The decomposition temperature of a flame retardant and the plastic often determine whether the flame retardant can exert a high level of flame retardancy in that plastic. The decomposition temperature of the flame retardant should not be higher than the decomposition temperature of the plastic, but it also cannot be too much lower. For example, the decomposition temperature of aluminum hypophosphite is much lower than that of PA66, so it cannot provide flame retardancy in PA66. Similarly, the decomposition temperature of ADP is much higher than that of PP, so it cannot provide flame retardancy in PP. The better the match between the temperature resistance of the flame retardant and the decomposition temperature of the plastic, the better the flame retardant effect, and the less flame retardant is needed to achieve the same flame retardancy. If the decomposition temperature of the flame retardant and the polymer are not well matched, even a large amount of flame retardant will not achieve the ideal flame retardant effect, nor will it yield flame-retardant products with better performance.

1. In the design of flame retardant formulations, the effective synergistic effect of flame retardants should be fully considered, and the principle of scientifically using and combining them should be followed to strive for the minimum amount of flame retardant used, the lowest cost, and to minimize damage to physical and mechanical properties while achieving the same flame retardant effect.

2. Choosing the correct standards and methods for determining flame retardant performance is crucial, as is scientifically assessing the flame retardant efficiency of a particular flame retardant. Flame retardant efficiency is related not only to the polymer's chemical structure, the physical state of additives, glass transition temperature, melting temperature, specific heat capacity, decomposition temperature, and thermal conductivity, but also to factors such as combustion mode, sample shape and size, existing conditions, placement direction, airflow direction, and air temperature. Currently, the cone calorimeter method and the oxygen index method are commonly used methods for determining the final flame retardant performance.

3. When selecting a flame retardant, its state within the polymer processing temperature range must be considered. The optimal state is the melted, flowing state, and it is best if this processing temperature is significantly lower than the flame retardant's decomposition temperature. In other words, choose flame retardants with melting points below the polymer's processing temperature and decomposition temperatures much higher than this processing temperature.

4. It is advisable to choose flame retardants whose thermal decomposition curves are 60-75°C lower than the polymer's thermal decomposition curve. This is because flame retardants that begin to decompose when the polymer has decomposed by 50%, reaching its maximum decomposition rate, will produce the maximum flame retardant effect.

5. The thermal decomposition temperature of the flame retardant must be higher than the processing temperature of the polymer. Otherwise, it will decompose during polymer processing, causing the flame retardant to exhibit its flame-retardant properties prematurely and failing to achieve a true flame-retardant effect. Therefore, its thermal stability, i.e., a suitable thermal decomposition temperature, must be considered when selecting a flame retardant.

6. It is important to note that the thermal decomposition curve of the flame retardant must cover the thermal decomposition curve of the polymer. Only in this way can the gases and debris generated during thermal decomposition continuously surround the polymer, allowing the flame retardant to exert its effective effect. A flame retardant whose thermal decomposition curve covers that of the polymer can exert its flame-retardant effect and is a well-matched flame retardant to the polymer.

Besides the basic element of temperature matching, the flame-retardant effect of flame retardants in plastics must also follow the principles of bromine-antimony combination, phosphorus-nitrogen combination, and carbon source-gas source-acid source combination to achieve a better flame-retardant effect.