Graphene Offers Weight Reduction in Automotive Composites

Lightweight Automotive Composites with Graphene: Next-Generation Reinforcement Material Today's vehicle production demands high performance, competitive pricing, design and safety alongside durability, lightweight construction, fuel efficiency and environmentally-conscious properties that minimize carbon emissions. For this reason, plastic parts have begun replacing metal components in vehicles in recent years. Glass, carbon and aramid fiber-reinforced composites have increasingly been adopted in aerospace and space industries due to their superior properties compared to other engineering materials. These materials are attracting significant interest due to their high impact resistance, hardness, low weight, corrosion resistance and high thermal stability [1,2]. Additionally, recyclability of components used in next-generation vehicles is another area of growing attention. For this reason, many interior and exterior trim parts in vehicles are now being manufactured from polyethylene, polypropylene, polyamide 6 and polyamide 66-based thermoplastic prepregs. Various filler materials are used to impart functional properties to polymers and achieve structural improvements. A study has shown that three times more glass fiber by weight than montmorillonite clay is required to double the modulus of nylon 6 [2]. With nanofillers used at 3-5% by weight, it is possible to observe the performance provided by micron-sized fillers used at 20-30%. In this way, nanocomposites provide a significant advantage in weight reduction compared to conventional composites, while nanofillers increase interfacial interactions and surface area, thereby also raising modulus values. Nanofillers are categorized according to their dimensions: nanotubes and nanowires are one-dimensional, nanoclays and graphene are two-dimensional, spherical and cubic nanoparticles are three-dimensional. Particularly among carbon materials, graphene and carbon nanotubes can impart extraordinary properties to polymers thanks to their high aspect ratios and high mechanical strength. Graphene layers are present in graphite structure and are held together by van der Waals bonds. Three different techniques are widely used for graphene production: arc plasma, chemical vapor deposition and chemical exfoliation. When cost and production capacity are considered, the chemical exfoliation technique offers more advantages. In the chemical exfoliation technique, strong oxidizing agents are used to break the bonds between graphene layers within the graphite structure and open spaces between the layers [3, 4]. Figure 1 contains a scanning electron microscopy image of graphene produced from graphite. However, strong oxidizers used during oxidation (potassium permanganate and sulfuric acid) both complicate the process and carry explosion risk [5], and long production and purification times also increase costs. The proposed project will use electrochemical exfoliation technique for graphene production at moderate conditions, with reduced cost and high yield. In the electrochemical method, graphite is used as an electrode and positive and negative charges are applied to the material in the presence of electrolytes, enabling both diffusion of intercalants between graphene layers and initiating the flaking process. Another problem encountered in graphene production is that graphene layers obtained after oxidation and reduction processes reunite, reducing surface area. Therefore, surfaces need to be functionalized and made compatible with the selected matrix. For this reason, the carbon/oxygen ratio and functional groups on the surface are determined and either a reduction process or direct surface modification with solvents is performed. Looking at these processes generally, solutions have remained at laboratory scale and do not offer solutions suitable for scaling, environmentally friendly and low-cost. One of today's greatest problems is that virgin or recycled plastic waste is not biodegradable and its disposal causes irreversible environmental pollution on land, air and water. These wastes can remain in nature without degradation for thousands of years. With an average annual growth rate of 5%, plastic production reached 400 million tonnes in 2020, and plastic consumption reached the highest levels with the pandemic. Traditional methods for plastic waste disposal such as incineration or landfilling cause groundwater and other resource contamination, generation of dust, smoke and toxic gases, leading to increased carbon footprint and greenhouse gas effect. Management of waste plastics causing environmental pollution is becoming an increasingly growing problem. In this regard, by developing an environmentally-friendly and cost-effective method through upcycling, producing graphene from recycled carbon black obtained from waste tires, I have advanced my scientific work from Technology Readiness Level (TRL) 1 to 8 and, with my company Nanografen established with TÜBİTAK 1512 support, have successfully moved my work in this field to commercial scale and entered among the few global companies in this sector. As of November 2021, Nanografen entered the official supplier list of a global automotive company and became the only company in the world demonstrating that graphene-enhanced materials can be used in high-volume production in thermoplastic composites. The use of such waste materials by OEMs provides both compliance