In-depth comparison of the properties of Guangxi heavy calcium carbonate and Guangxi light calcium carbonate, and how to choose calcium carbonate in the rubber and plastics industry? Guangxi calcium carbonate can not only reduce the raw material cost of rubber and plastic products, but also improve certain properties of rubber and plastic materials. Different types of calcium carbonate, when used properly, can significantly improve the performance of rubber and plastic materials. However, the distinction between light calcium carbonate and heavy calcium carbonate has always plagued most users. Guangxi calcium carbonate manufacturer Xiangfa Powder takes the most in-depth approach to understanding and distinguishing them, and how to choose them in the rubber and plastics industry.

Guangxi Heavy calcium and Guangxi In-depth comparison of the performance of heavy and light calcium carbonate: How to choose calcium carbonate in the rubber and plastics industry? Guangxi Calcium carbonate not only reduces the raw material cost of rubber and plastic products, but also improves certain properties of rubber and plastic materials. Different types of calcium carbonate, when used properly, can significantly improve the performance of rubber and plastic materials. However, the distinction between light calcium carbonate and heavy calcium carbonate has always plagued most users. Guangxi Xiangfa Powder, a calcium carbonate manufacturer, has conducted the most in-depth research to understand the differences between them and how to choose them in the rubber and plastics industry.

　　I. Guangxi In-depth comparison of the practicality of heavy calcium and Guangdong light calcium

　　1.1 Different sources

　　 Guangxi Light calcium carbonate is chemically synthesized calcium carbonate, also known as precipitated calcium carbonate (PCC), colloidal calcium carbonate, or active calcium carbonate. Nanometer calcium carbonate can even be produced. It is also called light calcium. It is made by calcining limestone to produce lime and carbon dioxide, then adding water to digest the lime to produce lime milk (the main component is calcium hydroxide), and carbonating the lime milk with carbon dioxide to produce calcium carbonate precipitate. It is then dehydrated, dried, and pulverized. Alternatively, it can be produced by a double decomposition reaction between sodium carbonate and calcium chloride to generate calcium carbonate precipitate, which is then dehydrated, dried, and pulverized. Heavy calcium carbonate, abbreviated as heavy calcium, is made by directly crushing natural calcite, marble, chalk, shells, etc., using mechanical methods.

　　 Guangxi Light calcium production process

　　1.2 Different bulk densities

　　 Guangxi The most obvious difference between heavy calcium and Guangdong light calcium lies in the difference in bulk density. The bulk density of heavy calcium products is generally higher, ranging from 0.8 to 1.3 g/cm³; while the bulk density of light calcium products is lower, ranging from 0.5 to 0.7 g/cm³; some nano-calcium carbonate products have even lower bulk densities, reaching around 0.28 g/cm³. The packaging volume of the product can also roughly distinguish between heavy calcium and light calcium products. Heavy calcium products are generally 25 kg/bag, with a smaller packaging volume, while light calcium products of the same weight have a significantly larger packaging volume. Some nano-calcium carbonate products are also packaged in 15 kg/bag or 20 kg/bag.

　　Conventionally, we use the sedimentation volume to measure the size of the calcium carbonate density. The sedimentation volume is the volume (ml) occupied by a unit mass of calcium carbonate in 100 ml of water after shaking and standing for 3 hours. The larger the sedimentation volume, the smaller the particle size, the lighter the density, and the higher the grade of the product. 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. The difference in sedimentation volume can be used to preliminarily identify light calcium carbonate, heavy calcium carbonate, and nano-calcium carbonate.

　　Actually Guangxi The actual density of the composite products of heavy calcium and Guangdong light calcium is not much different. The actual density of heavy calcium is generally 2.6-2.9 g/cm³, while that of light calcium is 2.4-2.6 g/cm³. Some people say that the actual densities of the two are the same, only the bulk density is different. The reason is that the particles of light calcium are spindle-shaped or jujube-shaped, occupying a larger volume; while the appearance of heavy calcium is mostly block-shaped, occupying a smaller volume.

