What are the factors that affect the flame retardancy of plastics? Today, the editor of Dongtuo Chemical will follow you to discuss the conditions that determine the flame retardant performance of engineering plastics.
The lower the melt index of the plastic resin itself, the more flame retardants are used. The higher the melt index, the less flame retardant is used. In PE plastics, products with a melting index of 0.5-1.0 have the worst flame retardant effect, and the amount of flame retardant is 5-10% more than that of products with a melting index of 4-7. Mixed use of several plastic resins or due to processing equipment causes the flame retardant masterbatch to be locally poorly dispersed in the polymer, which affects the flame retardancy. Recycled materials have different effects on flame retardancy due to the reduction of melt index and the inclusion of different types of plastics and fillers.
1. Masterbatch
Some toners will act as a "wick" in the plastic, promoting the thermal conduction of the plastic. When the additive of color masterbatch contains calcium carbonate, magnesium carbonate and silicon powder, it will seriously interfere with the flame retardant.
Certain lubricants used in the production of masterbatches can interfere with flame retardants. For example, zinc stearate and zinc oxide will interfere with the formation of the SbCl3 barrier layer on the surface of the flame retardant plastic.
2. Filling
The "wicking effect" of the filler increases the thermal conductivity of the plastic, increases the internal temperature of the plastic, aggravates the decomposition of the plastic, and releases more volatile combustible substances.
The filler increases the viscosity of the plastic and reduces the heat carried away by the flow of the plastic and the molten droplet, especially for 94ULV2-V1 grade products.
The fillers gathered on the plastic surface can form a barrier for mass and heat transfer, and some fillers also help to form the sintered surface layer and carbon layer. Therefore, fillers can also increase radiant heat loss from the combustion surface and heat transfer by conduction, delaying the flow of volatile products from plastic decomposition in the gas phase.
3. Examples
Calcium carbonate, silica, and glass fiber fillers in plastics can affect the microstructure of polymers, form nucleating agents in plastics, and play a "wick effect" that intensifies combustion.
Interference effect: For example, when the plastic containing silicon powder is burned, stable silicon bromide will be formed on the surface, which will interfere with the gas phase flame retardant of the plastic.
Adversarial effect: Plastics containing calcium carbonate and magnesium carbonate have an antagonistic effect on flame retardants, increasing the amount of flame retardants used.
4. Product shape and thickness
For 94UL-VI-V2 grade flame retardant products, the larger the thickness, the larger the amount of flame retardant masterbatch.
For 94UL-V0 grade flame retardant products, the larger the thickness, the smaller the amount of flame retardant masterbatch.
5. Saturation of flame retardants
When the oxygen index of polyolefin reaches 30-32, adding more flame retardant masterbatch will not increase the oxygen index indefinitely.
All right. The above is an analysis of some factors that affect the flame retardant properties of plastics.
Edited by: Suzhou Eastop Chemical Co., Ltd.
