Extrusion International 3-2021

47 Extrusion International 3/2021 arti fi cial grass its premiere in 1966 on the playing ground of the Astro- Dome in Houston. It was a carpet- like fl ooring, made from polyamide yarns. But as it was laid without a shock-absorbing substructure or fi ll- ing material it posed a risk of injury for the players. In the 1980s an evolu- tionary version was introduced with the grass blades made from polypro- pylene strips and sand as the fi ller material. This reduces the injury risk, but there was still a lack of impact damping properties. The next evolu- tionary stage in the 1990s combined PP and HDPE grass mats with sand and rubber granulate fi llings, which offered the desired damping prop- erties and made the UEFA and FIFA approving synthetic lawn systems for football stadiums. At the beginning Innovative recycling methods turn arti fi cial grass sustainable Experience has shown that an arti fi - cial grass system can be in intense use for 12 to 15 years before it is due for renewal. And there is the question regarding the best possible disposal. As land fi lling or thermal disposal in waste incineration are no longer accepted options due to the sharp increase in quantities there is no get- ting around recycling. Especially since better and more cost-effective meth- ods are available to recycle almost 100 percent of the plastic and single- material systems are in the pipeline. The later in order to improve recy- clability through the manufacture of the blades of the synthetic grass and the base fabric from the same mate- rial (PE) and to replace the method of connection by gluing by means of thermo- fi xation. This will signi fi - cantly simplify the technical efforts required for recycling. But as the sin- gle-material systems are just to be in- troduced they will be due for renewal only in 12 to 15 years. But until then, also conventional synthetic lawn can be recycled into valuable secondary raw materials. The MAS-Recycling-Options The renewal begins with the re- moval of the worn lawns (Picture 2). But before these can be removed and rolled up, the fi lling material (rubber granulate and sand) is to be vacuumed off. The better and more of the 2000s, the 4th generation of arti fi cial lawn systems came onto the market. Their distinguishing feature is the combination of stiff, upright and soft, curled PE-grass blades on a PP base fabric. The stalks and car- rier fabric are joined together on a so-called tufting machine. There, the stalks are fed from rolls as yarn, pierced into the carrier fabric and then usually cut to a length of 42 mm. The blades are permanently fi xed by coating the back of the fab- ric with a latex/PU-adhesive. After laying, the arti fi cial grass is fi lled up to a height of 30 mm with sand and shock-absorbing rubber granulate. This combination comes very close to a natural turf without showing its sensitivity to mechanical and climatic stresses (Picture 1). Scaper Material Dust Heavy component Cleaning principle Cleaning principle Material discharge Material: – Dry* (residual moisture up to < 1%) – Clean* (residual moisture up to < 0,5%) Material intake – Material – Contamination (earth, sand) up to 30% – Plant residuals – Stones, metal fragments, glass – Moisture up to 25% Dust discharge – dust – air – moisture Heavy component separator – glass – stones – metal fragments – wires – … Heater Heated air Picture 4: The functional principle of theMAS dry cleaning system: The fi lm fl akes are dried in turbulent hot air. The decreasingmoisture causes the debonding of granular and dusty substances, which are separated tangentially by centrifugal force (Picture: MAS) Picture 3: Processing stage 1: Shredded worn arti fi cial grass (Photo: MAS)