In order to improve the bonding ability between resin and reinforcing materials, some reinforcing materials need to be surface treated with coupling agents before use. Different coupling agents are used for different resins and reinforcing materials.
Principle of action of coupling agent:
There are two functional groups in the molecular structure of the coupling agent. One functional group can form a good combination (chemical or physical) with the polar group on the surface of the inorganic substance (glass, filler, metal). ), another functional group can combine well with the resin (chemically or physically). Based on this, the coupling agent combines two materials with very different properties through chemical bonds, thereby increasing the strength of the composite material. improve.
Coupling agents have been developed into several varieties in the following five categories:
Old coupling agent – organic acid chromium complex.
It is a complex of organic acids, represented by Volan, a complex of chromium methacrylate chloride.
The most commonly used coupling agent – organosilane coupling agent
The general structural formula of organosilane coupling agent is R—Si—X3
R—: Amino, mercapto, cyano, vinyl, epoxy, and methacryloyloxy groups can react with resin to form a strong chemical bond;
X—: Hydrolyzable alkoxy group, commonly used are methoxy, ethoxy, etc., which can react with polar groups on the surface of the filler and firmly bind to the surface of the filler.
New coupling agent – titanate coupling agent
Titanate coupling agent is a coupling agent developed by the American Kenlich Petrochemical Company in the late 1970s. Good coupling effect for thermoplastic polymers and dry fillers.
This type of coupling agent can be represented by the general formula: ROO(4-n)Ti(OX-R’Y)n (n=2,3);
RO- is a hydrolyzable short-chain alkoxy group, which can react with the hydroxyl group on the surface of inorganic substances to cause chemical coupling; OX- can be a carboxyl group, an alkoxy group, a sulfonic acid group, a phosphorus group, etc. These groups It is very important to determine the special functions of titanate. For example, the sulfonic acid group gives organic matter a certain thixotropy; the pyrophosphoryloxy group has flame retardant, anti-rust, and enhanced bonding properties.
This type of coupling agent is similar to silane coupling agent. With titanium as the central atom, four types of coupling agents have appeared: monoalkoxy type, monoalkoxy pyrophosphate type, integrated type and ligand type. Titanate coupling agent. However, due to its efficient coupling function, which plays an important role in improving the mechanical properties of materials, it has received widespread attention and its applications are expanding day by day.
Aluminate coupling agent:
Aluminate coupling agent is a new type of coupling agent independently developed in my country. Its molecular structural formula is: (C3H7O)x·Al(OCOR)m·(OCOR²)n·(OAB)y Similar to titanic acid Ester coupling agent, centered on aluminum atom, with hydrolyzable groups and other organic groups, current varieties: SG-Al821 (distearoyloxyisopropyl aluminate), DL-411, DL-411AF , DL-411D, DL-411DF, anti-settling aluminate ASA. Mainly DL-411 series products.
The mechanism of action of aluminate coupling agents is similar to that of TTS titanate coupling agents, that is, one end of the coupling agent molecule contains a group that can react with active hydrogen, so it can absorb water with hydroxyl groups, carboxyl groups or surfaces. The inorganic filler is bonded to improve the affinity and binding force between the inorganic filler and the organic polymer. The other end forms a physical entanglement with the polymer, thereby producing an anti-settling effect and improving the bonding strength. It is widely used in foam molding, extrusion, injection molding, blow molding products of various plastics and various plastic products such as films, packing tapes, flat filaments, color masterbatch, and filling masterbatch.
Other coupling agents:
Zirconium coupling agent is a low molecular weight inorganic polymer containing zirconium aluminate. In addition, there are magnesium coupling agents and tin coupling agents.
