In-depth comparison of the practicality of heavy calcium and light calcium
Calcium carbonate not only can reduce the raw material cost of plastic products, but also has the effect of improving certain properties of plastic materials. Different types of calcium carbonate can significantly improve the performance of matrix plastics when used, but light calcium carbonate and heavy carbonic acid. The distinction between calcium has been plaguing most users, so this time we will understand the difference in the most in-depth way.
Light calcium carbonate is a chemically synthesized calcium carbonate, also known as precipitated calcium carbonate, colloidal calcium carbonate or activated calcium carbonate, and even can produce nano calcium carbonate, referred to as light calcium. It calcinates the limestone raw material to form lime and carbon dioxide, and then adds water to digest the lime to form lime milk. The main component thereof is calcium hydroxide, which is formed by carbon dioxide carbonized lime milk to form calcium carbonate precipitate, which is obtained by dehydration, drying and pulverization, or by sodium carbonate. It is metathesized with calcium chloride to form a calcium carbonate precipitate, which is obtained by dehydration, drying and pulverization. Heavy calcium carbonate, referred to as heavy calcium, is produced by mechanically pulverizing natural calcite, marble, chalk, shells, and the like.
Different stacking density
The most obvious difference between heavy calcium and light calcium is that the bulk density of the product is different. The bulk density of heavy calcium products is relatively large, generally 0.8-1.3g/cm3; and the bulk density of light calcium products is small, mostly 0.5-0.7. g/cm3; some nano-calcium carbonate products have even lower bulk density and can reach about 0.28g/cm3. The packaging volume of the product can also roughly distinguish the heavy calcium and light calcium products. Generally, the heavy calcium products are mostly 25kg/bag, the product packaging volume is small, and the packaging volume of the same quality light calcium product is obviously larger, some nano calcium carbonate. The product is also available in 15kg/pack or 20kg/pack.
It is customary to use the sedimentation volume to measure the density of calcium carbonate. The sedimentation volume is the volume (ml) of calcium carbonate per unit mass after shaking in 100ml of water and standing for 3h. The larger the sedimentation volume, the smaller the particle size and density of the product. The lighter, the higher the product grade. The sedimentation volume of heavy calcium carbonate is 1.1-1.4 ml/g, the sedimentation volume of light calcium carbonate is 2.4-2.8 ml/g, and the sedimentation volume of nano-light calcium carbonate is 3.0-4.0 ml/g. Different light calcium carbonate, heavy calcium carbonate and nano calcium carbonate can be initially determined.
In fact, the true density of composite products of heavy calcium and light calcium is not much different. Generally, the true density of heavy calcium is 2.6-2.9 g/cm3, and the light calcium is 2.4-2.6 g/cm3. It is also said that the true density of the two is the same, but the bulk density is different. The reason is because the particle shape of light calcium is spindle-shaped or jujube-shaped, which takes up a large volume; while the appearance of heavy calcium is mostly blocky and the volume is relatively small.
Because heavy calcium products are relatively more impurities, the product whiteness is generally 89% to 93%, and very few products can reach 95%. Light calcium products are made of chemical synthesis, which removes a lot of impurities, and the purity of the products is very high. Therefore, the whiteness is mostly 92% to 95%, and some products can reach 96% to 97%. This is also the use of light calcium products for high-grade products. Or the main reason for filling light-colored products.
Different moisture content
The moisture content of heavy calcium products is generally 0.2% to
0.3%, and the moisture content is relatively low and stable, and some high-grade heavy calcium products can even reach about 0.1%. Ordinary light calcium products have a moisture content of 0.3% to 0.8%, and sometimes there is a certain fluctuation that is not stable. Traditionally, the distinction between heavy and light calcium is to test the moisture with a water-based instrument. When the water is as large as 1%, it is light calcium, and as little as 0.1% is heavy calcium.
