PA / Nylon Injection Molding

There are very few plastics in the manufacturing industry that combine the versatility, performance, and value of Polyamides. 

Polyamides can be processed through standard injection molding. It demonstrates various chemical and physical properties that make it an ideal choice for manufacturing both, thin- and thick-walled parts.

Nylon is a hygroscopic substance as it readily absorbs water from its environment. Hygroscopic materials tend to attract water either through absorption or adsorption. Nylon is also known in the injection molding industry for its many variations. In this article, we have described such features and their various types in-depth.

Table of Contents

What is PA Plastic and Nylon?

Polyamide, abbreviated for PA, is a popular injection molding material. A polyamide is a type of polymer that has amide groups in a recurring form in the main polymer chain. The chemical formula for amide groups is (R―CO―NH―R′) and the chemical structure of polyamides is as follows: 

pa plastic chemical structure

How is PA formed?

Polyamide refers to a type of plastic that is composed of polyamide resins, which is obtained either through the polycondensation of diamines and dibasic acids or through the ring-opening polymerization of lactams which is formed by the dehydration of amino acids. 

polyamide polycondensation
polymide open polymerization

Is Nylon and PA different?

Nylon was developed by DuPont and is a generic name for polyamides. DuPont refers to E. I. duPont de Nemours, an American company that was founded in July 1802. Since the 20th century, DuPont has invented various types of polymers that are extensively applied to a wide array of industries. Some of the popular plastics besides Nylon are Lycra, Teflon, Freon, Neoprene, etc. 

Nylon was patented by DuPont in 1935 and has since then been one of the most popular plastics to be used in various industries. 

difference between polyamides and nylon

The very first example of Nylon that was developed by Dupont’s team was Nylon 66. Later, many other variations were developed. Today, nylon comes in four main grades: Nylon 11, 12,  46, and 66. Nylon can be reinforced with glass for greater mechanical strength and that refers to the various grades of Nylon. In addition, there are many varieties of PA such as PA6, PA66, PA610, PA11, PA12, PA1010, PA612, PA46, PA6T, PA9T, and MXD-6 aromatic polyamide, etc.

PA / Nylon Plastic Properties

Nylon is a hygroscopic material that must be dried properly during processing to maintain its physical properties. In appearance, nylon plastics can be either white, milky white, or yellowish, and are either transparent or translucent crystalline resins. Polyamide resins can also be imparted with any color. 

Nylon resins exhibit excellent strength, stiffness, heat resistance, resistance to wear, and chemical resistance to hydrocarbons. Nylon is a relatively low-cost polymer that is easy to process and can be reinforced with glass or carbon fiber to increase mechanical and thermal properties. Let’s take a look at some of its properties through the below infographic: 

PA plastic properties

Nylon Plastic Variations

Nylon 6 / Nylon 66

The numbers 6 and 66 refer to the type and quantity of polymer chains in their chemical structure. Nylon 6 is made from one monomer which has 6 carbon atoms whereas Nylon 66 is made from 2 monomers in which each one has 6 carbon atoms, thus it’s called Nylon 66. 

nylon 6 chemical structure
nylon 66 chemical structure

Nylon 6 & 66 are both synthetic polyamides that are semi-crystalline and possess great strength and excellent durability. 

Properties of Nylon 6/66

Nylon 6 & 66 share some core properties. These are listed below: 

  • High mechanical strength and excellent wear resistance. 
  • Both types exhibit stiffness and hardness.
  • Great fatigue resistance and high mechanical damping ability.
  • Good electrical insulating properties.
  • Good resistance to high energy radiation such as gamma & x-ray.

While Nylon 6 and 66 are primarily very similar, they also have distinct differences. These differences are largely due to the differences in their chemical structure and are illustrated through the following infographic: 

nylon 6 vs nylon 66

One of the major differences between the two types of Nylon is mold shrinkage. The mold shrinkage of Nylon 6 is lower than Nylon 66 and thus, the dimensions of the final plastic part manufactured are generally as expected with Nylon 6. In the case of Nylon 66, you need to account for the higher mold shrinkage.  

The next major differences are the water absorption rates and heat deflection temperatures. Nylon 6 tends to absorb more water and has lower heat deflection temperatures than Nylon 66. It is thus not suitable for applications that require the plastic to be exposed to water at high temperatures. 

