Waste to paste: VTT Finland develops “revolutionary” recycling device

12 Feb 2019 --- VTT Technical Research Centre of Finland has developed the first prototype of a cylindrical extruder which has shown promise in “revolutionizing the processing of recyclable materials.” The extruder can be used, for example, to turn problematic textiles and plastics as well as food waste into pellets. VTT say that the first prototype has already exceeded the industrial steering group's expectations during initial testing. VTT is currently looking for a partner to commercialize the technology.

An extruder is a device commonly used in plastics factories. It is capable of melting, mixing and extruding paste through a shaped nozzle. The plastics industry uses extruders to make, for example, pipes and profiles and they also have various applications in the food and feed industry.

VTT's research scientists have been testing their cylindrical extruder prototype’s performance with, for example, pieces of plastic film, mixed plastic waste, various kinds of textiles and bread. In addition to recycling, the device has been used to produce long fiber composites.

VTT's extruder can be used to convert textiles, plastics and food waste into pellets.“Since this is the first prototype of the novel extruder technology, we have concentrated on proving the possibilities to treat and convert various different materials,” Tomi Erho, Principal Scientist, VTT, tells PackagingInsights.

“We have made combinations of plastics and fibers, for example, to create a composite to be used in injection molding. Alternatively, we have used the output material as infeed for thermolysis. A mixture of textile waste containing both PP and PET fibers could be treated in such a temperature that PP melts and forms a solid matrix around the PET fibers, thus directly creating a composite material for further use,” Erho explains.

Behind the idea for the novel extruder is VTT’s Research Scientist, Hannu Minkkinen, who discovered that materials can rotate around the device's hollow cylinder. The device was designed and the prototype built with funding from Business Finland’s and VTT’s funding instrument for commercialization of research results.

Commercialization: New possibilities
Commercializing the device could create completely new possibilities both in terms of waste processing and novel material combinations.

“Many textile recycling processes are only suitable for products containing homogeneous fibers,” adds Pirjo Heikkilä, Senior Scientist, VTT. “However, textiles are often made of a mix of fibers, and many products are comprised of different layers.”

“The new extruder opens up a revolutionary opportunity to recycle mixed textiles and materials without having to separate fibers or components. We have successfully tested the device, for example, for recycling pillows without removing the filling in the course of a project called Telaketju,” she explains.

“We have also treated and compacted residual bread with the equipment to form a dense paste which could potentially be used for further processing to animal feed or then for conversion to bioethanol,” Erho adds.The prototype has a screw diameter of 30 cm instead of the 3-4 cm typically found in conventional devices of the same output.

30 cm screw diameter
The diameter of the extruder screw determines the size of the feed throat and also the kinds of materials that the device is capable of processing. The first prototype has a screw diameter of 30 cm instead of the 3-4 cm typically found in conventional devices of the same output.

The large diameter combined with a shallow screw channel makes it possible to mix different components of problematic, porous and lightweight materials and to make the mixed mass compatible with the next stage of the production process.

Benefits compared to traditional extruders:

• VTT claims that thanks to the simple design of the device, it is cheaper to make than traditional mixing twin-screw extruders.
• VTT’s first prototype is less than two meters long and weighs 1.5 tons. Thanks to its short length, the device can also be mounted upright if necessary.
• The compactness of the device makes it easily transportable.
• The design enables accurate temperature control combined with efficient mixing and, considering the size of the device, “exceptionally” long residence time. This can be a benefit when processing materials such as food and feed.
• Long fibers can be processed without cutting them, which is useful when processing textiles, for example, or when mixing fiber composites.

VTT is a leading European research and technology organization, which uses science and technology to prove to the industry that plastic can be part of a strong circular economy. It typically focuses on the addition of bio-based raw materials and sustainable design, as well as a three-pronged approach to recycling: mechanical, chemical and biological.

Last month, VTT joined the international Think Beyond Plastic’s User Facility Network as an R&D partner. Its role will be to support the New Plastic Economy Innovation Center’s innovators and entrepreneurs by offering R&D services to accelerate the development of innovations in the area of circular plastics.

In July 2018, VTT successfully developed a thermally formable, biodegradable material, which is 100 percent bio-based. Biocomposites made from entirely bio-based raw materials can be used to replace fossil raw material derived plastics, which have traditionally been used in industrial applications.

By Joshua Poole