In recent years, with the rapid development of calcium carbonate processing technology and the rapid development of calcium carbonate surface treatment technology, it can not only reduce the cost of products but also improve many properties of products, significantly improve the overall performance of materials and increase the added value of products.
Common modification effects of calcium carbonate
(1) Improve the rigidity of composite materials
Calcium carbonate can improve the flexural strength, flexural modulus, hardness, wear resistance and other properties of composite materials. For plastic films, the rigidity of composite materials can significantly increase the film’s stiffness, which is beneficial to the smoothness and curling of the film.
(2) Improve the dimensional stability of composite materials
The improvement of dimensional stability is reflected in reduced shrinkage, reduced warpage, reduced linear expansion coefficient, reduced creep, favorable isotropy, etc. Calcium carbonate filling can significantly improve dimensional stability.
(3) Improve the heat resistance of composite materials
Calcium carbonate can improve the thermal stability of composite materials because it absorbs substances that promote decomposition. For example, the thermal stability of PBAT/calcium carbonate composites is significantly higher than that of pure PBAT. For another example, adding light calcium carbonate to PVC products can absorb the hydrogen chloride produced by decomposition and greatly improve the processing thermal stability of PVC.
(4) Improve the tear resistance of the film
General plastic films have the disadvantages of high longitudinal strength and low transverse strength, especially PBS, PLA, and PHA aliphatic polyester films. After adding calcium carbonate, the isotropy of the composite material can be increased, and the tear resistance can be significantly improved.
Special modification properties of calcium carbonate
(1) Effect on tensile and impact properties
Not all calcium carbonate can improve plastic films’ tensile strength and impact strength, which are affected by the particle size of calcium carbonate and surface treatment.
Influence of particle size: Different particle sizes of calcium carbonate have different modification effects on plastics, as shown in Table 1. Generally, the particle size is below 1000 mesh, which is mainly used for incremental modification; the particle size is between 1000 and 3000 mesh, and the addition amount is below 10%, which has a certain modification effect; the particle size is above 5000 mesh, which is functional calcium carbonate and has Obvious modification effect can improve tensile strength and impact strength. Although nanoscale calcium carbonate has finer particle size, it is currently difficult to disperse and can only achieve the same modification effect as 8000 mesh calcium carbonate.
| Coupling agent treatment of heavy calcium carbonate (30%) mesh size | 2000 | 1250 | 800 | 500 |
| Melt flow index (g/10min) | 4.0 | 5.0 | 5.6 | 5.5 |
| Tensile strength (MPa) | 19.3 | 18.4 | 18.7 | 18.1 |
| Elongation at break (%) | 422 | 420 | 341 | 367 |
| Bending strength (MPa) | 28 | 28.6 | 28.2 | 28.4 |
| Flexural modulus (MPa) | 1287 | 1291 | 1303 | 1294 |
| Izod impact strength (J/m) | 113 | 89 | 86 | 78 |
It can be seen from the table that as the particle size of calcium carbonate becomes finer, the impact strength, tensile strength, and elongation at break increase, the flexural strength and flexural modulus are the same, but the fluidity decreases.
Effect of surface treatment: If the surface treatment is good, calcium carbonate with appropriate particle size can improve the tensile strength and impact strength of composite materials. In recent years, with the continuous development of organic/inorganic composite theory, CaCO3 has changed from a simple filler to a new functional filler material. For example, the notched impact strength of homopolymer PP/CaCO3 composite materials made of calcium carbonate can be more than double that of base plastic.
(2) Smoke suppression effect during combustion
CaCO3 has an excellent smoke suppression effect. The principle is that it can react with (capture) the hydrogen halide in the smoke to generate stable CaCl2. Therefore, CaCO3 can be used as a smoke suppressant for polymers that produce hydrogen halide when burning, such as vinyl chloride, chlorosulfonated polyethylene, chloroprene rubber, etc. Since the combustion reaction is a solid-gas heterogeneous reaction and can only occur on the surface of solid particles, the particle size of CaCO3 particles becomes an important factor in the smoke suppression effect. Only tiny particles have a much larger specific surface area. The finer the calcium carbonate particle size, the better the smoke suppression effect.
(3) Anti-adhesive agent
The blown cylindrical film containing calcium carbonate has good opening properties and will not cause adhesion when curled. The calcium carbonate acts as an opening agent.
(4) Increase thermal conductivity rate
The addition of calcium carbonate increases the thermal conductivity rate of the film, thereby cooling the film bubble of the blown film faster, improving production efficiency and increasing the output of the extruder. Taking 25% light calcium carbonate added to a PVC sheet as an example, it only takes 3.5 seconds to heat to 200°C, while a pure PVC sheet takes 10.8 seconds, and the thermal conductivity rate is increased by as much as 3 times.
(5) Improve liquidity
Calcium carbonate can improve the fluidity of the composite system, reduce melt viscosity and extruder torque, increase extruder output, and improve production efficiency. Different types of calcium carbonate have different effects on flow. The order of fluidity of specific composite materials is large calcite calcium carbonate > marble calcium carbonate, dolomite calcium carbonate > small calcite calcium carbonate > light calcium carbonate.
