THE SUSTAINABLE FUTURE OF NYLON
Nylon – probably one of the most known synthetics in the textile world besides polyester. In fact, Nylon shares at its first glance a similarity with polyester: they are referring to a group of plastics with different properties. The most known and used polyester is PET (polyethylene terephthalate), for Nylon basically many people do not know the different types.
Nylons are polymer substances composed of a long and multiple numbers of molecules in which the repeating units are linked by amide groups1.
Nylon is a trade name of the company DuPont. Most clothes made of Nylon are with its chemical name labelled Polyamide. In this report Nylon is being used instead of Polyamide to simplify the reading.
According to the latest Textile Exchange Preferred Fiber and Materials Market Report from 2021, Nylon fibers had with around 5.4 million tons a market share of about 5 percent of the global fiber production market in 2020. Global total Nylon fiber production increased from 3.74 million tons in 1990 to 5.4 million tons in 2020. In 2020, the global Nylon fiber production decreased from 5.58 million tons in 2019 to 5.45 million tons in 2020 due to COVID-19 2.
The History of Nylon
Nylon was first discovered in 1931 by the American chemist W.H. Carothers of the company DuPont which started commercializing it in 1938. They named it Nylon 6.6, because it is made from two different monomers each of which has six carbon atoms.
It was the first fiber to be synthesized from petrochemicals and claimed a novelty no other product could match 3. Originally developed as a replacement for silk, hosiery in Nylon 6.6 was on display at the New York World‘s Fair in the summer of 1939 and available nationwide in 1940 4. Later, Nylon found its way into technical applications such as balloon cloth, glider tow ropes, airplane tire cord, and military apparel to support the United States in the World War II.
At the end of World War II, applications of Nylon 6.6 fibers were expanded from hosiery to many other textile and industrial uses 5.
Besides the development of Nylon 6.6 in the United States, in 1937 the German chemist Paul Schlack of company I.G. Farben polymerized caprolactam to Nylon 6 – also known as Perlon. In 1941, British Nylon Inc. began Nylon 6 production in Great Britain and opened the door for synthetic fiber inventions that revolutionized the global textile industry 6.
In the past, the tradename Nylon referred to Polyamide 6.6 and tradename Perlon to Polyamide 6. Nowadays, Nylon is the common international term in the textile industry including both types.
After the World War II, Europe faced a dramatic shortage in crude oil which led into the development of an alternative route for producing Nylon. The small French company called Organico commercialized in 1947 the first known Nylon made of 100% biobased content, using castor oil as its feedstock. This Nylon 11 is known under the brand name Rilsan® produced by the French chemical company Arkema 7.
In 1969, Neil Armstrong planted a Nylon flag on the moon while wearing a Nylon and aramid spacesuit, which made a momentum for the technical capabilities of Nylon 4. Over the years Nylon became more and more popular in the consumer and industrial area and several new types were developed and commercialized.
Nowadays, Nylon is being used in different kind of applications such as fibers, molds, resins, and films. Segment applications including textiles, automotive, carpets, and sportswear due to their strength and durability 1.
The term Nylon refers to a generic material group and not to a single material type. Unfortunately, also textile labeling rules only list the Nylon material group as »Polyamide« or »Nylon« (depending on regional area). Thus, behind the content label information »Polyamide« can stand all types of Nylon such as Nylon 6, Nylon 6.6, Nylon 10.10 etc. For the user this creates problems as one does not know which specific material is being used. Considering End-of-Life textile recycling schemes, an identification of the material type creates difficulties when using only the generic material group name. With the development of digital product passports, this issue needs to be addressed. The detailed material content type shall be included, otherwise sorting is made more difficult.
Nylons are crystalline polymers typically produced by the condensation of a diacid and a diamine or formed by a ring-opening polymerization. There are several types, and each type is often described by a number, such as Nylon 66 or Polyamide 66 (PA 66). The numeric suffixes refer to the number of carbon atoms present in the molecular structures of the amine and acid respectively (or a single suffix if the amine and acid groups are part of the same molecule) 8.