　　1.3 Different whiteness

　　Because Guangxi Heavy calcium products contain relatively more impurities, so their whiteness is generally 89% to 93%, with very few products reaching 95%. Light calcium products, because they are chemically synthesized, have removed many impurities and have high purity, so their whiteness is mostly 92% to 95%, and some products can reach 96% to 97%. This is the main reason why light calcium products are used in high-grade or light-colored products.

　　1.4 Different moisture content

　　 Guangxi The moisture content of heavy calcium products is generally 0.2% to 0.3%, which is relatively low and stable. Some high-grade heavy calcium products can even reach 0.1%. The moisture content of ordinary light calcium products is 0.3% to 0.8%, and sometimes there are fluctuations and instability. Traditionally, the distinction between heavy and light calcium is based on moisture content testing using a moisture meter. If the moisture content is close to 1%, it is light calcium; if it is below 0.1%, it is heavy calcium.

　　1.5 Different particle sizes

　　 Guangxi The particle size of heavy calcium products ranges from 0.5 to 45 μm, depending on the pulverization equipment. The particle size of ordinary light calcium products is generally 0.5 to 15 μm. Because of their spindle shape, it is difficult to accurately determine the particle size, so it is usually a range. The particle size of nano-calcium carbonate in light calcium is even finer, generally ranging from 20 to 200 nm. The particle size of ordinary Guangdong light calcium carbonate is generally around 2500 mesh, which can meet the performance requirements of PVC pipes and profiles. Therefore, traditionally, PVC pipes and profiles have used light calcium carbonate. In the past, due to limitations in pulverization equipment, Guangxi Heavy calcium carbonate could not reach this fineness, but now Guangxi The particle size of heavy calcium carbonate can fully meet the requirements, and it can even be finer than light calcium carbonate. Therefore, both heavy and light calcium carbonate can now be used for PVC pipes and profiles.

　　1.6 Different tastes

　　 Guangxi Light calcium generally has higher whiteness and purity because many impurities are removed after the calcination of limestone. However, much of the domestically produced light calcium has a lime taste due to incomplete calcium oxide reaction. If used in the food industry, such as filling biscuits, it will have a pungent taste, while Guangxi Heavy calcium does not. In addition, excessive calcium oxide can cause the product to be alkaline in aqueous systems or difficult to adjust the pH value, resulting in unstable finished products.

　　In addition, the phosphorus content of the two is different. Sometimes, a small amount of phosphoric acid is added to light calcium to adjust the pH value to a reasonable range, while heavy calcium does not.

　　1.7 Different particle shapes

　　Under a high-power microscope, the particles of ordinary light calcium carbonate are relatively regular, and usually appear spindle-shaped when fully dispersed, as shown in the figure below. For light calcium carbonate, the particle shape of the synthetic product can be artificially controlled, and control agents can be added during the carbonation process to achieve this control.

 

 

　　Currently developed control agents include inorganic acids, inorganic bases, organic acids (amino acids), alcohols, sugars, proteins, and biopolymers with special structures. For example, amphiphilic block copolymers PEG-b-PMAA can be used to produce rhombohedral, peanut-shaped, rod-shaped, spherical, and dumbbell-shaped calcium carbonates at different concentrations and pH values. Branched polyaspartic acid can be used to produce spiral-shaped calcium carbonate, and the addition of anionic dextran can yield spherical calcium carbonate.

　　 Guangxi Heavy calcium carbonate products, due to mechanical crushing and grading, generally have irregular shapes such as cubes, polyhedrons, and rectangular parallelepipeds, as shown in Figure 1. For different heavy calcium carbonate processing methods, the microscopic shape of calcium carbonate is different; for example, calcium carbonate processed by a Raymond mill is spindle-shaped, while that processed by an air-flow mill is granular.

　　For Guangxi Heavy calcium carbonate from different origins has a fixed crystal form, and crushing and refinement do not change the crystal form. Generally, calcite heavy calcium carbonate is hexagonal, and marble heavy calcium carbonate is cubic. For light calcium carbonate, during the specific carbonation preparation process, three types of calcium carbonate crystals appear in different proportions. To obtain a single, pure crystal form, the forming process must be controlled.

