The differences between nylon 6 and nylon 6/6
4.5 minutes | 09 Dec 2019
Nylon is used to make everything from barbed snap rivets and push rivets to cable twist ties, door panel retaining clips and cable strain reliefs. The material is a polyamide with many variants, but the most common we see used in engineering applications are nylon 6 and nylon 6/6, also referred to as nylon 66 and nylon 6.6, or using the polyamide name, PA 6 and PA 66.
The question then, is what’s the difference between these two nylons? The answer is in the numbers, which signify the type and quantity of polymer chains in their chemical structure.
Nylon 6 is derived from one monomer, which is a molecule that can be bonded to other identical molecules to form polymers. For nylon 6, the monomer has six carbon atoms, hence the name nylon 6. Nylon 6/6 is made from two monomers. Each of these monomers has six carbon atoms, which is reflected in the name nylon 6/6.
As you’d expect, nylon 6/6 is stiffer and usually more durable. However, they do share many of the same characteristics:
Nylon 6 and nylon 6/6:
- High mechanical strength
- High toughness, stiffness and hardness
- Good fatigue resistance
- Good impact resistance
- Excellent wear resistance
- Good electrical insulating properties
- No resistance to UV rays
- Lightweight; sometimes used in applications in place of metals
- Excellent fuel and oil resistance
- Attacked by strong mineral acids and absorbs polar solvents
- High water absorption
Nylons and UV rays
Nylons are not UV resistant, although you can add stabilizers to give them almost any effect you desire. On their own, nylon 6/6 is the more sensitive, though nylon 6 is still vulnerable without stabilizers. UV light weakens nylon through interaction with the chemical structure’s pi electrons, specifically double bonds and aromatic groups. Nylon 6, for example, absorbs UV light in its amide bonds. Polymers that lack pi electrons, such as polyethylene, can stand up better to UV rays.
Let’s be fair, however. UV rays affect all materials, not just nylons. But with stabilizers, nylon can perform extremely well outdoors. For example, these mini snap together rivets made of nylon 6/6 with a UL94 V-2 flammability rating are ideal for outdoor applications:
How are nylon 6 and nylon 6/6 different?
It comes down to a lot of little things. While both are cost effective, Nylon 6 typically costs around 30% less. Here’s a closer look at the differences:
|Nylon 6||Nylon 6/6|
|Machinability – low tool wear & surface finish||Good||Better|
|Water absorption rate||Higher||Lower|
|Impact strength||Izod: cm-N/cm of notch: 160||Izod: cm-N/cm of notch: 160|
|Tensile strength||6.2 x 104 kPa (Good)||8.2 x 104 kPa (Better)|
|Crystalline melting point||437°F / 225°C||509°F / 265°C|
|Density||1.15 g/ml||1.2 g/ml|
|Typical molding shrinkage ratio||1.2%||1.5%|
How they compare in manufacturing
Both have very good flow for easy processing.
As shown in the table, nylon 6 processes at a lower temperature, while nylon 6/6 has a higher melting point. This presents more challenges for processing nylon 6/6. When nylon 6/6 is exposed to ambient air temperatures and begins to solidify, mold shrinkage occurs and shapes can change. However, you can get around this by increasing the dimensions of your extrusion dies and injection molds. Nylon 6 is another matter, which processes much easier. Because its mold shrinkage is lower than nylon 6/6’s, you get more reliable final part dimensions.
Another issue with processing nylon materials is moisture and water absorption. In this regard, nylon 6 absorbs more than nylon 6/6, but both materials will need to be dried before being molded. The reason: nylon absorbs moisture from the air. Failure to dry the material will lead to splays and marks on part surfaces. Keep in mind that oxidation occurs due to heat and water, so if you skip the drying process, you’re also looking at compromised mechanical properties as a result of material degradation.
Injection molding and drying nylons
If you over-dry nylons, the finished part could come out brittle. Follow these guidelines for both nylon 6 and nylon 6/6:
If moisture content is greater than 0.2%:
|Method of drying||Temperature||Duration|
|Hot air oven||176° F (80° C)||16 hours|
If nylon has been exposed to air for longer than 8 hours:
|Method of drying||Temperature||Duration|
|Vacuum||221° F (105° C)||8 hours|
What is glass-filled nylon?
You can add powdered glass to nylon resins, which will increase:
- Tensile strength
- Compression strength
This process will also give you a lower thermal expansion coefficient than unreinforced nylon. Remember, nylon absorbs moisture. That, in turn, causes the material to expand. Adding glass fibers offsets this problem, increasing stability when the nylon is exposed to temperature changes.
In the first table we showed you, nylon 6’s typical molding shrinkage ratio is 1.2%, and nylon 6/6, 1.5%. By adding 30% glass fibers to nylon 6, this can be reduced to 0.4%. Add 33% to nylon 6/6, and you’re looking at 0.5%.
All that aside, when you need to enhance the strength of nylon, glass filled, or GF nylon, is ideal. In fact, by using glass as an additive, you can strengthen your nylon by up to 70% more than untreated nylon.
An example of a GF nylon solution is Essentra’s hexagonal standoff, which is 25% glass filled, nylon 6:
Nylon’s characteristics make it a popular material across all industries and applications. Here are some examples of its versatility:
General purpose, across all industries.
Can easily open to make routing changes. A wire cable clamp is used in everything from electrical cable enclosures to PCBs.
Nylon rivets are used in everything from appliances to computers and panels.
From automotive to office machinery and equipment, cable management twist ties come in different mounting types.
Keeps thick doors and panels securely closed by mounting through diameter holes.
Industrial door pull handles made of nylon 6 are ideal for machine covers.
Mount your PCB in tight spaces while giving them a level of protection.
Ideal for PCBs. Non threaded spacers don’t require assembly tools. You can easily install them by hand.
What about other materials?
Nylons aren’t ideal for every application, of course. For instance, nylon panel fasteners work great in many instances, but other plastics might suit your project better. Or, perhaps you should consider other materials for your fasteners. You can also learn more about materials in general with our Ultimate Caps and Plugs Guide.
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