»The more carbon atoms in the monomers, the less water absorbent is the Nylon.«
* indication based on available LCA data
Difference between Nylon 6 and Nylon 6.6
Nylon 6.6 is the preferred choice if higher tenacity and high temperature resistance is demanded. On the other hand, Nylon 6 provides better recyclability (due to only one monomer) and higher impact stress. Selecting the best Nylon from the material group is often a matter of compromising one or more properties against others11.
Some Nylons are suitable for extruded waterproof breathable films when used as a Polyether-Block-Amid (abbreviation: TPE-A). Most recognized are the Pebax® compounds from the chemical company Arkema. The Nylon type used in there is either Nylon 12 (Pebax®) or Nylon 11 (Pebax® Rnew®). Those Nylon films offer some interesting features:
- High breathability
- High elasticity
- Low weight
- High resistance to cold temperatures
- Recyclable (because it's a thermoplastic material)
- Do not contain isocyanates, DMF, VOC, PFC
- Possible with biobased content (Pebax® Rnew®)
Selected differences between Nylon 6 and Nylon 6.610
Nylon fibers are exceptionally strong and elastic and stronger than polyester fibers. The fibers have excellent toughness, abrasion resistance, are easy to wash, and to dye in a wide range of colors (depending on Nylon type). The filament yarns provide a smooth, soft, and lightweight fabric of high resilience 12.
The water absorption rate is higher compared to other synthetics, especially to Polyester. It allows the development of more comfortable fabrics due to the evaporative cooling. If a lower water absorption rate is needed, longer Nylon chain types could be a solution.
Usage of Nylon
Nylon is used in lot of different industries for numerous applications. Setting the focus on sportswear, below listed are some examples in which Nylons are present.
- Waterproof jackets
- Down jackets
- Trekking pants
- Cycling pants/shorts
- Athleisure pants
- Functional underwear
- Performance tents
- Reinforcement material for socks and wool products
Before the introduction of POM (Polyoxymethylene), Nylon has been the predominantly used material in the sportswear industry for small plastic applications (trims). There are still numerous products on the market depending on their technical requirements. Especially when looking on coil zippers, where Nylon is the dominant material to use.
The used Nylons are sometimes reinforced with glass fiber to increase the tenacity and stiffness.
When looking on mono-material designed products, plastic components are playing a crucial role to allow a better recyclability with higher yield in the combination of Nylon fabrics. That is why it might go back to Nylon components for increase circular material output instead of POM.
Membrane / Film
Nylon films are traditionally used in the food packaging sector due to their superior barrier properties. But there also existing a few thermoplastic elastomers, Polyether-Block-Amides, which can be used as a waterproof breathable membrane. Available compounds are listed in previous chapter.
The traditional Nylons like 6 and 6.6 are made from crude oil. Concerning global trends, the dependency on fossil resources needs to be phased out. There are currently several options available and Nylon from recycled feedstocks is dominating the market. But there are also routes from biomass existing which could prove a viable alternative to petrochemicals.
The global recycled Nylon fiber production volume in 2020 is estimated at around 0.11 million tons. Considering technical challenges and low prices for fossil-based Nylons, the market share of recycled Nylon is with 1.9 % of all Nylon fiber very low 2. Several brands made commitments and pledges to increase the usage of recycled Nylons or even phasing out fossil Nylons 13, so the number of recycled Nylon will increase within the next years.
Recycling Nylons can be produced from post-industrial / pre-consumer or post-consumer waste 2. There are several standards existing, to ensure the chain-of-custody of recycled Nylons, such as the Global Textile Recycling Standard (GRS) and the Recycled Claim Standard – to name the most used.
Compared to recycled PET, which is up to now widely available thanks to existing waste streams from plastic bottles, Nylons are facing a crucial hurdle: There are no waste streams existing.