　　 Guangxi The three crystal forms of light calcium carbonate are introduced as follows:

　　(1) Calcite crystal form

　　 Guangxi The most stable crystal form of calcium carbonate, belonging to the hexagonal system. Under normal conditions, mineral calcium carbonate exists in this crystal form. Calcium carbonate with this crystal form has high covering power, high whiteness, good purity, heat resistance, corrosion resistance, and chemical stability.

　　(2) Aragonite crystal form

　　At room temperature, it is a metastable crystal form of calcium carbonate, belonging to the orthorhombic system. Calcium carbonate with this crystal form has a high length-to-diameter ratio and is often used in reinforcing composite materials for polymers.

　　(3) Vaterite crystal form

　　The least stable crystal form of calcium carbonate. It only exists in small amounts in organic materials and automatically transforms into calcite or aragonite in a short time. Calcium carbonate with this crystal form plays a very important role in the life and health of organisms. Studies have found that branched polymer dielectrics and some low-molecular-weight polymer dielectrics can promote the formation of stable vaterite crystals.

　　1.8, Different oil absorption values

　　The oil absorption value of light calcium carbonate is 60-90 ml/100mg, which is much larger than the 40-60 ml/100mg of heavy calcium carbonate. Therefore, it has good liquid absorption and resin absorption properties. If the formulation contains liquid auxiliaries, heavy calcium carbonate with a low oil absorption value should be selected. Inorganic powders with high oil absorption values will lead to an increase in the amount of coupling agent required. For example, if the oil absorption value of calcium carbonate increases from 40 to 50 ml/100mg, the amount of coupling agent will increase by 30%. In PVC formulations, if light calcium carbonate is selected, more liquid auxiliaries and PVC resin will be consumed. Therefore, from the perspective of oil absorption value, heavy calcium carbonate with a low oil absorption value should be selected as much as possible.

　　1.9, Different fluidity

　　From the perspective of fluidity, Guangxi Light calcium carbonate has a spindle-shaped microstructure, and its oil absorption value is relatively high, so it can absorb components that promote flow in the formulation, such as lubricants, plasticizers, coupling agents, and dispersants. Therefore, its fluidity is not as good as that of heavy calcium carbonate. Generally, if the addition amount exceeds 25 parts, the fluidity will be seriously affected. Heavy calcium carbonate is granular and can promote fluidity, and the addition amount is unlimited. In PVC pipe formulations, if the addition of calcium carbonate needs to exceed 25 parts, heavy calcium carbonate should be selected from the perspective of fluidity.

　　 Guangxi Note from calcium carbonate manufacturers: Sometimes, performance technicians may prefer to use light calcium carbonate, but due to equipment dispersion issues, the performance of the final elastomer material may decrease, and the requirements may not be met when high fluidity is required.

　　1.10, Different prices

　　 Guangxi Heavy calcium carbonate is mainly processed by mechanical crushing and grinding; light calcium carbonate is produced by chemical reaction precipitation. The latter process is much more complex than the former, and the requirements are correspondingly stricter. Therefore, heavy calcium carbonate of the same particle size is about 30% cheaper than light calcium carbonate. If performance permits, heavy calcium carbonate is more economical.

　　1.11, Different modification functions

　　Heavy Guangxi The modification effects of heavy and light calcium carbonate have subtle differences. Heavy calcium carbonate is better for tensile strength, while light calcium carbonate is better for impact strength and rigidity. Plastics using light calcium carbonate generally have a smoother surface and lower density; plastics using heavy calcium carbonate have better processing fluidity, and heavy calcium carbonate with smaller particle sizes also results in better plastic performance.

　　1.12, Different controllable color light

　　Hue is the main color tone, while color light is the residual light of the color. Different calcium carbonates have different color lights, specifically white, red, cyan, and yellow. The reason is the difference in their crystal forms. Different crystal forms of powder have different hues, and calcium carbonate has three different crystal forms, so it also has different hues.

　　For Guangxi For heavy calcium carbonate, the base color emitted by calcium carbonate from different origins is different, and crushing and refinement will not change it. For example, Sichuan calcium carbonate has a blue base color, Guangxi calcium carbonate has a red base color, Jiangxi calcium carbonate has a cyan base color, and so on. For light calcium carbonate, because it is artificially made by chemical synthesis, the type of crystal produced can be controlled during the synthesis process, so the type of color light can be controlled.

