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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.

Comments

Markus
Alvar, To my understanding the grade used on 3D printing is PA12. The mechanical properties should be about 80% of the injection molded components (data sheet values), direction of the layers does of course have an influence on this.
Pravin Jasud
Hello Markus, Very nice article. I have a question, How we will decide the GF%.
kim andreasen
Hi i have a 2 post car lift i need some lifting nuts to Its a 2500 kg Max load Can i use pa66 to make them ??
Markus
Hello Pravin, You should use as small a percent as possible, but still enough in order to meet your strength and stiffness requirements. If 20% is enough, go with that. If not, try 25 or 30%. Most likely you can increase the % according to your experiences with the mold, but of course it is good to have a good first guess to design the mold properly. Changing from unfilled grade to filled grade using the same mold might easily cause problems.
Markus
Hello Kim, That depends totally on the number of nuts and their size. To me that 2500 kg sounds like something that would require metal..especially if the load is constant. Markus
NEERU
What are the important properties ,which we have to check in QA for PA66-GF-25 ,V0
Markus
Hello Neeru, If the material is classified V0, there is always some additive that might change the properties. In addition to checking the datasheets and comparing them to standard grades, I would ask if the supplier has a physical sample. Tensile strength or impact strength might be different...not to mention the visual properties. The material is hardly the same.
Mehdi Talakesh
Hello, I am producing automobile parts. Material of our parts are POM and PA66 that those are in contact with each other. After 50000 contact cycles, loss weight of PA66 is 50%. I am going to reduce the wear rate of PA66. What material should I add to the PA66 to reduce wear? thanks mehdi talakesh Email: mehdi_talakesh@yahoo.com
Markus
Hi Mehdi, Have you tried aramid fibers? Please check out the following links: http://www.rtpcompany.com/wp-content/uploads/2013/09/afc.pdf http://web.rtpcompany.com/info/data/0200/index.htm That could be one option for you.
Nick Morris
What is PA6 resistance level against 24/7 immersion in industrial wastewater with pH of 2, temp 20-30 deg C? Looking for a resistant conduit material for submersible electrical equipment. Thanks
Mark
Hello Markus, did you ever experience that pure PA6 (no glass, no carbon) goes grey while injection moulding? Some grades do that some not. I did not find any link between or why. May bebad drying? Many Thanx in advance for your ideas. Mark
Markus
Sorry Nick, I don't have experience of PA in such environment. What makes you think that PP or PE would not do? Markus
Markus
Hello Mark, Could it be that the screw or the machine is oversized for the cavity volume? Did you dry the granulate properly? I would ask this in some plastic processing orientated LinkedIn group. There is a lot of know-how and people are eager to comment interesting topics. Markus
Stanko
Hallo Marcus I am an architect. I woud like to know what is beter material for carpet tiles PA6 or PA 6.6. Best regards.
Alex
Hello Markus, nice work with the article, I have a question regarding a component for wiring harnesses made from PA66, we hade to scrap a lot of this components because they broke in the assembly procces because they were to stiff, now the supplier proposed to keep them for 1h in 80 degrees hot water to ensure absortion of humidity withing the material to make it more elastic and then put them in some plastic bag (not air tight). Does this influence the elasticity of the components or is it usefull what we can do to make it more elastic??? Please Help....cheers
Mike Kaufman
Great article. Thanks. We have a manufacturer that produces pool rakes for us with nylon netting. They use PA66. We are wondering, though, in terms of overall durability, abrasion resistance, UV resistance and overall lifespan, if there is another material that would be a better option? We offer a lifetime guarantee on the rakes, and, even though our replacement rates are low, we are always on the hunt for ways to improve the quality of our product.
Bhushan
Hi Markus, I want to know which grade of PA has highest mechanical strength. PA6 or PA66.
Markus
Mike, have you tried PBT or POM? Or another grade of PA? I would exclude all the amorphous grades.
Markus
Hello Bhushan, To my experience difference is so small that there might be bigger variance between different PA6 grades than between PA6 and PA66 grades.
Markus
Alex, sorry for late reply. Moisture does decrease the tensile modulus of the product and makes it more flexible, but also tougher. This might eliminate the problem in production. I don't think the treatment will cause any permanent change to the product performance (It would do good to dry the assembled products before delivering them. ), but this is easy to test.
