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

Abstract

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 can not 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.

Preparation and properties of thermally conductive polypropylene composites

“…The use of BN for thermal conductive thermoplastic materials and particularly for PP has been reported in the literature [14,[19][20][21][22][23][24]. With low filler contents of 4 vol.-% only a minor increase of the thermal conductivity up to 0.27 W/mK was achieved [14].…”

“…More significant increases to thermal conductivity values higher than 1 W/mK can be achieved with higher BN loadings of e.g. 30 vol.-% [22,23] or 40 wt.-% (approx. 20 vol.-%) [21].…”

“…It is generally expected that BN contents needed to enhance thermal conductivity reduce the melt processability substantially. Highly filled PP/BN composites have been studied extensively [20][21][22][23], however, in these works the rheological behavior of the melts and processability were not investigated sufficiently. Moreover, Nurul et al [19] showed that high filler contents resulted in reduced mechanical properties of the composites, particularly indicated by a significant drop in the elongation at break.…”

“…This was attributed to a changed crystal structure (length of crystals). Moreover, Suplicz et al [22] pointed out, that the crystallinity of especially highly filled polymers is significantly influenced by the thermal conductivity during injection molding. Even though the fillers act as nucleating agents highly filled composites can also show a decreased crystallinity what is attributed to the increased cooling rate enabled by the increased thermal conductivity.…”

Mixing Efficiency Study of Nano and Micro Filled PP Systems

“…Because of the remarkable development in electronics polymer composites having good thermal conduction are in the focus of several researches [2] [7].…”