Analysis: Composite materials can already be found in everything from boat hulls, to cars, and wind turbine blades. What about planes?
We are all aware of our need to cut down on plastic consumption, with moves towards reusable and recyclable packaging, and initiatives like the Deposit Return Scheme becoming more prevalent in our lives. However, what if certain types of plastics could help cut down carbon emissions? For example, could plastics be used in aviation so that airplanes are lighter and more fuel efficient?
Plastics are created from polymers, and it is these polymers that may prove to be beneficial in terms of carbon reduction. On their own, polymers may not have the strength required to create a structure safe enough for air travel. However, introducing a reinforcement to the polymer in the form of a continuous fibre alters these properties, in a similar fashion to steel reinforcing in concrete.
Continuous fibres, for example carbon fibres, that are held in place by the polymer provide significant improvement in strength. These continuous fibre reinforced polymers are more commonly referred to as composite materials, they can be found in a range of applications, from boat hulls, to cars, and wind turbine blades. This may lead to the question, "why aren't composites already used in aviation?"; the answer is they are. However, there is still a lot of development required to extract the full potential of composites for aerospace applications.
From TED Ed, From DNA to Silly Putty: The diverse world of polymers
Generally, the process to manufacture an aviation safe component involves precisely laying thin, composite sheets on top of each other. This stack of composite sheets, then needs to be consolidated together to form a laminate using heat and pressure, usually in an oven called an autoclave. An autoclave is similar to a pressure cooker but can be as big as two double decker buses.
While autoclave manufacturing can produce high quality composite parts for aerospace applications, it does have some drawbacks. Firstly, the process can be relatively slow, it can take up to 12 hours for composite aerospace components to be consolidated. Secondly, the process has a high energy demand due to the heating required to reach the consolidation temperature. The process also uses a considerable amount of disposable consumable materials. Finally, the process is only suitable for relative thin components, such as skin and wing panels. Therefore, in order to produce more complex composite components, alternative manufacturing systems and alternative polymer materials may be the next step in composite development.
Read more: Why we need plastics (and what to do about it)
Thermoplastic polymers offer the potential to manufacture composite components without the use of an autoclave. Commonly, thermoset polymer composites are used to manufacture large components, as they do not require temperatures as high as thermoplastics during processing, however an autoclave is still required. For thermoset composites, increasing the temperature speeds up a chemical reaction that occurs within the polymer.
This chemical reaction permanently changes the thermoset polymer, turning it from a glue-like substance to a solid part that can not be reshaped. In contrast, heating a thermoplastic composite causes the polymer to melt, and when cooled it solidifies again. As there is no chemical reaction in thermoplastic polymers, they are considered recyclable. Thermoplastic composites therefore introduce potential for composite component manufacturing that does not require an autoclave, as there is no chemical reaction, the composite does not need to be above the melt temperature for an extended period of time, only long enough to bond each layer together. Therefore, a process that involves placing a layer and bonding it to the previous layer introduces a more time efficient and energy efficient manufacturing process.
From University of Limerick, Here's how an Automated Tape Placement (ATP) System works
One example of an advanced manufacturing process is an automated tape placement system, which is made up of a high-power heat source and a robotic arm. This automated system places the composite layers that make up the component, removing the need for hand lay-ups, while the heat source locally heats the polymer above the melt temperature.
Once the polymer in the composite is above the melt temperature, a roller then applies pressure onto the composite, which bonds each layer together and builds up the desired composite laminate. The material then rapidly cools, returning to a solid state and resulting in a composite component. This series of events repeats until the desired component geometry is reached. This system removes the size and energy limitations associated with autoclave manufacturing while also removing issues associated with part size.
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There are still some issues associated with the automated tape placement system, as it currently cannot manufacture components of the same quality as an autoclave. However, it is being used as a first step in aircraft safe composite component manufacturing, with processing in an autoclave needed afterwards. Research is still ongoing in order to remove the requirement for post processing, which would result in aircraft safe composite components at a lower production cost and energy cost. Additionally, it would result in a more fuel-efficient aircraft that has lower associated CO2 emissions.
So, while it’s unlikely airplanes will be made of just plastic in the future, there will a significant amount of fibre reinforced polymer composites in our skies.
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
