or above virgin PET

The rPET-resin processed according the PET-MTM -technology does not require any adjustments of the equipment or conversion of any conventional PET-made product. The items (food containers) produced of this resin can be fully recycled using any existing recycling method just like any type of conventional PET or rPET. Compared with conventionally treated recycled PET, it features an increased resistance against oxidation. The mechanical properties, such as elasticity, tensile strength are at high level sufficient for its application in production of bottles even for carbonated soft drinks without the necessity of blending it with virgin resin. Essential feature for the container production application, the gas permeability is lower. Last but not least, material is in high demand from thermoforming producers because of its performance in processing and the attractive price. Generally speaking the production of the rPET using PET-MTM technology is not only economically efficient but also contributes to the sustainability of the material life-cycle with all positive aspects like resource conservation, energy saving and stimulation of the global growth of post-consumer PET waste recovery. The most recent production facility using PET-M technology on an industrial scale, with an hourly capacity of 3 tons was developed by Verdeco Recycling Inc. in South Gate, California. (Fig.4a + b).The South Gate facility has been fully operational since September 2012 and its output has been successfully used by multiple customers in injection/blow-molding as well as thermoforming applications. In fact, you would find bottles and other PET packaging made from Verdeco-produced rPET resin on the shelves of major supermarket stores in the U.S. Additional recycling systems around the world to use PET-M technology are currently in various planning stages.

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Interview with Zeev Ofer, President of PTP Group Ltd

What are the typical benefits of PET-M process compared to conventional mechanical recycling process?

Of course we see the obvious contrast between our PET-M technology and the existing "conventional" methods of PET recycling. Mainly, because our “chemical repair” concept allows retaining and incorporating the low molecular fractions of the rPET that were generated by thermal and mechanical degradation processes back into the polymer matrix. The technologies invented earlier were all designed to remove those oligomers by extensive use of energy. Nevertheless, our “unorthodox” approach has a clear evidence of its efficiency. The theory is verified by the performance of our rPET in industrial applications on both sides of the Atlantic. As the actual benefit we get a remarkable reduction of energy consumption required for the production of the food & bottle grade resin which means lower flake-to-resin conversion costs, smaller carbon footprint and increase of the material yield.

What about the crucial properties of the modified rPET?

This question is answered by the numerous positive test certificates from all major examination bodies. They can be provided on demand to all interested parties. The main features that can be interested for your readers are the following: customers can produce high quality bottles for carbonated soft drinks using 100% of our rPET without increasing weight of the pre-form, the level of benzene and limonene is below 0.01 ppm. The modifier will never migrate into foodstuffs because its connections with PET molecules are very stable and they remain during all subsequent processing and conversion procedures.

What are the AA values​​ of the rPET produced with PET-M^TM-technology?

As it was mentioned, the material characteristics of the rPET manufactured using PET-MTM technology are in full compliance with all the industrial standards accustomed in PET packaging production. We achieve AA-value ​​of less than 1 ppm, however it still may depend on the quality of the input material.

What goals is PTP pursuing? Material producer or R&D focused company?

We have a very clear position: We are suppliers of the technological solution and we want to compete with the existing providers post-consumer PET recycling technologies. We are a R&D focused company. Our goal is, to provide know-how, technology and an efficient business model as a licensor to all interested parties worldwide. In fact we are offering them an innovative, green, sustainable and at the same time, profitable business project.

What is  the economic side of the PET-M production?

We have developed a technology which allows a very economically effective food grade rPET resin production. The equipment package with the production capacity of 3 tons per hour of Hi-End rPET resin is in the range of about 4.3 million USD. But don’t be mistaken, this budget includes only machinery for two production lines without investment into buildings and infrastructure. This production set-up makes flake-to-pellet conversion costs very competitive both CAPEX (Capital Expenditure) and OPEX (Operational Expenditure) wise.

What potential do you see for the modification process with other plastics?

For the time being, we are concentrating on the further development of our PET-M technology. But the starting idea as you know was the modification of Polyolefins. We can imagine that this field of application of the chemical modification concept will be back on our agenda again. Summarizing, I would like to state again, that we still see a lot of potential for our technology.

Mr. Ofer,thank you for your time.

About Plastic Technologies and Products s.r.o.

Author  Reinhard Bauer - TECHNOKOMM

E-Mail: This email address is being protected from spambots. You need JavaScript enabled to view it. 

Figures:

Fig: PTP

Fig.1: The mechanism of action between Polysiloxane and a carbon polymer. The silicon polymer is in the position to establish chemical bondings to up to four polymer molecules.

                                                   Photo: PTP

Fig.2: The liquid modifier is extracted via a precision metering pump from a container and added to the PET flakes in the feed opening of the extruder.

                                   Photos: PTP

Figure 3a + b: The central component of the PTP production system is the twin-screw extruder from the Austrian manufacturer MAS with conical co-rotating screws. It guarantees for a maximum gentle plasticizing of the PET flakes.

         Photos: PTP

Fig.4a+b: The PTP-production system on an industrial scale, consisting of two production lines with an annual capacity of 23.000 tons of PET-M^TM.