CLOSE

Mechanism of Silane Coupling Agent Action


The function and effect of silane coupling agents have been recognized and affirmed by people, but there is still no complete set of coupling mechanism to explain why a small amount of coupling agent on the interface can have such a significant impact on the performance of composite materials. There have been many studies on the mechanism of coupling agents at the interface between two different materials, and explanations such as chemical bonding and physical adsorption have been proposed. Among them, the chemical bonding theory is the oldest but also the most successful theory.


Chemical bonding theory of silane coupling agents


This theory believes that organosilane coupling agents contain a chemical functional group that can form a covalent bond with the silicon hydroxyl group on the surface of glass fibers or other inorganic fillers; in addition, the coupling agents also contain another different functional group that can bond with polymer molecules to obtain good interface binding. The coupling agent acts as a bridge connecting the inorganic phase and the organic phase.


Take silane coupling agents as an example to illustrate the chemical bonding theory. For example, amino-propyltriethoxysilane, when used to treat inorganic fillers (such as glass fibers), the silane is first hydrolyzed into a silanol, and then the silanol group reacts with the inorganic filler surface by dehydration to form a chemical bond, as shown below: the silane groups hydrolyze—in the hydrolysis, the hydroxyl group reacts with the inorganic filler—when the treated inorganic filler is filled to prepare composite materials, the Y-group in the coupling agent will interact with the organic polymer, finally building the bridge between the inorganic filler and the organic phase.


Silane coupling agent wetting effect and surface energy theory


Experts have concluded that good wetting of liquid resin to the adherent is of paramount importance in the manufacture of composite materials. If complete wetting can be achieved, then the physical adsorption of the resin to high-energy surfaces will provide adhesive strength higher than that of organic resins.


Silane coupling agent deformable layer theory


In order to mitigate the interface stress caused by the different thermal shrinkage rates between the resin and the filler during cooling of the composite material, it is hoped that the resin interface adjacent to the treated inorganic material is a flexible and deformable phase, so that the toughness of the composite material can be maximized. The surface of the inorganic material treated with organosilane coupling agents may preferentially absorb a certain compatibilizer in the resin, leading to unbalanced curing in the interphase region, which may result in a much thicker flexible resin layer than the multi-molecular layer between the polymer and the filler. This layer is called the deformable layer, which can relax the interface stress, prevent the extension of interface cracks, and thereby improve the interface bonding strength and mechanical properties of the composite material.


Silane coupling agent constraint layer theory


In contrast to the deformable layer theory, the constraint layer theory holds that the resin in the inorganic filler area should have a modulus that is intermediate between the inorganic filler and the matrix resin, and the function of the coupling agent is to "tighten" the polymer structure in the interphase area. From the perspective of the enhanced properties of the resulting composite material, a constraint layer is required at the interface to obtain maximum adhesion strength and hydrolysis resistance. As for titanium ester coupling agents, they mainly interact with organic polymers in thermoplastic systems and filled thermosetting composites through long-chain alkyl compatibility and entanglement, and form covalent bonds with inorganic fillers. These assumptions reflect the coupling mechanism of the coupling agent from different theoretical aspects. In the actual process, it is often the result of the combined action of several mechanisms.


Products

Have a question or request?

Click below,we’ll be happy to assist.

NO.20 HUAYIN NORTH ROAD, HIGH-TECH INDUSTRIAL PARK, QUZHOU CITY, ZHEJIANG PROVINCE.CHINA
E-mail sales5@ztsilicone.com

Contact Us +86-570-8598022