　　During specific color matching, Guangxi The color of calcium carbonate should be consistent with the hue of the main colorant. For example, calcium carbonate with a blue hue will eliminate the coloring power of yellow pigments. Calcium carbonate with a blue hue is also often used to eliminate the yellow hue in products. Lightweight calcium carbonate with a blue hue is commonly added to PVC products to eliminate their inherent yellow hue. This is one of the reasons why PVC used to prefer adding Guangdong lightweight calcium carbonate instead of heavy calcium carbonate.

　　1.13 Different pH values

　　 Guangxi The pH value of lightweight calcium carbonate is 9-10, while that of heavy calcium carbonate is 8-9. This means that lightweight calcium carbonate is more alkaline than heavy calcium carbonate, and it is easier to absorb acidic decomposition gases during the combustion of calcium carbonate composite products. Therefore, the reason why calcium carbonate composite products burn with low-toxicity gas is that calcium carbonate itself is alkaline and can absorb acidic gases such as HCl and H2S produced during combustion, eliminating the risk of dioxin generation from acidic substances encountering chlorine elements.

　　Only when inorganic calcium carbonate (CaCO3) is filled can the calorific value be reduced during incineration. During incineration, it turns into powder without dripping oil or emitting black smoke, producing no secondary pollution, and does not damage the incinerator, conforming to the international trend of environmentally friendly products.

　　Therefore, considering the low release of toxic gases from the incineration of calcium carbonate composite products, lightweight calcium carbonate is the preferred choice and has greater environmental significance.

　　Conclusion: Correctly distinguishing between lightweight and heavy calcium carbonate is of great significance in the specific formula design to select suitable calcium carbonate. This allows for the selection of materials according to needs, meeting performance requirements while reducing costs.

　　II. How to choose lightweight or heavy calcium carbonate

　　2.1 Differences in application effects between lightweight and heavy calcium carbonate

　　Some believe that heavy calcium carbonate accounts for the majority of fillers used in foreign plastic products, with a classic ratio of 14-18:1. Therefore, the plastics industry should try to use heavy calcium carbonate instead of lightweight calcium carbonate.

　　Someone conducted a comparative experiment of adding heavy and lightweight calcium carbonate to rubber. The conclusion is that under the same dosage and processing conditions, heavy calcium carbonate is easier to mix and process, easier to disperse in the rubber matrix, and has higher tensile strength than lightweight calcium carbonate. However, rubber filled with heavy calcium carbonate has greater shrinkage and a rougher surface. The heavy calcium carbonate used was -400 mesh, and its price was only half that of the control lightweight calcium carbonate, resulting in significant economic benefits.

　　The use of heavy and lightweight calcium carbonate in plastic products is similar to that in rubber products. Some manufacturers have reported that under the same conditions, using -400 mesh heavy calcium carbonate instead of lightweight calcium carbonate has obvious advantages for products sold by weight. However, for products sold by length, area, or number, heavy calcium carbonate does not have an advantage over lightweight calcium carbonate.

　　For example, for pipes, with the same weight of material and the same filling amount, the length of the product obtained is different. Pipes filled with heavy calcium carbonate are a few thousandths of a millimeter shorter than those filled with lightweight calcium carbonate, which accumulates to a considerable amount. For artificial leather or synthetic leather measured by area, the difference in area is also noticeable. Therefore, plastic product processing plants do not easily abandon the use of lightweight calcium carbonate.

　　2.2 Heavy calcium carbonate or lightweight calcium carbonate? It cannot be generalized.

　　From an academic perspective, heavy and lightweight calcium carbonate have many differences, such as different crystal forms, specific surface areas, and oil absorption values. Moreover, the particle size and distribution of -400 mesh heavy and lightweight calcium carbonate are significantly different. In the plastic matrix, how heavy or lightweight calcium carbonate particles exist, whether they are individually distributed in the matrix macromolecules or in clusters, in a loosely aggregated form distributed in the matrix resin, and the interfacial state between these particles and the resin macromolecules, directly affects the mechanical properties of the material.

