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Yuan lei small classroom | heavy calcium and light calcium practical in-depth comparison

Release time:

2024-01-29 09:36

 

Yuan lei small classroom | heavy calcium and light calcium practical in-depth comparison

 

Calcium carbonate can not only reduce the raw material cost of plastic products, but also has the effect of improving some properties of plastic materials. Different types of calcium carbonate can significantly improve the performance of matrix plastics when used properly, but the distinction between light calcium carbonate and heavy calcium carbonate has been bothering most users, so this time we will understand and distinguish them in the most in-depth way.

 

 

Different sources






Light calcium carbonate is chemically synthesized calcium carbonate, also known as precipitated calcium carbonate, colloidal calcium carbonate or active calcium carbonate, and can even produce nano calcium carbonate, referred to as light calcium. It is calcined limestone raw materials to generate lime and carbon dioxide, and then water is added to digest lime to generate lime milk. Its main component is calcium hydroxide, and carbon dioxide is introduced into carbonized lime milk to generate calcium carbonate precipitate, which is dehydrated, dried and crushed, or sodium carbonate and calcium chloride are decomposed to generate calcium carbonate precipitate, which is dehydrated, dried and crushed. Heavy calcium carbonate, referred to as heavy calcium, is directly crushed by mechanical methods of natural calcite, marble, chalk, shells, etc.



 

 

different bulk density






The most obvious difference between heavy calcium and light calcium lies in the different bulk density of the products. The bulk density of heavy calcium products is relatively large, generally 0.8~1.3g/cm. However, the bulk density of light calcium products is relatively small, mostly 0.5~0.7g/cm. The bulk density of some nano calcium carbonate products is even lower, reaching about 0.28g/cm. Heavy calcium and light calcium products can also be roughly distinguished by the packaging volume of the products. Generally, heavy calcium products are mostly 25 kg/bag, and the packaging volume of the products is smaller, while the packaging volume of light calcium products of the same quality is obviously larger. Some nano calcium carbonate products also use 15 kg/bag or 20 kg/bag packaging.

Traditionally, we often use sedimentation volume to measure the density of calcium carbonate. The sedimentation volume is the volume (ml) of calcium carbonate per unit mass after oscillating in 100ml of water and standing for 3 hours. The larger the sedimentation volume, the smaller the particle size, the lighter the density and 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. Light calcium carbonate, heavy calcium carbonate and nano calcium carbonate can be preliminarily judged by different sedimentation volumes.

In fact, the real density of composite products of heavy calcium and light calcium is not much different. Generally, the real density of heavy calcium is 2.6-2.9g/cm, while that of light calcium is 2.4-2.6g/cm. It is also said that the true density of the two is the same, but the bulk density is different. The reason is that the particle shape of light calcium is spindle-shaped or jujube-shaped, occupying a relatively large volume; while the appearance of heavy calcium is mostly massive, occupying a relatively small volume.




 

 

Whiteness of different sizes




Because heavy calcium products have more impurities, the whiteness of the products is generally 89% ~ 93%, and very few products can reach 95%. However, light calcium products are made by chemical synthesis, which removes many impurities and has high purity, so the whiteness is mostly 92% ~ 95%, and some products can reach 96% ~ 97%. This is also the main reason why light calcium products are mostly used for filling high-grade or light-colored products.




 

 

different moisture content






The moisture content of heavy calcium products is generally 0.2%~ 0.3%, and the moisture content is relatively low and stable at the same time. The moisture content of some high-grade heavy calcium products can even reach about 0.1%. Ordinary light calcium products moisture 0.3%~ 0.8%, sometimes there will be some fluctuations are not stable. Traditionally, the distinction between heavy and light calcium is to test water with a water instrument. Light calcium is when the water content is as large as close to 1%, and heavy calcium is when the water content is as small as below 0.1.



