Case MODIX | New Way of Homogenizing and Compacting Plastic Waste Feedstock

Author: Ugur Kaya and Farzin Javanshour, VTT

An innovative pretreatment method of plastic waste was developed during the TREASOURCE project. The invented all-in-one modular shredder-mixer-extruder (MODIX) enables cost-effective and high-capacity compacting and homogenisation of bulky plastic waste feedstock for recycling. The aim of MODIX pretreatment is to support circular business development and creating economies of scale for plastic recycling. 

According to Nordic Council report on plastic waste market (2018), annually half a million tonnes of valuable potential recycling feedstock from Nordic countries is exported outside EU due to insufficient plastic waste treatment resources. For effective circular business model and value retention, plastic processors need large quantities of recycled plastic that meet strict specifications at competitive prices. Feedstock material diversity and heterogeneity, as well as contamination and impurities of the feedstocks have been described as technical barriers. Complicated and expensive process for recycling plastic leads to a higher price compared to virgin plastic, which is an economical barrier for circular economy.  

What is MODIX?

In modular extruder MODIX, two cylinders are nested where the molten plastic passes through enabling a large contact area for accurate temperature control together with high shear. The product of MODIX processing is compacted homogenous material without any pre-treatment required for the input. The product can be used in pyrolysis treatment for instance thanks to its homogenization ability of the mixed plastic waste which include a variety of different polymer types and compacting them into smaller particles that can be directly fed into pyrolysis reactor.

One of the most important benefits of MODIX is possessing large feeding zone which allows feeding bulky material directly without any pre-treatment. MODIX treatment not only provides efficient mixing with short screw length, but also enables the possibility for long processing times with a compact system requiring minimal floor space. The investment costs of the MODIX extruder are lower due to simplified design and easy maintenance with decreased costs.

More MODIX, Less Landfill

In TREASOURCE project we focus on recycling plastic waste streams which are often rejected from established sorting and recycling operations due to, for instance, their bulky and fluffy nature, and multi-material composition. We use the MODIX technology to pretreat as-received bulky and challenging waste streams into extruded polymer filaments as (i) feedstock for mechanical recycling for production of value-added plastics, and (ii) feedstock for chemical recycling to produce hydrocarbon oils for production of virgin and value-added products.  

As a use case, agricultural plastic waste rejects from mechanical recycling were fed into MODIX. The plastic extrusion was successfully implemented without any washing or pretreatment.
Based on the elemental and thermal analysis results, the MODIX output was in the form of homogenised LDPE and HDPE extruded plastic which are commonly used in agricultural and various packaging applications. The MODIX treated plastics were found as suitable feedstock for chemical recycling by pyrolysis as only trace amount (below RoHS limits) of hazardous elements such as arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) were detected. The detailed elemental and thermal analysis results can be found the in the project report provided here as a reference. 

Based on the results, MODIX can be utilised as a viable pretreatment route for valorisation of currently burned or landfilled rejected plastic streams from mechanical recycling as a feedstock for chemical recycling. The current operational limit of MODIX is 12 kg/hour with an average electric energy consumption rate of 0.7 kWh/kg. The proposed lab-scale technology can be potentially used in future plastic waste sorting and recycling facilities for high throughput and homogenised production of recycling feedstock at competitive prices which are the main bottle necks for plastic recyclers.