Polyamide (commonly known as nylon) is prone to darkening, embrittlement and performance degradation when exposed to ambient air or heated up. In view of this phenomenon, New Star Chemical has introduced a highly effective composite antioxidant, which can effectively improve the phenomenon of polyamide's easy yellowing.

1、 Product introduction

Sunox ® 542 Chemical name: highly effective antioxidant compounded by hindered phenols and inorganic phosphate

Plastic Knock ®  542 is a highly effective antioxidant specially formulated for the yellowing of polyamide in the production, processing and high temperature and high humidity environment, with excellent high temperature resistance.

Sunox ® 549 Chemical name: highly effective antioxidant compounded by hindered phenols and acrylate

Plastic Knock ®  549 is a highly effective antioxidant specially formulated for the yellowing of polyamide, which can protect the material from thermal oxidative degradation during production, processing and final use, and maintain a low color change.

2、 Performance test

1. Thermal decomposition performance-TGA

Table 1 Thermal decomposition performance data for polyamide antioxidant

The above data shows that the antioxidant for nylon is continuously heated to 650 ℃ at 10 ℃/min under nitrogen protection atmosphere. The thermal decomposition performance of the material is shown in the data on the left side of the table above. The three columns of data on the right side are heated to a set temperature at 10 ℃/min, and then heated at a constant temperature for 30min. Observe the thermal decomposition performance of the antioxidant, and then continuously heated to the second set temperature, and heated at a constant temperature for 30min. From the data in Table 1, it can be seen that the antioxidant plastoc ® The thermal decomposition performance of 168 is relatively poor, especially under the high temperature of 280 ℃, the oxidation decomposition of the antioxidant itself occurs quickly in a short time; The thermal decomposition properties of the other three main antioxidants (including 10101098 and 549) are not very different. Under the condition of up to 330 ℃ and constant temperature for 30 min, the amount of self oxidation decomposition is less; The thermal decomposition performance of copper salt antioxidant H3336 is worse, and it decomposes nearly 75% at a temperature of 280 ℃ for 30 min. Compound antioxidant plastock containing inorganic phosphate ® 542 has better thermal decomposition performance.

2. Aging performance test

2.1 Effect of antioxidants on color difference and yellowness of pure nylon 6 after thermal oxygen aging

Figure 1: Effect of different antioxidants on YI value of nylon 6 color plate

Figure 2: Photos of nylon 6 color plate modified by different antioxidants after thermal oxygen aging

From the above thermal oxygen aging test chart, it can be seen from the table that the initial yellowness value of nylon 6 without antioxidant is higher, the initial yellowness value of nylon 6 with antioxidant is greatly improved, and the improvement effect of copper salt antioxidant H3336 is general; The photos after thermal oxygen aging at 150 ℃ are shown in Figure 2. Adding phosphite antioxidant 626 has a general improvement effect on the yellowness and color difference of the product, which may be due to the fact that phosphite is easy to hydrolyze and hydrolyze to three hydroxyl groups, which is easy to react with the amine group, thus causing a certain degree of cross-linking. In the aspect of anti-yellowing of nylon 6, conventional antioxidant 1010 combined with auxiliary antioxidant 168 has a limited effect on the anti-thermal aging of nylon.

Figure 3: Photos of nylon 6 color plates modified by different antioxidants after vacuum thermal aging

Figure 3 shows the color change of nylon sample after being heated for 72h in a vacuum oven at 180 ℃. Antioxidant 549 can improve the yellowing resistance of nylon 6. Antioxidant 549 uses its bifunctional stabilization mechanism to capture the carbon free radicals produced by the degradation of nylon 6, effectively inhibit the reduction of the viscosity and molecular weight of nylon 6, inhibit the formation and content of its carboxyl end group, and further improve the thermal oxygen stability of nylon 6. Antioxidant 542 can effectively inhibit the aging degradation of nylon color plate under high temperature conditions by using its inorganic salt structure, and has better thermal decomposition performance.

2.2 Effect of antioxidants on mechanical properties of pure nylon 6 after thermal oxygen aging

Figure 4: Effect of different antioxidants on notch impact strength of nylon 6 spline

The addition of antioxidants can not only effectively improve the color change of PA6 during thermal oxygen aging, but also effectively improve its mechanical properties during thermal oxygen aging. It can be seen that under the condition of 150 ℃, after 12h and 24h, the notch impact strength is basically balanced, and even slightly improved. After 24h, the notch impact strength of multiple formulations is significantly decreased. The mechanical properties of the samples added with copper salt antioxidant decreased significantly, which may be due to the aging of nylon 6 samples catalyzed by metal ions, while adding Sunox ® 549, and Sunox ® The notched impact strength of 542 nylon samples is slightly increased, which is closely related to the aging mechanism of nylon 6. Most of the active free radicals produced by nylon 6 are consumed by antioxidants. At the same time, a small amount of active free radicals will initiate the crosslinking of nylon 6 polymer chain, and a small amount of crosslinking improves the mechanical properties of the material.

3、 Summary

According to the above experimental results, the initial yellowness of nylon products added with antioxidants is low ® 542, Plastic Knock ® With its unique structure, 549 has the most obvious effect on improving the heat and oxygen aging of nylon 6.