Nylon is increasingly becoming one of the most widely used materials for manufacturing daily used plastic products. The food bowl you use daily for dinner or lunch could be a bio-grade grade of nylon plastic.
Following this, have you ever wondered about the astonishing material of your teeth brush bristles, which makes your teeth glow? You will be surprised to discover these bristles are also made of Nylon Plastic.
For shading purposes, while walking through a street in heavy sunlight, a nylon plastic umbrella is used even in heavy rain because of its hydrophobic nature.
What is Nylon?
Nylon is a synthetic plastic material used in several industrial and domestic applications. You can study Nylon and will be amazed to discover its remarkable properties, versatility as an engineering plastic, and transformability in highly precise fibers, films, and especially in injection molding nylon parts.
The nylon plastic injection molding has been adopted because of the higher thermal stability of the three-dimensional nylon structure and tuneable mechanical properties.
Since nylon is thermoplastic, it may be mixed with various additives to produce many injection-molded nylon plastic items.
Nylon plastics are generally termed polyamides because of amide groups in their polymer backbone chain. If you are considering nylon injecting molding, your first preference should be running injecting molding nylon 66.
Nylon 66 is a hard, scratch-free, rigid plastic with high-performance stability below its melting point.
Variants of Nylon
The following table lists the eight primary variants of nylon:-
| Sr. | Variant | Property/Source |
| 1. | Nylon 6 | This variant of nylon is synthesized through a ring-opening mechanism. |
| 2. | Nylon 6,6 | This variant was discovered and patented by Wallace Carothers. It is synthesized by step growth polymerization and condensation polymerization. |
| 3. | Nylon 4,6 | This is an aliphatic nylon variant formed by poly-condensation. |
| 4. | Nylon 6,9 | The polymerization of Azelaic Acid synthesizes this. |
| 5. | Nylon 6,10 | This variant is obtained from pentamethylene diamine acid. |
| 6. | Nylon 6,12 | It’s a copolymer made of 12 carbon chains with 12 different di-acids. |
| 7. | Nylon 11 | The basic source of Nylon 11 is Castrol oil. 11-Aminoundecanoic Acid is extracted from Castrol Oil which is used for the polymerization of Nylon 11. |
| 8. | Nylon 12 | This variant is synthesized by ω-amino lauric acid in which each auro-lactam monomer contains 12 carbons. ω-Aminolauric Acid is a bi-functional monomer containing a single carboxylic and single amine group. |
Injection Molding Characteristics of Nylon
Regarding durability and strength, injection molding is a superior and more efficient way to manufacture nylon plastic products compared to other manufacturing techniques.
Furthermore, injection molding offers you low production time with greater efficiency consuming less energy because of the high production rate.
Being a synthetic and petroleum or plants derived material, it is thermally stable and considered a thermoplastic polyamide presenting its uniform response towards heat.
When nylon is heated closer to its melting point, it melts, turns to a liquid, and may then be utilized again in a part or shape that is new or different. This is one of the advantages that nylon plastic never degrades till its melting point on the heating again for reusing.
In general, nylon plastic has high tensile strength, good chemical and water resistance, high thermal stability, and low friction properties.. The chemical structure of nylon enables it to be used for high-temperature applications i.e. heavy mechanical machinery and mobile engines.
This property of a high melting point i.e. 220oC, makes it a considerable alternative to metals as it normally withstands a high friction application.
Mechanical Strength
Nylon plastic represents a higher tensile strength, which, combined with high melting temperature, offers greater abrasion resistance properties. Injection molding grades of nylon offer tensile strength up to 90 MPa or 13000 Psi.
A higher strength of nylon offers higher flexibility and ductility, making it a suitable material alternative to metals, as the same properties are not found in metals. A set of high thermal and mechanical properties of nylon is very advantageous. Nylon 66 is considered a high-duty polyamide material.
It may be used in very extreme parameters or conditions. It is a semi-crystalline polymeric material offering a softening temperature of more than 200oC. Its low abrasion properties enable it to be used in higher mechanical duty applications.
In this heavy-duty mechanical work, a huge amount of heat is produced, which is undesirable and requires a well-sorted cooling system increasing the utility cost of the process. In this case, nylon plastic is preferred as being high heat-stabilized material.
Chemical Resistance
Nylon plastics are resistant to many chemicals because of their well-directed three-dimensional structure of polyamide backbone chain. The bonding in this chain is stronger enough to resist many organic materials, chemicals, or solvents.
Moreover, several inorganic chemicals are also resisted by nylon plastics as well. However, nylon plastics, especially nylon 66, resist strong acids poorly. Furthermore, they may possess some resistance in response to interaction with dilute acids.
Nylon plastics are also resistant to alkalis. Because of this characteristic, you can utilize nylon for injection molded nylon plastic containers.
However, the substance with lower pH, i.e. less than 7, may not strictly be stored in these containers due to their acidic nature. Its finished products are highly resistant to water.
An example of an umbrella perfectly represents its properties addressing rain and sunlight resistivity.
Hardness
Nylon shows higher mechanical properties. Nylon is a hard, rigid, and impact-bearing material. The Shore A Hardness of nylon is around 120. Nylon 66, the hardest material in this series of nylon, has very high abrasion, stiffness, wear, and rigidity qualities. This high value of hardness also improves the thermal stability of Nylon 66.
Impact Strength
Apart from hardness, nylon 66 also represents a very high impact strength. The izod impact test has shown its impact for the 0.6 ft-lb/in value. This may be improved to 2.1 ft-lb/in a while, having a 30% blend with glass fiber.
