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By ZHOULEI | 17 April 2019 | 0 Comments

What are the differences between PA6 and PA66?

Abstract: PA is one of the common engineering plastics, and PA6 and PA66 are the most common nylon materials. The two structures are similar and have many things in common. So what is the difference between the two? Let's take a look at Han Teng Plastic today.


PA is one of the common engineering plastics, and PA6 and PA66 are the most common nylon materials. The two structures are similar and have many things in common. So what is the difference between the two? Let's take a look at Han Teng Plastic today.

First, the background


PA66 was successfully polymerized into a PA66 polymer by adipic acid and hexamethylene diamine in 1935. The process of manufacturing PA66 by melt spinning was discovered from 1936 to 1937, and was commercialized by DuPont in the United States at the end of 1939.

                  Carothes 
PA6 is a PA6 polymer synthesized by German IG Schraker using a single caprolactam as raw material ε-aminocaproic acid as initiator. The test production of PA6 fiber was carried out in 1939, and commercialization was carried out by German company Faben in 1943. .




Second, the structure


To analyze the difference between them, we must start with their structure. As we all know, PA6 is formed by ring-opening polymerization of caprolactam, and nylon PA66 is obtained by condensed polymer of hexamethylenediamine and adipic acid. PA6 and PA66 have the same molecular formula, but the structural formula is different, as shown in the following figure:


      Figure PA6 and PA66 structural differences


It is precisely because of this difference that the nature of the difference, such as the intermolecular hydrogen bonding force is different.



          Figure PA6 and PA66 different types of hydrogen bonds

The number of hydrogen bonds in PA66 is higher than that in PA6. The inter-molecular force of PA66 is stronger than that of PA6, so PA66 is better than PA6 in thermal properties (so processing temperature is higher), PA66 is better than PA6, and the toughness of PA6 Better than PA66, PA6 has a faster water absorption rate than PA66. The difference in PA6 and PA66 properties is mainly caused by the above hydrogen bonding factors.



Third, performance
 

PA66 has a melting point of 260 to 265 ° C and a glass transition temperature (dry state) of 50 ° C. The density is 1.13~1.16 g/cm3.

 

PA6 translucent or opaque milky crystalline polymer particles, melting point 220 ° C, thermal decomposition temperature greater than 310 ° C, relative density 1.14, water absorption (24 ° C water 24 hours) 1.8%, with excellent wear resistance and self-lubricating It has high mechanical strength, good heat resistance and electrical insulation performance, excellent low temperature performance, good self-extinguishing and chemical resistance, especially excellent oil resistance.

 

Compared with PA66, PA6 is easy to process and form, has good gloss on the surface of the product, and has a wide temperature range, but has high water absorption rate and poor dimensional stability. It has low rigidity, low melting point, long-term use in harsh environments, and sufficient stress in a wide temperature range. The continuous use temperature is 105 °C.



Overall, the performance differences between PA66 and PA6 are as follows:


                                        Mechanical properties: PA66 > PA6

                                      Thermal media performance: PA66 > PA6

                                                Price: PA66 > PA6

                                            Melting point: PA66 > PA6

                                           Water absorption: PA66< PA6

                                         Weather resistance: PA66< PA6

                                        Condensation time: PA66< PA6

                                       Molding performance: PA66 < PA6





Fourth, the process conditions


Drying treatment

 

PA6 absorbs moisture easily, so special attention should be paid to drying before processing. If the material is supplied in a waterproof material, the container should be kept closed. If the humidity is greater than 0.2%, it is recommended to dry in hot dry air above 80 °C for 3-4 hours. If the material has been exposed to air for more than 8 hours, it is recommended to dry at 105 ° C for 1-2 hours or more. It is best to use a dehumidifying dryer.



PA66 If the material is sealed before processing, then there is no need to dry. If the storage container is opened, it is recommended to dry in a hot, dry air at 85 °C. If the humidity is greater than 0.2%, it is also necessary to carry out vacuum drying at 105 ° C for 1 to 2 hours. It is best to use a dehumidifying dryer. Molding temperature: 260~310 °C, 280~320 °C for enhanced varieties.

 

Mold temperature

 

PA6: 80~90 °C. The mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of the part.

For thin-walled, longer-flowing parts, it is also recommended to apply higher mold temperatures. Increasing the mold temperature increases the strength and stiffness of the part, but reduces the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40 °C. For glass reinforcement the mold temperature should be greater than 80 °C.



PA66: 80 °C is recommended. The mold temperature will affect the crystallinity, which will affect the physical properties of the product.

For thin-walled plastic parts, if a mold temperature lower than 40 ° C is used, the crystallinity of the plastic part will change with time, and in order to maintain the geometric stability of the plastic part, annealing treatment is required.

 

Melting temperature



PA6: 230~280°C, 250~280°C for enhanced varieties.

PA66: 260~290 °C. The product for glass additives is 275~280 °C. The melting temperature should be avoided above 300 °C.

 

Injection pressure



Both are generally between 750 and 1250 bar (depending on material and product design).

 

Injection speed



Both are high speed (slightly lower for reinforced materials).

 

Runner and gate



Since the setting time of PA6 and PA66 is very short, the position of the gate is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than with a conventional runner because the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the minimum diameter of the gate should be 0.75 mm.





Fifth, the application


PA6 engineering plastics have high tensile strength, good impact resistance, excellent wear resistance, chemical resistance and low friction coefficient. They can be modified by glass fiber, mineral filler modification and flame retardant. It makes it more comprehensive, mainly used in the automotive industry and electronic appliances.


                                      Figure Glass fiber reinforced PA6 spare tire groove


PA66 has good comprehensive performance, high strength, good rigidity, impact resistance, oil and chemical resistance, wear resistance and self-lubrication, especially hardness, rigidity, heat resistance and creep performance. PA66 is more used for the production of industrial yarns such as cords because of its higher strength than PA6.


         PA66 has good comprehensive performance, high strength, good rigidity, impact resistance, oil and chemical resistance, wear resistance and self-lubrication, especially hardness, rigidity, heat resistance and creep performance. PA66 is more used for the production of industrial yarns such as cords because of its higher strength than PA6.
 

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