Applications of Nylon 6

Since its invention, Nylon 6 has been applied to various industries. It has been a popular choice and has been applied to various projects such as surgical sutures, musical instrument strings, toothbrush bristle threads, fishing nets, and filaments. In addition, it is a popular choice in the textile industry for hosiery and knitted garments. 

nylon 6 application
Image credit: unsplash.com

Applications of Nylon 66

Nylon 66 exhibits excellent abrasion resistance thus, Nylon 66 polymer is extensively applied to carpets, upholstery, and conveyor belts.

Nylon 11 / PA 11 / Polyamide 11

Nylon 11 also referred to as Polyamide 11 or PA 11 is a non-biodegradable polyamide. Nylon 11 has lesser amides in its structure and it thus exhibits increased resistance to dimensional changes that are often observed due to moisture absorption. 

In comparison to other Nylon grades, PA 11 has lesser desirable mechanical properties but it has various advantages such as being lightweight and lower water absorption rate. 

The chemical process of Nylon 11 involves the following steps: 

  • Ricinoleic acid is transesterified with methanol to form methyl ricinoleate. 
  • Methyl ricinoleate is dissociated to form heptaldehyde and methyl undecylenate. 
  • Heptaldehyde and methyl undecylenate undergoes hydrolysis to create methanol which is re-used in the initial transesterification of ricinoleic acid, and undecylenic acid. This is added to hydrogen bromide. 

After hydrolysis, hydrogen bromide undergoes nucleophilic substitution with ammonia to form 11-aminoundecanoic acid, which is polymerized into nylon 11.

nylon 11 chemical structure

Properties of Nylon 11

  • PA 11 has a water saturation rate of 2.5% which is lower than other Nylon grades. 
  • Comparatively, it exhibits higher strength and better heat resistance. 
  • It has a reasonable UV resistance and a lower environmental impact. 
  • Taking a look at some of its disadvantages, it is more expensive and exhibits lower impact strength as compared to the other Nylon grades.

Applications of Nylon 11

  • Nylon 11 is applied in projects that require increased dimensional stability when exposed to moisture due to its low water absorption rate. It is thus widely used for tubing in various fields. 
  • It is also applied to cable and wire sheathings in the electrical industry. 
  • Nylon 11 is widely applied in the sports industry. It is used to manufacture footwear, racket strings, and badminton shuttlecocks.
nylon 11 application
Image credit: unsplash.com

Nylon 12 / PA 12 / Polyamide 12

Nylon 12 also referred to as Polyamide 12 or PA 12 is one of the several polyamides.

It is polymerized either through omega trinitrophenyl aminolauric or laurolactam monomers. They both have 12 carbons, hence the name ‘Nylon 12’. 

Nylon 12 can be produced in one of 2 ways: 

  • The first being polycondensation of omega trinitrophenyl aminolauric with one amine and one carboxylic acid group.
  • The second is through ring-opening polymerization of laurolactam at 260-300˚C / 500-572˚F.
nylon 12 chemical structure

Properties of Nylon 12

  • Compared to most polyamides, the melting point of nylon 12 is the lowest at 180˚C /356˚F.
  • It has the lowest water absorption with saturation at approximately 2%. It thus exhibits good dimensional stability and electrical properties. 
  • It is also tougher than most polyamides. 
  • Nylon 12’s various mechanical properties, such as hardness, resistance to abrasion, and tensile strength are similar to nylon 6 and 66.
  • Nylon 12 is also resistant to chemicals and stress.

Applications of Nylon 12

  • Nylon 12 has a wide array of applications. They are used as packing material films in the food industry. 
  • Nylon 12 is applied for covering cables and insulating material in the electrical industry. 
  • It is also applied to prepare oil and gasoline-resistant tubes in the automobile industry. 
  • Nylon 12 has also been applied for producing sporting goods.

Nylon 46 / Nylon 4/6 / Polyamide 4/6

Nylon 46, also referred to as Polyamide 4/6 is a semi-crystalline, yellowish thermoplastic. It is made through condensation polymerization of 1,4-diaminobutane with adipic acid. 



nylon 46 chemical structure

Properties of Nylon 46

  • Nylon 46 has excellent wear resistance and great electrical insulation properties. 
  • It has high chemical resistance to many chemicals including fuels and oils at elevated temperatures. 
  • It has a higher heat deflection temperature, tensile strength, and heat resistance.
  • It has a higher moisture absorption compared to the other polyamides due to the more polar backbone. 
  • Nylon 46 is highly crystalline which is why it’s more sensitive to stress cracking. 

Applications of Nylon 46

  • Nylon 46 is used in many industries where high mechanical strength and ductility, good dimensional stability, and high heat and chemical resistance are required or recommended. 
  • Its important applications include electrical connectors and electrical components such as gears, bobbins, fasteners, crankshaft saddles, pump parts, and actuators. 
  • In many cases, it can replace metals, thermosets, and more expensive thermoplastics such as PEI, PES and PPS.

