Relaxation of loose agglomerates of magnesium hydroxide in a polymer melt

The study of agglomerates of magnesium hydroxide badly dispersed in an olefinic polymer by means of oscillatory shear flow in the melt indicates that the agglomerates behave as a distinct phase. Optical and rheo-optical measurements carried out on these agglomerates also show that they are wetted by the melt and that they can be easily deformed under shear. However, the relaxation of shape in oscillatory shear is also the trace of the existence of an effective interfacial tension between the agglomerates containing high amounts of filler and the polymer matrix. The analogy with the behavior of polymer blends and the modeling by the Palierne model enables the calculation of such an interfacial tension. The surface free energy of magnesium hydroxide that can be calculated from this result by a simple mixing law is 95 mN m(-1). This value is compared with data from the literature on brucite and similar minerals. (C) 2012 Elsevier Ltd. All rights reserved.