31 Mar Comparing Nylon-Polyamides
Nylon-polyamides are an excellent choice if you’re looking for a dependable, economical material for your application. After all, when looking at the vast choices of thermoplastic materials, polyamides alone provide nearly unlimited problem-solving options. But with close to 50 different polyamides to choose from, how do you know which one is the best choice for your application? Understanding polyamides, from their history to their characteristics, and learning how they stack up against one another will help ensure you pick the perfect one for your needs.
The History of Polyamides
The first polyamide ever developed was Nylon 66. Invented at the DuPont Company in 1938, it debuted at the NYC World’s Fair in 1939 as nylon hosiery for women. Many people do not know that nylon gets its name from the joint development efforts at DuPont between teams in New York (NY) and ICI in London (LON). Following Nylon 66, many polyamides were developed from the late 1930s onward, with PA410 and PA4T being two of the latest developed within the last ten years.
When it comes to plastics, the real challenge isn’t inventing different polymers – it’s bringing them to commercialization. If it were not for DuPont’s interest in making synthetic fiber, it’s unlikely that polyamides would have taken off when they did in the world of engineering plastics. Their scale of fiber manufacturing drove creative, cost-efficient routes to make both the polymers and their monomers.
Polyamides 101
Polyamides are synthetic polymers. They are created by reacting a di-acid with a di-amine and are simple to produce. Some specialty polyamides can be produced with renewably sourced materials, a rapidly growing market segment. For example, PA1010, PA11, and PA610 are all made with monomers that can be extracted from castor beans. Most other polyamides are created with monomers derived from petrochemical feedstocks linked to benzene and propylene. In terms of global production, PA6 and PA66 are at the top, with eight million metric tons produced a year.
Most polyamides are semi-crystalline and feature the following characteristics:
- medium to high melting points
- excellent elevated temperature performance
- high mold shrinkage
- good chemical and fatigue resistance
- anisotropic shrinkage (not uniform)
- valuable electrical properties
- lubricious nature
- a sharp melting point
There are amorphous polyamides, but they are much less common. Grilamid, Trogamid and Selar are three well-known brands. These polyamides are transparent and because they are amorphous, can be more challenging to process. However, they have good mechanical properties, dimensional stability, and uniform shrinkage; they soften, meaning they do not have a melting point.
The plastics industry is filled with acronyms – nylon, of course, being the most widely used. The other is PPA, which is shorthand for polyphthalamide. Polyphthalamide is also a catch all abbreviation for all aromatic polyamides, which include PA6T, PA66T, PA4T and PA6I/PA6T. The ‘T’ is terephthalic acid and ‘I’ is isophthalic acid, which are both di-acids.
All polyamides are unique in that they absorb moisture, changing dimensions as they do so. Some, however, absorb less moisture, including PA11, PA12, PA410, and PA612. The semi-crystalline polyamides have a high Vicat softening temperature and heat deflection temperature, which makes them a versatile choice to design with, as their performance remains stable over a wide range of temperatures. Another thing that sets polyamides apart from other polymers in the plastics industry is how many options there are for fabricating parts. Injection molding; sheet, film, and fiber extrusion; reaction injection molding; and, more recently, 3D printing are all possible with polyamides.
Choosing the Right Polyamide
When comparing polyamides, understanding your requirements is key to finding the best solution. At PolySource, we use our design funnel daily to help customers decide the best material to use for their products while keeping the essential qualities in mind. When it comes to polyamides, we start with the three pillars of selecting material – physical, chemical, and thermal characteristics – and ask questions about dimensional stability, chemical resistance, and temperature. What happens to the part as it absorbs moisture? What is it going to be exposed to? Where do you want to use the material in terms of temperature? These questions are critical to finding the best polyamide for your application.
After evaluating the top of the funnel, we can move down to the more complex area of impact, strength, and stiffness. We’ll consider if it is a sliding or rotating part, the load that will be applied, if there is fatigue, and more as we think about the types of mechanical forces and the chemical environment of the part. Using the design funnel provides a focus for our search and helps us understand what we need and are working with, allowing us to cover everything critical to quality (CTQ). Asking so many upfront questions generates answers that lead to the best polyamide options.
One factor you’ll want to consider in your quest to find the perfect polyamide is the moisture absorption rate. Pay attention to the footnotes, however, as the data you’re looking at could be measuring equilibrium moisture or immersion/saturation moisture. PA11, PA12, PA410, and PA612 are all relatively low moisture-absorbing materials and, as a result, have lower changes in dimension. In contrast, PA46 is at the top of the list regarding moisture absorption, but that doesn’t mean it isn’t useful. PA46 can work great in many elevated-temperature automotive applications, such as components inside a transmission that are continuously immersed in transmission fluid. You’ll also want to remember that moisture absorption can affect glass transition temperature and tensile strength. Moisture effects are reversible and understanding the reversible effects of moisture on a polyamide’s physical and mechanical properties is vital in the design. Ultimately, you need to understand where you are and what your part will do with an increase or decrease in size or swelling.
Chemical exposure is another major factor to think about. Be aware of the use conditions and be sure to define the specifics. While almost all polyamides can handle common organic solvents, more aqueous solvents can prove to be a challenge. Many polyamides may also struggle with automotive chemicals, alcohols, acids and bases, and peroxy oxidizers. The most important thing to remember is that deciding if a particular chemical is suitable for use with a specific polyamide comes down to time, temperature, concentration, working load, and design.
Examples of Polyamide Applications
With so many polyamides to choose from, it’s no surprise that you can find a wide variety of products created from them. Some notable polyamides and products derived from them include:
- PA6/6: This glycol-resistant polyamide is used in radiator end tanks and air intake manifolds, where it performs well in terms of fatigue resistance and strength retention, even at high operating temperatures.
- PA46: This polyamide outperforms almost all other polyamides; one common application is transmission wiring harnesses. PA46 can withstand continuous exposure to automatic transmission fluid while maintaining its dimensions and functioning at an elevated temperature.
- PA12: Found in hand cranks for ice augers and swimming pool lenses and bezels, this polyamide features low moisture absorption, long-term hydrolysis resistance, and excellent toughness and clarity.
- PA6I/6T: Used in a coffee machine distribution block, it’s easy to process, provides long-term hydrolysis resistance, and exceptional weld line and toughness.
- PA66-PA6I: This polyamide was used to replace traditional materials used for the wheels and rims of high-performance bicycles in Europe. When compared to metal, it provides better weight reduction and corrosion resistance. It’s a tough material to begin with and molds with an excellent surface appearance.
- PA410: Engine coolant expansion tanks used PA410 for its ability to withstand high temperatures and excellent retention of properties when exposed to glycol/water coolants. It provides 30% weight reduction and 50% cooling reduction when compared to the commonly used PA66 and offers a great solution for an application if PA66 fails to meet the requirements.
Takeaways
Don’t be intimidated by polyamides if you’re looking to select a thermoplastic material for an upcoming project. By understanding how polyamides compare to one another and what design considerations you should keep in mind, you’re sure to find the perfect fit – and if you still need help, PolySource is here. We’ll guide you every step of the way to ensure you have the ideal polyamide for your needs.