Analysis and solutions of precipitation of PP flame retardant materials

      PP flame retardant materials are well received by more and more manufacturers as its low density, excellent weather resistance and low composite price. In some places, they have been successfully replaced flame retardant PS, ABS and other fire-retardant materials. But there is a troubling problem that is precipitation problem, which is especially in halogen-free flame retardant PP.

       Precipitation of flame retardant not only produces powder agglomeration, sticky mold during injection. but also often precipitates in the finished article and affect the product`s appearance and lead to decreased flame retardant effect.

       Before we solve the problem, we should discuss two important factors which cause precipitation:

       1. The compatibility of PP and flame retardant

      There are two states of flame retardant in PP: one is similar as fillers, and another is melting in PP. As PP is non-polar materials, interfacial compatibility exist between the polar flame retardant and PP.  The worse of interfacial compatibility, the more easily produce precipitation.

       2.Temperature

         PP is semi-crystalline material, it has low glass transition temperature. When the ambient temperature is higher than its glass transition temperature, as the temperature increases, thermal motion of the amorphous segments will be accelerated so that the small molecule flame retardant which is poor compatibility with PP can be relatively easy to overcome resistance migrate to the surface. High temperature injection molding process is the most obvious precipitation process.

          In conclusion, there are two ways to reduce the precipitation:

1. . Improve interfacial compatibility of PP and flame retardant. Such as introducing strong polar group (amino, carboxyl, epoxy group).

      2. Decreasing temperature (such as extruding and injection temperature) to reduce the thermal motion of amorphous segments.

      It should be pointed out that no-precipitation flame retardant PP is not meaning no-precipitation at all, it only reduce the transition of flame retardant. Currently no-precipitation flame retardant PP is often built on high technology costs, low-cost anti-precipitation PP is still a subject to improve.