Nishant
Sir, can u suggest me a PA-66 grade which can sustain its moisture percent for longer period of time(12 to 18 months) in any condition or any PA-66 grade which absorbs less moisture but have properties like good flexibility, less brittleness, good tensile strength and good impact strength so that it dosnt get brittle even after losing some moisture in unfavorable conditions. Nishant (nish.ndg@gmail.com)
Markus
Nishant, I'm afraid moisture absorption at some level is an inherent property of PA-66. Could you think of using PBT instead?
Ümitcan
Hello Markus, Thank you for the article but I just would like to say my opinion about the part "better ductility (due to higher toughness)". Toughness is the result, ductility is the reason. So I would prefer to use" higher toughness due to higher ductility". Also you do not always increase toughness when you increase ductility as you sacrifice strength for increasing ductility (except extraordinary situations such as grain refinement). Lastly, the information about their melting points is missing. Thank you again.
Markus
Hello Ümitcan, Thank you for good comment. I'll go through that. Markus
Chandan
Hello Marcus, can u let me know the wear resistance of pa6 vs pa66..and it's effect with glass enforced , I am struggling with wear on pa6 60 % gf and finding alternative to it in the same price range. Thanks in advance
Markus
Hello Chandan, I would be surpised if there was any difference between PA6 and PA66 with such a high glass content. RTP has some grades that are compounded to be wear resistant. https://www.rtpcompany.com/products/wear-resistant/ Those might be worth checking. BR, Markus
André Rêgo
Hello Markus! Congratulations on such a great article! I have a motorcycle that has a PA6 tank and our gasoline has something between 20% to 27% ethanol in it. By now you might probally guess that the tank has swelled a lot... My question is: Is there a way to make it reduce its volume back? And how long will it take? Also I did some reading and was thinking about filling up the tank with isopropanol (as it is very hydrophylic) to "capture" some of the water that is in the structure - Do you think that this might work? Best Regards! André Rêgo
Azharul Islam
We want to make piano switch using PC material and it should be fire retardant as well glossy. Do you recommend to use PA66 +G30 for this? B rgds
Markus
Hello André You mean the tank has absorbed ethanol? The tank works fine with normal gasoline, but swells when there is ethnol mixed? If you empty the tank and let it dry in dry conditions, I would assume it to recover even without any other chemicals. Unless it has really softened. I'm afraid you will most face the same situation again unless you manage to make some sort of an inner layer into the tank. I googled this and there really seems to be some other people facing the same problem. Thank you for bringing this up. I have to keep this in mind.
Markus
Hello Azharul, I don't see PA66+GF as a good option for this. Due to glass the surface is hardly glossy and you might face some issues with warpage (dimensional accuracy due to bending). Unfilled PA would offer better surface but not necessarily the accuracy that you need. Amorphous material like PC is less prone to warpage and glossy. But together with hand cream and nail polishing liquids it has its risks. Fire retandant grades might be considerably different from corresponding normal grades. Markus
PRABHAKAR
NICE JOB Mr Markus Paloheimo i need help from you I AM TOOL AND DIE MAKER I WANT TO MOULD SHRINKAGE ( SI METRIC) FOR PA66 33% karan2571@gmail.com
Markus
Hello Prabhakar, To my experience it is close to 0.5 %. Parallel to flow direction it might be a little less (or even not noticeable), normal to flow direction it is probably a little more. There is no absolute truth on this. It depends on material thickness, flow length, gating and a little on the length of fibre used. It is good to be in contact with the material supplier before making the mould.
S.Senthil Kumar
Dear Sir, I gone through your article, which is very helpful for me. Further to this i have some other clarifications to implement in my project. For one of our project, we are using the Nylon-6 material. During assembling, the dimensions got changed due to moisture influence. So we are looking for equivalent characteristics with lower moisture absorption properties. Shall we choose Nylon-66 for the below mentioned application. 1. Application area- In-house, Open area, temperature condition: 30-40 degrees. 2. In the above condition, the dimensional and material characteristic’s should not be changed upto 10 years. Which material will be suitable for me Nylon-6 or 66 or any other variants of Nylon-XX? Your advice will help us to overcome the problem which we are facing now. Also we don’t know how the Nylon material will be after 10 years. In my previous experience, Polystyrene material got brittle after 5 years of usage.
