Nylon 6 and Nylon 6/12: Differences, Advantages and Disadvantages
Learn more about Nylon 6 and Nylon 6/12
Nylon 6 and nylon 6/12 are both toxic-free synthetic polyamide compounds. Polyamide is a polymer of repeating amide bonds (-CO-NH-). The most crucial difference between these two plastic materials is their moisture absorption tolerance level; nylon 6/12 is more resistant to water and other liquids than nylon 6. Furthermore, nylon 6/12 has a melting point of 218 degrees C (424 degrees F), while the melting point of nylon 6 is higher, at 268 degrees C (514 degrees F). Nonetheless, both materials find their usages in similar industries: manufacturing, automotive, construction, and textiles, to name a few. Nylon 6/12 is also extensively used in the cosmetic industry. Both nylon 6 and nylon 6/12 share the same properties to some extent and may be easily used in plastic injection molding.
Nylon 6, also known as polycaprolactam, is a semi-crystalline polyamide formed by the ring-opening polymerization of caprolactam. Nylon 6 is represented by the chemical formula (C6H11NO)n. This polymer was invented in 1939 by the German chemist Paul Schlack. Nylon 6 became essential in today's fiber commerce almost immediately after its creation, and its uses and applications are still being explored and improved. There exist eight different types of nylons. The main difference between them is in the number of carbon atoms in the diamine and dibasic acid monomers from which they are formed. This material is known as Nylon 6 because it consists of 6 carbon atoms.
The following image shows the chemical structure of the building block of nylon 6 – caprolactam:
Building block of nylon 6 chemical structure.
Image Credit: StudioMolekuul/Shutterstock.com
Nylon 6 is a strong, highly elastic, and tensile-strengthening substance. This polymer is resistant to abrasion and various substances such as alkalis and acids. The glass transition temperature of nylon 6 is 48 degrees C (118 degrees F), while the melt temperature is 214 degrees C (417 degrees F). Moreover, it can absorb up to 2.4% of water, even though this reduces its tensile strength. Nylon 6 filaments are smooth and featureless, similar to glass rods. Nylon 6 becomes soluble in any dense phenol or acid and can be dyed with vat dyes, direct dyes, or acid dyes. Due to its properties, this material has the potential to be employed as a technical nutrient. Nylon 6's degree of polymerization, the number of monomers in a polymer molecule, is 100-250 units. The structural chemical formula and molecule model of nylon 6 are shown in the image below:
Nylon 6 structural chemical formula and molecule model.
Image Credit: Bacsica/Shutterstock.com
Nylon 6 is produced by ring-opening polymerization of caprolactam. Nylon 6 is primarily made by heating caprolactam to 250 degrees C and adding around 4% water. A carbonyl group is present in caprolactam and when water molecules are present, the oxygen of that carbonyl group absorbs a proton from the water molecule. From this, the oxygen atom has a positive electrical charge. Since this is undesirable, the molecule rearranges and leaves the positive charge on the carbonyl carbon atom. The nucleophile, in this case OH–, can then attack this carbon atom and as a consequence, the caprolactam molecule's ring is opened. This opened segment can force another ring to open, resulting in ring-opening polymerization. The amide bond within each caprolactam molecule is broken during polymerization. The active groups on both sides generate two new bonds as the monomer becomes part of the polymer backbone.
Nylon 6 is commonly used in the construction, packaging, textile, manufacturing, and electrical industries. This material finds its application wherever the resulting product should have a high level of lubricity, toughness, and wear. Nylon 6 has a vast spectrum of applications, such as:
- Panel catches
- Circuit insulation boards
- Guitar strings and pics
- Power tool housing
- Medical implants
The main advantages of nylon 6 are its stiffness and resistance to abrasion. Moreover, this material has excellent impact strength, wear resistance, and electrical insulating properties. Nylon 6 is a highly elastic and fatigue-resistant material, meaning it will return to its original proportions after being distorted by tension. This polyamide is non-toxic and can be combined with glass or carbon fibers to increase performance. The absorption capacity of the material grows in direct proportion to the quantity of moisture it absorbs. The high affinity of nylon 6 for some dyestuffs allows for more dyeing diversity, with the potential for brighter, deeper patterns.
The disadvantages of nylon 6 are its low melting point and high water absorption. Nylon 6 is hygroscopic, which means it can absorb water even from the air. Apart from that, this material may permanently lose breaking strength, elongation, and toughness if exposed to high temperatures or light for a longer period. Consequently, superficial yellowing and general discoloration of the fiber might happen. Moreover, nylon 6 is not UV resistant, but this can be fixed by employing stabilizers.
Nylon 6 is entirely free of all toxic properties and does not irritate the skin. This material is chemically inert and is proclaimed a non-dangerous substance by the GHS (Globally Harmonized System of Classification and Labelling of Chemicals). However, nylon 6 may be harmful if accidentally inhaled, since the particles are bio-persistent and will likely remain in the lungs for an extended period, causing respiratory tract irritation. Moreover, this polymer may cause skin irritation if absorbed through the skin. If molten material comes in contact with skin, the person should not attempt to remove it since doing so might cause severe tissue damage. Accidental indigestion of nylon 6 might also cause health problems, such as a gastrointestinal blockage.
