Modified plastics

Fibre reinforced and composite plastics

The property profile of a plastic can be selectively altered by introducing additives or fillers designed to achieve specific characteristics. The resulting plastic compounds offer various (usually increased) thermal, mechanical, electrical, optical or other properties that are improved over those of the unmodified base polymers. In addition to colourants, the most commonly used fillers and additives include reinforcing fibres, stabilisers and friction reducing additives.

Reinforcing fibres

In fibre reinforced polymers, the material properties of the compounds are determined by the reinforcing fibres. In many cases, the strength of the fibres exceeds the strength of the matrix materials. Often the strength is also higher than the tensile strength of metallic materials. The density of the most commonly used fibres, in contrast, is usually lower than that of aluminium, which allows for greater potential in designing parts for lightweight construction. In most cases, glass, carbon and aramid fibres are used in fibre reinforced plastics. From the designer's point of view, the mechanical characteristics of the material are particularly important.

Glass fibre reinforced plastics

Glass fibres are the most commonly used reinforcing fibres in reinforced polymers. Compared to the base polymer, glass fibre reinforced materials have better mechanical properties, such as greater rigidity or strength. They can also provide better surface hardness.

Glassfibre reinforced plastics

Carbon fibre reinforced plastics

Carbon fibre reinforced polymers are extremely strong and lightweight. They can be expensive to produce, but are mostly used wherever high strength to weight ratio and rigidity are required. These modifications are frequently applied in fields like aerospace, automotive and many other technical applications.

Carbonfibre reinforced plastics

Aramid fibre reinforced plastics

Aramid fibres are a class of heat resistant and strong fibers that are used in applications where extreme requirements are imposed in terms of impact strength, material damping and abrasion resistance, and where low weight is also a requirement.

Aramidfibre reinforced plastics

OTHER FILLERS

Other fillers usually offer no or only minimal technical advantages. They are mainly used to reduce cost or weight: Ensinger offers, for example, lime, talc or hollow glass beads.

Another innovative composite solution offered by Ensinger is ceramic filled plastics, which can be used to improve physical properties and machinability.

Reinforced with ceramics

Natural fibre filled plastics are also available to improve the stiffness and strength of a composite.

Reinforced with natural fibres

FRICTION AND WEAR REDUCING FILLERS

In addition to the well known sliding material PTFE (Teflon^®), the classic friction bearing materials PA and POM are also often used in their unfilled state due to their good sliding friction properties. It is possible, of course, to improve the properties of all materials, including PA and POM, in terms of their friction and wear properties, by using various additives that can be mixed into the polymer matrix. The four most common types of additive are listed here:

Graphite

Graphite is pure carbon which, when finely ground, has a high lubricating effect. By working graphite evenly into a plastic the coefficient of friction can be reduced dramatically, especially in damp environments.

Polyethylene

The addition of polyethylene can lead to an effect comparable with that of PTFE additive. The frictional properties are improved, but not quite to the same degree as with PTFE.

Molybdenum Sulphide

Molybdenum sulphide is used predominantly as a nucleating agent and forms a fine crystalline structure, even when added only in small quantities. As a result of the higher crystallinity, plastics achieve greater abrasion resistance as well as a reduced coefficient of friction. Ensinger can also offer specially formulated compounds that combine low friction additives. One example is Ensinger's PVX family of materials, which contains 10% each of PTFE, graphite and carbon fibre. The combination of PTFE and graphite gives the material excellent sliding friction properties, while the addition of carbon fibres results in higher strength and abrasion resistance. These materials also offer extremely good dry and emergency running properties under heavy load.

Polytetrafluorethylene

PTFE is a high temperature resistant fluoroplastic that also has pronounced anti adhesive behaviour. Under compressive stress, abraded material from PTFE filled plastics forms a fine polymer film on the mating surfaces. This phenomenon results in very low coefficients of friction being achieved. With suitable modification, it is also possible to reduce what is referred to as stick slip effect, or avoid it altogether.

Friction and wear behaviour