The differences between nylon 6 and nylon 6/6
Nylon uses vary from barbed snap rivets and push rivets to cable twist ties and cable strain reliefs. There are many different types of nylon, but the most common are nylon 6 and nylon 6/6. In this guide, we’ll explain how they differ, covering:
Is polyamide nylon? No, but if you ask, is nylon a polyamide, the answer is ‘yes’.
Nylon plastic is in the polyamide family, but where nylon is synthetic, polyamide material can be synthetic or natural (such as wool and silk).
Polyamide nylon has many variants. The most common we see used in engineering applications are nylon 6 and nylon 6/6, also written as nylon 66, nylon 6.6 and nylon 6,6, or using the polyamide name, PA 6 and PA 66 (also PA66).
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 structure is derived from one monomer, which is a molecule that can be bonded to other identical molecules to form polymers. The nylon 6 monomer has six carbon atoms, hence the name nylon 6. Nylon 6/6 structure 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 properties
- 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 stabilisers 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 stabilisers. 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 stabilisers, 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. Nylon 6/6 has better weathering properties, which if relevant, should be taken into consideration.
There are key differences, and it comes down to a lot of little things. While both are cost effective, Nylon 6 typically costs around 30% less. Nylon 6/6 does have better chemical resistance to saturated calcium chloride, and higher abrasion resistance.
Here’s a closer look at how the different nylon characteristics compare:
|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 moulding shrinkage ratio||1.2%||1.5%|
Both have very good flow for easy processing.
As shown in the table, nylon 6 density is lower while it also processes at a lower temperature, while nylon 6/6 has a higher melting point.
The melting point of nylon 6/6, along with other factors, presents some challenges. When nylon 6/6 is exposed to ambient air temperatures and begins to solidify, mould shrinkage occurs and shapes can change. However, you can get around this by increasing the dimensions of your extrusion dies and injection moulds. Nylon 6 is another matter, which processes much easier. Because its mould 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 properties mean that it absorbs more than nylon 6/6, but both materials will need to be dried before being moulded. 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 moulding 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 fibres offsets this problem, increasing stability when the nylon is exposed to temperature changes.
In the first table we showed you, nylon 6’s typical moulding shrinkage ratio is 1.2%, and nylon 6/6, 1.5%. By adding 30% glass fibres 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 and properties make it a popular material across all industries and applications. Here are some examples of its versatility when it comes to components.
Applications of nylon 6/6
Nylon cable ties
General purpose, across all industries.
Adjustable cable clamps
Can easily open to make routing changes. A wire cable clamp is used in everything from electrical cable enclosures to PCBs.
Plastic push rivets
Nylon rivets are used in everything from appliances to computers and panels.
Cable twist ties
From automotive to office machinery and equipment, cable management twist ties come in different mounting types.
Applications of nylon 6
Keeps thick doors and panels securely closed by mounting through diameter holes.
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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