Therefore, it is difficult to retrieve Nylon waste, especially from post-consumer source. Due to the scarcity of post-consumer Nylon waste, suppliers are often using post-industrial / pre-consumer feedstock for their recycled Nylons. To boost the usage of post-consumer recycled Nylon, efforts need to be taken in the establishment of more continuous collection of waste systems.
Post-industrial / pre-consumer Nylon
Probably the most used recycled Nylon type present.
Post-industrial / pre-consumer recycled material is diverted from the waste stream during a manufacturing process. Excluded is re-utilization of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it14.
The Textile Exchange Global Recycled Standard Implementation Manual 4.2 includes several examples of what can be claimed as post-industrial / pre-consumer material and what not – such as regrinds15.
Regrinds are shredded and / or granulated recover-ed plastics material in the form of a free-flowing material16. The term »regrind« is frequently used to describe plastics material in the form of scrap generated in a plastics processing operation and re-used in-house17.
Examples for regrinds
- Spinning wastage, generated in the yarn extruding process
- Runners, used in the injection molding process
Simply explained, regrinds can be compared to cookie backing: the remaining dough after cookie cutting is being knead and rolled out again and used up until no leftover is present.
Users of post-industrial / pre-consumer recycled materials should make sure that regrinds are excluded – not only from a legal perspective as described, but also from an economic and ecological perspective. If the demand of those regrinds increases, more virgin Nylon might be produced and the holistic efficiency in the process decreases.
Due to the fact, that post-industrial / pre-consumer Nylon feed-stock is often not contaminated with other materials, the mechanical recycling is the traditional technology.
Post-consumer recycled material is generated by households or by commercial, industrial, and institutional facilities in their role as end-users of the product which can no longer be used for its intended purpose. This includes returns of material from the distribution chain 14.
As for Polyesters (PET) a recycling is usually simple, thanks to the pure quality of the bottles, for Nylon instead it is different. Due to the fact, that post-consumer Nylons are already manufactured into products which are usually containing residues of other materials or finishes, the conventional mechanical recycling is often not suitable. Arising chemical recycling technologies are offering the possibility to remove residues and providing a virgin-like quality.
Post-consumer recycled Nylons are playing a crucial role in the circular economy to end up plastic wastage. Unfortunately, there are only limited quantities available in Nylon 6. Thanks to its single monomer content, a recycling of Nylon 6 is more feasible compared to bi-monomer Nylons.
Probably the best-known Nylon from post-consumer resources is ECONYL®18. The European manufacturer Aquafil is producing it in Slovenia. To ensure a steady waste input, they have formed collaborations with industrial carpet users and fish farms to collect their discarded fishing nets. Furthermore, they are working together with the Healthy Seas organization to retrieve ghost nets from the sea.
This idea has been taken up by the Taiwanese company Formosa Chemicals, which is also using chemical recycling technology to process discarded fishing nets 19. They are sourcing the material from Chile and aquafarms in Vietnam. Formosa Chemicals has an exclusive agreement for sale with a prominent American outdoor brand, hopefully it will be available to the public soon.
The idea of taking discarded fishing nets finds more and more supporters. Taiwanese Nylon spinning expert Zig Sheng Industrial company is providing recycled Nylon with a certain amount of mechanical recycled fishing nets 20.
The latest novelty comes from BASF. With their ChemCyling™ platform they can use mixed plastic waste from municipal waste collection and discarded automotive tires. This waste is chemically recycled into a pyrolysis oil which replaces crude fossil oil. The recycled amount is being allocated in the product via a certified mass balance approach. The quality is identical compared to conventional Nylon 6. In 2021 the first textile products have been presented to the market 21.
Despite all the efforts been made on synthetic recycling, the beginning of a material’s life should not be forgotten. And that is why it is important to investigate renewable feedstock resources.
