Most of the fillers used in composite materials are natural or artificially synthesized inorganic fillers, which are polar and water-insoluble substances. When they are dispersed in organic polymer resins with extremely low polarity, poor compatibility often occurs due to the polarity difference between the two, and direct or excessive filling can easily lead to a decrease in the mechanical properties of the material. Therefore, using physical or chemical methods to modify the surface of inorganic fillers to make them non-polar, thereby improving their compatibility with resins and enhancing the mechanical properties of composite products, has certain practical significance.
The surface modification of fillers in this experiment adopts the dry treatment method in surface chemical modification, and the process involves adding titanium acid esters in a 1:1 ratio (weight ratio)coupling agentPrepare an ethanol solution, drop it into the dried heavy calcium carbonate and stir for 40-60 minutes to fully coat the surface of the filler. Then place it in an oven at a temperature of around 40 ℃ for 3 hours.
There is no strong interaction between the polymer and the matrix, and the modulus of the polymer containing rigid particle fillers is also increased. The decrease in mechanical properties of composite systems is caused by the difference in polarity between fillers and resins. In the filling system, the filler is a dispersed phase, which is actually divided into a continuous phase composed of the matrix resin. Even if the filler particles are well combined with the matrix resin without bubbles or pores, the area of the matrix resin on the stress section is inevitably smaller than that of the pure resin fiber system. Due to the weak interaction between the filler and the matrix resin, when subjected to external forces, the matrix resin is pulled away from the particle surface, resulting in a decrease in the strength of the filled system compared to the unfilled system.
Titanium ester coupling agents contain two types of functional groups, one of which is a short chain alkoxy group that is easily hydrolyzed. When the monolayer on the surface of calcium carbonate binds to water, it binds to the surface of the calcium carbonate filler, making the filler surface non-polar. The long-chain alkoxy group on the other end of the coupling agent reacts chemically with the UP resin. Titanium ester coupling agents actually play a bridging role, improving the interfacial bonding between fillers and resins. The chemical bond theory suggests that interface bonding achieved through the formation of chemical bonds can theoretically achieve high bonding strength. The test results of the specimens showed that the strength and modulus of UP resin castings and GFRP filled with fillers modified with titanium ester coupling agents were improved to varying degrees.
The addition of calcium carbonate significantly reduces the tensile and bending strength of UP resin castings and GFRP, and becomes more significant with the increase of filler dosage. The tensile and bending strength of UP resin castings and GFRP filled with fillers modified by titanium ester coupling agents is significantly improved compared to unmodified filling systems, and has a good surface modification effect on calcium carbonate.
