They are mainly polydimethylhydroxysiloxane compounds and polymethylhydrosiloxane compounds.
Polydimethylhydroxysiloxane has a unique chemical structure and can form a hydrogen bond with the fiber. Due to the role of hydrogen bond, it can form a hydrophobic layer on the fiber and play the role of water repellent.
The treated fabric has good water repellency, but poor washing resistance. The Si-H bond in polymethylhydrosiloxane compounds has certain activity and is easy to hydrolyze in water to form Si OH bond]. The formed Si-OH group can react with its own Si-H dehydration condensation reaction, and can also react with hydroxyl groups on cellulose fibers to form ether bonds, so that the finished fabric has good water repellency and washing resistance.
The commonly used polysiloxane waterproof agent is a mixture of the two. The mixing ratio is: polymethylhydrosiloxane: polydimethylhydroxysiloxane = 3:7. Generally, the proportion of polymethylhydrosiloxane is less than that of polydimethylhydroxysiloxane. In the baking process, the Si oh on both sides of the polydimethylhydroxysiloxane compound reacts with the Si-H in the polymethylhydrosiloxane compound. Under the action of catalyst and high temperature, the mixed finishing agent will form a silicone rubber elastic film to cover the fiber surface. The finished fabric has excellent water repellency and good fabric elasticity. The disadvantage of this kind of finishing agent is that it will cause fabric pilling, water repellent but oil repellent.