 

 

Different particle size






The particle size of heavy calcium products ranges from 0.5 to 45um, and the particle size of the products varies with different crushing equipment. The particle size of ordinary light calcium products is generally 0.5 ~ 15um, because the particle shape is spindle shape, it is difficult to accurately determine, 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 about 2500 mesh, which can meet the performance needs of PVC pipes and profiles. Therefore, light calcium carbonate is traditionally selected for PVC pipes and profiles from the particle size. 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 fully meet the needs, even finer than light calcium carbonate, so now both PVC pipes and profiles can be selected.




 

 

Taste different






Light calcium has a high whiteness and purity due to the removal of many impurities after limestone calcination. However, a lot of light calcium in China has a lime taste due to incomplete reaction of calcium oxide. If it is used in the food industry, such as filling biscuits, it will have a choking taste, while 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 is not well adjusted, resulting in instability of the finished product.

In addition, the phosphoric acid content of the two is different, light calcium sometimes in order to adjust the PH value in a reasonable range need to add a small amount of phosphoric acid, and heavy calcium is not.




 

 

Different particle shapes






With a high-powered microscope, the particles of ordinary light calcium are more regular, and are usually spindle-shaped when fully dispersed, as shown in Figure 2. For light calcium carbonate, the particle shape of the synthetic product can be artificially controlled, and the control agent can be added during the carbonization process to achieve control.

At present, the developed control agents include inorganic acids, inorganic bases, organic acids (amino acids), alcohols, sugars, proteins and biopolymers with special structures. For example, carbonic acid with diamond shape, peanut shape, long rod shape, spherical shape and dumbbell shape can be made by using double hydrophilic block polymer PEG-b-PMAA at different concentrations and different pH values. For example, carbonic acid with spiral shape can be made by using dendritic polymer polyaspartic acid, as another example, spherical calcium carbonate can be obtained by adding anionic dextran.

Heavy calcium products due to the use of mechanical crushing and classification, the particle shape is generally cube, multi-prism, cuboid and other irregular forms, as shown in Figure 1. For different heavy calcium processing methods, the microscopic shape of calcium carbonate is different, for example, the calcium carbonate processed by rein grinding is spindle-shaped, and the calcium carbonate processed by air flow grinding is particle-shaped.

For heavy calcium carbonate from different producing areas, calcium carbonate has a fixed crystal form, and crushing and refining will not change the crystal form. Generally, heavy calcium of calcite is hexagonal crystal form, and heavy calcium of marble is cubic crystal form. For light calcium carbonate, in the specific carbonization preparation process, three crystal forms of calcium carbonate appear at different proportions at the same time, and to obtain a single pure crystal form, it is necessary to control the molding process.

 

The three crystal forms of light calcium carbonate are introduced 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. Calcium carbonate with such crystal form has large covering power, high whiteness, good purity, heat resistance, corrosion resistance and chemical resistance.

(2) arable crystal form

At room temperature, it is a metastable crystal form of calcium carbonate, which belongs to the orthorhombic crystal system, and the calcium carbonate with such crystal form has a high aspect ratio, and is commonly used in polymer reinforcement composite materials.

(3) Vaterite crystal type

The most unstable crystal form of calcium carbonate exists only in a small amount in organic materials, and will automatically convert to calcite crystal form or aragonite crystal in a short time. Calcium carbonate with such crystal form plays a very important role in biological life and health. It is found that dendrimer dielectrics and some low molecular weight polymer dielectrics can promote the formation of stable vaterite crystal form.




 

 

Different oil absorption value






The oil absorption value of light calcium carbonate is 60-90 ml/100mg, which is far greater than 40-60 ml/100mg of heavy calcium carbonate. Therefore, the liquid absorption and resin absorption properties are very high. If the formula contains liquid additives, heavy carbonic acid with small oil absorption and inorganic powder with large oil absorption value should be selected, which will lead to an increase in the amount of coupling agent to be treated. For example, the oil absorption value of calcium carbonate will increase from 40 to 50ml/100mg, it will lead to an increase of 30% in the amount of coupling agent. If light carbonic acid is selected in PVC formula, more liquid additives and PVC resin will be consumed. Therefore, heavy calcium carbonate with low oil absorption value should be selected as much as possible from the oil absorption value.




