Fillers, PVC reinforcements are traditionally used to reduce the final price of PVC products, but nowadays they are used not only to reduce the price, but also to strengthen the various properties of PVC products. For this reason, the consumption of fillers is growing along with the consumption of polymers, so that the annual consumption of fillers in the early 2000s is estimated at 14 million tons. Factors determine the final properties of the filler such as chemistry, particle shape, particle size distribution, surface area, optical properties, color, aspect ratio, density, hardness and density.
Mineral fillers in PVC matrix
To check the efficiency of fillers and choose a suitable filler for PVC mixture, several factors should be considered. The most important factors that should be considered are the size and size distribution of the particles, the morphology and chemistry of the filler surface. To determine the size of the filler particles, the diameter of the equivalent sphere is usually used. Another important property of fillers is their contact surface. The contact surface of the filler particles actually determines the ability of the filler to absorb and react with other particles such as antioxidants, thermal stabilizers and polar polymers.
The amount of reflection and dispersion of filler particles depends on the optical refractive index parameter and particle size distribution. The refractive index of PVC is about 1.54 and by using different amounts and types of fillers, transparent, semi-transparent and opaque products can be produced from PVC. For example, the refractive index of calcium carbonate and titanium dioxide is 1.66 and 2.76, respectively. Therefore, by using calcium carbonate in the PVC mixture, a semi-transparent product is obtained, while titanium dioxide causes the product to be completely covered.
In general, there are two methods for measuring paleness. The first method, which is also the simplest method, is actually visual evaluation and observation under certain conditions (D1729 and ASTM D-1535). In this method, you can quickly compare colors with each other and draw conclusions. But the results are completely influenced by the tester’s eyesight.
In the second method (E313, E97, E308, D2244 and ASTM), a spectrophotometer is used to accurately check the color of the sample. Specific density is also used to determine the volume price of PVC formulations.
The Moss hardness scale is sometimes used to express the hardness of fillers. The Moss hardness scale, which was invented by Friedrich Moss in 1812, actually evaluates the ability of a filler particle to scratch or be scratched by its adjacent filler particles. Another main criterion of fillers is density fraction. The particle density fraction is basically the volume fraction of the particles completely attached to the total volume occupied by the particles.
Of course, there is some limitation in reducing the particle size. Because with size reduction, despite the improvement of physical and mechanical properties, the tendency of particles to cluster also increases and problems arise in mixing and dispersion of particles in the mixture.
All kinds of commercial mineral enhancers and fillers – PVC reinforcements
PVC reinforcements – Calcium carbonate is a main component of limestone. This material exists naturally in the forms of gypsum, marble and coral stones such as calcite and aragonite. Calcite is a six-sided crystal that is thermodynamically stable at all pressures and temperatures below the temperature of thermal decomposition.
Kaolin or Chinese soil is actually a type of clay that is obtained from the decomposition of aluminum mineral fillers, such as mica and feldspar, due to atmospheric factors. Kaolin is a hydrous aluminum silicate that exists in natural hydrous and anhydrous calcareous forms, both of which are acidic. Hydrous kaolin has a dry brightness parameter of 85-95, a hardness of 5-6 and an average particle size of 0.3-10 microns.
Talc is a hydrous magnesium silicate that contains Mgo 31.7%, SiO2 5.63% and H2O 4.8%. This filler has a mass hardness of 1 and is one of the softest fillers in PVC formulations. Talc is mostly very fine (1-5 microns), very hydrophobic, slippery and resistant to heat (900 degrees Celsius) and is neutral to most chemicals.
Mica is the name of a wide group of aluminosilicate compounds. There are different types of mica filler such as muscovite, phlogopite, biotite, lepidolite, roscolite, feldspar phlogopite, facite and paragonite, and muscovite and phlogopite are the most widely used types of mica in PVC formulations.
Barium sulfate is available in two forms, natural ore and sediment. This material consists of rhomboid crystals with a melting temperature of 1580 degrees Celsius, a specific gravity of 4.5, informal and highly insoluble, and it has a hardness of 3.3-5, which shows that it is a relatively soft crystalline filler.
Of course, we can mention wollastonite, calcium sulfate, nepheline syenite, small glass spheres among the fillers and reinforcements of PVC.
Characteristics of natural fibers
Among the most important natural fillers of PVC mixtures, we can mention wood, which is used in the form of powder, single fiber and multiple fibers. Of course, wood powder is more interesting because it causes less dispersion and clustering problems than fibrous forms in the mixture and has a simpler process behavior. In the structure of wood, there are two main types of cells, which are the fibrous type and the vascular type, and the difference between different types of wood is due to the difference of these cells. In general, wood can be divided into two types, hard and soft.