Coupling agents are a class of substances with an amphiphilic structure. Some of the groups in their molecules can react with chemical groups on the inorganic surface to form chemical bonds. Reaction or strong intermolecular interaction, thus firmly combining two materials with very different properties.
Selecting a suitable coupling agent can improve the dispersion state of the inorganic filler in the polymer matrix, and improve the mechanical properties and performance of the filled polymer material.

1. General principles for selecting silane coupling agents
The hydrolysis rate of the silane coupling agent is taken from the silicon energy group Si-X, and the reactivity with the organic polymer is taken from the carbon functional group C-Y. Therefore, for different substrates or processing objects, it is very important to choose a suitable silane coupling agent.
The selected method is mainly pre-selected through experiments and should be carried out on the basis of existing experience or laws. For example, under normal circumstances, unsaturated polyesters mostly use silane coupling agents containing CH2=CMeCOO, Vi and CH2-CHOCH2O-; epoxy resins mostly use silane coupling agents containing CH2-CHCH2O and H2N-; phenolic resins are mostly Use H2N- and H2NCONH- silane coupling agents; polyolefins use vinyl silanes; sulfur-vulcanized rubbers use hydrocarbyl silanes.
The adhesion between dissimilar materials can be affected by a series of factors, such as wetting, surface energy, interfacial layer and polar adsorption, acid-base interaction, interpenetrating network and covalent bond reaction. Therefore, the preselection by test alone is sometimes not accurate enough, and the composition of the material and its sensitivity to the reaction of the silane coupling agent should also be comprehensively considered.
In order to improve the hydrolytic stability and reduce the modification cost, the silane coupling agent can be mixed with trihydrocarbyl silane for use; for difficult-to-stick materials, the polymer cross-linked by the silane coupling agent can also be shared. When silane coupling agent is used as tackifier, it is mainly achieved by forming chemical bonds and hydrogen bonds with polymers; wetting and surface energy effects; improving polymer crystallinity, acid-base reaction, and formation of interpenetrating polymer networks, etc. of.
The viscosity increase mainly revolves around 3 systems, namely:
(1) Inorganic materials versus organic materials;
(2) Inorganic material to inorganic material;
(3) Organic material to organic material.
For the first type of bonding, the inorganic material is usually required to be bonded to the polymer, so the reactivity of Y in the silane coupling agent with 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 material requires viscosity increase.

2. Selection principle of coupling agent
1. Silane coupling agent is mainly suitable for glass fiber and silicon-containing filler, such as quartz, wollastonite, etc. It can also be used for some metal oxides and hydroxides, but not for CaCO3. The resin is mainly a thermosetting resin.
2. The titanate coupling agent has a wide range of applications for fillers, such as CaCO3, titanium dioxide, etc., and can also be used in glass fibers. The resin is mainly a thermoplastic resin.
3. Acidic fillers should use coupling agents containing basic functional groups, while basic fillers should use coupling agents containing acidic functional groups.
4. The amount of coupling agent added. The dosage of silane coupling agent can be about 1% of the filler; the dosage of titanic acid is generally 0.25~2% of the filler.
5. Some surfactants will affect the performance of titanate coupling agent, such as HSt, so they must be added after the filler, coupling agent and resin are fully mixed.
6. Most titanate coupling agents are prone to transesterification with ester plasticizers. Therefore, such coupling agents can only be added after coupling agents are added. The synergistic effect is good when titanates and silane coupling agents are added together.