Step 1: incorporation of the silane into the polymer, either
by grafting of vinylsilane onto the polymer backbone or by
copolymerization of vinylsilane with ethylene in the polymerization reactor, and
Step 2: crosslinking in the presence of water, generally
catalyzed by tin compounds or other suitable catalysts. This second step can be controlled and made
during or after the extrusion process. This is the difference between a One-Step
and a Two-Step Process.
Step 1: Grafting of Vinylsilanes onto Polyethylene
Step 2: Moisture Crosslinking of Silane-Grafted Polyethylene
The use of silanes results in a more flexible and more economical
process for crosslinking. Silane crosslinked polyolefins are linked through
an Si-O-Si moiety instead of the C-to-C bond created via peroxide or radiation
cure. Siloxane bridges are less rigid than C-to-C bonds and give flexibility to
the crosslinked polymer, as shown in the figure below.
C-to-C bond:
rigid
Si-O-Si bond: flexible
Structure of PE crosslinked
by Peroxide or Radiation