Markus
Hello Senthil Changing to PA66 might help a little, but probably won't make a significant difference. If you want to continue with PA, then PA12 could be the solution. Please see the link below. http://www.emsgrivory.com/fileadmin/ems-grivory/documents/brochures/3001_en_Grilamid-L-PA12.pdf I don't see that 10 years as much of a risk without continuous UV light or permanent high load. I'm not suprised to hear your bad experiences with PS. Good luck, test as thoroughly as possible. Markus
Mahir
Hello Marcus, what are your experiences with PA66-GF30 shrinkage? I'm working on the design of a tool for a technical product and I'm not sure which percentage of the shrink to adopt. Size of the product is ca. 40x40x9, weight is 9 grams. Regards.
Markus
Mahir, It is good to notice that due to fiber orientation the shrinkage is smaller in the direction of flow compared to the direction against flow. This means that if you have a long bar and you gate from one end, the lenght of the product can be very close to the lenght of the cavity. On the other direction, I would rely on the information provided by the datasheet.
Paul
Dear Markus could you provide the basic properties of Hyprene 3155B material otherwise the link to provide the info..
Markus
Paul, I believe Hyprene is a TPE grade manufactured by Kingfa. It is not listed on Campusplastics nor Matweb... hmmm, perhaps you could try some other TPE? Markus
Mohankrishna
Dear Mr.Markus, I havea unique problem by using this material. Our customer has selected nylon 66 for internal bushing of a lift axle. In which a steel sleeve passes through. A toelrance of 600 microns was provided between nylon 66 ID and steel sleeve. We started facing squeaking noise issues due to stick-slip phenomenon at random. When we started analysing the reasons we narrowed down to the clearence between nylon bush and steel sleeve and reduction of available clearence due to properties of nylon 66. This pnenomenon is more evident during monsoon season. Though this product is designed by the customer their own team rejects this product citing noise issue. Need your suggestion on the following to update customer and correct the design tolerances to accomodate practical usage conditions. 1) what should be the clearence between nylon bush and steel sleeve. 2) what shrinkage allowance must be considered 3) how to overcome the permanent set properties of nylon 66 material while the job is assemled with 650 N-m torque. Torque is applied on the nuts tightened against bolts passing through steel sleeves.
Markus
Mohankrishna, Such surprising sound can be very disturbing. What is the diameter of the axis? The tolerance should be in correspondence to that. Does the system work if you make the bushing a little larger? Or could you change to POM? If lubrication eliminates the sound, you could consider some other grade with PTFE. Markus
Santosh.
Hi Markus, I am facing appearance issue with PA66 cable ties. Found white spots on the surface. these defect are occurred after couple of weeks of production. Could please suggest some information on this. thanks Santosh.
Markus
Santosh, My best guess is that the granulate has not been dried properly. Another option is that the screw of the machinge needs purging. Markus
Vivek Singh
Hello Markus, PA-66 and PA-6 both made from different polymerization techniques and different ingredients as well as conditions right, so their rate of crystallization of both polymer also should be different from each other. The mechanical strength of PA-66 in compare to PA-6 much better as my experience and heat resistance too.
Markus
Hello Vivek, Thank you for your comment. Interesting that you have experienced such a difference between their performance. It seems like both materials are worth testing before making the final desicion on the grade.
Gangadhar
Dear Sir, Want to know the tool life of PA66 30 GF material and PA6 30 GF material??
PRAKASH
Hii how to seperate iron from pa66-gf40 material after molding
Markus
Gangadhar, To my experience there is no difference. But due to high glass content you have to use hardened steel and pay special attention to the gating area. Good luck, markus
Markus
Pakash, You can do that manually using force. PA66 does not chemically bond to iron or any other metal. Markus
SKumar
Dear Markus, We have a product assembly made of two parts, out of PA6-GF30% and is used for filtration of water in the fields. Its thickness is 8mm, 300mm in diameter and a height of 900mm. it is fully exposed to the sun light. Recently we have received few complaints of cracking of the product after usage of one year. Most of the time it will be filled with water. Is it due to moisture absorption and weakening. Can you please comment.
Markus
Skumar, When PA absorbs water, it reaches a certain saturation point within a few days. After that it should not get any weaker. Is the plate always in touch with water? I could imagine that if it gets wet and dry, wet and dry, in a cycle this will cause some changes in dimensions. In addition it expands during the warm days and shrinks at night. If the plate is firmly fixed to the frame, this expansion could cause some fatigue. PA is not especially prone to UV-light, but in harsh conditions like this, it can be part of the cause. It is possible to block the direct sunlight in one way or another? Markus

Sivut

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