Modification Of Nano-Alumina
First, as with other inorganic nanoparticles. In the preparation process, nano-alumina inevitably has residual hydroxyl groups and residual charges on its surface, has high surface activity and surface energy, and is easily agglomerated by itself.
As a result, the surface energy is reduced and the surface activity is reduced, resulting in the loss of many excellent properties of nanoparticles. Based on this characteristic, its surface can be modified and modified in a targeted manner.
On the other hand, nano-alumina itself can be used as a modified material to modify different polymers (such as water-based polyurethane, polypropylene, linear low-density polyethylene, epoxy resin, PTFE, etc.) meet the usage requirements.
Surface Physical Modification.
Surface physical modification generally refers to the physical effect of the modifier on the nano-alumina particles.
Such as ultrasonic treatment, photoelectron irradiation treatment and heat treatment and plasma treatment. Common modification methods include adsorption, coating, and light radiation treatment.
(1) Adsorption;
Nano-alumina particles have extremely poor dispersibility in aqueous solution and are easy to agglomerate. The use of surfactants can prevent the agglomeration of nanoparticles and make their dispersion more uniform.
The surfactant has two groups with different polarities. The polar hydrophilic group is compatible with water, and the non-polar lipophilic group is adsorbed to the surface of the particle, so that the particle surfactant extends outward to form a particle beam. , preventing the mutual contact between particles and avoiding the occurrence of agglomeration.
(2) Coating;
Like the adsorption method, the coating is to deposit heterogeneous materials on the surface of nano-alumina through van der Waals forces, etc., to form a core layer of nano-alumina and a shell layer of a "core-shell" structure that is not chemically combined with alumina, preventing the formation of nano-alumina. For the agglomeration between particles, the coating amount is usually larger than the adsorption amount.
(3) Irradiation treatment;
Irradiation technology is a new technology that uses the physical and chemical effects produced by the interaction of ionizing radiation and matter. It uses high-energy rays to interact with matter to transfer energy to alumina in a short time, so that the surface of alumina is ionized and ionized. Exciting changes to produce various effects, so as to achieve the modification of alumina particles.
For example, UV-treated nano-sized α-Al2O3 has better dispersibility, and when the nano-alumina content is 6%, the abrasion resistance of PVC plastic is improved to the greatest extent.
(4) Other methods.
In fact, there are many physical modification methods that can be used in nano-powder dispersion, such as surface deposition, surface electroless plating, etc., which often form alumina-based composite materials, which improve the dispersibility of nanoparticles and also cover up to a certain extent. the properties of nanoparticles.
2. Chemical Modification Method.
Some hydroxyl groups and residual charges remain on the surface of nano-alumina. Using this property, the modifier can be selected to carry out chemical reaction, and the structure and state of the surface of alumina can be changed to achieve the purpose of surface modification.
The common methods of chemical modification of nano-alumina surface are as follows: ① coupling agent method; ② grafting method; ③ grafting-coating method.
(1) Coupling agent method;
Nano-alumina particles have high surface energy and poor affinity with organic systems with low surface energy. When the two are blended, phase separation tends to form. The solution is usually to use coupling techniques.
The coupling agent is generally a compound with a bifunctional group, which can react with inorganic and organic substances at the same time. When the coupling agent is processed, one end of the coupling agent is combined with the hydroxyl group on the surface of alumina, and the other end interacts with the dispersion medium. Commonly used coupling agents for nano-alumina surface treatment include silane coupling agents, titanate coupling agents, etc.
(2) Grafting method;
As mentioned above, there are active hydroxyl groups on the surface of nano-alumina. The hydroxyl group is used as the active point of the grafting reaction, and the oil-soluble group is grafted. The graft is generally a small molecule, and the coupling treatment is essentially equivalent to grafting. . The advantage of this method is that the amount of grafting can be controlled and the efficiency is high.
(3) Grafting-coating method.
In this method, a layer of organic matter (mostly small molecules) is formed on the surface of nano-alumina by grafting or coupling technology, and then an initiator is used to graft the monomer on the organic layer on the surface of the particle, and finally form a layer of aluminum oxide. As the core, the polymer layer is an inorganic-organic "core-shell" structure of the shell layer. The advantage of this method is that the thickness of the shell layer can be controlled by the addition amount.
