Achieving emission cuts necessitates stringent fuel efficiency standards for automobiles, which have forced OEMs worldwide to seek to reduce vehicle weight. The most effective way to reduce fuel consumption and decrease CO2 emissions is to produce lighter vehicles, and lightweight vehicle production has increased considerably. However, vehicle safety is usually compromised by lightweighting. Therefore, there is a need to develop new materials to overcome safety issues.
Use of composites
The primary advantages of using composites in automobiles is the weight reduction as the composites are up to 35% lighter than aluminium and 60% lighter than steel and the use of composites in automotive can leads to an overall vehicle weight reduction of up to 10%. In addition to this, tooling investments can be reduced up to 50% – 70%, as in one assembly, composites can replace eight metal stampings and hence have a positive impact on the energy associated with the assembly and tooling.
Lightweight materials are vital to the success of electric and hybrid vehicles to offset the added weight of their batteries. Approximately 10% reduction in mass can lead to 6-7% fuel savings. It is also anticipated that the reduction in mass will lead to the early introduction of alternative propulsion systems. The US Department of Energy (DOE) is targeting a vehicle weight reduction of 50% by 2050. In Europe, the objective for reducing emissions is to reach 125 g/km in 2015 and 95 g/km in 2020. Therefore, 200kg/vehicle must be saved by 2015-2020. In order to meet the CO2 emission targets set for Europe in 2020, i.e., 95 g CO2/km, a 200 – 300 kg weight reduction of the vehicle is required.
According to the DOE the limiting factor in use of lightweight materials in vehicles is availability of sufficient quantities at affordable cost. The automobile market requires high specific strength and modulus, low density and inexpensive reinforcements for engineering thermoplastics (polyamide 6 and 66, polyethylene terephthalate (PET) and polytrimethylene terephthalate (PTT). Teijin estimates that, in order to attain the objectives for reducing CO2 emissions, carbon composites will comprise 5-7% of all new vehicles in 2020. Virtually all North American and European original equipment manufacturers (OEMs) related to automotive industry have ambitious weight reduction plans in response to stricter environmental regulations.
Natural fiber composites
A trend in the automotive industry is the increasing use of natural fiber composites with thermoplastic and thermoset matrices for light weighting. Major automotive manufacturers in a number of regional markets are shifting from conventional plastics to natural fibre reinforced composites for door panels, seat backs, headliners, package trays, dashboards, and interior parts.. Natural fibers such as kenaf, hemp, flax, jute, and sisal offer advantages of utilizing natural fibres over conventional glass fibres, such as low cost, low density, high toughness and biodegradability.
Replacement of glass fibers with natural fibers allows lighter components as the density of natural fibers (1.5 g/cc) are lower compared to glass fibers (2.5 g/cc) while simultaneously increasing the proportion of renewable resource content within the vehicle. Application of natural in the automotive industry include:
- Various panels
- Trim parts
- Brake shoes
- Seat backs.
- Mercedes-Benz Travego Coach: flax reinforced engine/transmission cover;
- Mercedes-Benz A-Class: the spare wheel compartment cover.
Cellulose nanofibers are attractive for the development of polymer composites in the automotive industry due to their broad availability, renewability, low density, environmentally benign nature (non-toxicity) and outstanding mechanical properties that are superior to current natural fiber composites.
Figure 1: NFC composite. Image credit: Furukawa Electric.
American Process, Inc. (http://www.americanprocess.com/) is developing automotive composites and tire additives with several companies. The company is involved in a project with Futuris Automotive to develop a sprayable binder resin system containing nanocellulose as a reinforcing phase to replace steel in seating assemblies for application in electric vehicles. Greencore Composites (http://greencorenfc.com/) produces NCell Polymer additives that consists of a polypropylene or polyethylene matrix reinforced with up to 40% nanocellulose. NCell compounds are supplied in standard pellet form, and may be used as drop-in replacement on existing tooling and molding equipment. NCell is used in auto interiors and under-the-hood applications.
