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From field to flight: The role of sustainable composites

Composites in the context of Net Zero

Across all industries, businesses are working out how to get to Net Zero – or a carbon neutral position. In many cases, this requires a complete rethink about everything the business does – from supplier management to sourcing sustainable materials.

The materials issue is a significant one. How do we move from mining raw materials to harvesting them sustainably and reusing existing products? How can we develop new materials that meet relevant industry standards and are also sustainable beyond the end of life?

At Cascade Engineering, our business centres around structures. In particular, we deal with lightweight, efficient structures. With a global emphasis on improved energy and resource efficiency, we are seeing more industries looking to capitalise on these skillsets. Luckily the physics doesn’t change so the skills we have in design and analysis are easily transferred. Those skills are founded on an ability to think laterally about how to work within weight, performance and budget constraints, whilst also making sure we are taking a sustainable approach.

Materials in aerospace

For this discussion, let’s consider the aerospace industry. This is a multi-billion global industry that’s used to materials innovation and efficient structure design.

Aerospace projects tend to use both ‘standard’ metals and composite materials. The metals we use are usually well-known: steel, aluminium or titanium alloys. These have been around for a long time and the ability to recycle and reuse is well documented.

For composites the story is not so straightforward – the most common composite materials currently in use have fewer sustainable options at end of life. Typically, recycling or reusing these components is either impossible, uneconomic or impractical. This is compounded because most composites in use in aerospace have synthetic resin matrix systems derived from petroleum oil. These systems employ an irreversible curing process to harden, giving the needed material properties for the part but limiting options at end of life.

Meeting certification and regulatory challenges

For obvious reasons, the aerospace industry has strict certification and safety standards. Introducing new materials, including natural fibres and biodegradable resins, requires extensive testing and validation to ensure they meet the necessary requirements for building flight-worthy components.

With aerospace Regulatory Authorities already stretched due to revolutions in drone diversity and Advanced Air Mobility, it will be a challenge to find the right way to manage all the groups looking for their support at the same time. These are the times where it is important that industry is aware of the importance of this type of innovation, and willing to work in partnership with regulators – and also that governments do what they can to facilitate the various bodies and enable the adoption of novel and innovative approaches.

An introduction to sustainable composite materials

When we talk about at sustainability within the context of composite materials, we are focusing on investigating novel and innovative ways of approaching a complex problem. The good news is that we are seeing more and more of these types of materials being developed and used in real world applications. In this article, we’ll look at some natural fibres and matrices.

Sustainable natural fibres

Natural fibres were there at the start of composite structures, but their synthetic alternatives gave superior structural properties, better corrosion resistance and materials compatibility, improved processing repeatability, and greater design flexibility.

With environmental impacts, regulations and public opinion putting a renewed focus on sustainability, however, there’s been a return to investigating the role of natural fibres. On top of the environmental benefits, composites made from natural fibres have the potential to offer lower production costs and reduced weight in specific circumstances.

Natural fibres tend to come from plants that can be readily farmed, making them sustainable and biodegradable. Flax, hemp, bamboo, jute and kenaf are all being considered with varying levels of maturity. Within aerospace their use for flying parts has been limited, but the focus shows a good intent for the future. Examples of where natural fibres may struggle is with specific strength for high-performance applications and moisture absorption for service life and through-life maintenance.

Sustainable alternatives to natural fibres include recycled composites and aligned cellulose nanofibers, though these are often more costly to obtain and refine.

Sustainable resin matrices

Sustainability in resin matrix systems is available through biodegradable resin matrix systems. An alternative that gets you moving in the sustainability direction is recyclable systems. Both have pros and cons which we will consider here.

Biodegradable resin matrix systems

Many biodegradable resin matrix systems on the market are in development. Instead of using petroleum-based resins, bio-based polymers derived from renewable sources such as corn, soy, or sugarcane can be used as a more sustainable matrix in composites. The bio-based content varies in the products, and they need to be suitably matched to use, but they have a lower carbon footprint and reduce dependency on fossil fuels.

These systems are designed to be environmentally friendly and break down naturally over time to reduce the long-term effect on the planet. There are challenges though. Compared to their oil-based counterparts, they have comparatively low specific strength and stiffness as well as limited temperature and moisture resistance. As such, initial applications will be on non-critical or disposable components such as interior panels, non-structural parts or temporary structures.

Recyclable resin matrix systems

Recyclable resin matrix systems are becoming increasingly feasible, and they offer a route to inexpensive, high quality material. Both economic and environmental benefits will improve as the technology in the industry advances. Recycling is ranked poorly in the best ways to manage waste though, behind avoidance, reduction and reuse. Also, chemical recycling to acquire the highest-grade material is still in the research phase. Current techniques tend to downgrade the materials such that the recycled product is of lower structural capability than the original. Again, this limits their use on critical or highly loaded structures.

Cross-sector development

It is possible to see then, that the use of natural materials in aerospace composite components is limited by the nature of the industry in terms of routes to acceptance of novel and innovative technologies. As such it is likely that early adoption from other sectors will provide the demand necessary to make investment in growing supply chains worthwhile. Examples of industries that utilise natural composites include Automotive, Construction and Building Materials, Consumer Goods, Packaging, Marine, and Agricultural and Horticultural Products.

It is important to note that the adoption of natural composites varies among different industries and regions. The level of acceptance often depends on factors like material availability, cost, performance requirements, and environmental regulations. As the demand for more sustainable practices and eco-friendly materials continue to increase, the use of natural composites is likely to expand further across various industries. This will improve material quality and processing repeatability: something the aerospace industry values as part of its general acceptance.

Natural composites – what is Cascade’s role?

At Cascade, we understand the intentions and vision of the regulatory authorities and work with them to get a mutually acceptable route to success for any given project. For novel materials this can include derivation of material properties, prototyping and testing. Depending on our client’s wishes, we often take on responsibilities for some or all of these aspects.

A good example was when we were asked to assess a silicone rubber material for a duct within an aircraft cockpit cooling system. The material was a novel type of silicone rubber, and characteristics suitable for modelling the use of the material did not exist. Cascade developed a certification plan, then commissioned a set of tests from a world-leading test organisation. We were then able to create a Finite Element model that was thoroughly checked and validated. The detailed report also addressed adverse factors affecting rubber such as durability, creep and ageing.

Adapting materials to the drive for change

Pressure is being placed across all industries to rise to the challenge of sustainable and environmentally friendly materials use. This inevitably means change: for critical structures this means adopting new, innovative materials.

Change is often uncomfortable, but there is no choice – the planet’s resources are finite and we have to find better ways of working. At Cascade, we know it is better to be part of the change than play catch up later. You can mitigate risk by collaboration and partnership with those experienced in working with regulatory bodies to find common ground.

If you want to discuss a project you have that may need support achieving a route to certification, feel free to contact Cascade Engineering.

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