Mineral filled thermoplastic compounds
Fillers is a general term used to describe non-metal minerals, metallic powders, glasspheres, which are added to plastics in fairly high percentage and used as a reinforcement or an extender. Extenders consist of generally inexpensive fillers added either to reduce cost or to improve dimensional stability of a plastic. A reinforcing filler provides a mechanical or thermal property improvement to polymer matrix.
Minerals, historically have been referred to as fillers and extenders. Fillers and extenders, by definition, fill and extend resin to reduce the cost of the resin. In today's market place, function, not price, is the key selection criterion of a mineral products. Minerals are essential formulating ingredients for the production of polymer composites.
Mineral consists of two broad classifications. Commodity minerals and Speciality minerals. Generally, commodity minerals are used to reduce the cost of the resin, while speciality minerals are used where function or performance is a factor and the pricing is high.
Some minerals have inherent speciality. Calcium carbonate, Mica, Talc and Wollastonite are minerals with high aspect ratio particle shape defined as the ratio of length to width or length to thickness. This particle shape translates into reinforcement and improved mechanical properties in polymer composites.
CaC03 : Calcium carbonate is widely used in plastics due to it's wide range of particle size, low cost, good colour, low oil absorption characteristics, higher impact resistance, smooth surface finish, easy processing and dimensional stability.
Mica : The platelet particle shape of mica offers excellent flexural modulus properties, improved heat resistance, electrical property and mechanical properties. General reinforcing property and dimensional stability also add to mica's advantage. It's major use area is polyolefins.
Talc : It adds to stiffness,
dimensional stability, flexural modulus and resistance to creep. Talc also contributes to good flow, surface appearance and easier machinability of polymers. The primary use area of talc is PP.
Wollastonite : Wollastonite has g eneral properties of low moisture content, high purity, high brightness and acicular particle shape which provides reinforcement, dimensional stai bility, low creep, excellent electrical properties and good mechanical properties. The use area covers PP, NYLONS, POLYESTERS, POLYURETHANE. The speciality grades are widely used as partial replacement of glass fiber in polymer composites.
Hollow and solid glass micro-spheres are widely used in resin systems. Their spherically controlled particle size and density
Both solid and hollow spheres provides better flow properties. High-filler loading can be achieved without unacceptable increase in viscosity which results in better green strength, strong edges and corners and smoother, tougher surfaces.
Solid spheres are used in applications where strength is a concern. They modify the properties of the resin, especially flexural modulus and compressive strength and improve abrasion and corrosion resistance. They also reduce mould shrinkage and cycle time.
The primary function of hollow spheres is density reduction and the ability to displace large volume of higher priced polymers. Hollow spheres can selectively modify physical properties in speciality plastic applications such as flexural modulus and impact resistance. It also contributes to sound and thermal insulations and it has an ability of holdins nail and screw in finished parts.