Analysis and solution of the precipitability of fl

Analysis and solutions to the precipitation problem of flame retardant PP materials

flame retardant PP materials have been favored by more and more manufacturers because of their light density, excellent weather resistance and low comprehensive price. They have successfully replaced flame retardant PS, flame retardant ABS and so on in many applications. Behind the rise of flame retardant PP materials, there is a troublesome 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 retardant not only often produces mold scale, powdery caking and mold sticking in the process of injection molding, which affects the normal production, but also often precipitates in the finished products, which produces white foggy substances, which affect the appearance of the products and lead to the decline of flame retardancy

before solving the problem of flame retardant precipitation, we first discuss two important factors affecting the precipitation problem:

first, the compatibility between flame retardant and PP base resin

flame retardant generally takes two states in PP resin: filling the resin in the form of similar filler, and the other is evenly dispersed in the resin in the melting state. Because PP is a non-polar material, there will be interfacial compatibility between polar flame retardant and PP. The worse the interfacial compatibility, the easier it is to produce precipitation problems

II. Effect of temperature on the precipitation of flame retardant

PP is a semi crystalline substance with low glass transition temperature. When the ambient temperature is higher than its glass transition temperature, the thermal movement of amorphous chain segment will accelerate with the increase of temperature, so that the small molecule flame retardant with poor compatibility with PP resin can easily overcome the resistance and migrate to the surface

this is also the reason why precipitation sometimes occurs on the surface after the parts are stored for a period of time. The precipitation is most obvious in the high-temperature injection molding process, which is often reflected in the formation of mold scale on the mold. The higher the injection temperature, the more severe the precipitation is. The relationship between flame retardant migration rate and temperature can be roughly shown in Figure 4. Within the decomposition temperature range of flame retardant, its precipitation rate increases significantly with the increase of temperature. At constant temperature, precipitation also has a certain correlation with time

after understanding the causes of precipitation, the improvement of flame retardant precipitation can get twice the result with half the effort. There are two main methods:

scheme:

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

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

it should be pointed out that zhuneizhang indicates that the precipitation free flame retardant PP is not completely precipitated, but only reduces the mobility of flame retardant to a great extent. The current non precipitation flame retardant PP is often based on high technical cost, so low-cost anti precipitation is still a subject that needs to be improved