As a new type of inorganic material, barium sulphate nanoparticles are widely used in many fields because of their high specific surface area, high activity, and good dispersibility.
However, nano barium sulphate also has some disadvantages. On the one hand, due to its hydrophilic and oleophobic nature, there is a great polarity difference between it and the polymer matrix, so it is easy to agglomerate in the polymer which reduces its mechanical properties. On the other hand, due to its high surface activity, agglomeration or agglomeration easily occurs between adjacent particles.
Therefore, in order to improve the dispersion of barium sulphate in the polymer and improve its comprehensive performance in composite materials, surface modification is needed.
1. Coupling Agent Method
Coupling agent is a kind of substances with an amphoteric structure, which can connect the pro-inorganic group with the pro-organic group, thus enhancing the interfacial interaction between inorganic and organic substances. Typical coupling agents include silanes, aluminates, titanates, etc.
Silanes are the coupling agents with more applications and larger amounts and are very effective for inorganic nanoparticles with hydroxyl groups on the surface. However, the bonding between general silane coupling agent and barium sulphate surface is not strong, thus multi-component coupling agent is more frequently used. This method is costly and complicated to use.
Titanate coupling agent has a better modification effect for most inorganic particles because titanate can form chemical bonds with free protons on the surface of nano barium sulphate, thus forming an organic film on its surface, resulting in a change of surface properties. However, its application is becoming less and less due to its high price and the components hazardous to human health.
Aluminate coupling agent is a new type of coupling agent. Its easily-hydrolyzed alkoxy in the molecules can react with the free proton on barium sulphate surface, resulting in a single-molecule film, which is an irreversible Al-O bond, so as to improve product performance. Its performance is also better than other coupling agents.
2. Surfactant Method
One end of the surfactant molecule is a long-chain alkyl group, which can be uniformly dispersed in the polymer matrix. The other end is a polar hydrophilic group, which can have physical adsorption or chemical reaction with the surface of nano barium sulphate and cover the surface of nanoparticles for modification purposes. Commonly used surfactants include advanced fatty acids and their salts, alcohols, amines, phosphate esters, etc.
Surfactants are increasingly used due to their low cost, rich categories, and large production. Products with different properties can be synthesized with different kinds of surfactants, and the modification technology is more mature.
Fatty acid (salt) is a more commonly used and inexpensive surface modifier of nano barium sulphate, and the modified powder has better dispersion and affinity in the polymer. The modified barium sulphate is not easy to precipitate in water due to its surface tension, so the activation degree can be used to reflect the effect of surface modification.
3. Compound Modifier Method
Compound modifier is a compound formula made of two or more kinds of single modifiers, such as sodium palmitate/sodium stearate, sodium stearate/zinc sulphate, sodium stearate/sodium dodecyl sulphate/allyl polyoxyethylene ether, etc. Compound modifiers can give full play to the advantages of each modifier itself, making the modification effect better than a single modification.
It was found that by using sodium stearate to do the surface modification, the temperature and mass fraction of barium sulphate is reduced, energy is saved, and the activation degree can reach 99.9%. After being modified with sodium palmitate/sodium stearate compound modifier, the heat resistance of the product is improved, the particle size distribution is narrower, and the average particle size reduces from 0.89μm (unmodified) to 0.78μm.
This is because when the polar group of the modifier reacts with the barium sulphate nanoparticles, the non-polar group is covered on the outside, and the long carbon chains are entangled with each other to form a mesh structure, which enhances its hydrophobicity. The use of this modification method will be one of the future trends.
4. Precipitation Reaction Method
Precipitation reaction method is to add the modifier into the chemical precipitation reaction so that it forms a coating film on the surface of nano barium sulphate.
This method is also commonly used due to its low production cost, easy operation and easy control of precipitation conditions. Different modifiers and precipitating agents result in different particle sizes and morphology.
5. Inorganic Covering Method
Inorganic material coating modification is to form a covering film on the nanoparticle surface through physical action or van der Waals force without other reactions with its surface. Titanium dioxide, silicon dioxide, zinc oxide, and other metal oxides are usually used as modifiers.
In recent years, there are more and more studies on the modification of nanoparticle covering, because the surface covering of nano barium sulphate can prevent the oxidation, crystal growth, corrosion, and agglomeration of nanoparticles, which can improve the surface properties of barium sulphate nanoparticles and increase their surface activity.
This method enables the dispersion of inorganic particles in different media to be improved. However, the uniformity and strength of the covering are not easy to control, which is a problem to be solved in practice.
Hoyonn Nano Barium Sulphate
With our special surface modification technology, Hoyonn Modified Nano Barium Sulphate has low oil absorption, good distribution, and good affinity with various resins. These improved mechanical properties can increase the filling rate and reduce production costs. Learn more about Hoyonn Nano Barium Sulphate, or contact us for free samples.