BASF launches thermosetting acrylic

Fresh off its win in the Materials category of the Society of Plastic Engineer’s annual automotive Innovation Awards, BASF’s Acrodur thermosetting acrylic polymer was officially introduced to the North American market at a November meeting held in Flint, Mich. 

Described as a unique class of acrylic binder that allows the creation of composites with loadings as high as 70 percent, Acrodur is being touted as a potential replacement for steel and other plastics to further automotive manufacturers’ goals of reducing vehicle weight, lowering emissions, improving vehicle recycling and cutting costs.

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A one-component system consisting of a modified polyacrylic acid and a polyalcohol crosslinker, Acrodur solutions initially behave like a thermoplastic. Upon heating (120°C/248°F) the material melts and flows, allowing for impregnation of substrate materials such as natural fiber mats and the production of flexible prepreg/semi-finished rollstock or blanks. 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 molded 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/302°F. The strong ester bonds formed by crosslinking facilitate the creation of dimensionally stable, thin-walled parts with high stiffness.

The BMW 7 Series lower inner door panel, which won the SPE Auto Innovation Materials award, for example, is compression molded from Acrodur and 70 percent sisal fiber. Making the part from the Acrodur/sisal composite instead of the original ABS allowed engineers to decrease wall thickness from 0.25 inch/6.35 mm to 0.094 inch/2.4 mm, resulting in a 6-lb/2.7-kg weight savings for a four-door sedan.

“It is Acrodur’s ability to form mechanical as well as chemical bonds to the reinforcement that allows one to make composites with high loadings,” says Dr. Gero Nordmann, BASF market development manager. Nordmann reports that the use of bio-fiber based composites in automobiles is expanding rapidly. Daimler has more than 50 bio-based components in Mercedes-Benz automobiles. Flax, hemp and sisal are used in door liners, seatbacks and backseat shelves; coconut husk fiber 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 (part reduction), reduced tooling costs compared to parts made from metal, better corrosion resistance and better internal dampening of noise and vibration.

Nordmann says 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 percent of all composites going into automotive applications. The Honda Ridgeline cargo box with in-bed trunk, for example, consists of eight glass-reinforced SMC moldings. The SMC is 47 percent chopped glass with a unique polyester/vinyl ester hybrid matrix resin that optimizes balance between structural performance and aesthetics.

Another potential growth area for composites is hybrid automobiles in components such as hoods, front and rear bumper beam supports, deck lid and rear trunk compartment and underbody shields. In all of these applications, substitutions of glass-filled composites for standard sheet metal results in mass savings of 25 to 50 percent, as well as significantly lower tooling investments. BASF claims a composite of 70 percent natural fiber and 30 percent Acrodur can be competitive with glass-filled composites in hybrid automotive applications.

More stringent interior automotive air quality standards and cradle-to-grave automotive recycling requirements will also give a boost to natural-fiber composites and composites with low emissions. Nordmann reports that third-party testing of Acrodur found the material to be free of formaldehyde, phenol and VOCs. “The use of natural-fiber composites will expand,” says Nordmann. “The beauty is that this [Acrodur] material is ideal for binding wood and other natural fibers.”