Drinking water is the most important thing we consume. This is why it is subject to such strict quality controls. The requirements for drinking water pipes are accordingly high.
The pipes are composed of high-density polyethylene, for instance. The plastic must be crosslinked so that these remain stable even under high pressure and at high temperatures. To achieve this, pipe manufacturers employ a variety of techniques. Some irradiate the plastic to link the molecules. Others add peroxides to the extruded melt to create permanent, short, simple carbon-carbon bonds between polyethylene chains. Manufacturers that opt for Dynasylan® SILFIN 50 from Evonik go one step further. The chemical compound vinylsilane creates greater distances between the polyethylene chains, which makes the polymer more flexible and more elastic.
Similar to a suspension bridge
The image of a bridge helps to understand the process: While the transition built with peroxides resembles a bridge that creates the shortest link, stiff and resistant, the passage connected with Dynasylan® SILFIN 50 becomes as flexible as a suspension bridge. Transferring the analogy to a drinking water pipe, this means that it can expand more under stress, but is also crackproof and lighter due to the looser structure. To achieve this flexibility, it is enough to add around 1.5 percent of Dynasylan®SILFIN 50 to every 100 kilograms of polymers.
Cost-effective pipe production
The crosslinking process after extrusion, the pressing of the material, does not require any additional energy; it can also be carried out in normal ambient air. Pipes that are stabilized with peroxide, on the other hand, must be put into a hot water bath after extrusion in order to crosslink. “Customers who opt for our product find that it makes production more profitable and more cost-effective,” said application engineer Ioana Elena Mihailescu. “However, to achieve this, the customer must have good mastery of the process.” The crosslinker must react well, no matter how small the quantity involved, she said, adding that it was important to derive the byproducts arising during the crosslinking process in such a way that they are free of residues. This is the reason Evonik staff from Applied Technology offer their full support to pipe manufacturers in designing facilities and processes. In the end, they, too, must carry out strict quality controls of their products, like the water we drink every day.