Use of polyamide by industry
Figure 2: Use of polyamide by industry.[2]
Where is polyamide used?
Polyamide has conquered a place in countless industries. Here are a few examples:
Textile industry
Polyamide fibers, also known as nylon or Perlon, are found in hosiery, sportswear, underwear and many other items of clothing. The fibers are also used as technical fabrics, fishing lines and tennis racket strings.
Automotive industry
In addition to being used as fibers in the textile industry, polyamides are firmly established as engineering thermoplastics in the automotive industry — in fittings, mudguards or under the hood for tanks or fuel lines, brakes, transmission components and in e‑mobility.
Electrical and electronics industry
Polyamides can also be found in the electrical and electronics industry, as housings, in printed circuit boards, insulation materials, in household electrical appliances or pumps.
Construction industry
Polyamide is used here as a thermal break in profiles for windows and façade constructions.
Packaging industry
Polyamide mainly plays a role in flexible packaging. It can be found in vacuum packaging for foodstuffs such as cheese, sausage and frozen goods.
Chart 3 shows that the share of polyamide in the automotive industry is steadily increasing and that the share of the packaging industry is also growing.
Value of Polyamide (PA) 6 Consumed by end user industry
Figure 3: Industry shares of polyamide as technical compounds.[3]
Polyamide under the magnifying glass
But what exactly does polyamide look like and how is it produced? This requires a brief excursion into organic chemistry. Polyamides are linear polymers. Their special feature: regularly repeating amide bonds along the main chain. Almost all important polyamides are derived from primary amines. What does that mean? The functional group ‑CO-NH- occurs in their repeating units along the polymer chain (compare structural formula).
Structural formula of polyamide: The blue amide group is repeated along the polymer chain. R stands for the rest of the compound used for synthesis.
The amide group is formed during the production of polyamide from a carboxylic acid and an amine. The resulting amide bond is hydrolytically cleavable, i.e. it can be broken again by a reaction with water. The industry uses aminocarboxylic acids, lactams, diamines and dicarboxylic acids, for example, as monomers for polyamides.
Production of PA6 and PA66
PA 66 and PA 6 are often used as technical compounds. Although these two polyamides are chemically and physically similar, their manufacturing process is fundamentally different and is based on different starting materials. Polyamide 66 — known to everyone as nylon — can be produced from the diamine hexamethylenediamine (HMD) and adipic acid, a dicarboxylic acid. The carboxyl group (-COOH) of the adipic acid reacts with the amino group of the diamine (-NH2). This produces the peptide bond (-NH-CO-). This is the basic building block of all polyamides. Polyamide 6, on the other hand — known as Perlon — is formed by ring-opening polymerization from ε‑caprolactam with water as a starter. At elevated temperatures, ω‑aminocaproic acid (chemically: ω‑amino hexanoic acid) is formed from the ring-shaped ε‑caprolactam. It has a carboxyl group at one end and an amine group at the other. This property is referred to as bifunctional. It is possible for ω‑aminocaproic acid to react with itself to form long-chain polyamides.
DIN ISO 1043–1 defines the nomenclature of polyamides: PA is the abbreviation for all polyamides. The abbreviation is followed by the number of carbon atoms present in the monomers. For example, if it is Perlon, made from the bifunctional ω‑amino hexanoic acid with six carbon atoms, the abbreviation is PA 6. If the polymadi is made from a dicarboxylic acid with a diamine, as is the case with nylon, the carbon atoms of the two monomers are relevant, are counted and given one after the other. For this reason, nylon is called PA 66[4].
Properties of PA6 versus PA66 — similar and yet different
Both PA6 and PA66 have good sliding and damping properties, are very abrasion-resistant, impact-resistant and are resistant to weak alkalis, lubricants, oils and greases. Due to the different arrangement of the polymer chains, PA66 has slight advantages, as the table shows.
| PA6 | PA66 | |
|---|---|---|
| Melting point in °C | 220 | 260 |
| Glass temperature in °C (dry) | 50–60 | 50–60 |
| Density | 1.15 g/ml | 1.2 g/ml |
| Moisture absorption in % (23 °C, 50 % humidity) | 2,6–3,4 | 2,5–3,1 |
| Machinability — low tool wear and surface quality | Good | Better |
| Shrinkage | Low | Greater |
| Water absorption | Higher | Lower |
| Tensile modulus in MPa — dry | 2700–3500 | 2700–3500 |
| Tensile modulus in MPa — humid | 900‑1200 | 1000–1600 |
The different arrangement of the molecules results in slight mechanical advantages for PA66. PA66 is also more temperature-resistant and absorbs less moisture, making it more dimensionally stable. But PA6 also has some advantages. The surface quality of the glass fiber-reinforced grades in particular is better, as the melt solidifies more slowly. In addition, the lower processing temperatures of PA6 lead to lower energy consumption, resulting in lower production costs compared to PA66. Due to its higher moisture absorption, PA6 is more impact resistant than PA66.
