Nylon 6 vs. nylon 6/6

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What material is nylon?

It&#;s a high-performing engineering plastic. Specifically, it&#;s a thermoplastic linear polyamide with many variants. 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.

What's the difference between nylon 6 and nylon 6/6?

The difference between these two nylon materials is in the numbers, which signify the type and quantity of polymer chains in their chemical structure.

Polyamide structure

Nylon 6: 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. The chemical formula of nylon is (C6H11NO)n.

Nylon 6/6: Made from two monomers. Each of these monomers has six carbon atoms, which is reflected in the name nylon 6/6. Its chemical formula is (C12H22N2O2)n.

Polyamide production requires the repeated joining of two groups to form an amide link. Amide is the organic compound containing the group C(O)NH2.

Nylon 6

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 properties

Nylon uses are vast, including snap latch rivets, nylon hex nuts, flat washers, push rivets, cable twist ties, door panel retaining clips and cable strain reliefs.

Polyamide advantages &#; and a few of their disadvantages &#; include:

• 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. This is why nylon temperature range can vary. 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.

UV rays affect all materials, not just nylons. But with stabilizers, nylon can perform extremely well outdoors. For example, usage of nylon includes these mini snap rivets made of nylon 6/6 with a UL94 V-2 flammability rating ideal for outdoor applications:

At a glance: Nylon 6 and nylon 6/6 material properties

It comes down to a lot of little things. While both nylon plastics are cost effective, Nylon 6 typically costs around 30% less. Here&#;s a closer look at the differences:

Attributes Nylon 6 Nylon 6/6 Machinability &#; low tool wear & surface finish Good Better Mold shrinkage Lower Greater 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 nylon 6 and nylon 6/6 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
• Stiffness

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.

Find out more about glass-filled nylon in our guide, Pros and Cons of Glass-Filled Nylon.

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 applications

Nylon&#;s characteristics make it a popular material across all industries and applications. Here are some examples of products made from nylon plastic.

View our range of nylon components

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.

Nylon 6:

 

Panel catches

Keeps thick doors and panels securely closed by mounting through diameter holes.

 

Industrial handles

Industrial door pull handles made of nylon 6 are ideal for machine covers.

With competitive price and timely delivery, sft sincerely hope to be your supplier and partner.

 

Card guides

Mount your PCB in tight spaces while giving them a level of protection.

 

Snap-latch rivets

Ideal for applications that require maintenance work. Available in easy-grip or mini-grip designs for different panel holes and thicknesses.

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you&#;ve chosen the right product for what you need. 

If you&#;re not quite sure which solution will work best for your application, our experts are always happy to advise you.

Whatever your requirements, you can depend on fast dispatch. Request your free samples or download free CADs now.

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Many engineering materials are in truth families in their own right. Take, for example, steel &#; this ferrous (iron)-based material is in fact a wide-ranging class of materials, with different microstructures, heat treatments and alloy content. Materials range from utility steels to highly specialised variants which are manufactured in small quantities for a narrow range of applications.

And so it is with plastics. Take nylons (or polyamides). There are multiple different types of nylon including:

• Nylon 6
• Nylon 6/6 (aka Nylon 66, or Nylon 6,6)
• Nylon 6/9
• Nylon 6/10
• Nylon 6/12
• Nylon 4/6
• Nylon 11
• Nylon 12/12

The system of identification refers to the number of carbon atoms in the materials from which it is produced. Nylon 6, for example, is produced from caprolactam, which contains six carbon atoms, and nylon 6/6 is formed from hexamethylene diamine, with six carbon atoms, and adipic acid, also having six.

While the variations in properties are not as marked as they are with steels, variations in underlying structure and the fillers and additives used can in some cases lead to a wide variation in properties, with a combination of commodity and specialist grades. One supplier has almost 90 grades of Nylon 11 alone.

Nylon as engineering plastics

As a family, their characteristics of strength, stiffness and toughness have earned them a reputation as engineering plastics. Typical applications include small gears, grilles, door handles, bicycle wheels, bearings, brushes, sprockets, housings for power tools, terminal blocks and slide rollers.

An important design consideration is that nylon absorbs moisture, which can affect its properties and dimensional stability. Reinforcement, usually by glass, reduces this problem and produces an extremely strong, impact resistant material.

 

Nylon 6 and 6/6 are the cheapest of all the nylon types. Nylon 6/6 is the most widely used group of nylons, although for supplier reasons nylon 6 is historically the most widely used grade in Germany. Unfilled, it exhibits strength across the widest range of temperature and moisture of any nylon. It has good resistance to abrasion and the lowest permeability for gasoline, mineral oils and fluorocarbon refrigerants.

But 6/6 has high moisture absorption and low impact strength and ductility when dry. It is the most sensitive of all the nylons to UV and oxidative degradation. Both 6/6 and 6 have lower resistance to weak acids than 6/10, 6/12, 11 and 12.

