Summary:Calcium carbonate can not only reduce the raw material cost of rubber and plastic products, but also has the effect of improving certain properties of rubber an
Calcium carbonate can not only reduce the raw material cost of rubber and plastic products, but also has the effect of improving certain properties of rubber and plastic materials. Different types of calcium carbonate can significantly improve the performance of rubber and plastic materials when used properly, but light calcium carbonate (The distinction between Light Calcium Carbonate and ground calcium carbonate has always troubled most users, so this time we will use the most in-depth way to understand the distinction between them and how to choose them in the rubber and plastic industry.
1.1 Different source methods
Light calcium carbonate is chemically synthesized calcium carbonate, also known as Precipitated Calcium Carbonate (PCC), colloidal calcium carbonate or activated calcium carbonate, and can even produce nano-calcium carbonate, referred to as light calcium. It is made by calcining limestone raw materials to produce lime and carbon dioxide, and then adding water to digest the lime to produce milk of lime. Its main component is calcium hydroxide, and carbon dioxide is introduced to carbonize the milk of lime to produce calcium carbonate precipitation, which is dehydrated, dried and crushed, or made from sodium carbonate. It is produced by metathesis reaction with calcium chloride to produce calcium carbonate precipitate, which is prepared by dehydration, drying and crushing. Ground calcium carbonate is abbreviated as ground calcium, which is made by directly crushing natural calcite, marble, chalk and shells by mechanical methods.
Light calcium production process
1.2 Different bulk density
The most obvious difference between ground calcium and light calcium lies in the different bulk density of the products. The bulk density of ground calcium products is larger, generally 0.8～1.3g/cm³; while the bulk density of light calcium products is smaller, mostly 0.5～0.7 g/cm³; the bulk density of some nanometer calcium carbonate products is even lower, reaching about 0.28g/cm³. The packaging volume of the product can also roughly distinguish between ground calcium and light calcium products. Generally, ground calcium products are mostly 25kg/package, and the product packaging volume is small, while the packaging volume of light calcium products of the same quality is significantly larger. Some nano-calcium carbonates The product is also packaged in 15kg/bag or 20kg/bag.
We usually use the sedimentation volume to measure the density of calcium carbonate. The sedimentation volume is the volume (ml) that a unit mass of calcium carbonate has after shaking and standing for 3 hours in 100ml of water. 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 ground calcium carbonate is 1.1～1.4ml/g, the sedimentation volume of light calcium carbonate is 2.4～2.8ml/g, and the sedimentation volume of nano light calcium carbonate is 3.0～4.0ml/g. The difference can be preliminarily judged light calcium carbonate, ground calcium carbonate and nano calcium carbonate.
In fact, the true density of composite products of ground calcium and light calcium is not much different. Generally, the true density of ground calcium is 2.6-2.9 g/cm³, while that of light calcium is 2.4-2.6 g/cm³. Some people say that the real density is the same, but the bulk density is different. The reason is that the particle shape of light calcium is spindle-shaped or jujube-core shape, which occupies a relatively large volume; while the appearance of ground calcium is mostly blocky, and the volume is relatively small.
1.3 the whiteness is different
Because ground calcium products have relatively more impurities, the whiteness of the product is generally 89% to 93%, and a very small number of products can reach 95%. The light calcium products are made by chemical synthesis, removing a lot of impurities, and the product purity is very high, so the whiteness is mostly 92%-95%, and some products can reach 96%-97%. This is also the light calcium product mostly used for high-end products. Or the main reason for the filling of light-colored products.
1.4 Different moisture content
The moisture content of ground calcium products is generally 0.2% to 0.3%. The moisture content is relatively low and relatively stable. Some high-end ground calcium products can even reach about 0.1%. Ordinary light calcium products have a moisture content of 0.3% to 0.8%, and sometimes they may fluctuate and be unstable. Traditionally, the distinction between ground and light calcium is to test the water content with a water meter. The water content is close to 1% is light calcium, and the water content is less than 0.1% is ground calcium.