* Post-Consumer might contain Pre-Consumer waste
Biobased plastics utilize renewable resources and have the potential to mitigate climate change, through the usage of CO2 during the growing phase, when compared to fossil-based materials 22. In line with a broader vision, bioplastics are part of the transition toward a biobased economy.
The term bioplastics is often used as a collective term for different plastic types. Two aspects of bioplastics are generally mixed up:
- Its Composition: A plastic made of renewable resources, meaning that the material or product is fully or partly derived from biomass.
- Its End of Life: A biodegradable or compostable plastic. It refers to a chemical process during which, micro-organisms in the environment convert materials into natural substances such as water, carbon dioxide, and biomass. Some biodegradable plastics are also possible to recycle such as PLA, but their quality may be poor for technical applications.
Due to its unprotected meaning and its free use, bioplastic encompasses several expressions:
- Biobased – renewable natural feedstock
- Biopolymer – A polymer is a repeating chain of monomers. The raw material to get the monomers comes from a feedstock partly or fully biobased. e.g. PA 4.10, PA 10.10
- Bioplastic – Biopolymer + additive (commonly refers to hard plastics)
- Biosynthetic – Biopolymer + additive (commonly refers to textiles)
History shows that bioplastics are far from being a new type of material since they were the start of the plastic chemistry in the first place.
It is possible to separate bioplastics in two categories: An Old Economy and a New Economy.
Bioplastic economies based on IfBB
Old Economy / New Economy
The Old Economy refers to bioplastics which have been around since a long time, such as Cellulose Acetate or even Natural Rubber. Those bioplastics are used for their unique properties which cannot be replicated through oil chemistry, or at least not in a cost-competitive manner.
The New Economy follows the interest for new material properties. A part of it are the bioplastics. One sub-family is the chemically novel bioplastics. They are using new or rediscovered materials with properties differentiating from traditional fossil-based plastic counterparts. Until a relative recent past, bioplastics were mostly used for performance related applications, where fossil-based counterparts were not suitable, for instance in biomedical applications or in very specific engineered plastics for the automotive industry. The sustainable aspect wasn't the focus. For the textile / outdoor sports industry, there is a different approach: It is a necessity to find sustainable materials while keeping performances at least at the same level as before. Any change of the properties could be communicated as a performance benefit.
The other would be the so-called Drop-Ins. These plastics have the exact same chemical structure as traditional fossil-based plastics but coming from renewable feedstocks. Thus, they can go directly in the already existing recycling streams. Those are driven by sustainable demand and can be successors of our existing fossil-based plastics.
Taking the example of the Nylons and looking on it as a family, the PA 6 and the PA 6.6 as the parents, the new biobased Nylons like PA 4.10, PA 6.10, PA 10.10 can be correlated as the children or cousins.
- Link is also the fossil-based part
- Characteristics related to the parents
- 100% biobased
- Different characteristics than parents, but still part of the family
- 100% biobased
- Same characteristics as parents expected
There are several definitions of feedstock generations existing. So far none of them are really covering all the possible existing feedstocks and can lead into confusion. The ranking of feedstock should not be brought up in this early stage when other important information is not taken into consideration. Feedstock sources should be evaluated on yield, sustainability, and biochemical composition.
The source of feedstock for bioplastics is a topic which needs some background information. Re-newable feedstocks have generally a very high content of water, leaving a lower amount of matter to use to produce chemicals. Biobased chemical intermediates, from which are obtained bioplastics, are transformed from chemical structures found in renewable feedstocks, such as:
- Carbohydrates which are often referred as sugars, though being a simplification
- Lignin, which binds the cellulose and hemicellulose together
Those chemicals can be found in all plants, the main difference being that certain plants will have higher amounts of carbohydrates, and another higher amount of lignin. This plays a role on why some bioplastics are coming from a certain feedstock and not others. From the end-user side the focus lies on the plant from which the chemicals are extracted, and that is where most of the assessment of sustainability is being made.
