Silane Crosslinking Agent

The PEX-b method of producing PEX piping, often referred to as silane crosslinking agent technology or the moisture crosslinking process, originated in the Wire & Cable industry as a means of insulating metal conductors. Moisture-induced silane crosslinking agent technology was designed to replace PE compounds that were soaked in peroxide and then crosslinked by extrusion through a steam or molten salt vulcanization tube. This vulcanization process is not entirely unlike some current PEX-a process technologies used to produce PEX tubing.

PEX-b has been the fastest growing segment in the production of PEX piping due to its relatively low capital investment in comparison to PEX-a and PEX-c methods. A standard thermoplastic pipe extrusion line combined with a post-extrusion hot water treatment apparatus to flush and crosslink the tubing allowed a pipe manufacturer to enter the fast growing PEX market using Sioplas™ process technology. Invented and patented by Dow Corning in 1968, the Sioplas process extrudes tubing pipe from a reactive compound composed of silane groups which have been grafted onto PE polymer chains Ribarits . This is accomplished by a custom compounder who grafts the silane onto an HDPE by adding organic peroxide in a high temperature compounding, extrusion and pelletizing process. This reactive compound, when combined with a tin catalyst masterbatch and extruded into tubing by the pipe manufacturer, will the crosslink in PEX tubing after being flushed with hot water.

An alternate technology for PEX-b tubing production is referred to as the Monosil™ process and was developed jointly by Maillefer and BICC in 1974 as a one-step-process, where all of the components of PE base resin, additives, peroxide and silane are grafted in a specialized compounding extruder which also extrudes the pipe in-line Ribarits . Like the Sioplas technology, the Monosil technology also requires a post-extrusion treatment that flushes hot water through the pipe to initiate the crosslinking reaction.