Monosil process

One-step (Monosil) process, which involves a continuous feeding of liquid silanes during extrusion. The extruder is equipped with a long barrier screw and an injection system. This speeds up production but poses safety problems owing to the volatile and flammable nafure of silanes. 

Alternatively, as in Wacker Chemie s MONOSIL process, the extrusion steps can be combined into a one-step process for aeating a readily crosslinkable compound. Other suppliers such as Dow Coming have also tried to make one-step crosslinking easier for processors by offering preblended formulations that contain the aosslinking catalyst, peroxide and silane agent in one PE compoimd [15-3, 15-4). 

A one step process was developed by BICC with Maillefer for power cables which eliminated the compounding stage (the Monosil process) [15], in which all the additives were mixed with the polymer and grafting performed in the cable extruder. Direct injection has been used to inject a liquid mixture of silane, peroxide and tin catalyst into an add-on mixer to make cable [4] and hot water pipe [16]. The water pipes were steam autoclaved for four hours at 110 °C, which was well below the softening point of the HDPE used and the resulting crosslinked pipes withstood 1000 hours in water at 95 °C with a wall stress of 4.4 N/mm [ ] As with peroxides there are health and safety issues. Tri-methoxy vinyl silane is both very flammable and toxic. 

In the MonoSil process, the polyethylene resin is mixed with organic peroxide, a liquid silane, and catalyst in the hopper of the extruder. The tubing is then extruded and subsequently cured by exposure to moisture or steam. 

TABLE 9 Silane products for sioplas and monosil crosslinking processes... 

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