This astonishing improvement in impact has made this material able to apply in several metal replacement applications.
Surface Lustre
Among various nylon plastics, nylon 66 offers a glossy surface for its injection molded finished product. This property is highly considered for aesthetic-oriented applications as it attracts consumer consideration.
Nylon 66 also offers good abrasion resistance, which means this gloss lasts for a longer period.
Light Weight
The density of nylon is 1.31g/cm3, which is low, making it lightweight and suitable for transportation or carrying purposes. With low weight and higher mechanical properties, nylon may be the best replacement for metallic substances in many applications of various fields.
Moisture Content
One of the limitations of using Nylon Plastics, especially in the case of Nylon 6 for injection molding, is that it absorbs water. This water may be in the form of moisture.
However, it is recommended that you use Nylon 66 against nylon 6 because of its better resistive nature for water than nylon 6. It is well-understood that when something is soaked in water, it becomes weaker or easier to break.
In the same way, when nylon 66 comes into contact with water, it dominantly losses its stiffness becoming softer. So, this wet nylon is dried in the oven for hours, sometimes below its softening temperature.
Mostly vacuum drying is done, which ensures the avoidance of oxidation. Furthermore, drying is done just before the molding to avoid rehydration or oxidation again.
Temperature Profile
Nylon 66 has a very high transition temperature. This high transition temperature allows a wide range of softening temperatures. The nylon is heated sharply above its glass transition temperature for smooth injection molding processing to make it flow.
However, it gives you flow ability far before its softening temperature, providing you with a vast range to tune or optimize its end-use properties accordingly. However, a wide range of melting is also a risk because your slight temperature variation can affect or degrade the nylon plastic.
In the case of other materials, the thermoplastic temperature range is well-defined, and temperature optimization is done easily with some exceptions.
But in the case of nylon, the temperature determination becomes challenging due to processing in a wide softening temperature range or processing near melting temperature.
To overcome this scenario, you have to delay or stay from the point of melting to the injection of the nylon plastic tic inside the mold.
But, nylon 66 should not stay in a molten or liquid state for a long time as these materials come up with the yellowing of the plastic and start degrading at very high temperatures. The temperature precision is important and highly depends on the grade and type of nylon plastic for injection molding.
Mostly, the temperature range of nylon is 260 to 320oC. Furthermore, mold temperature during injection molding is crucial for the desired characteristics of end-use nylon plastic products, which are tuned accordingly.
Type of Screw
The thermal behavior of nylon is quite interesting as it does not become softer without reaching a temperature nearer its melting point. This thermal behavior determines which screw type you will use for processing nylon in injection molding.
The movement of the nylon plastic pallets inside the barrel is very important after gaining enough heat, which is the most important task of the screw. The screw has to ensure this movement and optimization of temperature exactly required for bubble-free molten nylon and injection into the mold.
A very sharp range of processing nylon can block the material inside the barrel, causing material burn and lowering the production rate and efficiency.
Injection Speed
The speed of the screw should be optimized. In the case of Nylon 66, the material usually remains in solid or pallet form. A very high-speed screw can damage the machinery. It will also lead to excessive abrasion, causing the production of a very high amount of heat due to friction.
The molten material’s time inside the barrel is low, and bubbles formation is common. A very high speed of injection can cause inefficient filling of mold i.e., air bubbles trap, incomplete filling of cavity, flashing, and burns on the product surface.
It is well understood the fact that the temperature of the mold is far lower than the melting temperature. So, due to the very high-temperature gradient, it is very challenging to control the final properties of nylon plastic injection molded products.
Nylon Plastic Injection Molding Challenges
Nylon is considered one of the most challenging materials to be molded. The material has extraordinary properties but requires a very efficient optimization of parameters for the best results sometimes. There are some problems related to nylon molding, which are discussed in this article.
Gassing
Gassing is crucial for injection molding because improper venting and gas in higher concentrations inside the barrel may lead to serious headaches. So, the gassing system of the injection molding should be optimized in such a way that it may not block the flow and heating of material inside the barrel.
However, many of you use an approach of temperature lowering to decrease gassing in response lower the flow ability of material and increasing the stay time of material inside the barrel, ultimately lowering the efficiency of the process.
So, the lowering or optimizing temperature should be so efficient that it may not affect the proper shearing movement of the material inside the barrel.
Moisture
The moisture content is one of the most common waste-producing defects during injection molding of nylon. This may be caused due to inefficient or poor drying. It is very important to know that nylon absorbs water or moisture, so one should be vigilant towards drying nylon efficiently.
On the other hand, it should also be considered that over-drying the nylon can also cause defective products, which may lead to more waste generation ultimately.
Shrinkage
Shrinkage is another significant challenge with injection-molded nylon products. Shrinkage can cause a huge loss of production, forming dimensional unstable products. Low and high shrinkage levels can significantly affect the product’s strength, aesthetics, color, and physical properties.
The shrinkage may be controlled efficiently by controlling the barrel parameters and mold temperature. Improvisation of approach, efficient handling of material, process design, and defined SOPs for injection molding of nylon can bring the production up to the higher consistency of physical stability leading to less wastage and increasing the profitability.
Applications
The use of nylon, especially in injection molded products, is increasing daily. Besides that, nylon has been used in various applications, i.e., in parachutes, ropes, and tooth bristles.
Cable ties, furniture items, and small assemblies like engine fittings, bolts, and equipment components have been discovered to be in more demand in injection molded nylon applications.
For heavy-duty machinery, such as engines, motors, and other mechanical equipment components, nylon has extensively been used in bushings, gears, plastic bearings, and other parts.