Yes, Nylon 6 is a suitable material for injection molding. The resulting molded nylon parts possess great strength, as well as chemical and temperature resistance. When molding nylon 6, the material is sometimes injected with a specified amount of glass fibers (usually between 10% and 40%) to boost its tensile strength. Glass fibers improve stiffness while also influencing how a part behaves under different conditions. For example, when subjected to stress, an item that is molded by a mixture of nylon and glass would break more quickly and easily than an item that has been molded with only nylon. Moreover, since UV radiation can be harmful to nylon, a UV stabilizer is frequently added to the material before injection molding to decrease the possible degradation of the item with time.
Nylon 6/12, also known as Polyamide 6/12 (PA 612), is a non-transparent copolymer made up of different di-acids with 12 carbon chains. The molecular formula of nylon 6/12 is C18H36N2O3. The main reason for the creation of this polymer was to solve the biggest problem of nylon 6 - moisture absorption.
PA 612 possesses balanced mechanical properties, excellent abrasion and chemical resistance, and is easy to process due to its intermediate carbon chain. Moreover, nylon 6/12 features better ductility and dimension stability as well as lower moisture sensitivity. Because of the lower moisture absorption, the polymer is less ductile than nylon 6 and other nylons. The density of this material is 1.06 - 1.07 g/cm³, while its melting point is 218 degrees C.
Nylon 6/12 is produced by combining two compounds in one precursor, just like all other nylon polymers with a two-number nomenclature. This precursor is then polymerized to create the final material. The numbers after the word nylon represent the number of carbon atoms in each initial reactant. Nylon 6/12 is made up of a diamine known as hexamethylenediamine and a diacid known as dodecanedioic acid. This acid contains 12 carbons, which increases the distance between the amide groups, resulting in worse mechanical characteristics and a lower melting point. However, because the amide group is responsible for the polymer's moisture affinity, nylon 6/12 is more resistant to moisture absorption than other types of nylon.
Nylon 6/12 is commonly used in the manufacturing, aerospace, automotive, and cosmetic industries. It is mainly utilized in extruded tube applications. However, it may also be used in injection molding, but mostly if glass-reinforced. Nylon 6/12 is one of the most often used polymers for filaments. Some of the primary usages of this material include:
- Electric and electronic appliances
- Personal care products
- Precision mechanical components
- Automobile parts
- Cosmetic products
- Brush bristles
- Fuel systems
The most crucial advantage of nylon 6/12 is its low moisture absorption property. As a result of this characteristic, this material doesn't swell quite as much as nylon 6. Moreover, nylon 6/12 has excellent strength and wear resistance, which means that the material would suffer less damage or loss due to wear or usage. Nylon 6/12 has good electrical insulation properties and is less sensitive to stress cracking than other polyamides. Apart from these, some other significant advantages of this polyamide include heat resistance, chemical resistance, and lubricity.
One of the main disadvantages of nylon 6/12 is its relatively low chemical resistance to strong acids and bases. Moreover, it is often more expensive than other nylons, primarily because of its restricted availability. This polymer has reduced crystallinity, and due to this, its physical characteristics and heat deflection temperature are also reduced. More specifically speaking, this material has lower flexural and tensile strength, a lower heat deflection temperature (HDT), and more mold shrinkage than nylon 6.
Nylon 6/12 has been proven to be generally safe for human health. Since it is commonly used as bulking and opacifying agent in cosmetics, the Cosmetic Ingredient Review Expert Panel had to test the possible toxicity of the polymer. After examining relevant animal and human data, the panel stated that nylon 6/12 is not likely to penetrate the skin and as such is considered non-toxic. Inhaled droplets/particles deposited in the nasopharyngeal and thoracic areas of the respiratory system may have harmful consequences depending on their chemical and other features. However, the current evidence shows that unintentional inhalation would not lead to major local respiratory or systemic problems except for maybe irritation, given the minimal actual exposure in the breathing zone and the quantities at which the chemicals are employed. Furthermore, accidental indigestion of nylon 6/12 might result in inflammation and other health issues. When in contact with eyes or skin, nylon fibers may irritate the skin and cause eye discomfort. Aside from particle-induced mechanical irritation of the skin and eyes, no significant health consequences are indicated.
Nylon 6/12 is poor at absorbing moisture because it was created to prevent moisture absorption. Nylon 6/12 is a copolymer, which means it's made up of 12 different di-acids with 12 carbon chains. When these di-acids are combined with a 6-carbon diamine, they polymerize into nylon. Nylon 6/12 has a higher number of carbon atoms separating the amine groups in its chemical structure than nylon 6, and this ratio and chemical geometry give nylon 6/12 greater resistance to moisture absorption.
Yes, Nylon 6/12 can be used in injection molding. At its melting point, nylon 6/12, like other thermoplastics, becomes liquid and can be heated, chilled, and then reheated without any significant deterioration. Because of this, nylon 6/12 is a good material to be injection molded into various plastic items and then eventually recycled. Nylon 6/12 can be filled with glass, minerals, impact modifiers, flame retardants, UV stabilizers, and other modifiers to improve some of its properties. Injection molding glass-filled nylon, for example, boosts tensile strength and makes the designed material less flexible and stiffer by adding glass fibers to polyamide plastic. Other common additives can be used with nylon to generate toughened, conductive, and high-temperature polyamide plastics with increased strength, durability, and flexibility.
This article went through the most critical information regarding two specific types of polyamides, or nylons – nylon 6 and nylon 6/12. Both plastic materials don't affect human health except as potentially a mild irritant if inhaled or ingested. Moreover, they are both stiff, wear-resistant, and have excellent electrical insulation properties. Since nylon 6/12 is better at preventing moisture absorption, this material should be used out of the two when manufacturing waterproof products.
If you know your application requires nylon injection molded parts, make sure to get a quote on your designs today.
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