In modification of engineering plastics, based on cost and performance considerations, polymers are mixed with several components and then a certain amount of inorganic minerals is added for melt mixing process.
There is no affinity between molecules of some polymers, as well as between polymers and inorganic fillers. Mere blending cannot achieve goal of increasing productivity and even has opposite effect. In order to improve this situation, it is very necessary to add a certain amount of sizing to formula, because there are two different chemical groups in molecular structure of sizing, one is an inorganic group and other is an organophilic group, structural formula is as follows:
RO is a short chain alkyl group that is easily hydrolyzed or exchanged, M is central atom, which can be silicon, titanium, aluminum, boron, etc., A is an organophilic group with a longer a chain that is stable with central atom, such as ester group -COR-, long chain alkoxy group (RO-), phosphate acyl group, etc. The material reflects that two groups undergo chemical reactions or physical influences, one unites with surface of filler, and other is physically entangled or reacted with resin, so that filler and resin with very different surface properties can be well bonded. Compatibility, improve interfacial properties between polymer materials or fillers, improve interfacial adhesion, improve performance of filled or reinforced polymer materials.
1. Silane Coupling Agent
It is mainly used for surface treatment of silicon-containing fillers or glass fibers. Its general structure is RSiX3 where R is an active group having affinity or reactivity with resin molecules such as amino, epoxy, vinyl, methacryloyl. etc., X is a hydrolyzable group such as methoxy, acetyloxy, ethoxy, etc. This type is a hydrolyzed silane, when X is a -O-OR oxidation group, it is called silane oxide, and when X is a group containing sulfur polyatoms -S-R, it is called polysulfide silane.
2. Titanate Coupling Agent
For thermoplastic polymers and dry fillers, it has a good bonding effect, which further expands scope of silane coupling agents, and greatly improves bonding effect of non-polar calcium plastic fillers.
2.1 Monoalkoxy type, RO-Ti(OXRY)3 structure, mainly used in PP, PS, PF. This type of coupling agent is water sensitive and only suitable for binding dry fillers. Improved type of monoalkoxy pyrophosphate, since molecule contains pyrophosphate groups, overcomes limitations of monoalkoxy devices. Hydrolyzable, suitable for aqueous fillers.
2.2 Chelating type, with high hydrolytic stability, widely used in PVC, PS, PF, EP.
2.3 Coordination type, structure (RO)4Ti·(HPOOR)2, this type of sizing can avoid exchange reaction between resin and other additives, thereby expanding its application area, mainly used for PO, PC, polyester.
2.4 New type of oxygen, structure R1C(R2)(R3)CHOTi(OXRY)3.
3. Zirconia Coupling Agent
The low molecular weight inorganic zirconium aluminate polymer contains two kinds of organic ligands in molecular structure. One ligand gives it excellent hydrolytic stability, and other ligand has good organic reactivity. Therefore, viscosity coefficient of filler can be greatly reduced, and adhesion effect can be achieved. It is suitable for calcium carbonate, kaolin, aluminum hydroxide, titanium dioxide, silica, etc.
4. Aluminate Coupling Agent
It can improve physical and mechanical properties of product, such as increase impact strength and heat distortion temperature. It is comparable to titanate coupling agents, but price is half that of titanate coupling agents. It is light in color, non-toxic, easy to use and other characteristics, better thermal stability than titanate coupling agent, and has an excellent effect on dispersion of pigments.
Structural formula: (C3H7O)xAl(OCOR)m(OCORCOOR)n(OAB)y
There are two types of aluminate bonding agents: milky white waxy solid and light yellow liquid, and addition amount is 0.3-1.0% filler.
5. Aluminum Titanium Composite Coupling Agent
It has dual characteristics of titanate and aluminate pair links, low cost and wide application.
There are currently two grades on market: OL-AT1618 and OL-ART2760.
6. Organic Chromium Coupling Agent
One end of molecular structure is a living unsaturated group that can react with resin, and other end relies on a chromium-containing oxygen bond and a silicon-oxygen bond on glass surface, which are strongly bonded by chemical bonds. Therefore, it is mainly used for glass fiber reinforcement of polyester.
In addition, there are zircoaluminate coupling agents, borates, stannates, phosphates, etc.