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Modification of nano calcium carbonate and its application in PVC industry
Release Date:
2021-06-08
Plastic filling modification has a long history, its original intention is to reduce costs, such as adding calcium carbonate to PVC hard products, not only can reduce production costs, the appropriate amount of addition can also improve the mechanical properties of PVC hard products. With the focus of material science research turning to nano-materials, the application of nano-calcium carbonate in PVC industry has been widely valued.
At present, the preparation of nano-calcium carbonate/PVC composites in China is mainly to use different methods to modify nano-calcium carbonate to make it lipophilic, and then use in-situ polymerization or melt blending to compound with PVC to improve the performance of the composites.
1. Surface modification of nano calcium carbonate
The surface modification of nano-calcium carbonate is to adsorb or react the modifier on the surface of nano-calcium carbonate by physical or chemical methods to form a coating, reduce the cohesion between calcium carbonate particles, and enhance the binding force between polymers and fillers.
At present, the modifier used in China includes surfactant, coupling agent, copolymer surface treatment agent, etc. The activation degree of modified nano calcium carbonate reaches more than 95%, and the oil absorption value can be reduced by 30%, which realizes the transformation of nano calcium carbonate from hydrophilic to hydrophobic.
(1) Dry modification
Dry modification is mainly modified by directly mixing nano-calcium carbonate dry powder with coupling agent. The principle of surface modification of calcium carbonate by coupling agent is that the polar group at one end of the coupling agent molecule reacts with the hydroxyl group on the surface of calcium carbonate particles to form a stable chemical bond, and the other end reacts with the organic polymer chain, so that the two polar differences are closely combined, and the composite material is endowed with better physical and mechanical properties.
(2) Wet modification
Wet modification is to directly add the modifier (including treatment agent, dispersant, solvent) to the calcium carbonate suspension, and carry out surface modification treatment under the action of a certain temperature and mechanical force. In recent years, in addition to the use of surfactants, wet modification also used titanate, aluminate and other coupling agents to modify nano-calcium carbonate.
In the process of surface treatment of nano calcium carbonate, the selection of modification method and modifier is the key factor.
In the process of dry modification, the modifier can only modify the outer surface of the agglomerated particles, and the problem of agglomeration has not been fundamentally solved. In the nano calcium carbonate slurry, the calcium carbonate particles exist in the liquid phase in the form of nanoparticles, and the added modifier can fully contact with the nano calcium carbonate to achieve the purpose of modification.
In the selection of modifier, because the modified nano calcium carbonate needs to be applied in the PVC industry, it is not only necessary to consider the combination of modifier and nano calcium carbonate, but also to consider the compatibility of the organic chain in the modifier with the PVC molecular chain, whether the two molecular chains can be more easily entangled, and the stability of the modification effect in the composite process of modified nano calcium carbonate and PVC.
2. Nano calcium carbonate and PVC composite technology
At present, the composite methods of modified nano-calcium carbonate and PVC mainly include in-situ polymerization and melt blending.
(1) In-situ polymerization method
The in-situ polymerization method is to uniformly disperse the nano calcium carbonate in the vinyl chloride monomer, make the surface of the modified nano calcium carbonate particles chemically react or physically adsorb with vinyl chloride, and then carry out in-situ polymerization of the vinyl chloride monomer with nano calcium carbonate to generate PVC/nano calcium carbonate composite resin.
The compound technology of nano-calcium carbonate and PVC by in-situ polymerization method solves the problem of agglomeration of nano-calcium carbonate particles in PVC matrix, but in the process of suspension polymerization, the addition of nano-calcium carbonate affects the original polymerization dispersant, initiator system, reaction temperature, reaction stability, pressure drop time and other process control parameters, but also causes the change of PVC resin viscosity, apparent density, whiteness and other performance parameters.
(2) Melt blending method
The melt blending method is to premix the modified nano calcium carbonate, PVC resin and processing aids in a high-speed stirring pot at high temperature (100~110 ℃) to realize the dispersion and preliminary physical adsorption of nano calcium carbonate and PVC resin, and then in the subsequent melting process of PVC resin particles, the organic end of nano calcium carbonate and the extended PVC molecular chain are wound and combined to improve the performance of the composite material.
The technology of melt blending composite nano calcium carbonate and PVC, using the process of PVC resin post-processing, solves the problem of nano calcium carbonate to improve the mechanical properties of PVC materials, its operation is simple, favored by many enterprises, is a method widely used at present.
With the development of processing technology and material science, there will be more composite technology of nano-calcium carbonate and PVC resin. Its development direction is to simplify the process, facilitate industrial application, and solve the problem of agglomeration of nano-calcium carbonate in PVC matrix, so as to improve the performance of composite materials. This will enable nano calcium carbonate in the PVC industry to be more widely used
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