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PA6/PA66 - properties, experiences and useful links

The members of the polyamide family are coded with cryptic extensions like 6, 11, 12, 66, 46 and 69. The numbers describe the type and number of polymer chains in their chemical structure. This approach, the normal practice in the industry, is not very user-friendly from the product designer’s perspective.

The two most commonly used polyamide grades by far are PA6 and PA66. The remaining members of the polyamide family are primarily used in applications that require unusually high service temperatures or tolerance of moist conditions. Bio-based and transparent (amorphous) PA grades are also available. In machine design purposes PA is often reinforced with glass or - in case of highly demanding applications - with carbon-fiber. Reinforcement changes the characteristics of the material and its applications considerably and therefore I’ll write a separate article on them later. This article focuses on unfilled PA6 and PA66.

What is the difference between PA6 and PA66 then?

Here is a summary:

PA66 compared to PA6

  • absorbs slightly less moisture
  • higher modulus
  • better wear resistance
  • better short term heat resistance

PA6 compared to PA66

  • better ductility (due to higher toughness)
  • better long term heat resistance
  • better impact resistance in low temperatures
  • better surface quality
  • better creep resistance
  • better UV-resistance (depends on modification)
  • lower cost

The differences are small, however, and in some circumstances some of the items on the list above may be invalid, depending on the exact grade in use.

For further information, the RTP-company provides good overviews of PA6 and PA66.

One of PA’s basic characteristics is its tendency to absorb water. This decreases its strength and modulus, but makes it tougher. More on PA water absorption can be read in Dry vs. Conditioned Polyamide Nylon Explained by UL-IDES

High gloss and good fatigue-, wear- and impact resistance makes PA a good option for plastic high end chairs.

Polyamide is commonly called nylon, which is also a trademark of Dupont. Here is a story about how nylon got its name.

Practical experiences of unfilled PA6/PA66:

  • Water absorption is a well-known property of PA and worth taking into account. The difference can be felt when a product that has been stored outdoors over winter is taken indoors for a few days: its stiffness invariably increases.
  • High quality cable ties are made of PA66. This illustrates well the strength and toughness of the material. It also reveals that unfilled PA is suitable for applications that require high flexibility or even integral hinge. Apart from cable ties, products made of unfilled PA66 are not very common. PA6 appears to be much more popular choice.
  • Because of its good surface appearance PA6 is also often used (rather than amorphous plastics ABS, PC, PC/ABS) on housings of some outdoor applications like this tractor. Read the full article on Basf site.
  • Even though parts made of PA can have a glossy surface, replacing amorphous grades like ABS with PA might cause problems because of the higher shrinkage and therefore warpage.
  • If you are trying to determine if a product is made of PA, cut a little piece off and burn it. The odor of PA is similar to burning hair.

I’ll add more links to the page every time I find something useful. If you have a good link, case or a story in mind, please email me at markus@plasticprop.com or add it in comments below.

To fully grasp the look and feel of PA you can order the Plasticprop Essentials sample kit including 20 of the most common plastics. It has been carefully designed to convey and explain the characteristics of each material. Read here what the sample tells about unfilled PA6.

This blog focuses on the hands-on design of injection molded plastic products. If it is something close
to your heart, please share your own experiences with all of us. You can also follow plasticprop.com on
LinkedIn or Facebook.

Thank you for reading,

Markus Paloheimo, Managing Editor, plasticprop.com

  • Markus Paloheimo (Ms.Sc) is a Product Designer with two decades of experience in the field of functional consumer and industrial products. His specific area of expertise and source of enthusiasm is injection molded plastic products. Markus Paloheimo is in LinkedIn.