1.5 Different particle size
The particle size of ground calcium products ranges from 0.5 to 45um, and the particle size of the product 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, generally within 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, considering the particle size, traditional PVC pipes and profiles are light calcium carbonate. In the past, due to the limitation of crushing equipment, ground calcium carbonate could not reach this fineness. Now the particle size of ground calcium carbonate can fully meet the needs, even finer than light calcium carbonate, so now both PVC pipes and profiles can be used .
1.6 Different taste
Light calcium removes a lot of impurities after calcination of limestone. Generally speaking, the whiteness is higher and the purity is also higher. However, many domestic light calcium has a lime flavor due to the incomplete reaction of calcium oxide. If used in the food industry, such as filling biscuits, There will be a choking taste, but ground 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 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 in order to adjust the PH value in a reasonable range in light calcium, but ground calcium does not.
1.7 Different particle shapes
With a high-power microscope, the particles of ordinary light calcium are relatively regular, and they are usually spindle-shaped when fully dispersed, as shown in the figure below. For light calcium carbonate, the particle shape of the synthetic product can be controlled manually, and control agents can be added during the carbonization process to achieve control.
The currently developed control agents 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 polymer PEG-b-PMAA at different concentrations And under different pH values, it can be made into diamond, peanut, long rod, spherical and dumbbell-like carbonic acid, and then using dendritic polymer polyaspartic acid can be made into spiral-shaped carbonic acid, or adding anion Dextran can obtain spherical calcium carbonate.
Due to the mechanical crushing and classification of ground calcium products, the particle shapes are generally cubic, polygonal, rectangular and other irregular shapes, as shown in Figure 1. For different ground calcium processing methods, the microscopic shape of calcium carbonate is different. For example, the calcium carbonate processed by the beating mill has a spindle shape, and the calcium carbonate processed by the jet mill has a particle shape.
For ground calcium carbonate from different origins, calcium carbonate has a fixed crystal form, and crushing and refining will not change the crystal form. Generally, calcite ground calcium is hexagonal crystal type, and marble ground calcium is cubic crystal type. For light calcium carbonate, in the specific carbonization preparation process, three crystal forms of calcium carbonate appear at the same time in different proportions. In order to obtain a single pure crystal form, the molding process must be controlled.
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 exists in this crystal form. Calcium carbonate with this crystal form has large hiding power, high whiteness, good purity, heat resistance and resistance. Corrosion, chemical resistance and stability.
(2) Aragonite crystal form
At room temperature, it is a metastable crystal form of calcium carbonate, which belongs to the orthorhombic crystal system. Calcium carbonate with this crystal form has a high aspect ratio and is often used in polymer reinforcement composite materials.
(3) Vaterite crystal form
The most unstable crystal form of calcium carbonate, only a small amount exists in organic materials, and will automatically be converted into calcite crystal form or aragonite crystal in a short time. Calcium carbonate with this crystal form is beneficial to the life and health of organisms. Playing a very important role, studies have found that dendritic polymer dielectrics and certain low molecular weight polymer dielectrics can promote the formation of stable vaterite crystal forms.
1.8 Different oil absorption values
The oil absorption value of light calcium carbonate is 60-90 ml/100mg, which is far greater than the 40-60 ml/100mg of ground calcium carbonate. Therefore, the liquid absorption and resin absorption performance are very good. If the formula contains liquid additives, oil absorption should be used Small ground carbonic acid and inorganic powder with high oil absorption value will increase the amount of coupling that needs to be processed. For example, increasing the oil absorption value of calcium carbonate from 40 to 50ml/100mg will increase the amount of coupling agent by 30%. If you choose light calcium carbonate in the PVC formulation, you will consume more liquid additives and PVC resin. Therefore, considering the oil absorption value, you should choose ground calcium carbonate with low oil absorption value as much as possible.
