Application of modification technology in polymers and attention points

In recent years, as a nanocomposite, nano-calcium carbonate filled polymer modification has become a newcomer in materials science, which has aroused people's great interest. These materials have the advantages of both organic and inorganic materials. Because of the very large interfacial area between the inorganic and polymer, and the chemical bonding between the polymer and the inorganic filler interface, it has ideal bonding properties and can eliminate inorganic substances. The thermal expansion coefficient of the two materials in the polymer matrix does not match, and the excellent mechanical properties and heat resistance of the inorganic material are fully utilized. Because such nanocomposite melts or fluids have similar rheological properties, they have wide applicability to various types of molding processes and have broad development prospects.

At present, in the process of using nano-calcium carbonate, many nano-powder-filled polymer composites prepared by conventional blending and compounding methods are far from reaching the level of nano-dispersion, but only belong to micro-composites. The reason is that when the particle size of the filler is reduced to the nanometer size, the surface energy of the particles is so large that the self-aggregation between the particles is very significant, so it is difficult to obtain uniform blending on the nanometer scale by using the existing blending technique, and The existing interface modification technology is difficult to completely eliminate the interfacial tension between the filler and the polymer matrix, and achieve an ideal interfacial bonding.

If the dispersion of the filler in the polymer matrix reaches the nanometer scale, it is possible to perfectly combine the rigidity, dimensional stability and thermal stability of the inorganic filler with the toughness, processability and dielectric properties of the polymer to obtain excellent performance. Polymer based nanocomposites.

First, the strengthening and toughening mechanism

As a functional filler in polymers, nano-calcium carbonate is mainly influenced by particle size, aggregation state and surface activity. The particles of nano calcium carbonate are finer than ordinary calcium carbonate. With the miniaturization of particles, the proportion of the number of atoms on the surface of the particles increases, and the electron and crystal structure on the surface of the particles change. At the nanoscale level, the filler particles will become a collection of finite atoms, so that the nanomaterials have A series of excellent physical and chemical properties. The most obvious and most representative is the change of specific surface area and surface energy. The smaller the particle, the larger the specific surface energy per unit mass, which increases the contact area between the filler and the polymer matrix, which provides a physical entanglement. Guarantee.

According to the toughening theory of inorganic rigid particles in a polymer, a necessary condition is that the dispersed particles and the resin interface are well bonded. When the resin is subjected to an external force, the rigid nano-sized calcium carbonate particles cause the matrix resin to absorb the energy by the silver streak, thereby improving the toughening effect. From the aggregation state of the nano calcium carbonate, some of the nanoparticles form a chain structure, which belongs to the primary structure. The more such a structure, the higher the level of structuring of the filler and the greater the likelihood of entanglement with the polymer. In addition, the acidity and alkalinity of the filler is also a reflection of the chemical activity of the surface, which can affect the vulcanization rate and physical properties of the rubber compound.

From the analysis of the above aspects, it is known that nanometer calcium carbonate is an optimized material from the viewpoint of optimization of inorganic fillers, which has physical entanglement due to fine particles and chain structure, and has surface activity. The resulting chemical bonding exhibits a good reinforcing effect in polymer filling.

Second, the application in the polymer

1. Polypropylene

The nano-scale calcium carbonate is mixed in the PP material, which has obvious induction effect on the crystallization of PP, and plays a heterogeneous nucleation effect, which improves the crystallinity of PP. When the nanometer calcium carbonate has a small particle diameter, a large specific surface area, a large number of surface layers, and a high surface activity, the particles of the PP crystal body are small.

Due to the high interfacial bonding strength between the nano-sized calcium carbonate and the polymer, the impact strength of the PP and the mechanical properties of the polymer are improved. Experiments show that as the filling amount increases, the amount of melt absorption first rises and then decreases.

