Abstract：Calcium carbonate was first used in polyvinyl chloride plastics, and light calcium carbonate is used in plates, pipes and decorative materials.
Professor, can you give everyone a popular science on the classification of plastics? What types of plastics is calcium carbonate mainly used in?
Professor: There are two main categories of plastics. One is based on application: engineering plastics, general-purpose plastics, and special plastics. The other is classified according to the properties of plastics: thermoplastics, thermosetting plastics, and special plastics.
Calcium carbonate was first used in polyvinyl chloride plastics, and light calcium carbonate is used in plates, pipes and decorative materials. Later, constrained by environmental protection policies, cost and other factors, heavy calcium carbonate has replaced light calcium carbonate in large quantities in the past ten years, and it is used in polypropylene, polyethylene, ABS (acrylonitrile-butadiene-styrene copolymer), and nylon.
Professor: Calcium carbonate is used in plastic products, and the amount of calcium carbonate added varies depending on the product. For example, the filling rate of calcium carbonate in plastic film and garbage bags is about 30%; the filling rate of calcium carbonate in products such as woven bags and fruit baskets reaches 30-50%, which is close to half.
Up to now, countries such as Europe, America, and Japan still need to add calcium carbonate to plastic films and garbage bags. In addition to reducing costs, the main reason is to facilitate incineration of plastics after application. If calcium carbonate is not added, polypropylene and polyethylene plastics are easy to melt and form a film during combustion, the blowing effect is poor, oxygen is blocked by the film, which is not conducive to combustion, and the treatment effect is not good; after calcium carbonate is added to polypropylene and polyethylene, It is easy to form a "mesh" during the combustion process, with sufficient oxygen, sufficient combustion and good treatment effect.
Professor, can you tell us about the modification process of calcium carbonate for plastics? What are the commonly used modifiers?
Professor: Calcium carbonate is an inorganic material, plastic is an organic material, and the two are opposites. Therefore, the compatibility of calcium carbonate, additives, and resins is an important factor affecting the quality of plastic products. The surface of calcium carbonate after activation treatment is evenly coated with lipophilic additives with properties similar to those of the resin. During the blending process with the resin, the interfacial compatibility of different materials is improved and the performance of the product is improved. The surface activation modification process must meet certain conditions such as temperature, pressure, friction, and time. For example, when the additive is at 60°C~120°C, it will be melted, distributed, and coated on the surface of the powder for 3 to 5 minutes. Hydrophilic calcium carbonate transforms into a lipophilic material.
In terms of modifiers, there are many types and are relatively complicated. In the calcium carbonate industry, aluminate coupling agent was first used, and it is still the most used modifier at present. In addition, silane coupling agents and phthalate coupling agents are also used in the calcium carbonate industry, but because of the price (the price of silane coupling agents and phthalate coupling agents is high), application scenarios (the color of some coupling agents will affect Calcium carbonate whiteness) and other factors, there are certain differences in the application of modifiers.
Professor, what is the application ratio of heavy calcium and light calcium in plastics? What is the price of calcium carbonate for plastics?
Professor: Light calcium and heavy calcium have their own advantages, and neither can replace the other in terms of application. The earliest polyvinyl chloride used light calcium, but the production process of light calcium is relatively complicated, and it is not conducive to environmental protection, and waste gas and waste water are easy to pollute the environment. Heavy calcium has the advantages of environmental protection, and the production cost is also lower. The particle size, strength, functionality, purity and light calcium of water milled heavy calcium are basically the same.
In terms of price, as the mineral reserves of calcium carbonate become less and less, especially the shortage of good calcium carbonate ore, the price of calcium carbonate is getting higher and higher. Thirty years ago, there were many calcium carbonate resources, which were mined and sold to plastic, paint, and putty powder factories after simple grinding. The products were very cheap. Mineral resources are now decreasing, especially ores with high purity and whiteness above 94-95° are less and less, and the 1250-mesh heavy calcium reaches more than 600 yuan/ton.
Professor, can you judge the application trend of calcium carbonate in the field of plastics? What is the application potential and value of calcium carbonate in degradable plastics and engineering plastics?
Professor: Calcium carbonate is not just a filler material in the field of plastics, it is also a functional material. Calcium carbonate can improve many defects of plastics, and the requirements for calcium carbonate in the field of plastics are also getting higher and higher. Now after the appearance of wet grinding heavy calcium, the feedback from the plastic market is very good, so calcium carbonate is also gradually developing towards high-value applications.
The application of calcium carbonate in functional plastics is mainly to change the shrinkage of engineering plastics. The shrinkage rate of ordinary engineering plastics (nylon) is about 2%. If you do not add calcium carbonate to inject a large-volume product, it will be easily dented and deformed after cooling. In addition, some precision electrical parts made of plastic will affect the application after denting. Add some superfine calcium carbonate or nano silica to reduce shrinkage variation.
Degradable plastics is an industry advocated by the state, but the product price is high, raw materials for production are in short supply, application performance needs to be improved, and there is a certain gap between industrialization development and expectations. However, after adding 40%~60% heavy calcium carbonate to polylactic acid, the cost can be reduced by 30%~40%, the plastic performance can also be guaranteed, and it is green and environmentally friendly.
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