1.9 Different liquidity
In terms of fluidity, the microstructure of light calcium carbonate is spindle-shaped, and its own oil absorption value is relatively large, and the components that promote fluidity in the formula such as lubricants, plasticizers, coupling agents, dispersants, etc. Absorption, so its fluidity is not as good as ground calcium carbonate. Generally, the addition of more than 25 parts will seriously affect the fluidity. The granular form of ground calcium carbonate can promote fluidity, and the addition amount is not limited. It is used in PVC pipe formulations. If calcium carbonate needs more than 25 parts, it is best to use ground calcium carbonate in terms of fluidity.
Toughness brother Note: Sometimes, technicians will prefer to use light calcium for performance, but in the end, due to the dispersion of the equipment, the performance of the rubber and plastic materials that use light calcium may be reduced, and higher fluidity is required. During , it cannot meet the requirements.
1.10 the price is different
The processing of ground calcium carbonate is mainly achieved through mechanical crushing and grinding; the production of light calcium carbonate is prepared by chemical reaction and precipitation. The latter has a much more complicated process and correspondingly stricter requirements. Therefore, ground calcium carbonate of the same particle size is about 30% cheaper than light calcium carbonate. If performance permits, it is more economical and cheaper to choose ground calcium carbonate.
1.11 different modified functions
The modification effects of ground and light calcium carbonate are slightly different. Ground 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 will be lower; the fluidity of processing with ground calcium plastic is better, and the performance of ground calcium filled plastic with smaller particle size is also better.
1.12 The controllability of color light is different
Hue is the main hue of the color, and color light is the afterglow of the color. Different calcium carbonate has different shades, specifically white, red, cyan, and yellow. The reason is the difference in crystal form. Powders of different crystal forms have different hue, and calcium carbonate has three different crystals. Type, so it has a different hue.
For ground calcium carbonate, the backlight color of calcium carbonate from different origins is different, and the crushing and refinement will not change. For example, the backlight color of Sichuan calcium carbonate is blue, the backlight color of Guangxi calcium carbonate is red, and the backlight color of Jiangxi calcium carbonate is blue. As for light calcium carbonate, because it is artificially made by chemical synthesis, the type of crystal formation can be controlled during the synthesis process, so the type of color light can be controlled.
In the specific color matching, the shade of calcium carbonate should be consistent with the color of the main colorant. For example, calcium carbonate with bluish shade will eliminate the coloring power of yellow pigments. Calcium carbonate with blue shade is often used to eliminate the blue shade of light calcium carbonate in yellow shade products. We usually add it to PVC products to eliminate its own yellow shade. This is also one of the reasons why PVC liked to add light calcium carbonate rather than ground calcium carbonate.
1.13 PH value is different
The PH value of light calcium carbonate is 9-10, and the PH value of ground calcium carbonate is 8-9, which means that the alkalinity of light calcium carbonate is stronger than that of ground calcium carbonate. In the combustion process of calcium carbonate composite products In, it is easier to absorb acid decomposition gas. Therefore, the reason why calcium carbonate composite products burn low-toxic gas is that calcium carbonate itself is alkaline, which can absorb acid gases such as HCl and H2S generated by combustion, and eliminate the hidden danger of dioxin produced by acidic substances when encountering chlorine.
Only when it is filled with inorganic calcium carbonate (CaCO3) can the calorific value be reduced during incineration, and it will turn into powder during incineration without dripping oil, emitting black smoke, generating no secondary pollution, and not damaging the incinerator, which is in line with the international standard of environmentally friendly products. trend.
Therefore, considering the low emission of toxic gas from the incineration of calcium carbonate composite products, the first choice of light calcium carbonate has a more environmentally friendly social significance.
Conclusion: It is of great significance to correctly distinguish between light calcium carbonate and ground calcium carbonate. It is of great significance to select calcium carbonate that suits you when designing specific formulas. In this way, materials can be selected according to needs, which can meet performance and reduce costs.
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