In Part 1, we uncovered the secrets behind stronger and more cost-effective plastics, exploring the fundamental roles of calcium carbonate, talc, and wollastonite. But the world of plastic fillers doesn’t stop there. Now, let’s discover how materials like kaolin, mica and silica can be the key to your next innovative plastic compound.
Kaolin
Kaolin (Al₂O₃·2SiO₂·2H₂O), a type of clay mineral powder also known as pottery clay, white clay, or china clay, is a layered silicate primarily composed of hydrated aluminum silicate. It has a soft and smooth texture, with a density of 2.2–2.6 g/cm³ and a pH value of 5–6. It is non-toxic and exhibits flame-retardant properties. Kaolin offers better processability than calcium carbonate, allowing it to be molded even when the filling amount reaches three times the resin weight, whereas calcium carbonate becomes difficult to process at a 1:1 filling ratio.
As a plastic filler, kaolin provides excellent electrical insulation properties, making it suitable for PVC insulated wire sheathing, PE and PP cables, and film composites. For instance, adding 10% kaolin by weight to PVC can improve electrical insulation performance by 5 to 10 times. Kaolin can also be incorporated into polystyrene-based film composites for producing printing paper. In polyesters and epoxy resins, it helps adjust viscosity and processing performance while enhancing wear resistance. Additionally, kaolin acts as a nucleating agent for PP and offers certain flame-retardant effects.
The typical addition rate of kaolin in plastics ranges from 5% to 60%, with a particle size of 100 mailles or finer. It is important to note that kaolin is highly hygroscopic, so storage must prevent moisture absorption and clumping. Before use, kaolin must be dried to avoid affecting plastic product quality. Sometimes, surface treatment with lipophilic agents is applied to improve its compatibility with plastics.
Mica
Mica has a complex composition, being a layered hydrated aluminosilicate mineral containing aluminum, potassium, lithium, magnesium, iron, and other elements. As a filler, mica powder is produced by crushing and processing natural mica fragments. It typically has a particle size of 8–10μm and an aspect ratio of around 30, exhibiting a typical flaky structure with a glassy luster. Its water content ranges from 1.0% to 4.2%, and it is non-toxic, making it suitable for nourriture-contact products.
Mica powder can fill thermoplastic plastics such as PE, PP, PVC, PA, ABS, and polyesters, as well as thermosetting plastics like EP (epoxy resin) and PF (phenolic resin). The addition rate is generally 10%–40%, with a particle size of 100–325 mesh. As a plastic filler, mica significantly enhances the tensile modulus and flexural modulus of plastic products, providing excellent electrical insulation, heat resistance, dimensional stability, moisture resistance, and corrosion resistance. The main drawback is its relatively high cost.
Diatomite
Diatomite is a fossil formed by the deposition of single-cell algae at the bottom of oceans or lakes. Its main component is SiO₂, and it is porous, lightweight, and easily ground into powder. It appears as white or light yellow powder with a particle size of 25–40 μm and a density of 1.6–2.3 g/cm³.
Diatomite is a high-quality lightweight filler suitable for PVC, polyolefins (PO), and thermosetting plastics. It also serves as an anti-blocking agent in lightweight, sound-insulating, and heat-insulating building composites. However, its oil and resin absorption rates are relatively high.
Carbon Black
Carbon black is produced by the incomplete combustion of hydrocarbons under controlled conditions. It comes in various types, classified by production method into channel black, furnace black, and thermal black, among others. When added to polymers, carbon black not only protects against photodegradation and thermal oxidation but also enhances the rigidity of plastic products.
The fineness of carbon black affects product performance: finer particles provide higher blackness, stronger UV shielding, better aging resistance, and lower surface resistivity. However, finer particles can be more challenging to disperse. For filler applications, larger-particle furnace black is generally used, with a typical particle size of 25–75μm.
Silica
Silica (SiO₂) is a type of rock powder categorized into quartz powder and silica powder. Natural silica powder is primarily used in thermosetting resins, such as unsaturated polyesters and epoxy resins, for producing artificial onyx and marble.
Silica can also be synthesized, commonly known as white carbon black. It is a reinforcing filler second only to carbon black, providing a matting effect and improving the electrical insulation and hardness of plastics. Its main disadvantages are poor flowability and high viscosity.
Poudre épique
Poudre épique, 20+ years of work experience in the ultrafine powder industry. Actively promote the future development of ultra-fine powder, focusing on crushing, grinding, classifying and modification process of ultra-fine powder. Contact us for a free consultation and customized solutions! Our équipe d'experts se consacre à fournir des produits et services de haute qualité pour optimiser la valeur de vos opérations de traitement de poudre. Epic Powder : votre expert de confiance en traitement de poudre !