When the nano-sized calcium carbonate is less than 3.5% (mass fraction, the same below), the dispersibility in the matrix is ​​good, and the crystallinity of PP is greatly improved. When the content is more than 3.5%, the heterogeneous nucleation of the inorganic particles is weakened due to the agglomeration phenomenon, and thus the crystallinity of the PP is lowered. For ordinary calcium carbonate (about 9 μm), although the crystallization of PP is induced, the interfacial adhesion strength of the particles to the PP matrix is ​​poor. Therefore, as the ordinary calcium carbonate content increases, the mechanical properties of the material decrease. . The comprehensive mechanical properties of PP/nano-energy calcium carbonate materials are significantly better than those of PP and PP micron-sized calcium carbonate composites.

2. Polyvinyl chloride

PVC is one of the most commonly used general-purpose plastics. With the development of blending and modification technology, its application fields are becoming more and more extensive. Conventional PVC toughening modification usually involves adding a rubber-based elastomer to the resin, but at the expense of reducing the material's valuable rigidity, heat resistance, and dimensional stability. Modification with nanometer calcium carbonate can significantly improve the mechanical properties of PVC. Studies have shown that when the amount of nano-calcium carbonate is gradually increased, the tensile strength of the system also increases. When the dosage is 10%, the maximum value is 58 MPa, which is 123% of pure PVC (47 MPa), and then the amount is increased. The strength of the stretch is reduced.

The addition of nano-calcium carbonate has a large increase in the notched impact strength of the system. When the dosage is 10%, the notched impact strength reaches a maximum of 16.3kJ/m2, which is 313% of pure PVC (5.2kJ/m2); The maximum impact strength of the grade calcium carbonate to the system is 238% of pure PVC. This is because the nano-sized calcium carbonate particles are fine and distributed in a matrix, and there is no obvious gap between the particles and the interface of the substrate. Like sticking to the substrate, the matrix has a certain mesh-like yield in the impact direction, thereby improving the PVC. Comprehensive physical and chemical properties.

3. Silicone Rubber

In recent years, the research on the properties of silicone rubber by reinforcing filler silica has been deepened, but there are few reports on the influence of filled calcium carbonate on the performance of silicone rubber. Due to the stable performance of nano-calcium carbonate, the relative price is much lower than that of silica, the filling amount is large, and it has a certain reinforcing effect on silicone rubber, so it has received increasing attention.

The effect of nano-calcium carbonate on the properties of silicone rubber is mainly moisture, particle size and surface state. Under normal circumstances, the moisture of nano-calcium carbonate can meet the requirements. Even if a small amount of water is present, it can be dehydrated under a certain temperature by a kneading process to meet the requirements. The size of the calcium carbonate has a large influence on the tensile strength and elongation at break of the silicone rubber.

The smaller the particle size of the calcium carbonate, the larger the surface area acting on the molecular chain of the siloxane, and the more the reinforcing points, the greater the influence on the tensile strength and the elongation at break of the silicone rubber. The surface state is also an important factor affecting the tensile strength and elongation at break of silicone rubber. Nano-calcium carbonate is treated with fatty acid surface, the surface changes from hydrophilic to lipophilic, and the wetting and dispersing property with silicone rubber is good. The nano calcium carbonate is uniformly dispersed in the silicone rubber, which not only enhances, but also improves the rheological properties of the silicone rubber. The smaller the particle size of the calcium carbonate, the better the thixotropy of the system. Nano-brand active calcium carbonate produced by Shanghai Excellence Nano-New Materials Co., Ltd. is widely used in silicone rubber and has been well received by users.

In summary, the nanometer calcium carbonate is filled in the polymer, and has the function of reinforcing the filler itself, and the application performance of the polymer is remarkably improved. The main achievement is to improve the mechanical properties, thermodynamic properties and improvement of the plastic product. Molding processability.

Third, application points

The best way to get the nanometer calcium carbonate filling is related to how it is used. Practice has proved that under the same mixing equipment and formulation process conditions, nano-CaCO3 can be mixed with ordinary particles, with large heat generation and slow mixing speed.

In the application, it is necessary to select the appropriate activated varieties according to the type of rubber used to ensure compatibility; the formula design requires appropriate filling, the combination and matching of the entire filling system is reasonable; the process conditions include the feeding sequence and operating temperature, etc.; The compatibility with the compound is improved by selecting other suitable auxiliary dispersants.

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