Calcium carbonate has the advantages of wide source, high whiteness, stable composition and environmental protection. It is an important inorganic modified filler for polyvinyl chloride (PVC) products.
As an inorganic mineral, calcium carbonate exhibits strong chemical polarity and hydrophilic properties on its surface, and has poor compatibility with weakly polar PVC substrates. Agglomeration occurs in the matrix, which affects the comprehensive properties and application range of calcium carbonate/PVC composites.
At present, there are various means to realize the activation and modification of calcium carbonate surface, including mechanical activation, thermal activation, microwave-assisted modification and surface modification of coupling agent. Among them, coupling agent modification has the characteristics of simple operation and high efficiency, and has received more and more attention.
Calcium carbonate modified by titanate coupling agent has the following effects on the properties of PVC composites:
(1) The titanate coupling agent mainly modifies the surface of calcium carbonate by chemical reaction grafting, and its alkoxy group and the hydroxyl functional group on the surface of calcium carbonate condense to form a chemical bond. When the usage amount is 1.5%, the activation index is above 95%;
(2) The alkoxy group at one end of the titanate coupling agent is chemically bonded with the hydrophilic group on the surface of calcium carbonate, and the long alkyl polar aliphatic chain at the other end is entangled with the polar PVC molecular chain and forms a weak Hydrogen bonding force, the compatibility of filler and PVC matrix is improved, which significantly improves the mechanical properties, heat resistance and thermal stability of composite materials;
(3) The modification of the coupling agent can further improve the thermal stability of the composite material. The dispersed phase calcium carbonate in the PVC continuous phase can prevent the thermal flow and diffusion of pyrolysis products during thermal analysis, delaying the expansion of the thermal decomposition zone and the dechlorination and splitting of molecular chains. In addition, calcium carbonate with high heat resistance can prevent the heat conduction effect and reduce the rise of thermal decomposition temperature inside the composite material to a certain extent. The highly dispersed modified calcium carbonate particles in the matrix can better block the diffusion and heat conduction of thermal current; at the same time, the addition of coupling agent requires a higher decomposition temperature to effectively destroy the strong interface layer of the composite material;
(4) The interface between the modified calcium carbonate and the PVC matrix is strong, and the calcium carbonate has a stronger effect on the movement of PVC macromolecular segments. Higher temperature is required to cause the movement of PVC molecular segments, and the temperature of the Vicat softening point increases. ;
(5) The modified calcium carbonate has good dispersibility in the PVC matrix phase, and the interface interaction is strong, which can prevent the penetration of water molecules into the material, and the number of hydroxyl groups on the surface of the modified calcium carbonate is reduced, the hydrophilic ability is weakened, and the hydrophobic ability is weakened. Enhanced, further reducing the absorption and osmosis of water molecules.