INNOVATION | ODOUR REDUCTION
offers the heat exchanger Bulk-X-Change (BXC) to heat up the material before entering the silo. The BXC can also be used to cool down the material after the degassing process leading to more gentle conveying which keeps the product quality high. Coperion also offers customers degassing and deodorisation tests in its own test facility. This enables customers to evaluate the optimal param- eters for the deodorisation process regarding air flow, air humidity, pressure, temperature and duration. Starlinger has been active in odour reduction in
recyclates for some time and it is applying this experience to a comprehensive circular approach to the production and reprocessing of polypropyl- ene big bags within a closed loop. The bag making and plastics recycling technology group says that PP big bags are particularly well-suited to recycling because of their large size and weight. However, 75% of all big bags used worldwide are designed for single use, causing environmental damage and high CO2 impacts. “With the revolutionary concept ‘circular packaging’, Starlinger seeks to end this unnecessary waste of raw materials and create a circular economy in which big bags become big bags once more,” says the company. One difficulty with recycling big bags is that they come in different forms: with or without polyethyl- ene liner, coated or uncoated, and with loops and seams consisting of different polymer types. In addition, the different designs, applications and collection systems of post-use big bags result in a variety of contaminants that need to be removed during the recycling process. These contaminants
Right: Starlinger has developed a comprehensive circular approach to the production and reprocessing of PP big bags that includes an odour reduction stage
arise from different sources, including migrated substances from the filled goods, or labels and paper residues that can cause unpleasant smells during the recycling process. The big bag recycler also needs to deal with the odour of volatiles that are prevalent in recycled material. Depending on the source or type of the odour, its intensity, and the demands on the final material, Starlinger adapts the recycling and odour reduction process according to the needs of the big bag recycler. The company says the recycling process starts with washed flakes from used big bags being fed to the Starlinger recycling line. The company’s Smart feeder removes humidity through a combi- nation of temperature and friction. Melting and extrusion with vacuum degassing in a Starlinger recycling extruder reduces odour, and the process is enhanced when the granules pass from the pelletiser to the company’s Smell Extraction Unit at the end of the process. In this technology, pellets are stored in a drum with residence times depend- ing on the polymer type. The odour exits the unit by either applying a vacuum, or applying a pres- sure system to flush the smell out. The post-process unit is complementary to the
odour removal from melt filtration and degassing. Starlinger says the continuous melt filter efficiently removes any solid contaminants with minimal melt loss, and depending on the final application, an additional melt filter for fine filtration may be installed in front of the pelletising unit. The C-Vac degassing unit, which is set up in cascade forma- tion after the Starlinger extruder, enhances pellet quality by increasing the melt surface by 300%. Erema has also developed a post-extrusion technology for odour reduction called ReFresher. The company says: “End products such as plastic parts in cars or in the home call for an additional recycling step to neutralise the odour. And this is exactly what ReFresher, which is downstream of the extrusion process, was developed for. The process makes use of the latent energy generated by the preheated pellets during the extrusion process, which makes the entire process particularly energy-saving.” Melt filtration and degassing are also prerequi- sites in the odour reduction process and Erema says its Intarema TVEplus technology prevents unpleasant odours from developing in the course of extrusion. The interplay of preconditioning unit, Airflush technology, low melt temperature, efficient filtration and several degassing steps remove contaminants such as label residues leading to a higher quality recyclate. But the odour caused by migrated substances is more stubborn and this is
34 PLASTICS RECYCLING WORLD | May/June 2020
www.plasticsrecyclingworld.com
IMAGE: STARLINGER
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