Choose the general principles of the silane coupling agent

1、 General principle of selecting silane coupling agent

It is known that the hydrolysis rate of silane coupling agent is si-x, while the reaction activity with organic polymer is c-y. Therefore, it is very important to choose suitable silane coupling agents for different substrates or treatment objects. The selection method is mainly through test, pre selection and should be carried out on the basis of existing experience or laws. For example, in general, the silane coupling agent containing CH2 = cmecoovi and ch2-choch2o is used for unsaturated polyester; the silane coupling agent containing ch2chch2o and H2n is used for epoxy resin; the silane coupling agent containing H2n and h2nconh is used for phenolic resin; the vinyl silane is used for polyolefin; the hydrocarbon silane is used for vulcanized rubber. The bonding strength of dissimilar materials is affected by a series of factors, such as wetting, surface energy, interface layer and polar adsorption, acid-base interaction, interpenetrating network and covalent bond reaction. Therefore, it is necessary to consider the composition of the materials and their sensitivity to the reaction of silane coupling agents. In order to improve the hydrolysis stability and reduce the modification cost, three alkyl silanes can be added into the silane coupling agent, and the polymer crosslinked by the silane coupling agent can also be shared for the hard to stick materials.

When silane coupling agent is used as tackifier, it is mainly realized by forming chemical bond and hydrogen bond with polymer; wetting and surface energy effect: improving polymer crystallinity, acid-base reaction and formation of interpenetrating polymer network. There are three kinds of viscosity increasing systems: 1) inorganic materials to organic materials; 2) inorganic materials to inorganic materials; 3) organic materials to organic materials. For the first kind of bonding, inorganic materials are usually required to be bonded to the polymer, so the reaction activity of Y in the silane coupling agent and the functional group contained in the polymer should be given priority: the latter two belong to the bonding between the same type of materials, so the anti hydrophilic polymer of the silane coupling agent itself and the silane coupling agent selected when the inorganic materials are required to increase the viscosity.

2、 How to use

As mentioned above, one of the main application fields of silane coupling agent is the treatment of inorganic fillers used in organic polymers. The latter is treated by silane coupling agent, which can change its hydrophilic surface into hydrophilic organic surface. It can not only avoid particle aggregation and sharp thickening of the polymer in the system, but also improve the wettability of the organic polymer to the reinforcing filler. Through carbon functional silane, the reinforcing filler and the polymer can be firmly bonded. However, the use effect of silane coupling agent is also related to the type and amount of silane coupling agent, the characteristics of substrate, the properties of resin or polymer, and the application occasions, methods and conditions. This section focuses on two methods of using silane coupling agent, namely surface treatment method and overall mixing method. The former method is to treat the surface of the substrate with dilute solution of silane coupling agent; the latter method is to directly add the original solution or solution of silane coupling agent into the mixture composed of polymer and filler, so it is particularly suitable for the material system requiring mixing.

1. Calculation of silane coupling agent dosage

The number of reaction activity points per unit surface area of the treated product (substrate) and the thickness of the surface covered by the silane coupling agent are the key factors to determine the amount of coupling agent needed for the silylation of the substrate surface. In order to obtain the monolayer coverage, the SiOH content of the matrix needs to be determined first. It is known that the SiOH content of most siliceous matrix is 4-12 / m2, so when it is evenly distributed, 1mol silane coupling agent can cover about 7500m2 matrix. Due to the self condensation reaction of silane coupling agents with several hydrolyzable groups, the accuracy of calculation is affected. If y3six is used to treat the matrix, the monolayer coverage consistent with the calculated value can be obtained. However, because y3six is expensive and the covering has poor hydrolysis resistance, it has no practical value. In addition, the Si Oh number on the surface of the matrix also changes with the heating conditions. For example, the SiOH number is Five point three After heating at 400 or 800, the SiOH value can be reduced to Two point six 1 / m2 or 1 / m2. On the contrary, the high SiOH content can be obtained by treating the substrate with hydrothermal hydrochloric acid, and the anions of silanol can be formed by treating the substrate with alkaline detergent.

2. Surface treatment

In order to obtain the best wetting value and dispersibility, the inorganic and polymer interfaces are connected by silane coupling agent. In the surface treatment method, silane coupling agent needs to be acidized into dilute solution to facilitate full contact with the surface to be treated. Most of the solvents used are water, alcohol or mixture of water and alcohol, and it is suitable to use water without fluoride ion, cheap and non-toxic ethanol and isopropanol. Except for aminoalkylsilane, acetic acid shall be added to the solution prepared by other silanes as hydrolysis catalyst, and the pH value shall be adjusted to Three point five - Five point five 。 Due to the poor stability of long-chain alkyl and phenylsilane, they are not suitable for use as aqueous solutions. During the hydrolysis of chlorosilane and acetoxysilane, there will be serious condensation reaction. It is also not suitable for preparing aqueous solution or aqueous alcohol solution. For silane coupling agent with poor water solubility, it can be added first 0.1% - 0.2% The mass fraction of the non-ionic surfactant is then added to the water to be used as water emulsion. In order to improve the economic benefits of hydrolytic stability of the product, a certain proportion of non carbon functional silane can also be added into the silane coupling agent. In the treatment of refractory materials, a mixed silane coupling agent or a combination of carbon functional siloxane can be used.

After treatment, the solution can be treated by soaking, spraying or brushing. Generally speaking, block materials, granular materials and glass fibers are treated by impregnation; powder materials are mostly treated by impregnation