Woodbridge Foam Corporation is developing automotive foam applications of nanocellulose. Weyerhaeuser (https://www.weyerhaeuser.com/) has developed a proprietary, patent-pending thermoplastic composite with cellulose-fiber reinforcement derived from wood. They are working with Ford Motor Co.’s biomaterials research team to examine automotive applications where plastic composites made with cellulose fibers can replace thermoplastics with fiberglass or mineral reinforcements. Denso Corporation (https://www.denso.com/global/en/) is developing CNF -phenolic resin composites for automotive components. The company has incorporated CNF into the resin of large containers for vehicle air conditioners. Other Japan based companies with initiatives in automotive composites include Furukawa Electric, Seiko PMC and Toyota, who are seeking to develop a concept car using CNF by fiscal 2019. Yohei Kawada, deputy director of the Japanese Environment Ministry’s climate change projects office, has stated that Japan is focusing on CNF as the key to reducing vehicle weight as technologies for increasing the efficiency of automobile engines are approaching their limits. In 2016, DIC (http://www.dic-global.com) developed a masterbatch called Epiclon NCM consisting of 10 wt% cellulose nanofiber (CNF) dispersed in an epoxy carrier. Addition of the masterbatch to epoxy resin reportedly improves the traditional disadvantages of epoxy resins, namely their brittleness and lack of toughness. The company is applying the masterbatch in automotive applications, where it would be added to carbon fiber-reinforced plastics (CFRP) to improve toughness.
Figure 2: Cellulose Nanofiber (CNF) composite with polyethylene (PE)
Image credit: Fuji Pigment Co., Ltd.
Commercial resin pre-impregnated fabrics and tapes utilizing graphene have been developed to reduce the mass of vehicles without compromising strength or durability, while increasing fuel efficiency. The use of nanocomposites in automotive production requires less filler material than conventional materials while providing equivalent or improved performance characteristics. The addition of minimal amounts of graphene makes semi-finished parts electrically conductive, allowing for more efficient and environmentally friendly coating processes based on counter charged, solvent-free powder coating particles.
Graphene platelets deliver electrical conductivity similar to copper yet the material’s density is four times lower, resulting in lighter weight components. Graphene platelets are also fifty times stronger than steel with a surface area twice that of CNTs. Graphene nanoparticles at low loadings improve significantly mechanical and thermal properties of PP based nanocomposites for automotive applications.
UK-based Briggs Automotive Company has developed a vehicle made with graphene in its bodywork. Applied Graphene Materials (http://www.appliedgraphenematerials.com/) has also recently utilized graphene for automotive composites, on the W Motors’ Fenyr SuperSport car. Graphene has been used to improve the tailgate’s performance.
Figure 3: W Motors’ Fenyr SuperSport car.Figure 3: W Motors’ Fenyr SuperSport car.
Group NanoXplore (http://www.nanoxplore.ca/) has a $10.4M project with Sustainable Development Technology Canada (SDTC) to support the commercialisation of lighter, more reliable and higher-efficiency components for electric motor systems using graphene-enhanced engineering plastics in place of metals. Korea-based producer Standard Graphene (http://standardgraphene.com/) has a technical cooperation MOU with Local Motors utilizing graphene to improve the properties of the carbon fiber/ABS plastic composite used in the 3D printing of vehicles, as well as improving battery cell technology. Other partnerships include Korea Automobile Parts Association (KAPA) for heat radiation materials and lightweight components.
Main current application of carbon nanotubes (CNTs) in the automotive sector are in coatings and composites with enhanced anti-static and thermal properties. A growing market is additives for tire reinforcement. Properties of CNTs that are attractive for automotive applications include:
- Improved thermo-mechanical properties;
- Improved barrier properties;
- Flame retardancy;
- Conductivity greater than copper yet four times lighter.
Use of CNTs also allows for a reduction the cost of painting plastic fenders: adding minimal amounts of CNTs makes semi-finished parts electrically conductive.
Mitsui Chemicals America, Inc. produces AURUM CNT Grade, a dust-reducing, high-antistatic nanocomposite consisting of thermoplastic polymide and carbon under the trade name AURUM CNT Grade. Toyocolour Co., Ltd.’s Lioplax™ series of carbon black compounds and high conductive compounds formed by using Toyocolor’s unique CNT design to facilitate the dispersion of various types of binders and solvents. Lioplax carbon black compounds give a luxurious black colour to automobile interiors, electronics casings and other surfaces, due to an optical confinement effect generated in the CNT network.
Single-walled carbon nanotube producer OCSiAl has developed composites with Mahindra CIE Automotive that demonstrate improved mechanical strength, impact strength, are electrical semi-conducting and light weight.
Other nanomaterials utilized in automotive composites include:
- PP based nanocomposites.
- Thermoset resin additives.
- Automotive cabin filters.
- Composite resins.
- Reinforced thermoplastics for body panels and interior trim.
- Conductive sheet molding compounds
- Thermoset resins with superior thermal properties for under the hood components
- Vibration damping elastomers for automobile tires.