How to distinguish between PA6 (Nylon 6) and PA66 (Nylon 66)?

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This post was last edited by Guangzhou Jingxi Analysis on March 16, 2017, at 10:08. How to distinguish between PA6 (Nylon 6) and PA66 (Nylon 66)? First, let’s talk about what nylon is. Polyamide, whose English name is polyamide, abbreviated as PA, is commonly known as Nylon. It is a general term for polymers in which the repeating units of the macromolecular backbone contain amide groups. It is the variety with the highest production volume, the most varieties, and the widest range of applications among the five major engineering plastics. The main varieties of nylon are nylon 6 and nylon 66, which dominate the market. Nylon 6 is polycaprolactam, while nylon 66 is polyhexamethylene adipamide. PA6, also known as nylon 6, appears as semi-transparent or opaque off-white particles. Its melting point ranges from 215°C to 225°C. It exhibits thermoplastic properties, is lightweight, has good toughness, and offers excellent resistance to chemicals and durability. It is commonly used in automotive parts, mechanical components, electronic and electrical products, as well as engineering accessories. PA66, also known as nylon 66, is a semi-transparent or opaque milky white or yellowish granular crystalline polymer. It is plasticizable, with a melting point ranging from 250°C to 260°C. Compared to PA6, PA66 is more widely used in the automotive industry, instrument housings, and other products that require impact resistance and high strength. So, how should one distinguish between PA6 and PA66? Infrared (FTIR) + differential scanning calorimetry (DSC), etc., can be used together to quickly identify them. 1. Infrared (FTIR) -- The characteristic absorption peaks of polyamides (nylons) in infrared spectroscopy include 3300 cm⁻¹, 1635 cm⁻¹, 1540 cm⁻¹, etc. Although these peaks may vary slightly among different polyamides (nylons), their intensities are relatively similar. Figure 1 shows the infrared spectrum of sample 1 to be tested: http://www.suuwoo.com/uploads/allimg/170219/1-1F219124K3501.png. As can be seen from Figure 1, the peaks at 3305 cm⁻¹, 1641 cm⁻¹, and 1537 cm⁻¹ are all characteristic absorption bands of polyamides (nylon). As shown in Figure 2, this is the infrared spectrum of another sample to be tested, Sample 2: http://www.suuwoo.com/uploads/allimg/170219/1-1F219124TLc.png. In Figure 2, it can be seen that the peaks at 3304 cm⁻¹, 1643 cm⁻¹, and 1539 cm⁻¹ are also characteristic absorption bands of polyamides (nylon). 2. Differential Scanning Calorimetry (DSC) for melting point determination: The melting point of PA6 is 215°C–225°C, while that of PA66 is 250°C–260°C. As shown in Figure 3, this is the DSC curve of Sample 1; Figure 4 shows the DSC curve of Sample 2: http://www.suuwoo.com/uploads/allimg/170219/1-1F219124924350.png Figure 3 http://www.suuwoo.com/uploads/allimg/170219/1-1F219124944404.png Figure 4. The melting peak at around 255°C in Figure 3 corresponds to the characteristic behavior of PA 66, while the melting peak at around 218°C in Figure 4 corresponds to the characteristic behavior of PA 6. Thus, Sample 1 is PA 66, and Sample 2 is PA6.