Different pvc compound size
The pvc compound size of the heavy calcium product ranges from 0.5 to 45 um, and the pvc compound size of the product varies depending on the pulverizing equipment. The pvc compound size of ordinary light calcium products is generally 0.5-15 μm. It is difficult to accurately measure the shape of the pellet/compound/granule, which is generally a range; the nanometer calcium carbonate in light calcium has a finer compound size and generally has a size of 20 to 200 nm. The ordinary light calcium carbonate has a compound size of about 2,500 mesh, which can meet the performance requirements of PVC pipes and profiles. Therefore, from the viewpoint of compound size, lightly used calcium carbonate is commonly used for PVC pipes and profiles. In the past, due to the limitation of crushing equipment, heavy calcium carbonate could not reach this fineness. Now the particle size of heavy calcium carbonate can meet the needs completely, even thinner than light calcium carbonate, so now both PVC pipe and profile can be used. .
Light calcium is a lot of impurities after calcination of limestone. Generally, the whiteness is higher and the purity is higher. However, many domestic light calcium is incomplete due to the calcium oxide reaction, and there is residual lime smell. If used in the food industry, such as filling biscuits. There will be a sultry taste, but no heavy calcium. In addition, too much calcium oxide will cause the product to be alkaline in the aqueous system or the pH value is not well regulated, resulting in unstable products.
In addition, the phosphoric acid content of the two is different. In light calcium, sometimes a small amount of phosphoric acid needs to be added in order to adjust the pH value, and heavy calcium is not.
Different shapes of the pvc compounds
When viewed with a high power microscope, ordinary light calcium compound are relatively regular and usually have a spindle shape when fully dispersed. For light calcium carbonate, the pvc granule shape of the synthetic product can be artificially controlled, and a control agent can be added during the carbonization process to achieve control.
The currently developed control agents are inorganic acids, inorganic bases, organic acids (amino acids), alcohols, sugars, proteins and special structures of biopolymers, for example, with the double hydrophilic block polymer PEG-b-PMAA at different concentrations. And different pH values can be made into diamond, peanut, long rod, spherical and dumbbell-like appearance of carbonic acid, and then as a dendritic polymer polyaspartic acid can be made into a spiral shape of carbonic acid, such as adding an anion The dextran can obtain spherical calcium carbonate.
Due to the mechanical pulverization and classification of heavy calcium products, the pvc compound morphology is generally irregular shapes such as cubes, polygons, and cuboids. For different methods of processing heavy calcium, the microscopic shape of calcium carbonate is different. For example, calcium carbonate processed by ramming mill is spindle-shaped, and calcium carbonate processed by airflow is granular.
Calcium carbonate has a fixed crystal form for different calcium carbonate producing areas. The crushing and refining do not change the crystal form. Generally, the calcite is calcium hexagonal and the marble heavy calcium is cubic. For light calcium carbonate, in the specific carbonization preparation process, three kinds of crystalline calcium carbonate appear at different ratios at the same time. In order to obtain a single pure crystal form, it is necessary to control the molding process.
The three crystal forms of light calcium carbonate are described as follows:
(1) Calcite crystal form
The most stable crystal form of calcium carbonate belongs to the hexagonal crystal system. Under normal conditions, mineral calcium carbonate is stored in this crystal form. The calcium carbonate with such crystal form has large hiding power, high whiteness, good purity, heat resistance and resistance. Corrosion and chemical resistance.
(2) Aragonite crystal form
At room temperature, it is a metastable crystal form of calcium carbonate, belonging to the orthorhombic system. The calcium carbonate having such a crystal form has a high aspect ratio and is often used as a reinforcing composite material for polymers.
(3) Dolomite crystal form
The most unstable crystal form of calcium carbonate is only present in a small amount in the organic material, and will be automatically converted into calcite crystal or aragonite crystal in a short time. The calcium carbonate with such crystal form has life and health to the organism. It is very important to study that dendritic polymer dielectrics and certain low molecular weight polymer dielectrics can promote stable formation of vaterite crystals.
Different oil absorption values
Light calcium carbonate has an oil absorption value of 60-90 ml/100 mg, which is much larger than 40-60 ml/100 mg of heavy calcium carbonate. Therefore, it absorbs liquid and absorbs resin. If the formula contains liquid additives, oil absorption should be used. Small heavy carbonic acid, inorganic powder with large oil absorption value, will lead to increased coupling dose to be treated. For example, the oil absorption value of calcium carbonate is increased from 40 to 50ml/100mg, which will increase the amount of coupling agent by 30%. If you choose light carbonic acid in the PVC formula, you need to consume more liquid additives and PVC resin. Therefore, you should choose heavy calcium carbonate with low oil absorption value from the oil absorption value.
