Nylon, as we already know, is a synthetic polymer belonging to the group of polyamides (PA). In additive manufacturing we can find it in the form of a filament (PA6) for FDM technology, or in powder form (PA11 and PA12) for technologies such as selective laser sintering or HP MultiJet Fusion. Despite being a widely used material in the 3D printing industry, nylon has been the subject of debate at times, especially regarding its sustainability. This is due to several factors, such as the composition of some polyamides, the degree of recyclability and reuse of the material, or gas emissions during the manufacturing process. In addition, the commitment to the environment is an aspect that all companies are taking and must take into account today, something that we will also see later.
If we focus solely on nylon 3D printing, it is clear that, depending on the type of polyamide, its origin and composition, this material will have a greater or lesser impact on the environment. To better understand its role in the industry, as well as its carbon footprint, we will try to analyze the characteristics and properties of nylon, both in powder and filament form. So how are PA6 filaments printed, how are PA11 and PA12 different, where does the 3D industry stand in terms of nylon usage and sustainability, and are there viable alternatives? Below, we will provide answers to all these questions to better understand how sustainable this material is and the way forward for the manufacturing industry.
PA6, a demanding 3D printing filament
PA6 filament is a semi-crystalline thermoplastic polymer and is one of the most widely used polyamides worldwide. With a melting point of 220°C, PA6 is used in a wide variety of applications due to its good performance/cost ratio. Although it has traditionally been used in industrial manufacturing methods, it has gradually gained popularity in the 3D printing industry due to its interesting mechanical properties and ability to create high-performance parts. Also, PA6 is a much more difficult material to 3D print compared to standard plastics like PLA or ABS. Its operating temperature range is 250-270°C, so a suitable working environment must be ensured so that it does not shrink.
Regarding its origin, we can say that it differs from other types of polyamides in that it is formed by ring-opening polymerization, that is, by one of the ways by which many polymers are synthesized. This makes it a special case in the comparison between condensation polymers (the entire monomer molecule becomes part of the polymer) and addition polymers (part of the monomer molecule is lost when it becomes part of the polymer). When analyzing the environmental impact of polyamide 6 and moving towards a more sustainable material, two important aspects must be taken into account. Firstly, the production processes used to obtain the material, and secondly, the raw material involved in this conversion process; both will define the carbon footprint of this polyamide.
Composition and environmental impact of PA11 and PA12
In chemical terms, polyamides 11 and 12 are very similar, although they differ by only one carbon atom in the polymer backbone. However, that single atom makes a huge difference in how the polymer is organized to create matter. Apart from that, the main differences between polyamide powders for 3D printing lie in their origin. On the one hand, PA11 is a semi-crystalline polymer that is generated from a “green” raw material in a synthesis process that is closer to PA6 than to PA12. This type of nylon is bio-based, that is, it is produced from renewable raw materials derived from plant derivatives, mainly castor oil. Regarding its applications, polyamide 11 is mainly found where good chemical resistance, flexibility, low permeability and dimensional stability are required. That is, in aggressive environments and functional prototypes that are exposed to these conditions.
On the other hand, PA12 is a fine synthetic powder that is usually derived from petroleum. Its basic characteristics are given by the chemical structure of the polyamide itself, as well as by the addition of additives or fibers that are added to the composition. Its most important properties are high resistance to chemical agents, environmental conditions and impact, as well as low water absorption, high processability and, lastly, good resistance to abrasion and slipping. Among its main applications, this plastic is used in advanced industries, such as the automotive industry or aeronautics. As we have mentioned, this is due to its excellent mechanical properties, which are key in this type of professional sector.
While discussing its own PA11 HP, Sculpteo illustrates the disparities between the two polyamides, and more specifically their relationship to sustainable sourcing, with the website stating: “Our PA11 HP is based on 100% renewable biomass sources. Castor bean is extracted from the castor plant to make oil. The oil is then converted to the monomer (11-aminoundecanoic acid), which ultimately polymerizes into polyamide 11. This PA11 material is a sustainable alternative to PA12 and offers interesting properties for components that require skin contact.” This shows that, in terms of sustainability, nylon 11 should be the bioplastic to turn to first, although applications for final 3D printed parts should also be considered.