The mechanical and thermal properties of polyamide can be significantly improved by adding additives, glass or carbon fibers. This makes it possible to produce highly impact-resistant, heat-stabilized and hydrolysis-stabilized polyamides. PA6 and PA66 are suitable for processing in injection molding, extrusion and blow molding. For the fiber industry, the fibers are spun directly from the melt.
Advantages and disadvantages of polyamide
The advantages
The advantages of polyamide as a fiber are obvious: the material scores points for its high strength, durability, elasticity and dimensional stability. It is lightweight, quick-drying, resistant to moisture and less prone to creasing.
Polyamides have gained a steadily growing field of use in technical applications. Due to their high mechanical strength and chemical resistance, engineering plastics have now replaced many metal parts in vehicle construction. Highly stressed components with complex geometries can be produced comparatively easily and cost-effectively in large quantities. Replacing metal with polyamide reduces the weight of the vehicle and thus its fuel consumption.
Slide bearings, drive belts, gear wheels or rollers made of polyamide have proven their worth, as the material scores points for its high wear resistance and good sliding properties. Carbon fibers further improve the already existing sliding properties.
The electrical and electronics industry is the second largest consumer of technical polyamides after the automotive industry. They are used for housings and to insulate electronic components, as the material has high electrical insulation and tracking resistance. If required, the material can also be made electrically conductive by adding metal and graphite.
The disadvantages
However, where there is light, there is also shadow. Despite the numerous advantages, polyamide has some disadvantages. The material has poor chemical resistance to acids and bases.
The material also has disadvantages in terms of production, use and disposal. Crude oil is required for the production of virgin polyamide. Production is very energy-intensive, as is the processing of polyamide. The associated climate and environmental impacts are obvious.
Further environmental damage occurs when polyamides enter waterways and the environment — for example via clothing: The smallest fiber particles are rubbed off in the washing machine. These tiny particles, known in the media as microplastics, end up in wastewater. With the technologies available today, it is not possible for sewage treatment plants to completely filter out microplastics. In a single wash of nylon textiles, around half a million microfibers can end up in wastewater. [7]
Recycling polyamide: opportunities and challenges
Like many plastics, polyamide is also being discussed in terms of sustainability and environmental protection. A major topic here is recycling. This is the only way to minimize polyamide waste and return it to the material cycle. The advantages: No crude oil is required for the recyclates, the energy requirement per kilogram of recycled polyamide is far lower than that of virgin material and the material does not end up in landfills, incinerators or nature. This benefits both the climate and the environment. Polyamides are easy to recycle mechanically. However, due to the chemical structure and the technical requirements for processing, extensive know-how is essential. The challenge here is that the recyclate must achieve a consistent quality with properties as similar as possible to virgin material. This is the only way for plastics processors to manufacture high-quality products that perform optimally during their use in vehicles, aircraft or the electronics industry.
To achieve this goal, recyclers must be able to procure polyamide waste of a consistent quality and in sufficient quantity to process it carefully. It is precisely this ability that distinguishes ENNEATECH.
ENNEATECH: Recycled polyamide reducesCO2 footprint by 90%
The reason for the positivecarbon footprint of Enneatech’s products is the raw materials: polyamide by-products from the high-end textile industry form the core of the impact-resistant recycled polyamides. The company uses these to produce a homogeneous starting material. This is where Enneatech benefits from its many years of expertise in the textile industry and equally longstanding customer-supplier relationships. As the company is one of the pioneers in the market, it has a large supplier portfolio and can deliver reliably even in difficult market situations. By recycling high-quality textile waste, Enneatech produces polyamides with a traceable and documentableCO2 footprint.
Based on decades of experience in polyamide recycling, Enneatech has succeeded in offering an extremely impact-resistant, recycled filled PA6 and PA6.6 compound with the Entron Eco product line: Entron Eco Compounds. With its own compounding line, the company can meet individual customer specifications on request. The compounds not only boast outstanding mechanical properties, but also aCO2 footprint that is up to 90% lower than that of virgin material. In addition to the filled compounds, Entron Eco is also available as granulate. It is produced without foreign polymers and additives and forms the basis of the filled compounds. Of course, this also applies here: TheCO2 footprint is always 90% lower than that of virgin material.
