Calcium carbonate is the most commonly used inorganic powder fillers. It is inexpensive, abundant, non-toxic, and odorless. It has a whiteness of up to 96%, can be easily colored, and has excellent chemical stability. It is easy to dry and widely used in many plastics.
Calcium Carbonate
There are three kinds of powder fillers of calcium carbonate: heavy calcium carbonate, light calcium carbonate, and activated calcium carbonate.
Heavy Calcium Carbonate (Heavy CaCO₃)
Made by mechanical crushing, screening, classification, and surface treatment of limestone, etc. It is further divided into dry heavy calcium carbonate (commonly known as double-fly powder) and wet heavy calcium carbonate. The particle shape is irregular, and the average particle size is 1–10 μm, with 50% of the particles being below 3 μm. It has a density of 2.7–2.9 g/cm³ and is almost insoluble in water. Recent advances in grinding technologies (such as air jet mills) allow for the production of ultra-fine heavy calcium carbonate as small as 0.1 μm. Heavy calcium carbonate is commonly used in PVC to reduce costs, improve dimensional stability, and, when used with clay, enhance elasticity and thermal deformation resistance.
Light Calcium Carbonate (Light CaCO₃)
Produced through chemical methods, also known as precipitated calcium carbonate. Its particle shape is spindle-shaped, needle-like, or columnar, with particle sizes ranging from 1 to 10 μm, and 80% of the particles are under 3 μm. It has a density of 2.65 g/cm³. Light calcium carbonate is mainly used in polyolefins and has similar effects to heavy calcium carbonate, with better enhancement effects and better acid resistance.
Activated Calcium Carbonate
Also known as modified calcium carbonate or colloidal calcium carbonate. It is treated with surface modifiers (such as stearic acid, about 3% by weight) to activate light or heavy calcium carbonate. It appears as a white, fine, soft powder with a density of 1.99–2.01 g/cm³. Plastics filled with activated calcium carbonate have good strength, smooth surfaces, and excellent lubrication, making them easier to process.
Calcium carbonate is classified by particle size as follows:
- 1–5 μm: Micro-particle calcium carbonate
- 0.1–1 μm: Fine calcium carbonate
- 0.02–0.1 μm: Ultrafine calcium carbonate
- Below 0.02 μm: Super ultrafine calcium carbonate
To produce ultrafine calcium carbonate, a continuous spray carbonation and spray drying process (dual-spray process) is used. This process reduces the apparent agglomerates and ensures uniform surface activation. When the particle size is between 0.005–0.02 μm, its reinforcing effect is comparable to that of silica.
Talc Powder
Talc (3MgO·4SiO₂·H₂O) is mainly composed of hydrated magnesium silicate. It is a typical flake-shaped filler, chemically inert, and has a slippery feel. With a density of 2.7–2.8 g/cm³, talc powder is the second most used filler after calcium carbonate. As a plastic filler, it improves hardness, flame retardancy, acid and alkali resistance, electrical insulation, dimensional stability, and creep resistance. It also has lubricating properties, reducing wear on machinery and molds.
Talc powder is a plate-like filler, so when used in plastics, it significantly increases rigidity and reduces anisotropy. It is ideal for manufacturing large and flat products. Talc is mainly used in PP as a crystallization nucleating agent, improving crystal size and increasing rigidity. It is also used in PVC, PE, PA, and PC resins. The addition amount is typically 10%–40%. The processing conditions and equipment are similar to those used for calcium carbonate-filled plastics, including extrusion, molding, injection, and calendering methods.
Wollastonite
Wollastonite is the third-largest filler after calcium carbonate and talc. It is made from natural silicate minerals such as calcium silicate (CaSiO₃). The natural form of whiting has a needle-like, rod-like, and granular mixed structure, primarily in the needle-like form. It is a white crystalline mineral, non-hygroscopic, non-toxic, with a low coefficient of thermal expansion and excellent chemical resistance. Whiting has a refractive index of 1.62, which is close to that of PVC, making it ideal for PVC transparent products. Its needle-like structure reinforces plastics and can partially replace costly glass fibers.
Wollastonite is used in PVC, PP, PE, PA, polyester, epoxy resin, and phenolic resins. The typical usage amount is below 40%, and surface treatment with silane coupling agents is common.
Kaolin
Kaolin (Al₂O₃·2SiO₂·2H₂O) is a type of clay mineral. It is soft and slippery with a density of 2.2–2.6 g/cm³ and a pH value of 5–6. Kaolin has excellent electrical insulation properties and is used in applications such as PVC insulation, PE and PP cables, and composite films. When 10% kaolin is added to PVC, it improves electrical insulation by 5–10 times.
Kaolin is also used in polyester and epoxy resins to adjust viscosity, improve wear resistance, and enhance processing properties. It can also act as a nucleating agent for PP and has certain flame-retardant effects. The addition amount typically ranges from 5% to 60%, with a particle size of over 100 mesh.
Mica
Mica is a complex mineral composed of aluminum, potassium, lithium, magnesium, iron, and other elements. Mica powder is made by crushing natural mica flakes into powder, with particle sizes typically between 8–10 μm and a length-to-width ratio of approximately 30. Mica is a typical platelet structure with a glassy luster and contains 1.0%–4.2% moisture content. It is non-toxic and can be used in food-contact products.
Mica powder can be used to fill PE, PP, PVC, PA, ABS, and polyester plastics, as well as thermosetting plastics like EP and PF. The typical addition amount is 10%–40%, with particle sizes ranging from 100 to 325 mesh. Mica significantly increases tensile and flexural modulus in plastics and imparts excellent electrical insulation, heat resistance, dimensional stability, moisture resistance, and corrosion resistance. The drawback is its higher cost.
Diatomaceous Earth
Diatomaceous earth is a fossilized sediment formed by single-celled algae. It mainly consists of SiO₂, is porous, light, and easy to grind into powder. Diatomaceous earth is a high-quality lightweight filler used in PVC, PO, and thermosetting plastics, as well as building composites for soundproofing, heat insulation, and anti-stick applications. However, it has high oil absorption and resin absorption rates.
Carbon Black
Carbon black is produced through the incomplete combustion of hydrocarbons under controlled conditions. It has a wide variety of types, including furnace black, channel black, and thermal black. Carbon black adds protection against light degradation and heat oxidation when used in polymers. Its fineness impacts the performance of the product; finer particles provide better blackness, UV shielding, aging resistance, and lower surface resistivity, but can be more difficult to disperse.
For fillers, larger particles of furnace carbon black (25–75 μm) are often used.
Silica (SiO₂)
Silica (SiO₂) is a type of rock powder, mainly quartz and silicate minerals. Natural SiO₂ powder is used in thermosetting resins like unsaturated polyester and epoxy resins, as well as in the production of artificial agate and marble. Synthetic silica, commonly referred to as white carbon black, is a reinforcing filler second only to carbon black. It has a matte finish and improves the electrical insulation and hardness of plastics but has poor flowability and high viscosity.
Epic Powder
Incorporating powdered fillers into plastics offers a cost-effective way to enhance performance across various industries. At Epic Powder, we specialize in providing high-quality grinding and processing solutions to ensure that these fillers, such as calcium carbonate, talc, and silica, meet the precise requirements of modern applications. By leveraging advanced milling technologies, Epic Powder helps optimize particle sizes, improving the consistency and functionality of these materials in plastics, ultimately driving both cost savings and superior product performance.