How much do you know about coupling agents? Selection principle of coupling agent

Coupling agent is a kind of substance with amphoteric structure. Some groups in their molecules can react with chemical groups on the inorganic surface to form chemical bonds; Part of the group has the nature of organophiles, which can chemically react with organic molecules or produce strong intermolecular interactions, thereby firmly combining two materials with completely 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 speed of the silane coupling agent is taken from the silicon functional group Si-X, while the reactivity with organic polymers 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 rules. For example, in general, unsaturated polyesters mostly use silane coupling agents containing CH2=CMeCOO, Vi and CH2-CHOCH2O-; epoxy resins mostly use CH2-CHCH2O and H2N-silane coupling agents; phenolic resins mostly use Use H2N- and H2NCONH-silane coupling agents; polyolefins use vinyl silanes; use sulfur-vulcanized rubber to use hydrocarbon-based silanes.

Because the bonding between dissimilar materials is affected by a series of factors, such as wetting, surface energy, interface layer and polar adsorption, and the effect of acid and alkali , interpenetrating network and covalent bond reaction, etc. Therefore, pre-selection 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 need to be considered comprehensively.

In order to improve hydrolysis stability and reduce modification cost, trihydrocarbyl silane can be mixed into silane coupling agent; The polymers cross-linked by the linking agent are shared. When the silane coupling agent is used as a tackifier, it is mainly achieved by forming chemical bonds and hydrogen bonds with the polymer; wetting and surface energy effects; improving polymer crystallinity, acid-base reaction, and formation of interpenetrating polymer networks. of.

Thickening 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, it is usually required to bond the inorganic material to the polymer, so it is necessary to give priority to Y in the silane coupling agent and the content of the polymer. The reactivity of the functional group; the latter two belong to the bonding between the same type of materials, so the silane coupling agent itself is the anti-hydrophilic polymer and the silane coupling agent selected when the inorganic material requires viscosity increase.

Second, the selection principle of coupling agent

1. Silane coupling agents are mainly suitable for glass fiber and silicon-containing fillers, such as quartz, wollastonite, etc., and can also be used for some metal oxides and Hydroxide, but not CaCO3. The resin is mainly a thermosetting resin.

2. 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 amount of silane coupling agent can be about 1% of the filler; the amount of titanic acid is generally 0.25~2% of the filler.

5. Some surfactants will affect the performance of titanate coupling agents, such as HSt, etc., so they must be fully mixed with fillers, coupling agents, and resins. Mix and add.

6. Most titanate coupling agents are prone to transesterification reactions with ester plasticizers. Therefore, such coupling agents need to be coupled After the agent is added, it can be added. The combination of titanate and silane coupling agent has a good synergistic effect.