Carbon fibre reinforced compounds

As Henry Ford put it, “You can have any color, as long as it’s black”. The same is true for ICF products from AKRO-PLASTIC GmbH, as they also come only in black. What makes our innovative, carbon fibre-based compounds stand out is their extreme stiffness and extremely competitive price tag. 

Using proven compounding technology from our sister company, FEDDEM GmbH & Co. KG, we offer ICF compounds based on polyamide 6 (AKROMID® B), polyamide 6.6 (AKROMID® A), PPA (AKROMID® T), PA 6.6 with a partially aromatic CoPA (AKROLOY® PA) or PARA based (AKROLOY® PARA) as well as an aliphatic polyketone (AKROTEK® PK) and polyster (PRECITE®). The compounds are finished with a carbon fibre content of 10 % to 40 %.

AKRO-PLASTIC has developed new ways to incorporate dry, conditioned carbon fibre fabrics into a polymer melt in a manner which enhances the added value. This involves shredding the fabrics in a multiple-step process in such a way that they can be gravimetrically dosed on an extruder, like conventional cut-carbon fibres. The biggest obstacle in this process is a powder binder applied to the fabric. The powder binder is used to superimpose several layers of the carbon fibre fabrics and prevent slippage in subsequent processes. An important step during the conditioning of the fibres is the dosing of the fabrics, which can only be ensured with precise temperature control.

The synchronous twin-screw extruder used at FEDDEM GmbH & Co. KG has been equipped with a newly developed side feeder. Depending on the polymer, this side feeder is capable of gently delivering up to 40 % carbon fibre content to the conditioned polymer melts. A further critical step when incorporating the prepared carbon fibres is the proper electrical encapsulation of the system technology and suitable extraction of the dosing. Otherwise, the high conductivity of carbon fibres will relatively quickly result in the destruction of the contaminated electrical components.

Tensile testing shows that even at higher temperatures, approximately the same strengths can be achieved with lighter ICF compounds from AKRO-PLASTIC than with significantly higher glass fibre reinforcement. The elongation at break for carbon fibre reinforced compounds, however, is slightly less than for compounds with glass fibre reinforcement.

Compared with glass fibres, the use of carbon fibres gives rise to an extreme increase in stiffness in thermoplastic compounds. This becomes clear when looking at the specific tensile modulus, that is, the tensile modulus divided by density. The ICF compounds from AKRO-PLASTIC dominate, particularly when freshly moulded. But even for conditioned compounds, the specific tensile modulus for all compounds is higher than that of a glass fibre reinforced alternative compound.

New blowing agent systems result in weight reduction in engineering plastics, with optimal retention of the mechanical properties and surface qualities. These blowing agent masterbatches combine the advantages of dust-free, safe handling whilst providing nucleating agents and additives which can enable in-process realisation of an optimally fine-tuned product. 

In process control there are two different approaches, which are compared in the table below using dumbbell specimens in a 20 % carbon fibre reinforced (PA + PP) blend, loaded with 3.5 % masterbatch AF-Complex® PE 990310 TM. The respective compound, loaded with blowing agent and produced in a standard process, serves as the zero value. Moisture absorption influences the variants thus foamed to the same degree as the non-foamed variants. 

Full Shot: The component is filled completely without holding pressure. A weight reduction of 4 % compared with the standard process is realised with this variant. The mechanical properties, however, remain nearly identical. The blowing agent has a flow-enhancing effect and reduces weight only to a moderate degree, but the component surface is just as good as that achieved in the standard process, and the component is virtually free of deformation.

Short Shot: The component is nearly completely filled, but without compressing the melt. This variant is also produced without holding pressure and achieves a high degree of foaming and thus a weight reduction of 13 % compared with the zero value. The tensile modulus is reduced by 15 % – approximately the same amount by which the weight was reduced.