The sustainability of biobased Nylon should be verified with Life Cycle Assessments (LCAs). Certifications are important to assess the biobased content: CEN/TS 16295 | EN 16785 | ASTM D6866 | ISO 16620
Availability of biobased Nylons
Several biobased Nylons are commercially available. Driven in the first place by large industries such as the automotive industry, to obtain a demanded performance, the focus is now shifting in other industries, such as outdoor sports, toward a sustainable approach.
Most of the biobased Nylons currently available were developed for their specific performance compared to other fossil-based plastics, and not for sustainable benefits. This focus on high performing materials, which have properties different from the traditional materials used in the outdoor sports industry, is a constraint to deal with when looking at the current market situation.
For currently available biobased Nylons, castor oil represents an essential natural feedstock to produce specific monomer components, such as sebacic acid.
Important to note is that biobased Nylons are still a niche market. Even though several biobased Nylon granulates are commercially available, the extrusion and further processing into textile yarns still presents some difficulties. The difficulties are rather not due to the biobased source of the polymer, it is more a question of a different chemical structure and properties that manufacturers are not familiar with. In addition, the very high price of those Nylons represents the main hurdle in spreading the usage.
So called biobased drop-ins Nylons, virtually identically from the properties compared to the fossil counterparts, are not commercially existing. There are ongoing projects on Nylon 6 to develop and commercialize textile grades.
The EFFECTIVE project, a multistakeholder project funded by the EU Horizon 2020 BBI JU (Bio-based Industries Joint Undertaking), aims to develop Nylon 6 out of sustainable plant-based sugar resources such as sugar beet 23. The project started in 2018 and shall be completed in 2023. The technology to convert the plant-based sugars into chemical building blocks, comes from the San Diego-based biotechnology company Genomatica. Whose fermentation process has been listed by TIME magazine as one of the best inventions in 2019 24.
In August 2021, Canadian activewear company lululemon has announced a partnership with Genomatica to bring Bio-Nylon into their products to replace fossil-based materials 25.
Another variety is Nylon 6 derived from renewable raw materials, supplied by BASF (Ultramid® Biomass Balance Polyamide). Sustainable plant oils and organic wastes are transformed into biogas which serves as a replacement to crude oil in the very first step of Nylon production. The biobased amount is allocated mathematically via a certified system to specific products 26. The quality of final Nylon 6 granulate is identical to conventional Nylon 6. Yet, it cannot be classified or named simply as a biobased Nylon as its biobased carbon content cannot be addressed by the C14 method (radiocarbon dating method) 27.
As Nylon types are among most other plastic types are generally not biodegradable by their chemical structure, questions arising in the microplastic debate 28. Amni Soul Eco® of the Rhodia-Solvay group claims to be the world´s first biodegradable Nylon 6.6 yarn to quickly decompose after being disposed in landfills 29. Another example is the newly released Sensil® Biocare yarn of company Nilit. Enriched with an additive that accelerates the break down of microfibers in oceans and landfills 30.
There are no scientific articles available on the so called »oxo-degradable« or »enzyme-mediated« plastics 31 32. As no proof for the degradation process has been provided, environmental beneficial effects are highly questionable 27.
Amni Soul Eco® and Sensil® Biocare claim their biodegradability / accelerated break down based on ASTM D5511 – Standard test method for determining anaerobic biodegradation of plastic materials under high-solids 33 30. In addition, Sensil® Biocare claims to break down under aerobic conditions according to ASTM D6691 – Standard test method for determining aerobic biodegradation of plastic materials in the marine environment 30.
Strict laws in California regulate the marketing and labeling of degradable plastic products sold in California, including those claiming to be »compostable« or »biodegradable«. Environmental marketing claims, whether explicit or implied, must be substantiated by competent and reliable scientific evidence and meet specified standards. In 2011, legislation was passed that extended restrictions on use of degradability terms to nearly all plastic products 34.