From the perspective of fluidity, the microstructure of light calcium carbonate is spindle shape, and its own oil absorption value is relatively large, which can promote the flow-promoting components such as lubricants, plasticizers, coupling agents, dispersants, etc. in the formulation. Absorption, so its fluidity is not as good as that of heavy calcium carbonate. Generally, the addition of more than 25 parts will seriously affect the fluidity, while the heavy calcium carbonate will be granulated to promote the fluidity. The amount of addition is not limited, in the PVC pipe formulation. If calcium carbonate is added in an amount of more than 25 parts, it is preferable to use heavy calcium carbonate from the viewpoint of fluidity.
The processing of heavy calcium carbonate is mainly achieved by mechanical crushing and grinding; the production of light calcium carbonate is prepared by chemical reaction precipitation, the latter is more complicated than the former process, and the requirements are correspondingly strict. Therefore, the same size of heavy calcium carbonate is about 30% cheaper than light calcium carbonate, if the performance allows the choice of heavy calcium carbonate is more economical and cheaper.
Different modification functions
There are subtle differences in the modification effect between heavy and light calcium carbonate. The heavy calcium carbonate has better tensile strength, while the light calcium carbonate has better impact strength and rigidity. Generally, the surface of the light calcium plastic is smoother. Moreover, the density will be lower; the use of heavy calcium plastics for better fluidity, and the smaller particle size of heavy calcium filled plastics are also better.
Different shades of color
The hue is the main hue of the color, and the hue is the afterglow of the color. Different calcium carbonates have different color shades, specifically white, red, cyan, and yellow. The reason is that the crystal forms are different, the powders of different crystal forms have different hue, and the calcium carbonate has three different crystals. Type, and therefore have a different hue.
For heavy calcium carbonate, the ground color of different origins of calcium carbonate is different, and the crushing and refining will not change. For example, the color of calcium carbonate in Sichuan is blue, the color of calcium carbonate in Guangxi is red, and the color of calcium carbonate in Jiangxi is blue. For light calcium carbonate, because it is artificially produced by chemical synthesis, it can control the type of crystal form during the synthesis process, and all of them can control the type of color light.
In the specific color matching, the color of the calcium carbonate should be consistent with the color of the main coloring agent. For example, calcium carbonate with blue color light will eliminate the tinting strength of the yellow pigment. It is also often used to use calcium carbonate with blue color light to eliminate the light color calcium carbonate in the yellow colored light with blue color. We usually use it to add PVC products to eliminate the yellow color of its own. This is one of the reasons why PVC used to choose to add light calcium carbonate instead of heavy calcium carbonate.
Different pH values
Light calcium carbonate has a pH of 9-10, while heavy calcium carbonate has a pH of 8-9, which means that the basic calcium carbonate of light calcium carbonate is stronger, in the combustion process of calcium carbonate composite products. In the middle, it is easier to absorb the acid decomposition gas. Therefore, the reason why the calcium carbonate composite product incinerates the low toxic gas is that the calcium carbonate itself is alkaline, and can absorb acid gases such as HCl and H2S generated by combustion, thereby eliminating the hidden danger of the dioxin produced by the acid property substance in response to chlorine.
Only when filled with inorganic calcium carbonate (CaCO3) can reduce the calorific value when incinerated, when it is incinerated, it will be turned into powder without dripping oil, no black smoke, no secondary pollution, and will not damage the incinerator, which is in line with environmental protection products. trend.
Therefore, considering the low release of toxic gas from incineration calcium carbonate composite products, the preferred light calcium carbonate has a more environmentally friendly social significance.
Conclusion: It is of great significance to correctly distinguish between light calcium carbonate and heavy calcium carbonate. It is important to choose the calcium carbonate suitable for your own formula design, so that you can select materials according to your needs, which can meet the performance and reduce the cost.