Adding an appropriate amount of calcium carbonate to PVC pipes can significantly improve the impact resistance of the pipe and reduce the cost of the product. However, the modification effects of different varieties of calcium carbonate are very different. This article focuses on how to distinguish light calcium carbonate from heavy calcium carbonate. calcium carbonate.
As we all know, heavy calcium carbonate (referred to as heavy calcium) and light calcium carbonate (referred to as light calcium) are used in the plastics industry. Powder filler with the largest quantity and widest application range. The annual output of plastic products in our country has exceeded 10,000 tons. Calculated based on the fact that the amount of powder fillers used for plastics accounts for 8% of the total plastic products and calcium carbonate accounts for 70% of the total amount of various powder fillers. Currently, various types of plastic fillers used in our country’s plastics industry every year Calcium carbonate of this specification is about 5.7 million tons. Calcium carbonate has become the preferred additive material in the plastic processing industry due to its low price, easy use, and few side effects, bringing huge business opportunities to the calcium carbonate industry.
The plastic products industry uses 5.7 million tons of calcium carbonate every year. Its economics are self-evident. Because it can replace synthetic resins based on petroleum, it is equivalent to the country’s construction of 2-3 large-scale petroleum projects. Chemical plants can not only save tens of billions of yuan in investment, but also save oil, which is non-renewable on the earth and has increasingly become a strategic resource that the country must compete for, making an indelible contribution to the environment.
Years of application practice have shown that calcium carbonate can not only reduce the raw material cost of plastic products, but also improve some properties of plastic materials. Research in recent years has achieved gratifying results. Many colleges and universities Research results from universities and scientific research units show that different types of calcium carbonate can significantly improve the performance of matrix plastics if used properly. However, the distinction between light calcium carbonate and heavy calcium carbonate has always troubled most users. The author of this article divided Introducing its differences.
How to distinguish between light calcium carbonate and heavy calcium carbonate 1 Different sources
Light calcium carbonate is chemically synthesized calcium carbonate, also known as precipitation Calcium carbonate, colloidal calcium carbonate or activated calcium carbonate can even produce nano calcium carbonate, referred to as light calcium. It is made by calcining limestone raw materials to generate lime and carbon dioxide, then adding water to digest the lime to generate lime milk. Its main component is calcium hydroxide. Carbon dioxide is introduced into the lime milk to carbonize it to generate calcium carbonate precipitate. It is made by dehydration, drying and crushing, or it is made from sodium carbonate. It undergoes metathesis reaction with calcium chloride to form calcium carbonate precipitate, which is obtained by dehydration, drying and crushing. Heavy calcium carbonate, referred to as heavy calcium, is produced by directly crushing natural calcite, marble, chalk, shells, etc. using mechanical methods.
How to distinguish between light calcium carbonate and heavy calcium carbonate 2 Different packing densities
The most obvious difference between heavy calcium and light calcium lies in the accumulation of the product The density is different. The bulk density of heavy calcium products is larger, generally 0.8-1.3g/cm potassium trifluoroborate3; while the bulk density of light calcium products is smaller, mostly 0.5-0.7g/cm3; some nano calcium carbonate products The bulk density is even lower, reaching about 0.28g/cm3. Heavy calcium and light calcium products can also be roughly distinguished from the packaging volume of the product. Generally, heavy calcium products are mostly 25kg/pack, and the product packaging volume is small, while the packaging volume of light calcium products of the same quality is obviously larger, and some nano calcium carbonate The product is also packaged in 15kg/bag or 20kg/bag.
How to distinguish between light calcium carbonate and heavy calcium carbonate 3. The whiteness is different
Since heavy calcium products have relatively more impurities, the whiteness of the products Generally it is 89%-93%, and only a few products can reach 95%. Light calcium products are made of chemical synthesis and have removed many impurities. The product has high purity, so the whiteness is mostly 92%-95%, and some products can reach 96%-97%. This is why light calcium products are mostly used in high-end or high-end products. The main reason for filling light-colored products.