In addition to the common applications of nylons, 6/6 is popular for electrical components, stimulated by improved fire retardancy. It is commonly used as a metal replacement for diecast hand tool bodies.

Selecting the best nylon from the family is often a matter of compromising one or more properties against others. This is an area where materials selection systems such as UL Prospector really come into their own, combined with a qualitative understanding of the basic differences, as described below. Here, other engineering polymers, such as acetals, thermoplastic polyesters and others should also be considered.

One of the differences between Nylon 6 and Nylon 66 is that, under moist conditions, nylon 6 has better impact strength and flex fatigue life than 6/6. Compared to 6/6, it can be processed at lower temperatures and is less crystalline, which means mould shrinkage is low and closer tolerances are possible. Transparent grades are also available.

But it has the highest moisture absorption of any nylon, with attendant dimensional instability and changes in mechanical and electrical properties. Some of these effects can be offset by alloying with low density polyethylene (LDPE).

As a result of these properties, it is used for components requiring higher impact strength than 6/6, but not requiring higher yield strength.

Since the original version of this article was published in , readers have reported that because of longer chains, nylon 6/6 has better chemical resistance than nylon 6 to saturated calcium chloride. Most sources report that 6/6 has better weathering properties. One important advantage of 6/6 compared to 6 is a higher HDT.

All nylons will severely degrade when exposed to fermented 15% ethanol gasoline.

 

Other nylon grades

Nylon 6/10 and 6/12 are used for electrical insulation where their lower moisture absorption justifies the extra cost. Nylon 6/10 has lower moisture absorption and a very low embrittlement temperature. Nylon 6/12 is progressively replacing 6/10 as it is cheaper (though more expensive than 6 and 6/6) and has better heat resistance. Its properties are generally between 6 and 6/6, with slightly superior creep properties to 6/6 under moist conditions.

Nylons 11 and 12 have still lower moisture absorption, with 12 having the lowest of all unfilled nylons. They have greater flexibility and impact strength than 6, 6/6, 6/10 and 6/12. This comes at the expense of higher cost, lower strength and lower maximum service temperatures. Weathering resistance is the best of nylons, although more recently, grades of so-called super-tough nylons (in effect alloys) have challenged this position. Nylon 12/12 has better properties than 6 and 6/6, but less expensive than 11 or 12.

Nylon 4/6 has high impact, low creep and higher stiffness at high temperatures. The fatigue behaviour is better than 6/6. The processing window is lower.

Other variants which might be encountered on occasions are 6 and 6/6 flexible copolymers, cast nylon 6, transparent amorphous nylons, sintered grades and more recently forms suitable for 3D printing.

Nylon films exhibit high tensile strength and elongation, good impact strength, impermeable to gases. Low temperature properties (-70C) are good, with good flex-crack resistance and clarity. Increasing moisture content reduced barrier properties but increases elongation and flexibility.

Nylon is also available as fibres, which are notably strong.

Acetals vs nylons

Acetals &#; sometimes also known as polyoxymethylene (POM) &#; like nylons, are semi-crystalline thermoplastics, and some of their characteristics overlap, such as their fatigue resistance, chemical resistance, and wear resistance with a sharp melting point. Both are used for small components such as washers, discs, and spacers.

One of the most popular properties of acetals is their ease of machining compared to various other engineering plastics, including nylon, as well as such as HDPE and UHMW. Acetals tend not to deflect away from or grab machining tools and they also chip nicely, making them ideal if an application requires the material to be machined.

There are distinct differences between nylons and acetals:

• nylon offers superior tensile strength and bending stiffness
• nylon can also handle higher loads and higher temperatures
• nylon is susceptible to UV radiation unless special additives are incorporated
• nylon reacts poorly to changes in humidity, which cause it to swell and lose tensile strength
• nylon is a self-lubricating material
• acetal provides higher impact resistance and cold resistance
• acetal is suitable for moderate loads.
• acetal has much better wear resistance and chemical resistance
• acetal has greater dimensional stability and resists moisture and humidity
• acetal is shiny, while nylon appears dull in comparison

Like nylon, acetal comes in different formulations, though not so many, of which the main two are acetal copolymer (acetal-C) and acetal homopolymer (acetal-H).

The differences are slight: H has better mechanical properties than C, including higher strength and stiffness, better creep resistance and higher hardness rating. However, C has the better chemical properties, hydrolysis resistance, higher continuous allowable service temperature in air and less outgassing.

One of the biggest differences between C and H is centreline porosity, which is a characteristic of H but not C. Centreline porosity is caused by gasses trying to escape during the cooling process after extrusion or compression. It can appear as small bubbles in thicker rods or a white line down the middle of each cut edge of a sheet.

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