Given the properties of both polyamides, the bioplastic might seem, at first glance, to be a better alternative to conventional plastic, as it is made in part from renewable resources and can be biodegradable. However, Nuno Neves, responsible for the design of FICEP S3, tells us: “To determine whether bioplastic is better for our environment compared to conventional plastic, we need to consider several factors throughout the life cycle of conventional plastics versus bioplastics, including production, greenhouse gas emissions, greenhouse effect and recycling opportunities. Something we do at FICEP S3 with every material we use and every product we design. We make decisions based on the data and the scientific reality of a given situation, beyond wanting to jump on the eco-friendly bandwagon”. That said, and taking into account the properties of nylon, let’s see its use in 3D printing as well as its relationship in terms of sustainability.
Nylon, 3D printing and sustainability
As with other synthetic plastics, nylon is not a material that can be degraded by the environment. This would be the case for other natural resources, such as paper, wood or glass, which oxidize and decompose over time. For this reason, the most recurrent method to combat the complex disposal of plastics on our planet is recycling, that is, its transformation. One aspect to take into account is that bioplastics, such as PA11, are difficult to recycle, since most cities do not have the necessary facilities for this type of transformation. Many of them end up in landfills, causing them to be deprived of oxygen. This triggers the release of methane into the atmosphere, a greenhouse gas 23 times stronger than CO2, which would contribute to greater depletion of the ozone layer than traditional plastics.
Focusing on the two main technologies used, we see that in terms of sustainability, SLS nylon 3D printing has a key advantage. Once the manufacturing process is finished, the parts are wrapped in unsintered powder, which in turn acts as a support for the printed parts. In SLS technology, up to 70% of this unsintered powder can be reused for future prints. From a sustainability and recyclability point of view, this is a huge advantage over the FDM method, as the support materials being printed cannot be converted for reuse.
To evaluate and control the environmental impact of companies, there is the so-called CSR or Corporate Social Responsibility, which refers to the responsibility that each organization has towards the environment. This aspect is increasingly present in the activity of all the actors in 3D printing. In fact, many companies in the industry are already developing bio-based solutions to reduce this environmental impact.
Arkema is one of the most recognized chemists in the industry and has a wide range of materials for additive manufacturing, including nylon. In particular, the company has unique experience and knowledge in the chemistry of castor plants. A wide range of high-performance, long-chain biodegradable polyamides can be developed from this plant, as is the case with the company’s Rilsan® polyamide 11 range. Jean-Luc-Dubois, Director of Catalysis, Processes and Biomass Conversion at Arkema, commented, “Our bio-based processes demonstrate that renewable raw materials can be used to manufacture technical and cost-competitive products that meet real market demand.”
Future prospects for nylon in terms of sustainability
It is evident that all the manufacturing materials used in the manufacturing industry have some impact on the environment, either due to the emission of gases or due to the degree of recyclability of the parts. In addition, while there is currently no viable replacement for petroleum-based polyamide, highly promising biotech-based polyamide building blocks are currently being investigated. As the price of oil continues to fluctuate and awareness of the climate crisis increases, it is likely that more alternatives to today’s nylon components will be developed.
Still, focusing on the 3D printing process itself, we know that the technology is known for reducing manufacturing times and the amount of material used. Regarding the use of polyamide 11, the Arkema team states on its website: “More and more companies are demanding clean and sustainable materials. PA11 is a 100% biobased polymer and its selection fits perfectly with this green strategy to help achieve corporate social responsibility goals.” Regarding the global use of nylon, Nuno Neves from FICEP S3 gives us a more contrasted vision: “The solution is not to stop manufacturing and using petroleum-derived plastics, but to use them more intelligently, recycle them correctly and stop thinking that everything ‘bio’ is synonymous with good, that it is rarely that simple.”
Contrasting both points of view, it is clear that the additive manufacturing industry is on the right track when it comes to the use of nylon. However, there is still a long way to go to do, as Neves says, the “bio” positive and achieve more sustainable manufacturing with less environmental impact.
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*Cover photo credits: Sculpteo