How to distinguish between light calcium carbonate and heavy calcium carbonate 4. The moisture content is different
The moisture content of heavy calcium products is generally 0.2%-0.3%. It is relatively low and relatively stable. The moisture content of some high-end heavy calcium products can even reach about 0.1%. The moisture of ordinary light calcium products is 0.3%-0.8%, and sometimes there will be certain fluctuations and instability. Traditionally, the distinction between heavy and light calcium is to test the moisture with a moisture meter. If the moisture is close to 1%, it is light calcium, and if the moisture is less than 0.1%, it is heavy calcium.
How to distinguish between light calcium carbonate and heavy calcium carbonate 5. Different particle sizes
The particle size of heavy calcium products ranges from 0.5-45um. Product particle size varies with different crushing equipment. The particle size of ordinary light calcium products is generally 0.5-15um. Because the particle shape is spindle-shaped, it is difficult to accurately measure, and it is generally a range. The particle size of nano-calcium carbonate in light calcium is finer, and the size is generally 20-200nm. The particle size of ordinary light calcium carbonate is generally around 2500 mesh, which can meet the performance needs of PVC pipes and profiles. Therefore, considering the particle size, light calcium carbonate is traditionally used for PVC pipes and profiles. In the past, due to limitations of crushing equipment, the fineness of heavy calcium carbonate was larger. Now the particle size of heavy calcium carbonate can fully meet the needs, and is even finer than light calcium carbonate. Therefore, both PVC pipes and profiles can currently be used.
The particle size of calcium carbonate can be measured with a particle size analyzer.
How to distinguish between light calcium carbonate and heavy calcium carbonate 6. The taste is different
Light calcium has a lot of impurities removed after calcining the limestone. Generally speaking, the whiteness is higher. High, the purity is also high, but some domestic light calcium has a residual lime taste due to incomplete calcium oxide reaction. If used in the food industry,�Filled biscuits will have a choking taste, but heavy calcium does not. In addition, too much calcium oxide will cause the product to be alkaline in the aqueous system or the pH value cannot be adjusted well, resulting in unstable finished products. In addition, the phosphoric acid content of the two is different. Sometimes a small amount of phosphoric acid needs to be added to light calcium to adjust the pH value to a reasonable range, while heavy calcium does not.
How to distinguish between light calcium carbonate and heavy calcium carbonate 7. The particle shapes are different
Looking with a high-power microscope, heavy calcium products are mechanically crushed and classified. , the particle shapes are generally irregular shapes such as cubes, polygons, and cuboids, as shown in Figure 1. For different heavy calcium processing methods, the microscopic shapes of calcium carbonate are different. For example, calcium carbonate processed by ramming mill is spindle-shaped, and calcium carbonate processed by air-flow mill is granular.
The particles of ordinary light calcium are relatively regular and usually have a spindle shape when fully dispersed, as shown in Figure 2. For light calcium carbonate, the particle shape of the synthetic product can be artificially controlled, and control agents can be added during the carbonization process to achieve control. Control agents currently developed include inorganic acids, inorganic bases, organic acids (amino acids), alcohols, sugars, proteins and biopolymers with special structures, such as the use of dual hydrophilic block polymers PEG-b-PMAA at different concentrations. Carbonic acid with a diamond-shaped, peanut-shaped, long rod-shaped, spherical and dumbbell-like appearance can be made respectively under different pH values. Another example is that the dendritic polymer polyaspartic acid can be used to make spiral-shaped carbonic acid, and another example is adding anion right Glycoside can obtain spherical calcium carbonate.
