Reasons for Using Modified Calcium Carbonate to Fill Masterbatch

Calcium carbonate is an extremely important inorganic chemical product widely used in industries such as plastics, rubber, coatings, and papermaking. In recent years, due to the continuous expansion of various synthetic resins and chemical raw materials, energy consumption has been increasing. Therefore, in industries such as plastics and rubber, people are increasingly considering adding resource rich and low-cost inorganic fillers to polymer synthetic materials. While adding inorganic fillers (such as calcium carbonate) to plastic and rubber products as much as possible, it is necessary to ensure the physical and mechanical properties of the products.

Ordinary inorganic fillers, such as ordinary calcium carbonate, are difficult to meet these requirements and need to be modified to improve their overall performance. With the rapid development of the composite materials industry, calcium carbonate is no longer just a filler, but also an important modifier.

Filling plastic products with high-performance active calcium carbonate can not only reduce costs but also improve the hardness, elastic modulus, dimensional stability, and thermal stability of the products. Activated calcium carbonate is obtained by modifying ordinary calcium carbonate, thus achieving the dual purpose of filling and modifying in composite material products. These modifications include modifications to the crystal morphology, particle size, particle size distribution, and surface properties of calcium carbonate.

Change granularity

Fine refine or ultrafine the calcium carbonate particles (including changing the crystal morphology and particle size distribution of calcium carbonate), improve their dispersibility in resins with different crystal morphologies of fine or ultrafine calcium carbonate, and obtain reinforcement effects in plastic, rubber and other products with small particles and large specific surface area.

This modification method requires improvements to the carbonization, pulverization, and dehydration drying techniques of traditional calcium carbonate production processes. The production process is complex, and drying conditions are difficult to achieve during mass production, resulting in high product costs.

Improving the surface properties of calcium carbonate

Transforming it from inorganic to organic, thereby increasing the compatibility between calcium carbonate and organic resin, improving the processing performance and physical and mechanical properties of the product.

This method mainly uses amphiphilic molecules (with both inorganic and organic functional groups, including surfactants, long-chain organic acids, and coupling agents) to modify the surface of calcium carbonate. The process and equipment are relatively simple and easy to implement. In recent years, coupling agents have been developed to treat calcium carbonate with different particle sizes, and the modification effect is very good. They have been increasingly applied in the production of composite materials such as plastics and rubber, which is an effective way to expand new varieties of calcium carbonate fillers.

There are many substances that can modify the surface of calcium carbonate, but previous research has mostly focused on using organic acids to modify the surface of calcium carbonate and produce corresponding active calcium carbonate products. Due to the fact that the main function of organic acids on the surface of calcium carbonate is physical adsorption, they provide lubrication at the interface between calcium carbonate and resin during the mixing process with the resin. Therefore, modifying with organic acids can change the rheological and processing properties of the material, with almost no improvement in the physical properties of the product.

In recent years, in-depth research has shown that when modifying calcium carbonate with coupling agents, the inorganic and organic ends of the coupling agent molecules can undergo chemical reactions with the surface of calcium carbonate and organic resin, respectively, while also entangling with the organic resin. In the presence of crosslinking agents, crosslinking phenomena can also occur. This effect not only changes the surface polarity of calcium carbonate, but also increases the interfacial adhesion between calcium carbonate and organic resin. Therefore, modifying with coupling agents can not only improve the processing performance of calcium carbonate filled products, but also enhance their physical and mechanical properties.

Titanium ester coupling agents and aluminum ester coupling agents are more effective for surface modification of calcium carbonate. However, calcium carbonate treated with titanium ester coupling agents may change color due to oxidation when used in certain polymers. During storage or processing of filled products, the hydrophilic end of titanium ester molecules is prone to hydrolysis or alcoholysis, and the thermal decomposition temperature of titanium ester is also lower than that of aluminum ester. Therefore, it is ideal to use aluminum ester coupling agents to treat calcium carbonate.

The mechanism of activating calcium carbonate with aluminate coupling agent is as follows: the molecular system of aluminate coupling agent belongs to amphiphilic structure, with one end being an inorganic group and the other end being an organic group. When the coupling agent acts on the surface of calcium carbonate, the calcium ions and carbonate ions on the surface of calcium carbonate particles come into contact with water molecules in the atmosphere and undergo hydrolysis, resulting in an alkaline and oleophobic hydroxyl surface.

The surface hydroxyl groups of calcium carbonate can chemically bind with the inorganic end of aluminate coupling agents, resulting in surface modified calcium carbonate particles. These surface modified calcium carbonate particles are blended with resin, and the organic end of the coupling agent molecules can entangle with the resin molecules. Due to the action of coupling agents, calcium carbonate has an activating function, which increases its affinity with organic resins and achieves the modification and enhancement effect on the resin.