Innovative extrusion technology from Conenor and its manufacturing partner, Maillefer Extrusion, opens up exciting new opportunities for using municipal and other waste to produce value-added materials with a small capital outlay and at low operating costs.
As living standards rise around the world, society is generating increasing amounts of waste that need to be disposed of or, more preferably, recycled. Ever-tougher waste regulations and taxes in the EU, for example, are forcing the closure of more and more landfills – 12 sites were closed in Finnish Lapland in 2007 alone, leaving only two operational. The distances that waste must be transported are growing as a result, bringing additional costs and increasing the environmental impact associated with every kilo of waste.
Juice cartons, meat trays and containers, beverage and detergent bottles, and a wide range of plastic-coated paper and board all offer good opportunities for being converted into recycled raw materials and new products through the use of advanced extrusion technology. Today, however, much of this type of waste, if collected and sorted, is used only as fuel to generate electricity.
Packaging containing aluminium, such as juice cartons, is not an attractive fuel, as it reduces the operating life of boilers significantly – which is where the recycling and extrusion process developed by Conenor comes in. Conenor’s technology is ideal for this and other waste, as there is no need to separate out any of the layers of the different materials for individual processing: the Conenor process simply uses the waste ‘as is’.
|Twin-rotor CWE extruder in the open position.
Simple yet innovative
Conenor’s recycling and extrusion process for biofibre and plastic waste, incorporating a speciality CWE extruder, offers the dual advantages of a simple concept and low costs.
Sorted waste is first downsized using commonly available shredders and/or granulators, before a pellet press or plastic agglomerator densifies the fluffy materials to give it a higher bulk density and ensure problem-free extrusion. The pellet presses typically used to produce 6-8 mm wood pellets for biofuel are ideal.
The various pellet streams from the materials in question – such as beverage cartons, waste plastic, wood, or other fibre – are then fed to a mixer, which doses them in the appropriate proportions. The resulting blends are then coextruded.
The CWE extruder used has been designed specifically for extruding waste material mixtures containing plastics and biofibres. Unlike most units, this consists of two nested, individually controlled rotors, each of which is fed with its own mix, resulting in multilayer products.
The rear rotor typically produces lower-quality materials and mixed colours, and the front rotor higher-quality materials in a specific colour with or without additives. The material mix in the front rotor encapsulates that coming from the rear unit, effectively hiding the lower-quality material under the outer surface of the end-material.
The amount of energy used in pelletising is very low, at around 0.1 kW per kilo of output. Where pellets are fed directly to an extruder, some of this energy can be recovered, as the material arrives in preheated form. Overall, the total energy needed to recycle waste back into a sellable product, such as panel board or profile, is also low. Depending on the materials used, the energy requirement can be as low as 0.5 kW per kg of final product.
The main reasons for this are the fact that no separate drying processes are used and that the extruder itself is compact and of energy-saving construction. The process is designed to ensure that the formulation reaches the minimum melt temperature of the polymer in question and wets the fibres, but goes no higher. Low-rpm rotors provide good-quality output at homogenous low melt temperatures, also saving on energy.
An extrusion line investment, including material downsizing and densifying equipment, costs in the region of €1 million for output up to 500 kg/h. Assuming that the waste used as raw material is free, the manufacturing cost of an extruded product, including depreciation on capital investment, can be as low as €0.3/kg.
Excellent product opportunities
Cost is only one issue, however. Quality also has to be taken into account when using waste as a raw material.
Unlike the heated press techniques typically used for making panel board – which rarely homogenise the material mix sufficiently and cannot produce thicker products because of unacceptably long heating times – the Conenor waste extrusion process is free of such limitations. The process also enables hollow profiles to be produced; and foaming options enable product weight to be further reduced.
In cases where the flexural strength or stiffness of the waste material used results in insufficient properties for an application, oriented wood or other fibres or cross-linked polyethylene waste can be added at minimal extra cost to provide the necessary reinforcement.
Attractive product application opportunities include decking, panel board and profiles for the construction industry and vehicles, sound barrier elements, fencing, poles, pallets, protection trim, and cores and tubes.
|Waste material flow using two CWE extrusion lines, giving up to 1 t/h of output. The process can also use agricultural fibre waste directly without predrying, opening up very attractive opportunities for biofibre-based, environmentally friendly products.