How to distinguish between light calcium carbonate and heavy calcium carbonate 8 different crystal forms
For heavy calcium carbonate, calcium carbonate from different origins has a fixed crystal form. Crushing and refining will not change the crystal form. Generally, calcite heavy calcium is in the hexagonal crystal form, and marble heavy calcium is in the cubic crystal form. For light calcium carbonate, during the specific carbonization preparation process, three crystal forms of calcium carbonate appear at the same time in different proportions. If you want to obtain a single pure crystal form, you must control the forming process of tetrahydrofuran. The three crystal forms of light calcium carbonate are:
8.1 Calcite crystal form
This is the most stable crystal form of calcium carbonate and belongs to the hexagonal crystal system. Under normal conditions, the mineral calcium carbonate They all exist in this crystal form. Calcium carbonate with this crystal form has great hiding power, high whiteness, good purity, heat resistance, corrosion resistance, and chemical resistance and stability.
8.2 Aragonite crystal form
It is a metastable crystal form of calcium carbonate at room temperature and belongs to the orthorhombic crystal system. Calcium carbonate with this crystal form has a high aspect ratio and is often used in Polymer reinforced composites.
8.3 Vaterite crystal form
It is the most unstable crystal form of calcium carbonate. It only exists in small amounts in organic materials and will automatically convert into calcite crystals in a short period of time. Calcium carbonate with this crystal form plays a very important role in the life and health of organisms. Studies have found that dendritic polymer dielectrics and certain low molecular weight polymer dielectrics can promote stable vaterite crystal forms. generate.
How to distinguish between light calcium carbonate and heavy calcium carbonate 9. The oil absorption value is different
The oil absorption value of light calcium carbonate is 60-90
ml/100mg, much larger than the 40-60 of heavy calcium carbonate
ml/100mg, so the liquid absorption and resin absorption properties are very good. If the formula contains liquid additives, heavy carbonic acid with small oil absorption should be used. Inorganic powder with large oil absorption value will increase the coupling dose that needs to be processed, such as carbonic acid. The oil absorption value of calcium increases from 40ml/100mg to 50ml/100mg, which will cause the dosage of coupling agent to increase by 30. If you choose light carbonic acid in the PVC formula, more liquid additives and PVC trees will be consumed, so in terms of oil absorption value Consider choosing heavy calcium carbonate with low oil absorption value as much as possible.
How to distinguish between light calcium carbonate and heavy calcium carbonate 10. Different fluidity
Considering fluidity, the microstructure of light calcium carbonate is Spindle shape, its fluidity is not as good as heavy calcium carbonate. Generally, adding more than 25 parts will seriously affect the fluidity. Heavy calcium carbonate is granular, which can promote fluidity. The added amount is not limited. In the PVC pipe formula If more than 25 parts of calcium carbonate are added, it is best to use heavy calcium carbonate from the perspective of fluidity.
How to distinguish between light calcium carbonate and heavy calcium carbonate 11 Prices are different
The processing of heavy calcium carbonate is mainly through mechanical crushing and grinding. Achieved; the production of light calcium carbonate is produced through chemical reaction precipitation. The latter process is much more complicated than the former, and the requirements are correspondingly stricter. Therefore, heavy calcium carbonate of the same particle size is better than light carbonate. Calcium is about 30% cheaper. If the performance allows, you can choose heavy calcium carbonate, which is more economical and cheaper.
How to distinguish between light calcium carbonate and heavy calcium carbonate 12. Different modification functions
There are subtle differences between the modification effects of heavy and light calcium carbonate. The difference is that heavy calcium carbonate is better for tensile strength, while light calcium carbonate is better for impact strength and rigidity. Generally, plastics made with light calcium have a smoother surface and lower density; heavy calcium plastics are used for processing fluidity. It is better, and the performance of heavy calcium-filled plastic with smaller particle size is also better.
Conclusion
It is of great significance to correctly distinguish between light calcium carbonate and heavy calcium carbonate, and to select according to the required performance when designing specific formulas, so that materials can be selected as needed. It can satisfy both performance and cost reduction.
Source: Bohan Plastic Processing Circle
�Plastic processing ring
