Waste produced during the manufacture of irrigation systems can be challenging to recycle. Comprised of drip tapes and irrigation pipes that accumulate as waste during the production of irrigation systems or are rejected during quality inspection, the high volume of the bulky input material, as well as the material composition of the drip tapes and irrigation pipes, make high demands on the recycling system used.
The shredder-extruder combination built by recycling technology provider Pure Loop makes it possible to produce recycled pellets from this waste that can be reused in proportions of up to 20 percent, without any loss of quality compared to production from virgin material.
And even this level of reuse could be increased, said Manfred Dobersberger, managing director of Pure Loop, ‘thanks to the high quality of the recycled pellets’.
Irrigation systems make use of either thin-walled HDPE drip tapes laid on the surface or HDPE irrigation pipes buried in the ground are used. The water is distributed through emitters. In the case of the thin-walled drip tapes (150 - 250 µm), these are LLDPE injection-moulded parts that are spaced at regular intervals of around 20 cm. In the case of thick-walled irrigation tubes (over 300 µm), the emitters are also fitted with a silicone membrane for pressure compensation, so that the same flow rate of water is discharged from each emitter over the entire length of the tube and the flow of water is not obstructed by soil, sand or roots growing into the emitter.
"The proportion of foreign polymers in this material is a real challenge in recycling,” said Manfred Dobersberger. “But it's one that our ISEC evo shredder-extruder combination with double degassing and EREMA laser filter can handle perfectly.”
In the laser filter, three scrapers rapidly and continuously remove contaminants - mainly silicone from the emitters - from the filter screen during each revolution, enabling high throughput rates and recycled pellet quality. The equipment can handle everything from bulky hose bundles and start-up lumps to regrind material or complete rolls with drip tapes and is designed for gentle processing of the plastic material.
Irrigation system producers in the USA, Israel, Italy and Mexico using the system have achieved throughputs of 100 to 500 kg/h. They reuse the recycled pellets produced in proportions of up to 20 percent in the production process of thin-walled tapes and thick-walled pipes. However, practical tests have shown that significantly higher proportions of recycled pellets would be possible in the end product. "Even for very thin drip tapes with a wall thickness of 100 µm, we were able to use a proportion of 10 percent recycled pellets in a 48-hour trial without any loss of quality," said Dobersberger.