Natural fibre boost from BASF binder

published: December 11th, 2009
website: http://www.ecocomposites.net

As a one-component system consisting of a modified polyacrylic acid and a polyalcohol crosslinker, solutions of the binder initially behave like a thermoplastic. On heating at 120°C, the material melts and flows, allowing for impregnation of substrate materials such as natural fibre mats. After impregnation and drying to room temperature, Acrodur forms a ‘film' that mechanically binds to the substrates. These materials can then, for example, be compression moulded at temperatures above 120°C, at which point the molecules begin to crosslink to form a thermoset. Crosslinking is fully completed at temperatures above 150°C.

The lower inner door panel of the latest BMW7 Series received a 2009 Automotive Innovation Award from the The Automotive Division of the Society of Plastics Engineers (SPE), in the materials category. The panel consists of a 70% sisal fibre mat – needlepunched in Germany by J. Dittrich & Söhne and compression moulded with Acrodur into the part by Tier One supplier Dräxlmaier Group.

Acrodur's high wetout of natural fibres and ability to form chemical as well as mechanical bonds to the reinforcement allows for production of composites with very-high fibre loadings – 70% in the BASF door panel – yielding lightweight parts with high stiffness in thin walls. The resulting panel saves weight and cost, significantly reduces VOC emissions, and its rapidly renewable natural fibre mat reduces the vehicle's carbon footprint without sacrificing performance.

BASF reports that the use of natural fibre composites in automotive is expanding rapidly, with Daimler, for example, now using more than 50 bio-based components in Mercedes-Benz cars. Flax, hemp and sisal are used in door liners, seatbacks and backseat shelves while coconut husk fibre is used in seat cushions and head restraints.

Market drivers for increased use of composites include not only reduced weight, but also lower manufacturing complexity, reduced tooling costs compared to parts made from metal, better corrosion resistance and better internal dampening of noise and vibration.

BASF is currently conducting performance gap analysis benchmarking to identity competing materials and market entry points for Acrodur. One promising area is heavy duty trucks, which consume more than 50% of all composites going into automotive applications. Another potential growth area for composites is in hybrid vehicles such as hoods, front and rear bumper beam supports, deck lids and rear trunk compartments and underbody shields. In all of these applications, substitutions of glass-filled composites for standard sheet metal results in mass savings of 25-50 percent, as well as significantly lower tooling investments.

BASF believes a composite of 70% natural fibre and 30% Acrodur can be competitive with such glass-filled composites.