Thursday, 28 March 2019

Reviewing Key Engineering Plastics – Polyamide 6 and Polyamide 6.6 [incl. Video]

Hello and welcome to this post on reviewing key engineering plastics. Today, we have a closer look at polyamide 6 and polyamide 6.6.
Similarly to the last time with ABS, we review the chemistry including the simplified petrochemical flowchart, discuss the properties and applications of polyamides and look at their global demand and producers. I will provide you some price indications as well.

Here you can find the youtube video of the review:

Before we start with the chemistry I would like to spend some words on the history of polyamide. Wallace Carothers, working 1930 at DuPont Company, developed together with his assistants the two most widely used synthetic polymers of the 20th century: nylon or polyamide and neoprene (synthetic rubber). We will focus in this review on polyamide 6 (PA 6) and polyamide 6.6 (PA 6.6). Although they may seem quite alike they are different e.g. in terms of glass transition and melting temperature as well as water uptake. The latter is higher for PA 6.

Polyamide chemistry

PA chemistry and simplified flow chart: Where do PA 6 and PA 6.6 have their roots?
PA 6 is made by ring-opening polymerization of e-amino caprolactam which is obtained over the benzene route (from benzene over cyclohexane to caprolactam). Cyclohexane is first converted to its oxime. An oxime is a chemical compound with a carbon-nitrogen double bond. The word oxime is a combination of the words oxygen and imine. Treating the oxime with acid initiates the so-called Beckmann rearrangement to obtain caprolactam. The global demand on caprolactam are 5 milllion tons. PA 6.6 can be polymerized using hexamethylenediamine and adipidic acid. Both have 6 carbon atoms leading to the nomenclature of 6.6. HMDA can be obtained over three routes: from adipidic acid route, from hydrogenation of acrylonitrile, and from hydrocyanation of butadiene.
Polyamide - Simplified Flow Chart

Poylamide properties
PA 6 shows good toughness at relatively high (80°C) and low temperatures as well as resistance to repeated impacts. This is rounded up with good resistance to abrasion and wear. Chemically, PA 6 exhibits resistance to many organic solvents, oils and gasolines. In comparison, Polyamide 6.6 can be used at higher continuous service temperatures (100°C – 120°C) combined with a better retention of stiffness, tensile properties, and shape at high temperatures.
Polyamide - Properties

PA Capacity and Global demand
The total consumption of Polyamides in 2016 was around 7.5 Million Tons. PA 6.6 has a consumption of 2.4 million tons and PA 6 of 5.1 million tons. 70% of the global PA 6.6 consumption was used in the automotive market. Half of the consumption of PA 6 is used for producing fibers.
Polyamide - Capacity and Global Demand
Geographically you can state that Asia is the largest market for PA 6 and it is preferred when flexibility and barrier properties are important. North America is the largest market for PA 6.6 and is mainly selected for engineering thermoplastic applications due to a higher melting point. Important to note is that both Nylons are interchangeable for most applications.
Polyamide - Capacity and Global Demand

PA Price to performance
Polyamides are forming the base of engineering thermoplastics and have a price range of 2.5€/ kg for base grades and high heat Nylons can reach up to 6.5€/kg.
Polyamide - Price to Performance

PA End uses
As previously shown, PA 6 is more selected for fiber applications such as tire cords, and filaments for fishing lines. PA 6.6 with a glass fiber reinforcement of 30% is used in many automotive applications where the combination of elevated temperature, toughness and long life time is needed. However, there are many other industry fields, where the properties of Nylon 6.6 can play a key role. Important to note is the water uptake of PA 6.6 which can be 2.5% at 50% relative humidity. PA6 has with 2.8% a bit higher water uptake. The water uptake results in dimensional changes, reduces the yield stress 29% of its original value. Elongation will be increased with the factor of 5 and toughness will be doubled. Overall stiffness can decrease almost 60%.

Typical polyamide applications Just to name a few of the typical applications: belts, guitar strings, car engine upper intake manifold and engine support mounts.

This was a review on polyamide, an important engineering thermoplastic used in many applications.

Thanks for reading & till next time!
Herwig Juster

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2. W. Kaiser: Kunststoffchemie für Ingenieure, Carl Hanser Verlag, München 2016

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