Electron Beam Processing - Crosslinking

Crosslinking

The cross-linking of polymers through electron beam processing changes a thermoplastic material into a thermoset. When polymers are crosslinked, the molecular movement is severely impeded, making the polymer stable against heat. This locking together of molecules is the origin of all of the benefits of crosslinking, including the improvement of the following properties:

• Thermal: resistance to temperature, aging, low temperature impact, etc.
• Mechanical: tensile strength, modulus, abrasion resistance, pressure rating, creep resistance, etc.
• Chemical: stress crack resistance, etc.
• Other: heat shrink memory properties, positive temperature coefficient, etc.

Cross-Linking is the interconnection of adjacent long molecules with networks of bonds induced by chemical treatment or Electron Beam treatment. Electron Beam processing of thermoplastic material results in an array of enhancements, such as an increase in tensile strength, and resistance to abrasions, stress cracking and solvents. Joint replacements such as knees and hips are being manufactured from Cross-Linked Polyethylene because of the excellent wear characteristics.

Polymers which are commonly crosslinked using the electron beam irradiation process include polyvinyl chloride (PVC), thermoplastic polyurethanes and elastomers (TPUs), polybutylene terephthalate (PBT), polyamides / nylon (PA66, PA6, PA11, PA12), polyvinylidene fluoride (PVDF), polymethylpentene (PMP), polyethylenes (LLDPE, LDPE, MDPE, HDPE, UHMWPE), and ethylene copolymers such as ethylene-vinyl acetate (EVA) and ethylene tetrafluoroethylene (ETFE). Some of the polymers utilize additives to make the polymer more readily irradiation crosslinkable.

Cross-linked polyethylene piping called PEX is commonly used as an alternative to copper piping for water lines in newer home construction. PEX piping will outlast copper and has performance characteristics that are superior to copper in many ways.