PEX: Peroxide technology
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Peroxides – some chemicals are activated with high temperatures, creating free radicals. The radical removes a hydrogen atom from the carbon atom in the chain of polyethylene, leaving the D-radical. This active molecule can connect with and form a similar relationship, ie crosslinks.
The most popular peroxide – 2,5-dimethyl-2 ,5-di-(butylperoxy) hexane. At room temperature – in the liquid phase, but can be adsorbed on a wide variety of surfaces. At high (180-220 ° C) temperature decomposes to form free radicals.
Peroxide is adsorbed on the lumps or rolls of polyethylene, then the mixture is fed into a cylinder with a piston, reciprocating, where he quickly melts (a process Thomas Engel). Passing through the usual spinneret PEX is formed in the PEX pipe. Continue heating the formed more liquid pipe leads directly to the reaction of peroxide crosslinking and performs its task. Most important in this process – to ensure the desired thermal profile, to prevent excessive crosslinking early in the barrel extruder, so that, in turn, prevent large losses. In such cases it is recommended to use special screws.
Only this technology (peroxide) has stitching in the molten phase. This ensures a random distribution of “stitches” stitching on the volume of the melt. The result is also a lower density of hardened material. It is fundamentally important temperature control. Typically, suppliers peroxide take it upon themselves to provide the necessary manufacturer of temperature-time zvisimostyami.
The maximum proportion of cross-linking determined by the amount of peroxide.
