Flame Retardant PP material is favored by more and more manufacturers because of its
fine density, excellent weather resistance and low comprehensive price. It has successfully
replaced flame retardant PS and flame retardant ABS in many applications. Behind the
rise of flame-retardant PP materials, there may be a problem that is often encountered.
That is the problem of flame retardant material precipitation, which is more obvious in
halogen free flame retardants.
The precipitation of flame retardants not only affects the normal production, but also
affects the normal production in the process of injection molding, such as powder
agglomeration, mold sticking and so on. In the finished products, it often precipitates
and produces white mist like substances, which affect the appearance of products and
cause the decrease of flame retardancy.
Before solving the problem of flame retardants, we first discuss two important factors
that affect the precipitation problem:
1. Compatibility of flame retardants with PP base resin
Flame retardants are generally two states in the PP resin: the resin is filled in the form
of a similar packing and the other is dispersed uniformly in the melting state. As PP is a
nonpolar material, there will be a problem of interfacial compatibility between polar flame
retardants and PP. The worse the interfacial compatibility is, the easier it is to produce
the precipitation problem.
2. the influence of temperature on the precipitation of flame retardants
PP is a semi crystalline material, has a lower glass transition temperature, when the temperature
is above the glass transition temperature, with the increase of temperature, the amorphous
segments will accelerate the movement of heat, small molecule flame retardant poor compatibility with PP resin can overcome the resistance of the easy migration to the surface.
This is also the reason that sometimes the surface will sometimes precipitate after storing for a
period of time, and the injection process is the most obvious process. The precipitation is often
reflected on the mold. The higher the injection temperature, the more severe the precipitation.
The relationship between the migration rate of flame retardants and temperature can be roughly expressed in Figure four. The precipitation rate in the decomposition range of flame retardants is accelerated obviously with the increase of temperature. At constant temperature, the precipitation is also associated with time.
After understanding the cause of precipitation, the improvement of the problem of flame retardancy can be twice the result. There are two main methods:
1. with the introduction of strong polar groups (such as amino group, carboxyl group and epoxy group), the interfacial action of flame retardant and PP can be enhanced, which can effectively reduce the precipitation of flame retardants.
2. improve the migration resistance between flame retardants and resins, and reduce the migration rate of low molecular weight flame retardants. Decreasing temperature can reduce the movement between segments or enhance the degree of polymerization of flame retardants and reduce the molecular weight distribution width, which will be an effective measure to reduce the emission of flame retardants.
It is necessary to point out that the precipitated flame retardant PP is not completely precipitated, but it only reduces the mobility of the flame retardants to a great extent. The present precipitation - free flame retardant PP is often built on high technical cost, so the low - cost anti - precipitation is still a subject that the current flame retardant PP material needs to be perfected.
