Calcium carbonate is the main filler of PVC pipe, and its properties are very important to the fluidity and physical properties of products in plastic processing.
The main three are particle size, specific surface area and surface free energy.
1 geometric features
Usually the powder material is used as a filler in the form of particles.
The shape of particles is not very regular, but for the properties of plastics, the geometric shape of filler particles has an important impact on the physical and mechanical properties of the filling system, so the particle shape of powder material is the first thing to pay attention to when using.
For flaky particles, the concept of diameter-thickness ratio is often adopted, that is, the ratio of plane size (longitudinal or transverse) of flaky particles to thickness.
For fibrous particles, the concept of length-diameter ratio is often adopted, that is, the ratio of the length of fibrous particles to the diameter.
The particle shapes of calcium carbonate are mostly rectangular, hexagonal, polygonal and irregular square.
2 size
An important point of the filling modification technology is that the powder particles are evenly distributed into the plastic substrate as far as possible, one by one, as large and small islands in the sea, known as island structure.
Generally speaking, the smaller the particle size is, the better the mechanical properties of the filling system will be if the particles can be dispersed evenly.
However, the smaller the particle size, the higher the processing cost, and the more difficult it is to realize its uniform dispersion.
Therefore, it is very important to know the size and distribution of powder particles and to select them according to actual needs.
At present, there are many kinds of expressions about the size and distribution of powder particle size. Before there is a unified naming method and regulation, the plastic industry often USES the method of mesh number, that is, the number of mesh number through which the particles of powder material can pass to express the particle size.
In fact, the number of items measured by this method refers to the maximum size of the particle with the largest size in the three-dimensional direction.
In plastic products, the narrower the particle size distribution of calcium powder is, the better, namely, the minimum particle size and the maximum particle size are graded. According to the use requirements, the products with particle size within a certain range are collected to ensure the dispersion, transparency, mechanical properties and oil absorption rate of the products.
3 specific surface area
The surface roughness of filler particles is different.
That is, the surface area of particles of the same volume is not only related to the geometric shape of particles (the smallest spherical surface area), but also to the roughness of the surface.
Specific surface area is the surface area of the packing per unit mass, and its size has a direct relationship with the affinity between the packing and resin, the difficulty and cost of surface activation treatment of the packing.
Surface free energy
The surface free energy of filler particles is related to the dispersion of filler in matrix resin.
When the specific surface area is fixed, the surface free energy is large, and the particles are easier to agglomerate with each other and harder to disperse.
Reducing the surface free energy is one of the main objectives in surface treatment of filler.
5 oil absorption value
The amount of the plasticizer dioctyl ester (DOP) that a unit mass filler can absorb is called the oil absorption value.
In the plastic products that use plasticizer, if the oil absorption value of filler is high, can increase the consumption of plasticizer.
The oil absorption value of packing is related to the size, distribution and structure of packing surface.
The oil absorption value of light calcium carbonate is often several times that of heavy calcium carbonate, therefore, the use of heavy calcium can reduce the amount of plasticizer in the case of achieving the same effect on resin plasticizing.
Generally, the oil absorption value of heavy calcium is less than 65mL/100g.
6 whiteness
The whiteness of the filler has a crucial influence on the color and appearance of the filling plastic materials and products.
Generally, the higher the whiteness is, the less influence it has on the coloring of the filled plastic.
As there is no completely transparent filler, so the filling plastic is often opaque, if the color of the filler is not white or other colors, only black or dark plastic products.
7 the moisture
Calcium carbonate itself is not easy to absorb water, does not contain structural water and crystal water, but in the usual ore collection, storage, processing and storage process, because the powder particles are very small, easy to absorb water.
Plastic in the use of water content is very high requirements, the powder standard requirements ≤0.5%, the actual application, the powder water content should be ≤0.3%, the smaller the water content on the plastic products less impact.
-- reprinted on the Internet
