Polyamide (called PA, commonly known as nylon) is a type of engineering plastic with a wide range of applications. At present, among five major engineering plastics, PA has become category with largest production volume, widest application and most varieties. PA6 has good comprehensive properties, including excellent mechanical properties, electrical properties, oil and heat resistance, wear resistance, electrical insulation, chemical resistance, weather resistance and self-lubricating properties, as well as low coefficient of friction, ease of processing. etc. At present, PA6 is mainly used in transportation, electrical and electronic, machinery and other industries. According to US UL94 standard, PA6 is a V2 level combustible material, especially in applications such as electronic devices that require reinforcement and flame retardant modification of PA6 products.
Fig. 1.MCA and PA6
1. Polymer flame retardant mechanism
The essence of fire resistance is to achieve goal of fire resistance by preventing or slowing down one or more elements. To date, there are three recognized flame retardation mechanisms, namely: gas phase flame retardation mechanism, condensed phase flame retardation mechanism, and intermittent heat exchange flame retardation mechanism.
Gas-phase flame retardant mechanism: On one hand, when flame retardant material is heated or burned, it can generate free radical inhibitors, which can trap free radicals of polymer combustion, thereby blocking combustion reaction; on one hand, when flame retardant material burns, it releases a large amount of inert gas (nitrogen, water vapor, carbon dioxide, etc.), which can dilute oxygen, reduce oxygen concentration around polymer, and stop combustion.
Condensed phase flame retardant mechanism: Condensed phase flame retardant mechanism refers to flame retardant effect that occurs by delaying or interrupting thermal decomposition of condensed phase flame retardant. When flame retardant material burns, a fire retardant, heat-insulating and oxygen-insulating layer of charcoal is formed on its surface, which can prevent ingress of combustible gas into combustible gas phase, thereby interrupting combustion process. for this reason it is used as a charring agent.
Interrupted heat exchange fire retardant mechanism: Intermittent heat exchange fire retardant refers to removal of part of heat generated by combustion of fire retardant materials so that material cannot maintain thermal decomposition temperature, and thus cannot continue to produce combustible gases.
2. Investigation of properties of fire-resistant composites MCA PA6
2.1 Material Formula
Batch PA6, MCA flame retardant, silicone powder and antioxidants 1010 and 168 according to proportions shown in Table 2-1 and control total to 100 parts. There are 3 formulas in total.
Table 2-1. Composition of flame retardant polyamide PA6
2.2 Conditions of extrusion process
The dried and high-speed mixed PA6 compound was extruded on a Type 35 twin screw extruder, and pellets were dried in an oven at 85°C for 2 hours. The rotation speed of extruder screw is 300 rpm, and temperature setting and actual measurement of each heating section are detailed in Table 2-2.
Table 2-2 Temperature parameters of each heating section of a twin screw extruder
3. Flame retardant analysis of MCA PA6 flame retardant
It can be seen from Table 3-1 that V-1 standard can only be met with addition of 8% ISA; when added amount exceeds 13%, flame retardant system can reach UL-94 Level V-0 Self-extinguishing standard.
Table 3-1 UL94 Vertical Flame Test Level
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