Users of those modified Nylons need to weigh the priorities. An overview of existing biodegradable plastics under various conditions can be found here: renewable-carbon.eu/biodegradable-polymers-in-various-environments-according-to-established-standards-and-certification-schemes-graphic-pdf/
NYLON AND THE CIRCULAR ECONOMY
Nylons are thermoplastic materials, meaning they are re-meltable and therefore recyclable. In fact, every Nylon type can be recycled, but it depends on existing recycling facilities and collection schemes 14. The combination of different Nylon types within a product poses similar difficulties as is the case for any material blend. On the other hand, Nylon is a suitable material to produce not only textiles from it – trims can also be made.
In 2019 Napapijri revealed its first mono-material Nylon jacket 35. Followed by a circular collection, using Nylon 6 in textiles, filling, and trims enables a fully circular product with an End-of-Life perspective to be recyclable 36.
Nylon 6 seems to be a perfect synthetic material to use in a circular economy. Due to its only one monomer content (caprolactam) a recycling is more viable compared to bi-monomer types. Thanks to the variety of different application sectors, Nylon 6 enables brands to create easy-to recycle products.
Other Nylon types than Nylon 6 are facing difficulties, as recycling systems need to be set up first.
Chemical recycling technologies are playing a crucial role in the utilization of post-consumer products to maintain quality of the polymers and to remove residues of the processed materials.
Important note in terms of a recyclability of a Nylon product is an existing and available recycling technology and take-back system which needs to be established by every player itself. Considering the EUs Waste Framework Directive, member states will have to set up by 2025 a separate collection for textiles 37. This could lead into a better availability of waste Nylon textile products.
THE FUTURE OUTLOOK
Nylon is an elemental material in the sportswear industry. The high-performance attributes make it suitable in a variety of durable products such as apparel and backpacks.
Once the product is made, it should have the longest lifespan possible without energy input needed: that means an increased durability, favoring re-use and second hand. Then, once the material is no longer suited for its use, it should be recycled, if possible, through local channels and in the same product loop.
The current feedstock for the most used Nylon types 6 and 6.6 is coming from fossil resources – crude oil. To reduce the dependency on fossil resources, alternative routes need to be established. Taking up the already existing waste in form of recycling will be the largest share in a decarbonized economy according to a forecast by the Nova Institute 38. The market needs to push Nylon recycling initiatives further to fulfill the demand for a conscious thinking sportswear industry.
Future projection for the world plastic production
Even though recycled Nylons are gaining ground, their origin remains fossil-based / non-renewable. Furthermore, virgin feedstock will be always needed to supply the demand of Nylon. Biobased Nylons seem here an interesting option. With chemically novel Nylon types, new performance attributes can be addressed. The market will show if those Nylon types remain in a niche market or become widely accepted. Approaches on biobased Nylon 6 represent a one-to-one substitution on its existing fossil counterpart, where large volumes are existing 23 25.
Renewable feedstock is a more valuable raw material than crude oil and its use should be preferred whenever possible. The sustainability of renewable feedstocks always must be analyzed and is not per se sustainable. The processing steps from fossil and biobased polymers are similar and none of them is more sustainable than another.
Nevertheless, there is a lot to do in term of eco-friendly Nylon manufacturing, with less energy-intensive, less polluting processes, and the usage of renewable energy.
RECOMMENDATIONS FOR ACTION
Phase out virgin fossil-based Nylons
Set targets for the use of recycled and renewable Nylon
Select recycling technology based on waste input type and quality
Discover the variety of biobased Nylons
A mono-material design philosophy will support recyclability
Compare environmental data to determine Nylon's footprint
Nylon 6 made of renewable or recycled feedstock can be recycled in the same way as conventional fossil- or virgin-based Nylon 6 – enabling a circular future of Nylon.
This report has been written by René Bethmann – Innovation Manager & Consultant of VAUDE Academy for Sustainable Business – on behalf of Performance Days in October 2021.