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PусскийUnderstanding the relationship between the structure and properties of titanate can help you choose various varieties correctly.
Tetravalent elements are the best molecular builders, such as tetravalent titanium carbon - forming the basis of life. Similarly, titanium chemistry has shown that tetravalent titanium can enable chemists to synthesize various molecular types of titanates as coupling agents, which in addition to providing good coupling effects for different fillers and polymer systems, also show various other functions.
The molecules of titanate coupling agents can be divided into six functional regions, which play their respective roles in the coupling mechanism. The six functional areas are shown in the table: functional area ① (RO)m - from inorganic matter and titanium coupling.
The titanate coupling agent is chemically coupled by its alkoxy group directly with a small amount of carboxyl or hydroxyl groups adsorbed on the surface of the filler or pigment.
Different types of coupling agents have been developed due to the difference in the functional area ① groups, each type is selective for the water content on the surface of the filler, and the characteristics of each type are:
1. Monoalkoxy type;
Monoalkoxy titanate produces a chemical bond at the interface between inorganic powder and matrix resin. Its extremely unique property is to form a monomolecular film on the surface of inorganic powder, but there is no polymolecular film on the interface.
Because it still has the chemical structure of titanate, in the presence of excess coupling agent, the surface energy changes and the viscosity is greatly reduced. In the matrix resin phase, due to the trifunctional group of the coupling agent and the transesterification reaction, the The titanate molecule is coupled, which facilitates the modification of the titanate molecule and the selection of the filled polymer system.
This type of coupling agent (except pyrophosphoric acid type) is especially suitable for dry filler systems that do not contain free water and only contain chemically bound water or physically bound water, such as calcium carbonate, hydrated alumina, etc.
2. Monoalkoxy pyrophosphate type:
This type of titanate is suitable for filler systems with high moisture content, such as clay, talc and so on. It can also be decomposed to form a phosphate group, combined with a part of water.
3. Coordination type:
The side reaction of tetravalent titanate in some systems can be avoided. Such as the transesterification reaction in polyester, the reaction with hydroxyl group in epoxy resin, the reaction with polyalcohol or isocyanate in polyurethane, etc. This type of coupling agent is suitable for many filler systems and has good coupling effect. Its coupling mechanism is similar to that of monoalkoxy type.
4. Sting type:
This type of coupling agent is suitable for high-humidity fillers and water-containing polymer systems, such as wet-process silica, clay, talc, aluminum silicate, water-treated glass fiber, lamp black, etc. In high-humidity systems, general The monoalkoxy type titanate has poor hydrolysis stability and low coupling effect, while this type has good hydrolysis stability, and in this state, it shows a good coupling effect.
Functional area ② -(--O...)-- has the function of transesterification and cross-linking.
This zone can undergo transesterification with polymers with carboxyl groups, or undergo esterification with carboxyl groups in epoxy resins to cross-link fillers, titanates and polymers.
Transesterification reactivity is governed by several factors:
1. The chemical structure of the coupling part between the titanate molecule and the inorganic substance;
2. The chemical structure of the OX group on functional area ③;
3. The chemical structure of organic polymers;
4. The chemical properties of other additives such as ester plasticizers.
Titanates do not undergo transesterification in thermoplastic polymers such as polyolefins, but in polyesters, epoxy resins or soft polyvinyl chloride plastics with ester plasticizers, transesterification does not occur. have a great impact. The activity of the transesterification reaction is too high, which will cause adverse consequences. For example, titanate such as KR-9S, when added to the polymer, can rapidly undergo transesterification, and the initial viscosity increases sharply, which greatly reduces the filling amount. However, titanate such as KR-12 has low activity of transesterification and no initial viscosity effect, but transesterification can progress gradually over time, so that not only the initial dispersibility is good, but also the filling amount can be greatly increased.
In coatings, the transesterification mechanism of titanate coupling agents can be used to crosslink and cure saturated polyesters and alkyd resins, so that a non-yellowing material (because it does not contain unsaturated structures) can be obtained. It can express thixotropy, so KR-9S with higher transesterification activity has thixotropy effect, and TTS also has a certain degree of transesterification ability.
Functional area ③ OX--the group connecting the titanium center.
The OX group in this part has different effects on the properties of titanate depending on the structure of the group. For example, the carboxyl group can increase the compatibility with semi-polar materials, the sulfonic acid group has thixotropy, and the sulfone group can increase the transesterification activity. Phosphate group can improve flame retardancy and softening of PVC; pyrophosphate group can absorb water and improve the impact strength of rigid PVC, phosphite group can improve oxidation resistance, reduce polyester or ring Viscosity in oxygen resin, etc.
Functional area ④ R---long-chain entanglement group of thermoplastic polymer, organic skeleton in titanate molecule.
Due to the existence of a large number of long-chain carbon atoms, the compatibility with the polymer system is improved, which causes the change of the surface energy on the interface of the inorganic material, which has the functions of flexibility and stress transfer, and produces self-lubricating effect, which leads to a significant decrease in viscosity and improves the The processing technology increases the elongation and tear strength of the product, and improves the impact performance. If R is an aromatic group, it can improve the compatibility of titanate and aromatic hydrocarbon polymer.
Functional area ⑤ Y---Reactive group of thermosetting polymer.
When they are connected to the organic framework of titanium, the coupling agent and organic materials can be connected by chemical reaction, for example, double bonds can be cross-linked and cured with unsaturated materials, and amino groups can be cross-linked with epoxy resins.
Functional area ⑥ )n It represents the functionality of titanate, n can be 1-3, so it can be adjusted according to needs, so that it can produce a variety of different effects on organic matter, in this regard, the flexibility is better than that of silane. Trialkoxy monofunctional coupling agent is large.
From the functions of the above six functional areas, it can be seen that the titanate coupling agent has great flexibility and versatility. It is not only a coupling agent, but also a dispersing agent, a wetting agent, an adhesive, a Coupling agent, catalyst, etc., can also have functions such as anti-rust, anti-oxidation, flame retardant, etc., so it has a wide range of applications and is better than other coupling agents.