(6) Color matching performance
Substitute some white pigments: High-whiteness calcium carbonate can replace white pigments such as titanium dioxide, thereby saving the content of high-priced titanium dioxide. Large calcite calcium carbonate is the first choice because of its high whiteness and large covering power. The reason why calcium carbonate can become a white pigment is mainly because it has a certain hiding power. The hiding power of paint refers to the minimum amount of paint required to apply the color paint evenly on the surface of an object so that the background color no longer appears. Using g/m2 means that the hiding power of various colorants in coatings is shown in Table 2:
| Pigment name | Hiding power (g/cm²) |
| Counterpoint red (light tone) | 18.1-16.3 |
| Counterpoint red (dark tone) | 17.1-15.0 |
| Lake red C | 23.8-18.8 |
| Lisol Red (Ba Lake) | 33.7-21.7 |
| Lisol red (Ca lake) | 49.0-33.7 |
| Lisol ruby red | 33.9 |
| pigment scarlet lake | 88.5 |
| Rhodamine Y (tungstate precipitation) | 25.1 |
| Rhodamine B (phosphotungstate precipitation) | 16.1 |
| Toluidine maroon | 34.8-34.7 |
| Lightfast date red BL | 12.4 |
| Titanium dioxide (rutile type, anatase type) | 18.4 19.5 |
| Zinc white (zinc oxide) | 24.8 |
| Barium sulfate | 30.6 |
| Calcium carbonate | 31.4 |
| Hansa Yellow G | 54.9 |
| Hansa Yellow 10G | 58.8 |
| Forever Orange | 29.6 |
| Malachite green | 5.4 |
| Pigment rate B | 2.7 |
| Malachite blue (phosphotungstate precipitation) | 7.7 |
| Peacock blue | 68.5 |
| Methyl violet (phosphotungstate precipitation) | 7.6 |
| Methyl violet (tannin precipitation) | 4.9 |
| Daylight fast purple | 10.2 |
| Phthalocyanine blue | 4.5 |
| Zinc barium white | 23.6 |
| Lead white (basic lead sulfate) | 26.9 |
| Antimony trioxide | 22.7 |
| Talcum powder | 32.2 |
The covering power of a material is related to the refractive index. The higher the refractive index, the greater the covering power and the higher the white hue. The refractive index of various white materials is shown in Table 3.
| White Material | Colorant Index Number | Refractive Index |
| Titanium dioxide (rutile type) | Pigment White 6 | 2.70 |
| Titanium dioxide (anatase type) | Pigment White 6 | 2.55 |
| Zirconia | Pigment White 12 | 2.40 |
| Zinc sulfide | Pigment White 7 | 2.37 |
| Antimony trioxide | Pigment White 11 | 2.19 |
| Zinc oxide | Pigment White 4 | 2.00 |
| Lithopone (zinc barium white) | Pigment White 21 | 2.10 |
| Barium sulfate | Pigment White 18 | 1.64 |
| Calcium carbonate | Pigment White 27 | 1.58 |
| Talcum powder | — | 1.54 |
Effect on coloring: The natural color of calcium carbonate is white, which has an impact on the matching of bright colors, and it cannot match bright colors; it also has an impact on matching with black, and it cannot match particularly black.
Effect on color light: In addition to its white color, calcium carbonate often also has different color lights, affecting the color’s purity. Color light is an incidental color other than the main color of an object. The color light at both ends of the color wheel diameter is complementary. For example, the complementary color of blue is yellow. When mixed, white light can be obtained, which is an effective way to eliminate color light.
In heavy calcium carbonate, calcium carbonate from different origins emits different background colors. For example, Sichuan calcium carbonate has a blue background, Guangxi calcium carbonate has a red background, and Jiangxi calcium carbonate has a bluish background. In the specific color matching, the color light of calcium carbonate should be consistent with the main coloring color. For example, calcium carbonate with blue color light will eliminate the coloring power of yellow pigments. Calcium carbonate with a blue color is also often used to eliminate the yellow color of products.
Improve the astigmatism of plastic products: Adding calcium carbonate does not increase the gloss of plastic products but has a matting effect that reduces the gloss.
(7) Increase breathability
Plastic films filled with calcium carbonate will produce tiny pores in the film when stretched, which can only pass through water vapor but not liquid water. Therefore, it can be used to produce breathable plastic products. For example, a typical breathable film is made of copper and a large amount of calcium carbonate. Made of padding and film stretching. Generally, only 3000 mesh calcium carbonate can be selected for calcium carbonate to produce breathable films, and the particle size distribution must be narrow.
(8) Promote product degradation performance
After the polyethylene plastic bag containing calcium carbonate is buried underground, the calcium carbonate may react with carbon dioxide and water to form Ca(HCO3)2 that can be dissolved in water and leave the film, leaving tiny holes on the film, increasing the risk of the plastic film and The area where the surrounding air comes into contact with microorganisms, thereby promoting product degradation.
(9) Play a nucleating role
Nano-CaCO3 has an inducing effect on the crystallization nucleation of polypropylene, which can increase the beta crystal content, thereby improving the impact toughness of polypropylene.
(10) Reduce the water absorption of PA plastic
The water absorption of PA/calcium carbonate composite materials is lower than that of PA pure resin. For example, if PA6 is filled with 25% calcium carbonate, the water absorption rate of the composite material will be reduced by 56%.
(11) Improve surface properties
Calcium carbonate can increase the surface tension of composite materials and has excellent adsorption properties to improve composite materials’ plating, coating and printing properties.
(12) Effect of calcium carbonate on foaming
Whether calcium carbonate affects the foaming performance of plastic materials is very complicated and depends on the size and amount of addition. When the particle size of calcium carbonate matches the foaming agent, it can act as a nucleating agent and play a positive role in foaming. The specific suitable size is less than 5 μm and larger than the size that does not agglomerate.
