A Second Life of Carbon Fibers
Plastics with carbon fiber reinforcement are being used increasingly in automaking. As a result, carbon fibers from production waste accumulate in various forms, for instance, as dry mats or as wet waste. AkroPlastic GmbH, Niederzissen, has found a way to reclaim dry carbon fiber mats that have not yet been impregnated with a polymer matrix and incorporate them into a polymer melt, enhancing its value.
This is accomplished by chopping the mats in a multistep process to the point where they can be metered gravimetrically on an extruder like conventional chopped carbon fibers. The key to optimal metering is precise temperature control during compounding. The twin-screw extruder used for this purpose was modified to include a newly developed side feed that can be used to incorporate up to 40% carbon fibers into the polymer melt in a gentle manner.
According to the information available, it is possible to produce carbon fiber-reinforced thermoplastics at a competitive price. The carbon fiber-reinforced compounds exhibit high strength in combination with a low density. Electrical shielding and good thermal conductivity properties qualify these carbon fiber-reinforced compounds especially for applications such as activated charcoal filters, brackets for control units or center consoles.
At 11000 Mpa, the modulus of elasticity of a polyamide reinforced with 15% carbon fibers (PA-CF 15) is about the same as the modulus of elasticity of a PA reinforced with 30% glass fibers (PA-GF 30). The density of the PA-CF 15, however, is only 1.19 g/cm³ compared to the 1.36 g/cm³ of PA-GF 30. At higher fiber loadings (compare PA-CF 40 with PA-GF 60), there is a beneficial increase in rigidity of up to 42% at a decrease in flexural strength of only 12%. The weight benefit amounts to 22 %.
The significant weight reduction can be exploited for structural components above all. Currently, various potential applications are being tested. Components located above the center of gravity of the vehicle are of special interest to automakers, since the weight reduction directly benefits the vehicle dynamics.
Article: " Components Made from Carbon-Fiber-Reinforced Compounds ", Kunststoffe International 2015/09