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Nanocomposites parts are finding applications in the automotive industry. General Motors was the first car manufacturer to produce commercial car parts filled with nanoclays in 2002, and since then, the business has been expanding with increased interest from other car manufacturers.
BARBARA PIETERS, PROJECT MANAGER, NANOTECHNOLOGIES, YOLE DÉVELOPPEMENT
(Published on July-August 2007 - JEC Magazine #34)
Together, the nanotechnologies constitute a multidisciplinary field that has elicited great interest in the past decade. The definition of nanotechnologies refers to critical dimensions, usually in the range of hundreds of nanometres, where novel properties are observed. The fields of applications are so numerous that several governments have elected nanotechnologies as a top-priority research field. Thus, the annual world funding for nanotechnologies is very high, reaching $4.6B for government funding in 2005. This almost equalled private funding (venture capital funds and corporate funding), which reached $4.5B.
“Nanomaterials” is a field within nanotechnologies that has been extensively studied and has led to new materials development, production and commercialisation. Two approaches are being used to achieve the nanoscale: The Top- Down approach consists in starting from “big” to make “small”, such as in the semiconductor industry, whereas the Bottom-Up approach consists in assembling atoms or molecules to build objects, such as in the chemical industry. Applications of nanomaterials are numerous and relate, for example, to energy, cosmetics, coatings, construction and packaging.
The automotive industry is one of many fields of applications that have seen the growing impact of nanomaterials. Nanomaterial products are finding uses in the automotive industry for a variety of functions. Examples are:
This article will focus specifically on this last application.
Introduction to nanocomposites
A nanocomposite is defined as a solid matrix (usually polymers) that contains a nanoscale filler, called a nano-object (for example nanoparticles, nanotubes, nanofibres, etc.). The main characteristics of nano-objects are 1) increased surface area (contact between the particle and its environment): this gives increased interaction between the particle and the surrounding matrix, resulting in improved mechanical, chemical, and thermal properties (1 g of particles of 25 nm has a surface area of 20 m2); and 2) transparency: when the particle diameter is lower than 30 nm, the reflection of visible light is negligible.
These characteristics are the drivers for the development of nano-objects. Thus, there is a wide range of nano-objects available on the market or under development today. Although nanotechnology is considered as a recent science, some of these nano-objects have been sold for decades, even in millions of tons per year. Examples of these are primarily nanoparticles: carbon black, precipitate and fumed silica, etc. Relatively new nano-objects have already found commercial applications, showing real added value when compared to older particles. These nano-objects are (see Figure 1):
Examples of nanoclay and nanotube nanocomposites for automotive
Nanoclays are the nano-objects most widely used in automotive parts. Natural nanoclays are nanosized, platelet-shaped particles agglomerated together. Depending on the dispersion of nanoclays in the polymer matrix, their effects are different. To get an exfoliated nanocomposite (i.e. where nanoclay platelets are separated from each other and dispersed throughout the whole polymer matrix), functionalization of the nanoclays is required.
General Motors showed the first commercial use of nanoclays in cars in 2002, with the Chevrolet Astro and GMC Safari vans. The step-assist was made of thermoplastic olefin filled with 3% nanoclays. It was much lighter, stiffer, and less brittle at cold temperatures than those made with the conventional talc filler. Although this application drew large media coverage, it has since been terminated. In 2004-2005, GM released the Chevrolet Impala with a body side trim made of nanoclays. A weight savings of 3 to 25% was achieved on the redesigned parts, but their performance is questioned. In 2005, GM’s Hummer H2 SUT cargo bed trim contained 3 kg of nanoclays per car.
Other car manufacturers commercialising nanoclay-filled parts include Maserati, Daimler Chrysler and Audi. Maserati engine bay covers are made of Ube nylon-6 nanocomposites, containing 2% nanoclays by weight. The results are reduced weight, increased mechanical performance, and an improved surface appearance (versus glass-reinforced nylon). Daimler Chrysler made the inner door handle of the Smart Forfour in Polykemi AB‘s polypropylene with nanofillers and conventional fillers. Audi and Putsch GmbH developed the heater vent of the A3 in PP/PS, filled with nanoclays to replace painted ABS. Nanoclays help to compatibilize 60-80% PP with 20-40% PS. The results are improved scratch resistance and a luxurious surface feel.
Part of the information presented in this article was extracted from the NanoSEE (Nanomaterials Industry Status and Expected Evolution) report, published by Yole Développement in 2006.
In automotive applications, carbon nanotubes are also eliciting strong interest as a mechanical reinforcement, or for their conductive properties. Renault used to reinforce PP/PPE alloys with nanotubes for Scenic fenders. Carbon nanotubes replaced carbon black in fenders for electrostatic painting. However, this has recently been halted for cost reasons. Fuel-delivery lines are also an application for carbon-nanotube nanocomposites.
Similarly to nanoclays, functionalization of the nanotubes is also required to obtain a good dispersion and distribution of the filler into the matrix. This competence in functionalization and compatibilization with the matrix is a very specific skill mastered by only a few players.
Today, only a limited number of nanotech products are integrated into automotive applications. North America was the starting point of this business. The performance-to-cost ratio is a major hurdle for broader market acceptance, since nano-objects are still expensive and their added value is not always sufficient to balance their cost. The evolution of these fillers is linked to nano-object prices, which will certainly decrease as production capabilities develop. Generally speaking, nanofiller prices are much higher than those of standard fillers. This increase in rawmaterial costs can be balanced by a reduction of the filler content and the reduced final weight of parts, combined with improved properties. Thus, the addition of nanofillers often requires rethinking the part (design changes) and the processing technologies (new moulds, modified rheological behaviour, etc.), which also needs to be considered in the part’s cost calculations.
Nanocomposites are developing in the automotive market, but proof of the competitive advantage of nano-objects remains to be confirmed, taking into account cost and performance. Significant further development and modification of current processing may yet be required (rethinking of the global system, including part design). Moreover, nanotoxicity and recycling are important subjects that must be taken into account while using these new materials.