　　The use of heavy or lightweight calcium carbonate in plastic products cannot be generalized. It should be decided based on a comprehensive consideration of technical and economic factors, while fully utilizing the advantages of each.

　　For example, in the production of polyvinyl chloride artificial leather, the manufacturing process can be divided into coating, calendering, and extrusion methods. The coating method uses polyvinyl chloride paste resin and requires the addition of a large amount of plasticizer. The oil absorption value of lightweight calcium carbonate is 4-5 times higher than that of heavy calcium carbonate. Therefore, using lightweight calcium carbonate requires more plasticizer than heavy calcium carbonate to achieve the same flexibility. If the amount of plasticizer can be reduced, using heavy calcium carbonate may be more economical.

　　For example, in unidirectional stretching products such as polypropylene woven bags, woven fabrics, and strapping, there is no significant difference in length when using heavy or lightweight calcium carbonate as a filler. Studies have found that filler particles are mostly located in the gaps between macromolecules formed by stretching. After several times of stretching and rapid cooling, the morphology of macromolecules is quickly frozen, and the true density of lightweight and heavy calcium carbonate is almost the same, so the effect on the final length of the product is not obvious. On the other hand, heavy calcium carbonate has better processing fluidity and a much lower price, so it dominates in such unidirectional stretching products.

　　In addition, China's technology for the molding and processing of plastic profiles for doors and windows was introduced from abroad. Along with the introduction of production lines, product formulas were also introduced, with lightweight calcium carbonate as the filler. It should be pointed out that the formulas provided by foreign countries are scientific, and the purpose of adding calcium carbonate is to improve the overall performance of the profiles, not to use cheap raw materials to reduce costs.

　　Now, replacing lightweight calcium carbonate with heavy calcium carbonate will inevitably face several problems:

　　① What particle size range of heavy calcium carbonate should be used to replace the currently used lightweight calcium carbonate?

　　② After equivalent replacement, will the material properties of the profiles change significantly? Will the appearance of the product be affected?

　　③ After equivalent replacement, should the processing equipment, die head, and process conditions be adjusted accordingly?

　　④ After equivalent replacement, due to the good processing performance of heavy calcium carbonate, can the material flow resistance (reflected in the change of screw torque) be reduced, thereby saving energy or increasing the speed to increase production rate?

　　⑤ From the perspective of gains and losses, is it worthwhile?

　　The production of plastic profiles is gradually developing towards large-scale and mass production. The replacement of a raw material affects the quality and stability of a large number of products, so plastic product processing plants will not easily replace a component in the formula.

　　2.3、 Guangxi How can calcium carbonate be better applied in the plastics industry?

　　 Guangxi Calcium carbonate has become one of the indispensable raw materials in the plastics industry. The rapid development of the calcium carbonate industry has provided material conditions for the plastics industry to choose and explore, and its good application in plastic materials has also guided the development of the calcium carbonate industry.

　　Here, we hope that powerful enterprises in the calcium carbonate industry will not only produce good calcium carbonate products, but also further develop new plastic materials and products using calcium carbonate as the main raw material, instead of simply producing a certain product and forcing the plastics industry to use it.

　　In addition, it should be said that the plastics industry is not short of experts and technical personnel in the field of filling and modification. However, for many plastics enterprises, many enterprises still do not specifically use the knowledge of fillers and filling modification. If our calcium carbonate industry personnel understand how to use their products in plastic processing products, and independently develop deep-processed products with calcium carbonate as the main raw material, and output the application technology of calcium carbonate while selling calcium carbonate, then the application prospect of calcium carbonate products in China will be broader.

　　2.4、 Guangxi How is calcium carbonate applied in the thermoplastic elastomer industry?

　　 Guangxi Calcium carbonate is commonly used in the thermoplastic elastomer industry, especially in the TPE-S and TPV industries. Generally, more heavy calcium carbonate is used in TPE-S, while more light calcium carbonate is used in the TPV industry. Generally speaking, the requirements for calcium carbonate for injection-grade thermoplastic elastomers are lower than those for extrusion-grade ones. From the perspective of cost and dispersion effect, heavy calcium carbonate is generally preferred. If performance is more important, light calcium carbonate is preferred.