Comments

dr.s.narayanamoorthy
Dear markus paloheimo, Very nice article. Your two decades of experience is felt in the write up. Keep it up and continue your good work in the interest of the plastic industry in general. Regards snmoorthy.
Markus Paloheimo
Thank you for your comment and kind words.
Andrew Billingsley
Hi Markus - an excellent article - is there a simple way to identify PA6 versus PA66? Regards, Andrew@plaswire.com
Markus
Hello Andrew, Hmmm...If you have a good owen you could try to heat the part. If it is PA6 it should totally collapse close to 220 C but if PA66 only after 250 C or so. Glass filling of course has an effect on this. How does this sound? Markus
Swamiray
Dear Markus - I like this article. I have a question.. -PAGG GF 50 can be replaced by PA6 GF50 ? For outdoor apllication(Non Visisble and structural part.) requiring strong environment resistance.
Markus
Thank you Swamiray, You mean replacing PA66 GF50 (not PAGG) by PA6 GF50? I don't see a high risk there other than that PA6 absorbs more water (with such amount of glass the difference should not be significant). If it is an existing product I recommend you simply mold some samples using PA6 and compare them. Stiffness is probably an essential part of the component's function, so you should do the comparison in moist conditions. That goes with durability test as well. You can simply have the components sunk in water over night.
Vikranth
Thank you....
alireza sheikhan
good article,thanks for your time spending on such. i wanted to ask ,after produced pa66 how can we make it strong and flexiable,when moisten it becomes weak. thanks. sheikhan323@yahoo.com
Markus Paloheimo
Hello Alireza, Perhaps you could consider using PBT instead?
John Irvine
I have a motorcycle gas tank that I believe is made of PA6, an MZ. After having it repainted the paints is bubbling and I am guess that vapors from the 10% ethanol fuel migrates through the material and then bubbles the paint. Does this seem to be a reasonable cause of was it just a bad paint job? I was thinking of using a tank liner such as a phenol novolac. Any idea if that would adhere to the PA6 and solve my problem. Thanks
Markus Paloheimo
Hello John, All semi-crystalline plastics are slightly difficult to paint due to their more or less greasy surface. Glass reinforcement usually helps on this. PA is rather resistant agains oil and gas, that is why it is commonly used in car industry. It is hard to believe that the fuel would migrate through the material. Is the tank injection molded or blow-molded? If blow-molded, I'd be suprised if it was PA. Usually PE is used on applications like that and it is even trickier to paint. When it comes to painting in general, you probably know more about it than I do.
Amit Mudgal
Hi Markus, I would like to know the UV Stability of PA6 reinforced material, Is PA6-Glass reinforced 30%+Heat Stabilized+ Black Color( Carbon Content) witness 600 hrs Weather-O-Meter Carbon Arc test or not?? Do you have any published data on PA6-Glass reinforced weather-ability performance? Need you help on it... Thanks!! Regards, Amit Mudgal
Markus Paloheimo
Hello Amit, The combination does not sound very sensitive to UV-light, but I recommend you have it tested with help of the material supplier. Unfortunately I don't have such data on my database. Markus
Martin Labaj
Hi Markus, Would be same mould tool that used to work with PA6 be able to take PA66 material? Moulder we dealing with experienceing with parst stuck in fixed half even parts just partially filled.
Markus
Hello Martin, To my experience the same tool goes to both grades with no problems. However, changing from PA6 to PA66 will probably not solve the sticking problem. On that you have to check the draft angles and surface roughness. In some cases small undercuts are added on the core side to secure part sticking on the ejection side. This easily extends the cycle time, though, since you have to cool the product a bit longer in order to withstand higher force on ejection pins.
Martin Labaj
Hi Markus, Thanks for your comments. I should specified that tool has been designed and ran with PA6 material with no issues. Due to increased requirements for better moisture ingression we have trailed PA66 material and at this point supplier advised issues with parts stuck at the fixed half of the tool.
Markus
Since PA66 is still quite common material, it should be no problem for your material supplier to deliver a bag for test run...
Nishant
Hi Markus, Can you tell me which polymer is good for barium ferrite powder for making injection molding products. ( For better elongation strength , Please help me in this ............................
Markus
Hello Nishant, Sorry to say, that is beyond my experience. Please turn to some material supplier that offers the said filling. Markus
Reto Zingg
Hi Markus, thanks for the helpful article. Can you tell something about the UV resistance of PA6. We would like to use a part which will be 25 years expose to sun. Can tell how much the ductility of PA6 gets reduced after time? Thanks for your respond, Reto
Reto Zingg
Hi Markus, Two questions more. 1. Is it possible to protect a PA6 part from UV by a paint layer? If yes, what kind of painting must be applied? 2. Is it true that a PA6 block in black color has better UV stability? If yes, why? Thanks for your respond! Reto
Markus
