Journal of Textile Research ›› 2023, Vol. 44 ›› Issue (11): 1-8.doi: 10.13475/j.fzxb.20220506001

• Fiber Materials •     Next Articles

Preparation method of and anti-dripping and flame retardant properties of polycaprolactam 6 composite resin based on homotriazine ring structure

ZHANG Wenqi1,2, LI Lili1,2, HU Zexu1, WEI Lifei3, XIANG Hengxue1,2(), ZHU Meifang1,2   

  1. 1. State Key Laboratory for Modification of Chemical Fibers and Polymer Material, Donghua University, Shanghai 201620, China
    2. College of Materials Science and Engineering, Donghua University, Shanghai 201620, China
    3. Shanghai Defulun New Material Technology Co., Ltd., Shanghai 201502, China
  • Received:2022-05-19 Revised:2022-12-09 Online:2023-11-15 Published:2023-12-25

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Abstract:

Objective Polycaprolactam 6 (PA6) is a polymer material widely used in daily life, but it is flammable. High-temperature oxidation during combustion process would cause its molecular chain to break, resulting in problems such as continuous combustion and melt dripping. At present, charring technology has become an important means to solve these problems. The homotriazine ring flame retardant has excellent charring performance by virtue of its conjugated stable structure, which has greatest potential to solve the problem of PA6 flame retardant.

Method Triazine flame retardant forms a carbon layer on the polymer surface to resist the further combustion of flame, hence improving the flame retardancy of PA6. Triazine ring structure also has certain structural compatibility with PA6 molecular chain, which would not affect the processing and mechanical properties of PA6. Therefore, homotriazine ring flame retardant (CFA) was added to PA6 by melt blending to improve the flame retardancy of PA6. The charring performance of the PA6 composite resin was studied through the thermal experiment. By examining the limiting oxygen index, vertical combustion and cone calorimetry experiment, the influence on the flame retardant and charring property on PA6 resin was studied, which was used for explaining the mechanism of the CFA flame retardant.

Results In this research, a series of composite resin were prepared by melt blending CFA flame retardant and PA6. After adding 8% CFA flame retardant to PA6 resin, the vertical combustion rating reached V-0 level, the limiting oxygen index increased from 24.5% to 33.4% (Tab. 1 and Fig. 2), and the total smoke release decreased by 13.3% (Fig. 3), suggesting the effectiveness of CFA in many aspects. The charring rate of CFA flame retardant itself in the air atmosphere reached 8.3%, and the charring rate of PA6 composite resin after adding 10% CFA was more than twice that of pure PA6, from 1.87% to 4.84% (Fig. 4), because of better isolation to oxygen and heat. By analyzing the four decomposition processes of CFA flame retardants in a nitrogen gasatmosphere, it was found that the charring performance of CFA was mainly by virtue of the tertiary nitrogen structure contained, and a stable carbon layer were be formed during the high-temperature process, thereby improving the high-temperature formation of the composites (Fig. 5). In order to understand the effectiveness of the flame retardant carbon structure, the structure of residual carbon and the composition of decomposition gas were analyzed. Compared with the carbon layer formed by the series of PA6 samples, it was revealed that the addition of CFA made the carbon layer rougher. When the mass fraction of CFA reaches more than 8%, the carbon layer began to become smooth again, facilitating effective protection to the internal PA6, thereby improving heat insulation and dripping resistance of PA6 composite resin (Fig. 6). The gas phase flame retardant mechanism was also found playing a role in improving the flame retardancy of PA6 resin (Fig. 8). Based on the above analysis, it was believed that good flame retardancy of PA6 composite resin is mainly because of the dilution effect of non-combustible gases in the gas phase and the barrier effect of the carbon layer in the condensed phase in the combustion process. The addition of CFA flame retardant did not lead to a decrease in the tensile break strength of PA6, but rather improved it. When the mass fraction of CFA was 8%, the tensile break strength of PA6 composite resin increased by 28.8%.

Conclusion After studying the performance of flame retardant PA6, It was found that CFA greatly increased the limiting oxygen index and vertical combustion of flame retardant PA6, and decreased smoke emission. CFA flame retardant can also improve the smoke suppression effect of PA6 to a certain extent, and enhance the tensile strength of PA6, greatly expanding the application range of PA6. The experimental results also verified the good compatibility between CFA and PA6 molecular chains. The research on PA6 flame retardant mechanism needs be further studied to improve the flame retardancy of PA6.

Key words: polycaprolactam 6, flame retardant modification, dripping resistant, homotriazine ring, charring performance, melt blending

CLC Number: 

  • TQ342

Fig. 1

Images of vertical combustion of PA6 and PA6/CFA8"

Tab. 1

Test results of vertical combustion"

样品名称 t1/s t2/s 是否点燃
脱脂棉		 熔滴 UL-94
等级
PA6 40 3 是 ☆☆☆☆☆ V-2
PA6/CFA2 2 3 是 ☆☆ V-2
PA6/CFA4 1 2 是 ☆☆ V-2
PA6/CFA6 0 2 是 ☆☆ V-2
PA6/CFA8 0 1 否 ☆ V-0
PA6/CFA10 0 1 否 ☆ V-0

Fig. 2

Limiting oxygen index of flame retardant PA6"

Fig. 3

Conical calorimetric test results of flame retardant PA6. (a) Heat release rate; (b) Total heat release; (c) Total smoke release"

Fig. 4

TG curves of flame retardant PA6 in N2 (a) and air (b) atmosphere"

Fig. 5

TG (a) and DTG (b) curves of flame retardant CFA in N2 and air atmosphere"

Fig. 6

SEM images of PA6 carbon residue before and after flame retardant treatment (×100 000)"

Fig. 7

Raman spectra of PA6 carbon residuel before and after flame retardant treatment"

Fig. 8

Py-GC-MS curves of PA6 at 450 ℃ before and after flame retardant treatment"

Fig. 9

Schematic diagram of combustion process of flame retardant PA6"

Fig. 10

Tensile break strength of PA6 before and after flame retardant treatment"

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