Injection molding of ceramic filled polypropylene: The effect of thermal conductivity and cooling rate on crystallinity

•BN, talc and TiO2 in 30 vol% were compounded with polypropylene matrix.•According to the DSC measurements, the fillers are good nucleating agents.•The thermal conductivity of the fillers influences the cooling rate of the melt.•The higher the cooling rate is, the lower the crystallinity in the polymer matrix.

Three different nano- and micro-sized ceramic powders (boron-nitride (BN), talc and titanium-dioxide (TiO2)) in 30 vol% have been compounded with a polypropylene (PP) matrix. Scanning electron microscopy (SEM) shows that the particles are dispersed smoothly in the matrix and larger aggregates cannot be discovered. The cooling gradients and the cooling rate in the injection-molded samples were estimated with numerical simulations and finite element analysis software. It was proved with differential scanning calorimetry (DSC) measurements that the cooling rate has significant influence on the crystallinity of the compounds. At a low cooling rate BN works as a nucleating agent so the crystallinity of the compound is higher than that of unfilled PP. On the other hand, at a high cooling rate, the crystallinity of the compound is lower than that of unfilled PP because of its higher thermal conductivity. The higher the thermal conductivity is, the higher the real cooling rate in the material, which influences the crystallization kinetics significantly.