Garden hoses are turned into garden hoses
Industrial gas specialist Messer at Powtech 2010 Hall 7, Stand 418
PVC – polyvinyl chloride – is one of the most widely used plastics in Europe. If plasticisers are added to the PVC, it can be used for floor coverings, dashboards or seals. However, landfilling or incineration of PVC waste is problematic for various reasons, and soft PVC reutilisation is also challenging.
Many plastics can only be recycled in powder form before once again being put to their original use. Garden hoses are currently being ground at the Messer Group’s cold grinding centre in Willich near Krefeld (Germany). As a result, new garden hoses can be made from the pure plastic powder that is produced.
The cold grinding process involves cooling and embrittling substances with cryogenic liquid nitrogen or carbon dioxide. And the grinding process is cooled, in addition to the product. This prevents an increase in temperature from the conversion of electrical energy of the grinder motors. Particle sizes significantly below 500 micrometres can be achieved by means of cryogenic grinding, which would scarcely be feasible with conventional warm grinding.
From the feed hopper, the material to be ground is moved via the metering screw to the precooler, where it is cooled by a liquid nitrogen spray before finally being moved to the grinder together with the nitrogen. As a result, the grinding process in the grinder is cooled at the same time. The nitrogen also performs another function: the low temperatures cause the various components to separate – in the case of garden hoses this is the soft PVC and the reinforcing mesh of polyester fibres. The embrittling effect causes the soft PVC to be broken down into very small pieces, while the polyester fibres are not reduced in size due to their high tensile strength and dimensional stability.
To achieve preliminary reduction of the garden hoses, the hose components are granulated without cooling. This produces a soft PVC granulate with a grain size of approximately one to five millimetres. At this stage, the first polyester fibres are separated from the PVC. A cryogenic pin mill is used to produce very finely ground PVC powder. The size of the polyester fibres remains largely unaffected by this. The fibres are separated from the PVC powder by a final screening process. They join together on the screen deck to form balls of fibres while the PVC powder drops through the screen deck, which has a mesh size of 500 micrometres.
The resulting high-quality powder can be reused as a material – for example to make new garden hoses.