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Designing plastic parts and components has been a large part of my design career. I often find myself analysing and scrutinising plastic parts everywhere I go. We often take it for granted and don’t actually realise how many plastic parts we interact with everyday. There is a massive push for sustainability in every industry and because of this, there has been a growing worldwide revolt against plastic. We can forget that plastic is a highly versatile material that can be used intelligently and sustainability if done right.

exploded part design comparing metal and plastic materials

The Big Picture

Plastic is a huge contributor to global waste and has a significant carbon footprint, there is no denying that. If we take a step back and analyse some of the advantages of using plastic compared to other materials, it can paint a different picture.

One advantage is that plastics save a huge amount of waste material, due to the way it is processed. Injection moulding is a common production method and is significantly more efficient long term, as there is minimal waste material during production if produced correctly.

Only 4% of the world’s oil production is used  for plastics and less energy is required to produce polymers compared to traditional materials. Furthermore, when most plastics reach their end of life they can either be recycled or can be recovered through energy from waste incineration.

The most significant advantage of plastic is the fact it is so lightweight and can achieve the same results as traditional materials (even better in some instances). Even if a plastic part technically has a higher carbon footprint to produce it, you need less material to actually produce it. If a metal part weighs six times more than its plastic counterpart (that achieves the same result), not only do you have to produce six times the weight of material, you also have to transport six times the weight of material when shipped across the world. You also have to deal with six times more of the material as waste at the end of life.

The aerospace industry is a clear example of how plastic is changing the game. Historically manufacturers have used aluminium, steel and titanium which make up 70% of an average aircraft. There is now a big push to switch to thermoplastics which initially are more expensive, however they allow for a significant reduction in weight. In some cases being almost ten times lighter than metal, carbon-fiber reinforced polymers can be responsible for reducing aircraft weight by 20% and thus saving significant amounts of fuel usage. The Airbus A380 is 22% plastic which helps reduce the fuel burn to a rate comparable to that of a standard family vehicle. Not only is weight saving an important property for an aircraft but so is durability and safety. Galvanic corrosion between dissimilar materials  is the primary cause of structural failure for aircraft fuselages using aluminium, which thermoplastics solve.

Similar comparisons can be drawn with the automotive industry. Through clever design and application of thermoplastics, 100kgs of plastic can replace 200kgs to 300kgs of traditional material in a vehicle, which equates to saving 750 litres of fuel for every 100kgs of plastic used.

Plastic does have its place in a sustainable world if we are able to use it wisely. Some design principles we have to keep in mind are:

Choosing the right material for the job

Plastic is a hugely versatile material and there is a science in even choosing the right type of plastic or polymer for the job.

Choosing the right material for a product is critical and is affected by several factors. Cost, mechanical properties, thermal properties, clarity and aesthetics, flexibility are all things to consider. Additives and modifiers can be added to improve tensile strength, UV resistance, rot resistance, chemical resistance, clarity, fire resistance etc. We can simply pick a suitable plastic for a particular application and customize the polymer makeup to suit exact requirements. However, with great power comes even greater responsibility as all these additives greatly improve the plastics properties, they can conversely reduce the ability to recycle the polymer at the end of its life. With any material there are pros and cons and there is no material that ticks all the boxes. The ability to understand these polymers, what they do and the implications and benefits the different additives provide is essential, to have a product that is fit for purpose yet still sustainably viable.

montage of plastic parts Blener has designed for clients

Design intent applied to the material

Designing a plastic part involves a lot more consideration than one would think. Here at Blender we have designed a substantial number of plastic parts between us over the years and have learnt a few things. Plastic polymers provide a huge amount of flexibility when it comes to design and because the material is inherently flexible, it provides opportunities to be innovative. Traditional fasteners can be replaced with snap fits that lock two parts together, hinges traditionally made from multiple components can be replaced with  flexible plastic hinges, plastic springs can be built into a design to replace traditional springs and material can be cored out to retain strength and reduce weight. Textures, finishes, labels and colours can be replicated perfectly and in high volume without the need for manual processing (usually in multiple steps).

Each design decision made when creating a plastic part should be carefully considered. Some manufacturing techniques save a huge amount of energy and cost for post assembly time and negate the need for additional parts or labour. An example is co-moulding, a process where a second thermoplastic is moulded onto an existing plastic substrate. This allows for a hard plastic component with softer rubber features such as grips, seals, or buttons. The catch here is that it can be difficult to recycle these bonded materials at the end of the product’s functional life, producing a controversial topic in sustainable practice. One could argue that the use of only one manufacturing process to achieve a part that would traditionally require two processes, saves on energy costs in the long term. As designers and engineers it is our responsibility to foresee these long term implications, weigh up the pros and cons and make decisions that benefit the parts we are designing, but also how they affect the environment at the end of their life.

sketch of features of plastic design which make it a good material to use

There has always been a large misconception that plastic is the enemy. In taking a step back we realise that when applied correctly, plastics can offer more sustainably viable options than some traditional materials. As advancements in material science continue, Bioplastics become more common and innovation grows in this sector, as the demand increases. For the time being though, plastic is here to stay and so is the ever greater need for sustainable material choices in product development.