In the research and production process of plastics, a large amount of inexpensive inorganic fillers (or reinforcing agents) are usually used. This can not only increase the weight of plastic and reduce product costs, but also improve certain properties of plastic products. However, due to significant differences in chemical structure and physical morphology between inorganic fillers and organic polymers, the lack of affinity between the two often leads to adverse effects on the mechanical and processing properties of plastic products. The use of coupling agents can solve the above problems.
Coupling agent is an organic compound that can enhance the affinity between inorganic fillers and organic polymers. It changes the surface of inorganic fillers from hydrophilic to oleophilic through chemical reactions or physical coating, thereby achieving a tight bond with polymers and improving various properties of plastic products. Among numerous coupling agents, silane coupling agent is the earliest researched and most widely used one. The use of organic silicon coupling agents in plastics can improve their mechanical properties, electrical properties, heat resistance, water resistance, weather resistance, flame retardancy, dispersibility, and processing performance.
Modification of inorganic fillers by coupling agents:
The combination of organic silicon coupling agents with inorganic fillers begins with the interaction between silane oligomers and hydroxyl groups on the surface of inorganic fillers. So for inorganic fillers with hydroxyl groups on the surface, the coupling effect is better, while for inorganic fillers without hydroxyl groups on the surface, it is difficult to achieve the corresponding effect.
With the high performance and multifunctionality of plastic products, higher requirements have been put forward for organic silicon coupling agents, which has prompted people to research and develop new products with different functions and needs. Some new organic silicon coupling agents developed in recent years have certain special properties. The reason why silicone organic silicon coupling agents can improve the bonding strength of plastic products is due to the comprehensive results of a series of complex factors, such as infiltration, surface energy, boundary layer adsorption, polar adsorption, and acid-base interactions. The actual usage methods of organic silicon coupling agents mainly include pretreatment and overall blending treatment.
The pre-treatment method of Suowei involves first surface treating inorganic fillers with silane, and then adding them to the resin. According to different treatment methods, it can be divided into dry treatment and wet treatment. Dry treatment involves adding inorganic fillers in a high-speed mixer, slowly adding a pre prepared silane solution while stirring, and evenly dispersing it on the surface of the fillers for treatment. Wet treatment, on the other hand, involves treating inorganic fillers in a silane solution before drying. Whether it is dry or wet treatment, in order to evenly coat the surface of inorganic fillers with coupling agents, it is necessary to pay attention to the control of the treatment process, especially the stirring and drying conditions.
When preprocessing is not feasible or insufficient, the overall blending method can be used. This method involves mixing organic silicon coupling agents into inorganic fillers and resin systems. Its advantage is that the amount of coupling agent can be adjusted freely and the ingredients can be prepared in one step, so it is often used in industrial production. However, compared with the pre-treatment method, in order to achieve the same modification effect, the overall blending method must use more organic silicon coupling agents. Organic silicon coupling agents can improve the dispersion and bonding properties of inorganic fillers in polymers, making them widely used in plastic filling (or reinforcement) modification. Especially when using inorganic fillers to manufacture plastics with various special functions such as electromagnetics, sound insulation, and flame retardancy, the use of organic silicon coupling agents will produce significant modification effects.
