A family of cross-linkable acrylic copolymer resins - which uniquely have a thermoplastic “B-stage” that enables thermoplastic prepregs and semi-finished goods to be produced - is providing the opportunity to manufacture durable automotive interior trim-panel substrates with comparable or higher performance at lower weight and fewer processing steps than common thermoplastic and thermoset composites long used in such applications. Owing to their special chemistry and very-low initial viscosity, the acrylic copolymers provide excellent wetout / impregnation of fibrous or particulate reinforcements, facilitating the production of composite parts with very-high fiber volume fractions (FVFs). Loading levels as high as 70-90% have already been achieved with natural fibers. In the presence of heat and pressure, the material cross-links to form durable copolymers with excellent thermo-mechanical properties. A range of stiffness and ductility are possible based on grade selection within the product family.
Unlike most thermosets, these new polymers neither contain hydrocarbon solvents nor other volatile-organic compounds (VOCs), nor produce toxic emissions during cross-linking. In fact, the only reaction by-product is water, so no special air-handling equipment is required during processing to protect workers, and the pre-cured polymer can be cleaned up using water alone, lowering the environmental impact of part production considerably. Further, since these polymers do not contain VOCs, emissions from cured parts are greatly reduced, protecting air and water quality throughout the life of the product and positioning OEMs to better meet tougher interior air quality requirements already in force in Europe and anticipated in the near future from the State of California.
Used previously in Europe as binder resins for nonwoven fabrics and more recently as a matrix for cork flooring, these materials are starting to expand their use into automotive interior components, particularly for parts reinforced with natural fibers. This paper provides an overview of this new green-composites technology, describes how it is typically used, and cites examples of emerging and commercial applications in the automotive industry.