Publications archive - Waste and recycling
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Prepared by Dr. John Scheirs,
ExcelPlas Polymer Technology (EPT) for
Environment Australia, June 2003
One of the largest PVC recyclers in Australia is Cryogrind (located near Geelong, Vic) who recycle post-consumer and post-industrial PVC such as wire & cable insulation, bottles and PVC film. Their process uses novel freezing technology to embrittle the PVC in order to comminute it into small particles, while other polymers such as PET and nylon remain largely whole and can be screened off. The PVC is then separated and melt reprocessed. Cryogrind recycle some 2,500 tonne per year of PVC (Siganakis, 2002).
Table 10.1 Material composition processed by Cryogrind
|Wire & cable insulation||
|Post-industrial film and purgings||
|Source: Siganakis, 2002.|
|End use markets|
|Industrial hoses, hot water hoses, garden hoses|
|Multilayer pipe, plumbing fittings|
|Source: Siganakis, 2002.|
The Cryogrind process is well suited for the recycling of PVC-insulated cable. The cable is first stripped of its PVC insulation by cable stripping companies such as Sims who recover the metal content (copper or aluminium) of the cables. The liberated insulation is sent to Cryogrind either as strippings (long slivers) or as a granulate. The plastic is purified through a flotation process, to remove residual copper (which can be as high as 1%), as well as polyethylene insulation that is floated off. The floatation process uses a slurry technology borrowed from the mining industry and the use of flat-vibrating inclined beds that contain slots to trap and remove residual copper wire (Siganakis, 2002).
After purification, the PVC is washed, dried and then passed through a rotating inclined freezing tunnel where the plastic is cooled to -30C. The chilled plastic then goes through a mill in which the PVC is pulverised while other polymers are largely unaffected. The stream is subsequently filtered over a 1.2 mm aperture screen through which the majority of the PVC falls. The major contaminant that affects this recycling process is rubber cable insulation which has both a similar specific gravity to PVC and behaves like PVC in the cryogenic process. The PVC powder is then compounded in an extruder with additives such as virgin PVC, stabilizers, plasticizers and impact modifiers as required. Finally, the PVC is melt filtered through 20-70 mesh filters to remove particulate contamination such as grit (Siganakis, 2002).
In another recycling application, the collection of PVC bottles is increasing under the initiative of the vinyl bottle manufacturers. Cryogrind acting on their behalf, are ramping up their PVC bottle recycling activities. Currently they are processing 120 t/a but are aiming at recycling 2000 t/a. The objective is thus to recycle 25% of the total PVC bottles produced. Pre-sorting will be carried out by the collectors in each state (e.g. Statewide in SA; Waste Services in NSW).
PVC is used to make bottles because it is relatively cheap, easy to mould, has good clarity and allows the formation of an integral handle. However, it is interesting to note that the use of PVC for bottles bottomed out at 4000 t/a in 1995-6 and has grown to 6,000 t/a today (Faulkner, 2002). This is still far lower than the 14,000 t/a produced in 1993.
In recycling PVC bottles, Cryogrind first granulate the bottles and then wash the flake through an ambient friction washing step using an non-foaming surfactant. Paper labels are the major problem encountered in bottle recycling (Siganakis, 2002). Residual paper and glue are difficult to remove in the ambient washing process. Paper fibre removal after dry milling is performed by blowing it off over a fluidised bed. The main applications for the PVC recyclate are flooring tiles and pipe fittings.
The other major PVC recycler in Australia is Nylex SRM (Dandenong, Vic.) who recycle approximately 3,000 t/a of PVC scrap and convert it to reformulated compounds. This includes 30 t/m of flexible PVC that they presently import from the UK. They could use another 20-100 t/m of plasticized PVC if it were available (Johnstone, 2002). Just recently they have placed their requirements on an internet trading site. Nylex SRM have a cable/hose recycling line and two melt compounding lines. The cable/hose recycling line involves size reduction steps (chopper, granulators, hammer mill) followed by air and gravity separation. This line handles reinforced PVC hose and PVC cable strippings but not whole cable.
Nylex SRM have two melt compounding lines where the waste PVC is granulated then fed into an intensive mixer along with pigments, plasticizers, fillers, stabilizers and off-specification resin. This is then transferred to a compounding extruder where new additives are incorporated into the recycled PVC. The melt is filtered through a 190 micron aperture continuous melt filter to remove any particulate contamination. Finally the melt is pelletized into free-flowing pellets (Johnstone, 2002).
There has been a change in the end-use market for rigid PVC. A few years ago recycled rigid PVC was used in injection-moulded storm-water fittings but now it is used more in multi-layer pipe.
The main input feedstocks for the Nylex SRM recycling process are decorative PVC sheet, flexible sheet, cable purging, cable strippings, hose, off-specification compounds and plastisols. It is important to note that 97% of the feedstocks that Nylex SRM process are post-industrial and just 3% (the PVC cable strippings) are post-consumer (Johnstone, 2002).
In the mechanical recycling of PVC cable scrap, polyethylene and rubber are the main contaminants. Copper is effectively separated from PVC on a shaker table with upwards air currents. Nylex SRM has not recycled PVC insulated copper cable for some 6 years now, but still actively recycles PVC cable purgings and small quantities of PVC cable strippings (Johnstone, 2002).
Key Plastics (Vic) recycle approximately 100 t/month of rigid PVC (UPVC) in the form of profiles, trimmings, cable cover, vacuum forming sheet, blister pack and skeletal sheet (Heavey, 2002). The recycle process generally consists of shredding, granulation and pulverizing. The PVC recyclate goes into multilayer pipe and plumbing fittings. A proportion is also used in the production of spirally-wound pipe.
Australian Plastics Recycling (NSW) recycle PVC bottles (post-consumer), PVC skeletal sheet and PVC profile. Presently they process 20 t/m by granulation to 6 mm flake followed by washing/drying (Sarrine, 2002). They employ automated sortation to remove contaminants such as PET bottles. They sell the PVC flake to industry. They don't micronize it, as most users prefer to micronize the PVC flake themselves (Sarrine, 2002).
Silverfox (NSW) presently recycle some 30-40 t/m of scrap PVC, mainly in the form of clear PVC sheet, coloured PVC sheet and profiles (Shaw, 2002). They produce both pelletized PVC recyclate and PVC flake. They generally restabilize and recolour the PVC during compounding.
Pacific Chemicals (NSW) recycle approximately 30 t/m of PVC skeletal sheet by shredding, granulation and pulverization (Lodge, 2002). They upgrade the recyclate through the addition of heat stabilizers, impact modifiers and processing aids to produce a compound that is used in slotted drainage pipe. They also buy cable strippings (~20t/m) which they sell to a NZ company that produces mats from it (Lodge, 2002).
Repeat Plastics recycle some 10 to 20 t/m of PVC cable scrap from Copper Recyclers Australia. They granulate the cable scrap and mould it into bollard bases for road traffic management and also, to a lesser extent road ramps (Yates, 2002).
Australian Synthetic Fibres (SA) recycle 16-20t/m of PVC sheet which they buy from packaging companies and recycle by size reduction and extrusion with heat stabilizers and processing aids. Their material is extruded into PVC brush bristles (Hann, 2002). The bristles are based on 100% recycled PVC.
Vision Plastics (Vic) collect clear and rigid PVC from Victoria and SA. They granulate it and of the 50 t/m that is processed, the majority is all exported (Walton, 2002).