Hello Reto, PA6 has relatively good resistance agains UV. It is used on stadium benches, for an example. http://www.prlog.org/10635708-high-tech-safe-stadium-seats-in-soccer-city-with-durethan-pa6-engineering-plastics-from-lanxess.html 25 years and straight sunshine make demanding conditions. I recommend you talk to material suppliers and try to find a reference case under the corresponding conditions. Painting PA components is possible, although semi-crystalline materials are always a bit greasy. If the paint is subjected to scratches or wear, it will most likely wear off. Painting will definitely protect the components as long as the paint is UV-resistant it self. Is your component reinforced with glass? That would help. Black components are less sensitive to UV. Visually they might turn from black to slightly gray but red would turn to pink. But it helps on mechanical properties as well. I guess the UV beams are not able to penetrate as deep into the structure. It is important that you select a UV-modified grade in the first place. There are plenty of options. I can not give you any value how much ductility is increased, material suppliers should be able to help you on that as well. I have experience of axe-shafts that are made of black glassfilled PA6 and have spent more than 20 summers outdoors. They still perform OK.
Kate
Hi Markus, I recently read a summary of a new market research report that characterizes PA 6 as a bio-based polyamide. Would the "bio-based" label be achieved via microbial production of caprolactam? I have read about this technology but did not realize it was commercialized. Your thoughts are appreciated!
Markus
Hello Kate, Thank you for your message. I am not very familiar with bio-based polyamides in practise. I tried to google the topic and it really appears to be a growing trend. Interesting. But sorry, I don't have an answer to your question. Perhaps somebody on LinkedIn groups would have more knowledge on that.
Hadi Tan
Dear Marcus, I have using a lot of PA66+30GF (Color red, white and yellow) for outdoor application. Do this PA66+30%GF are good in UV Resistance? Thank you.
Markus
Hello Hadi, I have a lot of experience on PA6+GF products that have been exposed to sunshine for several years. From mechanical point of view there are not big concerns. To my understanding PA66 is slightly more sensitive to UV than PA6 but the difference should not be dramatic. You will most likely, however, see some changes on color. Red might turn to pinkish, white to yellowish. Please notice that there are UV-modified grades of PA66 available.
jean-dominique
Dear Marcus, what about painting PA6 GF40 or PA66 GF40 ? to my understanding, is possible if GF% is relative low (Max 25%) ? what do you think about ? Thank you
Markus
Hello Jean-Dominique, All semi-crystalline plastics are a bit tricky to paint compared to amorphous plastics. PP, POM and PE are especially difficult, but PA (both PA6 and PA66) are much easier. To my experience high glass content only helps. The paint surface might wear off by time, but it is very unlikely that it would peel off. You should, however, test the suggested paint in practice in order to avoid uncomfortable surprises. Good luck!
Gerard
Hello Markus. Would you consider PA6 and PA66 (or PA's in general) as prone to stress cracking?
Markus
Hello Gerard, Stress cracking is a phenomenon that must always be considered in plastic product design. Compared to any amorphous plastic (like ABS, PC, PMMA) semi-crystalline PA is far less sensitive to stress-cracking. Among all available plastic grades (with reasonable cost), that might be your best choice. It is always good to try to find a reference case. Cable ties are made of PA and it is very rare that those fail under tension. Please bear in mind PA's tendency to absorb moisture in case that might affect the performance of your component.
Ling QUe
Hi, Markus, What is the mechanical property difference between PA66 GF 50% and PA 66 GF35%? Thanks
Markus
Hello Ling Que, If you increase glass content from 35 to 50%, the end end result will most likely be that: Tensile modulus is higher and (the product is stiffer) and strength is increased Due to higher modulus, you lose some of the toughness. Additionally: - shrinkage should be a bit lower. - service temperature is increased. - the product absorbs less moisture. - the product is slightly heavier. You might also see some glass on the surface of the product. And glass wears down the runner system of the mold.
Miguel Santiago
Hello sir, thank you for your very interesting webpage. A quick question: I'm aware that PA6 is subjected to degradation when in contact with biodiesel. Do you know any additive that can prevent or slow down that degradation? best regards
Markus
Hello Miguel, PA is a common choice when the product is in touch with synthetic oil or lubricants. But my experience is quite limited on that. There are some groups in LinkedIn that are focusing on plastics in automotive industry. For an example: https://www.linkedin.com/groups/8350409/profile Somebody there might know.
Jay
Hi Markus, i am using Pa 6 material for packaging sleeve & we store material properly , still after 1 or 2 month later sleeve get shrink. what will be the reason? whether it is due to moisture or due to use of regrind material?
Markus
Hello Jay, Do you dry the granulates properly before molding? I'm not sure if that has effect on dimensional stability in the long run, but still my guess is moisture. Can you test this by placing some products in moist and dry environment for a few days and then simply by measuring the difference?
David lee
Hi nice articel I have question Which one is better pa 6 or pp copolymer? What is the different? Im going to apply it on clip parts Thanks
Markus
Hello David, Mechanically PA6 is is better in general. Humidity absorption might cause some surprises but if you take this into consideration in design, you should be OK. PP is cheaper, though, so if it does the job why not use that. If your "clip part" requires some sort of a spring action, you might also consider using POM. That is the most common choice in such applications.
