Silicas fillers, drawback

To balance some of the drawbacks produced by the rubber toughening of thermosets, inorganic fillers that increase modulus and yield stress can be added to generate hybrid composites. Inorganic fillers such as glass beads, alumina, or silica - with high values of modulus and strength - are frequently included in thermoset formulations. 

Once the contents of the container are evenly distributed, the adhesive or sealant material can be removed. The use of pumps for transferring the adhesive or sealant has several drawbacks. Filled compounds have an abrasive action on the moving parts. This is particularly true with fillers such as silica. Compounds that polymerize easily will tend to begin their polymerization due to friction within the pump. This will gum up the moving parts and make them inoperable. Therefore, transfer is best done under some type of pressure. 

There are also other substances that can be used as fillers that behave like carbon black in terms of the reinforcing action. One example is silica, but it has the drawback of its price, and the properties of the reinforced elastomer are generally inferior to those obtained with carbon black. These... 

Silica, then, is an important part of all or nearly all silicone sealants. If the sealant is clear, silica s probably the only filler. If the sealant is opaque, silica may or may not be present for reinforcement but it s almost always present for flow control. The single drawback to fumed silica is cost therefore, only a minimum quantity is used and there is a continual search for ways to use less. 

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