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Analysis and solution of precipitate problem of flame retardant PP material

Flame retardant PP material because of its light density, excellent weather resistance and comprehensive low price, more and more manufacturers of favor, in many applications has successfully replaced flame retardant PS, flame retardant ABS, etc.. Behind the rise of flame retardant PP materials, there is a troubling problem that may often be encountered, that is, the precipitation of flame retardant materials, which is more obvious in halogen-free flame retardant materials.
The precipitation of flame retardants not only often produces mold scale, powder agglutination and sticky mold in the process of injection molding, but also often occurs in the finished products, resulting in white mist substances that affect the appearance of products and lead to the decline of flame retardancy.

Before solving the problem of precipitation of flame retardants, we first discuss two important factors affecting precipitation:

First, flame retardant and PP base resin compatibility

Flame retardants in PP resins are generally in two states: in the form of a similar filler in the resin, the other is evenly dispersed in the resin in a melted state. As PP is a non-polar material, there will be a problem of interface compatibility between polar flame retardants and PP. The worse the interface compatibility, the more likely it is to produce precipitation problems.

Influence of temperature on the precipitation of flame retardant

PP is a semi-crystalline material with a low glass transition temperature. When the ambient temperature is higher than its glass transition temperature, the thermal movement of the amorphous chain segment will be accelerated with the increase of temperature, so that small molecular flame retardants with poor compatibility with PP resin can easily overcome the resistance to migrate to the surface.

This is also the reason why the surface of parts is sometimes precipitated after a period of time, and the high-temperature injection process is the most obvious precipitation process, its precipitation is often reflected in the mold scale, etc., the higher the injection temperature, the more severe precipitation. The relationship between the migration rate of flame retardants and temperature can be roughly shown in the figure below. Within the decomposition temperature range of flame retardants, the precipitation rate accelerates obviously with the increase of temperature. At constant temperature, precipitation also has a certain correlation with time.

After understanding the cause of precipitation, the problem of flame-retardant precipitation can be improved with half the effort. There are two main methods:

Solution:

1, the introduction of strong polar groups (such as amine group, carboxyl group, epoxy group, etc.), enhance the interface between flame retardant and PP, can effectively reduce the problem of flame retardant precipitation.

2. Improve the migration resistance between flame retardants and resins and reduce the migration rate of low molecular weight flame retardants: reducing the temperature to weaken the movement between chain segments or improve the polymerization degree of flame retardants and reduce the molecular weight distribution width is an effective measure to reduce the precipitation of flame retardants.

It should be pointed out that: precipitation-free flame retardant PP is not completely free of precipitation, but greatly reduces the mobility of flame retardants. The current precipitation-free flame retardant PP is often established on the high technical cost, so low-cost precipitation resistance is still a topic to improve the current flame retardant PP materials.