with regulatory requirements and benefits such as tax reduction advantages. It is possible to use plastic waste as a carbon source for graphene production. Although plastic recycling provides various benefits, recycled plastics do not have the same performance as virgin plastic composites. Instead of traditional recycling processes, it is possible to produce high value-added carbon nanomaterials by utilizing the rich hydrocarbon source in plastics. In the study I conducted at Sabancı University Integrated Manufacturing Technologies Research and Application Center with TÜBİTAK 1003 support, using polypropylene sources and applying an environmentally-friendly, sustainable and cost-effective upcycling technology, I succeeded in growing graphene structures on talc, a natural filler with lamellar structure, and developed lightweight thermoplastic composites with this newly designed hybrid filler while reducing the main reinforcement amount in the targeted automotive part. In addition to polypropylene waste, recycling of aromatic plastics such as polyethylene terephthalate and polystyrene is complex and is highly sensitive to process design and conditions due to the presence of polycyclic aromatic hydrocarbons and C–O and/or C–C linkages between units. Here, the upcycling process becomes very important for obtaining high-value products from aromatic plastics. It is possible to produce 2-dimensional and 3-dimensional graphene structures on natural 2-dimensional substrates through thermal treatment using the carbon source in waste. In recent years, the adverse effects of global warming and greenhouse gas (GHG) emissions are triggering the need for industrial decarbonization across all sectors. The transport sector, which accounts for 27% of the European Union's greenhouse gas emissions, is responsible for 23% of CO2 emissions [6] and 92% of energy demand is dependent on oil [7]. Despite significant technological advances over the past decade, projected GHG emissions fall short of the Paris Agreement targets due to increasing demands in the transport sector. Therefore, to achieve policy targets toward net-zero greenhouse gas emissions by 2050, intensive research and innovation activities are needed for all transport vehicles. Particularly in hybrid and electric vehicles, lightweight component designs are important for increasing fuel efficiency and improving vehicle performance. Although glass fiber and talc-filled composites are widely used by the automotive industry due to their advantages, alternative solutions are needed in lightweighting efforts due to density and production costs. Studies show that reducing a vehicle's weight by only 10% increases fuel economy by 6-8% and reduces CO2 emissions by 15-20 g/km. Together with my team, considering CO2 emission reductions, I conducted comprehensive life cycle assessment to demonstrate the environmental benefits obtained from the proposed innovative upcycling solutions through comparative studies. Life cycle assessment (LCA) is a program that examines the environmental impacts of products, processes or services through a cradle-to-grave approach via production, use and disposal, and calculates the carbon footprint. For example, recycling 4 vehicle tires reduces CO2 emissions by 146 kg. Evaluated generally, LCA approaches today typically include material production and component production topics based on data obtained from design work. Through LCA analyses, systematic evaluation can be performed from both material synthesis through final application, and economic and environmental impact feasibility can be presented as a contribution to waste management systems. The Ministry of Science, Industry and Technology of the Republic of Turkey has highlighted the issue of "spreading the use of advanced technology with strong and competitive supply industry and domestic brands it produces, and increasing the added value ratio" in work on domestic vehicles. Upcycling technology targeting the basic needs of the automotive sector in lightweighting, based on the circular economy approach, will bring a new dimension to addressing today's plastic waste problem. References: [1] Davim J. P., Reis P., Antonio C., Experimental study of drilling glass fiber reinforced plastics (GFRP) manufactured by hand lay – up, Composites science and techology, 64, 289-297, (2004). [2] Fornes T. D., Paul D. R., Modeling properties of nylon 6/clay nanocomposites using composite theories, Polymer, 44, 4993–5013, (2003). [3] Saner B., Dinc F., Yürüm Y., Utilization of multiple graphene nanosheets in fuel cells 2. The effect of oxidation process on the characteristics of graphene nanosheets, Fuel, 90, 2609-2616, (2011). [4] Saner B., Okyay F., Yürüm Y., Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite, Fuel, 89, 1903-1910, (2010). [5] Hummers W. S., Offeman R. E., Preparation of graphitic oxide, Journal of American Chemical Society, 80, 1339, (1958). [6] European Environment Agency (EAA), Indicator Assessment: "Greenhouse gas emissions from transport in Europe", Prod-ID: IND-111-en, TERM 002, Published 18 Dec 2020, updated in 22 Jul 2021. [7] European Environment Agency (EAA), Briefing: "Transport: increasing oil consumption and greenhouse gas emissions hamper EU progress towards environment and climate objectives", Published 03 Feb 2020, Last modified 02 Sep 2021. Assoc. Prof. Burcu Saner Okan Academic Director Sabancı University Composite Technologies Center of Excellence Founder-Nanografen