Advantages and Disadvantages of PA Plastic Injection Molding

Polyamides are a popular material choice for injection molding techniques however, we must note that it has both advantages as well as disadvantages. 

Let’s understand them in-depth: 

Advantages

  1. Nylon exhibits high mechanical, tensile, and compressive strength. The specific tensile strength of Nylon is higher than metal whereas the compressive strength of Nylon is comparable to metal. Nylon plastic also possesses a strong absorption capacity which is great in withholding impact and stress vibration. You should also note that the impact strength of polyamides is much higher than other plastics.  
  2. Nylon has outstanding fatigue resistance thus, polyamides are applied where regular fatigue is commonly observed such as bicycle plastic rims and escalator handrails. In such cases, the original mechanical strength is maintained even after repeated bending. 
nylon plastic application
Image credit: unsplash.com
  1. Polyamides such as Nylon 46 have a high softening point and thermal resistance. It also allows for a high heat distortion temperature which enables long-term application under high-temperature conditions (150°C / 302°F). The same can be achieved with Nylon 66 when it is reinforced with glass fiber. The heat distortion temperature of Nylon 66 reinforced with glass fiber can be reached over 250°C / 482°F.
  2. Polyamides are a popular material choice in movable mechanical parts as it possesses a low coefficient of friction with high wear resistance. The surface is also smooth thus the material is self-lubricating thus no lubricant is needed. 
  3. Polyamides are inert to biological erosion and have excellent antibacterial and anti-mildew properties.  
  4. Polyamides also have excellent electrical properties. The volume resistance and the breakdown voltage of nylon are very high thus, they are great for electrical insulation. 
  5. Polyamides are corrosion-resistant. They are also highly resistant to alkali, weak acids, oil, gasoline, aromatic hydrocarbons, and general solvents. Thus, they have outstanding endurance and anti-aging ability. Due to this, they can be used as packaging material for lubricants and fuels.
  6. Polyamides are easy to mold and have a low melt viscosity. Thus, it’s able to flow quickly and the mold fills easily with molten Nylon. It also has a high freezing point thus, allowing for faster injection molding,  so the molding cycle is shortened which results in a high production efficiency.
  7. In addition to being tough and having a high heat resistance, polyamides are also lightweight thus, PA plastic parts are often lighter than the other plastic parts. 

Disadvantages

  1. Nylon is hygroscopic in nature thus, it tends to absorb water. It has a high water absorption rate and the water saturation can reach over 3%. This can affect the dimensional stability and electrical properties thus, it is essential that polyamides are dried well before processing for injection molding.
  2. Polyamides have poor resistance to light. They can be easily degraded by sunlight thus, a UV stabilizer needs to be added to improve performance. 
  3. Polyamides are not resistant to strong acids and oxidants.

Nylon Injection Molding Challenges and Considerations

Polyamides are a very popular injection molding material but just like any other plastic material, they are not suitable for every application. There are various issues that can arise in the nylon injection molding process. Some of the challenges and considerations that one must take into account before applying Nylon resins to an application are listed below: 

  • One of the major considerations is gassing as excess gas can cause visual defects such as chalky appearances in the nylon plastic. Some of the major causes of gassing in Nylon injection molding are higher mold temperatures and poor ventilation. Gassing can be avoided by setting the mold at the right temperature and allowing vents to help escape the gas during the molding process.
  • The second major challenge in Nylon injection molding is moisture. Since Nylon plastic is hygroscopic in nature, it absorbs excess moisture thus, Nylon resins need to be dried well before processing. Poor drying of the resins can cause various types of defects in the finished product. During Nylon injection molding, you must ensure that the loader line and receptacle have been cleared of the resins to allow the barrel time to soak heat.
  • Nylon resins are prone to shrinkage during the molding process which can compromise the integrity of the finished product. These can range from reduced strength, and poor color, to warped edges. Shrinking can be avoided by controlling the heat and molding temperatures.
Contact Us for Nylon Injection Molding?

 If your project requires plastic parts to endure high temperatures and resistance to chemicals and abrasion, Nylon can be a perfect choice. VEM Tooling has the expertise and the team that is required for your Nylon injection molding project. At VEM Tooling, we offer quick quotes and dependable service.

We ensure that you have a seamless manufacturing process from prototype to production. You can contact us to further understand how Nylon Injection Molding can be implemented for your project. Contact VEM tooling and request a quote today.