Influence of Calcium Carbonate on the Crystallization of Polypropylene at High Supercooling
This article describes how the Flash DSC was used to investigate the influence of calcium carbonate on the crystallization of filled polypropylene (PP) in the temperature range 120 °C to 0 °C. At low supercooling (above 80 °C), the presence of calcium carbonate reduces the crystallization rate of the -phase. Between 45 °C and 80 °C, the crystallization of the -phase is accelerated. The mesophase formation at low temperatures is not influenced by the filler.
Introduction
The crystallization of polypropylene (PP) under non-isothermal and isothermal conditions has been studied in detail [1].
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Figure 1. Conventional DSC cooling curves measured at 0.5 K/s (30 K/min) and Flash DSC curves recorded at 200 K/s of unfilled PP (black lines) and filled PP (blue lines). |
The introduction of the Flash DSC with its high cooling rates has made measurements possible that provide new information about crystallization processes over a large temperature range and in particular at high cooling rates and high supercooling [2].
It is well-known that in PP two different crystallization mechanisms occur. Above 60 °C, the monoclinic α-phase is formed through heterogeneous nucleation [3].
At low temperatures, the so-called mesophase is formed through largely homogeneous nucleation [3]. This phase is said to be conformationally disordered. It has properties that lie between those of the crystalline and the amorphous states [1]. Fillers can affect the crystallization of polymers and have been classified as active or inactive with regard to their nucleation activity.
The influence of fillers on the crystallization process of PP is often investigated by conventional DSC at low supercooling or low cooling rates. DSC measurements at crystallization temperatures that also occur in polymer processing (e.g. injection molding) can be performed by Flash DSC.
As far as we are aware, we do not know of any investigations dealing with the crystallization behavior of filled PP at supercooling levels relevant to industrial processes. In this article, we investigate the influence of calcium carbonate (CaCO3), an inactive filler, on the crystallization process of PP using DSC and Flash DSC.