 

 

Liquidity is different






From the perspective of fluidity, the microstructure of light calcium carbonate is spindle-shaped, and its own oil absorption value is relatively large, which can absorb the components that promote flow in the formula, such as lubricants, plasticizers, coupling agents, dispersants, etc., so its fluidity is not as good as heavy calcium carbonate. Generally, the fluidity will be seriously affected if the addition amount exceeds 25 parts, while heavy calcium carbonate can promote fluidity if it is granular, and the addition amount is not limited, in the PVC pipe formula, if the addition of calcium carbonate needs more than 25 copies, it is best to choose heavy calcium carbonate from the perspective of fluidity.



 

Different prices






The processing of heavy calcium carbonate is mainly realized by mechanical crushing and grinding. The production of light calcium carbonate is prepared by chemical reaction precipitation. The latter is much more complicated than the former in process and has stricter requirements. Therefore, heavy calcium carbonate with the same particle size is about 30% cheaper than light calcium carbonate. If the performance allows, heavy calcium carbonate is more economical and cheaper.



 

 

Different modification function






There are subtle differences between the modification effects of heavy and light calcium carbonate. Heavy calcium carbonate has better tensile strength, while light calcium carbonate has better impact strength and rigidity. Generally, the plastic surface with light calcium is smoother and the density is lower. The processing fluidity of heavy calcium plastic is better, and the performance of heavy calcium filled plastic with smaller particle size is also better.



 

 

The controllable degree of color light is different






Hue is the dominant hue of a color, while color light is the afterglow of a color. Different calcium carbonate has different color light, specifically white, red, cyan, yellow, the reason for the different crystal type, different crystal type powder has different hue, calcium carbonate has three different crystal type, so it has different hue.

For heavy calcium carbonate, the background color of calcium carbonate from different producing areas is different, and the crushing and refinement will not change. Such as Sichuan calcium carbonate background color blue, Guangxi calcium carbonate background color red, Jiangxi calcium carbonate background color cyan and so on. For light calcium carbonate, because it is made by chemical synthesis, the type of crystal form can be controlled in the process of synthesis, and the type of color light can be controlled.

In specific color matching, the color of calcium carbonate should be consistent with the color of the main colorant. For example, calcium carbonate with blue color light will eliminate the coloring power of yellow pigment. Calcium carbonate with blue color light is also often used to eliminate light calcium carbonate with blue color light in yellow color light products. We generally use it to add PVC products to eliminate its own yellow color light. This is also one of the reasons why PVC likes to add light calcium carbonate instead of heavy calcium carbonate.




 

PH value of different sizes






The PH value of light calcium carbonate is 9-10, while the PH value of heavy calcium carbonate is 8-9, that is to say, the alkalinity of light calcium carbonate is stronger than that of heavy calcium carbonate, and it is easier to absorb acidic decomposition gas during the combustion process of calcium carbonate composite products. Therefore, the reason why calcium carbonate composite products incinerate low-toxic gas is that calcium carbonate itself is alkaline, which can absorb acid gases such as HCl and H2S produced by combustion, and eliminate the hidden danger of dioxin generated by acid energy substances in case of chlorine elements.

Only filled with inorganic calcium carbonate (CaCO3) can reduce the calorific value when incinerated. When incinerated, the powder does not drop oil, does not emit black smoke, has no secondary pollution, and does not damage the incinerator, which is in line with the international trend of environmental protection products.

Therefore, from the incineration of calcium carbonate composite products on the low release of gas, the preferred light calcium carbonate has a more environmentally friendly social significance.


 

Conclusion: It is of great significance to correctly distinguish light calcium carbonate and heavy calcium carbonate, and to select the suitable calcium carbonate in the specific formula design, so that the material can be selected according to the needs, which can meet the performance and reduce the cost.

 

Contrast, calcium carbonate, different, product, light, can, general, density, with, volume

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