David lee
Hi thanks for the reply, another question I forgot to ask, which one is better pa 6 or pa 6.6, which one more stiff or harder? Thanks again
Markus
David, As said in the article, PA66 has slightly higher modulus, this makes the product stiffer. The difference is not remarkable but increases in moist conditions. PA66 absorbs less water, so it is probably slightly stronger in moist conditions as well. When it comes to hardness, the difference should be minimal to either direction. Markus
Varun Vohra
Hi Markus Great article!Just looking at the chemical structure of PA6, one is tempted to conclude that this material cannot be chemically resistant., (because of the amide group) still it is the first choice for under hood applications in the car. I would appreciate your comments on the chemical resistance of plastics in general.Thanks!
Markus
Hello Varun, Chemical resistance is a tricky topic, but it should always be taken into consideration in design. One link I have bookmarked is http://www.plasticsintl.com/plastics_chemical_resistence_chart.html The problem to me is that it is difficult to know which of these chemicals exist in the service environment. Let's say that my product will be in touch with chicken fat and sun-lotion (what ever the product might be). I always try to find a reference case where the chosen material has successfully been used for a longer period of time with similar circumstances. If such is not available, I try to arrange the test myself. Of course lack of time is then an issue (I can not wait for years to see what happens). Then I set the specimen in tension and in elevated temperature. This should accelerate the process. One good rule of thumb is that the more crystalline the material is, the better it withstands chemicals. When it comes to chemistry, I am on the level of conscious incompetence . That is why I always try to use the expertise of the material suppliers. Perhaps somebody can add something on this???
Varun Vohra
Hi Markus I am doing an FEA on a poly carbonate snap fit using Ansys. I read the literature on plastic snap fit designs and found that there is a stress Magnification factor depending on the Length to thickness ratios of the snap beam. Any kind of information or resources on fea of plastics would be greatly appreciated! Thanks.
Markus
Hello Varun, There is a big difference if the snap fit is used only once or a few times (for assembly for instance) or if it is intended to be used daily and hundreds or thousands of times during the lifetime of the product. You should calculate what is the stress or elongation on the outer face of the element as it is bent during the locking maneuver. (If possible you should mechanically limit this movement so it can't be bent more than necessary.) If the mechanism is used for assembly only, you should make sure you don't come close to the "stress at break" or "elongation at break" values. This should be in line with the magnification factor you mentioned. If the mechanism is used continuously, you should stay as far possible from the said "at break" values, preferably on the level of 30% or less. PC is an amorphous material and sensitive to fatigue. But it is even more sensitive to continuous stress, so make sure the element is in relaxed state when locked or unlocked. If not, it will fail by time for sure. Please check also that there is some clearance under the hook so it can easily snap behind the counter element. BASF has some good design guidelines on line, including snap-elements. You can find them here: http://www2.basf.us/webplasticsportal/cre?gui=1&dtitle=searchResult&dtext=1&objecttype=ktn_technical_documents&ktn_t_doctype=Design_Guide I hope this helped, good luck with your product.
Lawrence
Hello Markus, I was researching the different types of PA66 materials and I was wondering if you could help me figure out the U.S. equivalent of the PA66-GU30 from Japan? Thank you!
Markus
Sorry Lawrence, There are hundreds of different grades. I recommend you contact some domestic material supplier. They should help you out, Markus
KP Vidyashankar
A really great article. These Qs had been bugging me for last 15 years and I had located some answers with absolutely no help from manufacturers (probably bcoz we are small buyers). But You have put all details in one place and is a very good reference over time. Thanks again and we will ask you some Qs on a new design that we are starting for traction electronics especially since we are using PA66 30% GF and are looking to remove the glass. Many, many thanks. Rgds
Baris
Hello Marcus, Do you have any experience about adhesives which we can use for PA6 and PA66 bonding with tempered glass? Also the primers between adhesives and products (PA6, PA66, tempered glass). Which material provides us the better adhesive forces. Thank you.
Markus
Baris, If there is such adhesive available, I'm not aware of it. I might not the greatest expert on this, but I doubt if there would be any adhesion at all. Can you make the geometry such that the tempered glass would be mechanically joint with the surrounding plastic? Markus
Alvar
Dear Alvar, Thank you for such a clear and well explained summary of PA 6 and PA 6/6. I wonder how are the current PA 6 3D printed parts. I've been searching for a while but I couldn't find any datasheet online. I wonder how different are the properties between 3D printed (SLS) and injection molding PA 6. Do you have any idea?

Sivut

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