A chemical having an amphoteric structure is a coupling agent. While one group of their molecules exhibits the properties of an organophile and can chemically interact with organic molecules, the other group of their molecules reacts with chemical groups on the inorganic surface to establish chemical bonds. mix two materials with very differing qualities while also reacting or creating a significant intermolecular contact.

The mechanical characteristics and performance indicators of filled polymer materials may be improved by selecting an appropriate coupling agent, which can also enhance the dispersion state of inorganic fillers in the polymer matrix.

Basic guidelines for selecting a silane coupling agent

While the reactivity with the organic polymer is derived from the carbon functional group C-Y, the hydrolysis rate of the silane coupling agent is derived from the silicon functional group Si-X. Therefore, it is crucial to choose a silane coupling agent that is appropriate for the various substrates or processing items.

Pre-selection through experiments is the primary way of selection, and it should be used in accordance with previous knowledge or established procedures. For instance, unsaturated polyesters typically use vinyl silanes, whereas epoxy resins typically use CH2-CHCH2O and H2N-silane coupling agents, phenolic resins typically use H2N- and H2NCONH-silane coupling agents, and rubbers that undergo sulfur vulcanization typically use hydrocarbon-based silanes.

Since many elements, including wetting, surface energy, interface layer and polar adsorption, the impact of acid and alkali, interpenetrating network, covalent bond reaction, etc., affect the adhesion between different materials. As a result, pre-selection by test alone is occasionally insufficient, and it is also required to carefully take into account the material’s composition and sensitivity to the silane coupling agent’s response.

Trihydrocarbyl silane can be added to the silane coupling agent to increase hydrolytic stability and lower the cost of modification; for materials that are difficult to adhere to, the cross-linked polymer of the silane coupling agent can also be shared. When a silane coupling agent is employed as a tackifier, it primarily functions by creating chemical and hydrogen bonds with the polymer, as well as wetting and surface energy effects, enhancing polymer crystallinity, acid-base reactions, and the development of interpenetrating polymer networks, among other things.

Three systems are the center of viscosification, namely:

(1) The contrast between organic and inorganic materials;

(2) Inorganic to organic materials;

(3) Organic substance to organic substance.

The reactivity of Y in the silane coupling agent and the functional groups present in the polymer must be given priority because it is generally advised to bond inorganic materials to polymers for the first type of bonding; the latter two types pertain to the bonding between materials of the same type. The silane coupling agent must thus be employed when raising viscosity since it is necessary for the anti-hydrophilic polymer of the silane coupling agent itself and its inorganic components.

Second, the coupling agent selection criteria

• Silane coupling agents can be employed as oxides and hydroxides of various metals and are mostly utilized in glass fiber and silicon-containing fillers like quartz, wollastonite, etc., but they are not appropriate for CaCO3. Thermosetting resins make up the majority of resins.
• Titanate coupling agents may also be employed in glass fibers and are frequently used for fillers like CaCO3, titanium dioxide, etc. A thermoplastic resin makes up the majority of the resin.
• The basic filler ought to pick a coupling agent with acidic functional groups, whereas the acidic filler ought to pick one with basic functional groups.
• How much coupling agent was applied. Titanic acid is often employed in amounts ranging from 0.25 to 2% of the filler, whereas the quantity of silane coupling agent utilized can be up to 1% of the filler.
• Since certain surfactants, such HSt, etc., can impact how well the titanate coupling agent performs, they must be introduced after the filler, coupling agent, and resin are well combined.
• Transesterification reactions with ester plasticizers are common with most titanate coupling agents. This kind of coupling agent must thus be added after the coupling agent. It works more synergistically when titanate and silane coupling agents are used together.