process feature | Recycling
Film made from Clipp- recovered material is more transpar- ent than that recycled using conventional methods
with surfactant cationic agents. These processes include several stages (grinding, pre-washing, counter- flow extraction) requiring high levels of energy con- sumption and generating waste streams, such as sludge. In the case of organic solvents, there are volatile organic component (VOC) emissions to contend with. Because of these issues, the economic feasibility of these de-inking methods has limited their implementa- tion at industrial level.
Supercritial recovery A pan-European project, called Clipp, has studied the use of supercritical carbon dioxide technologies as a way of recycling printed or laminated plastic packaging films. Coordinated by Aimplas, it aims to demonstrate and
promote alternative technologies for increasing the recycling of printed films and lightweight packages in a cost-effective way. This EU-funded project has nine partners from four
countries: there are three technological centers (Aimplas, Fraunhofer-ICT, Plasttechnics Cluster of Slovenia - PCS); four SMEs (Extruder Experts, Gneuss, Skymark, Aligoplast); and two large companies (Grefusa, Emsur-Saymopack). The partners cover the whole value chain of the
product, including thermoplastic materials processors, manufacturers of equipment for plastic extrusion, film lamination and printing companies, packaging manufac- turers, recycling companies, and packaging companies from the food sector. The recycling system proposed by Clipp would reuse
scrap from post-industrial, out-of-specification printed films, off-cuts, process scrap, over makes and old redundant stock in a closed-loop management system. It would allow companies that generate such waste to reuse the recycled thermoplastic compound in compa- rable (but not food contact) applications.
12 FILM & SHEET EXTRUSION | January/February 2014
Continuous extrusion The technology for removal and compatibilisation of the ink fraction in the printed films relies on a continuous extrusion process by means of synergetic combination of carbon dioxide in supercritical conditions (sc-CO2
)
with microfilters and vacuum degassing in a fully integrated process. The injection of sc-CO2
gas into the molten polymer
matrix acts as a stripping agent for removal of organic components and also contributes to reduce melt viscosity – allowing fine filtration. This approach differs from previous attempts, which use conventional de-inking processes – multi-stage operations that use organic solvents or aqueous solutions with surfactants, which have environmental drawbacks and limited economic feasibility. Different machine configurations such as twin screw
extruder, tandem single screw extruder and multi rotation system (MRS) developed by partner Gneuss, were studied in order to optimise the removal of organic components and other contaminants from inks and varnishes, while enhancing degassing capacity for volatiles.
Injection port Two extruders are used in the operation. Extruder 1 incorporates an injection port for sc-CO2
. A rotating
screw melts and compresses the thermoplastic material in order to build up high enough pressure at the end of the extruder or compression zone, which helps to assure supercritical conditions for CO2
addition in the melt flow
for volatiles solubilisation and reduce melt viscosity. A filtering system is placed between the two
extruders in order to remove contaminant particles. A venting port, which is situated at the end of the extruder, allows for degassing. Extruder 2 then provides extended residence time,
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