Coatings for magnesium hydroxide fillers in polyethylene compounds

This study has been carried out to determine the effect of filler coatings on the physical and mechanical properties of medium density polyethylene (MDPE) filled with a fine grade of magnesium hydroxide filler. The filler coatings applied are of varying aliphatic chain length, the shortest being decanoic acid (C1O), and the longest being an acid-terminated PE, Mw=5000g/mol. The other coatings applied were stearic acid (C18), a commonly used coating, and behenic acid (C22). This selection of coatings provided a comparison of the effect of fatty acid chain length, with the acid group of the functionalised PE providing a similar reaction with the filler surface as the fatty acids, and also being of sufficient length. and compatibility to interact with the MOPE matrix. The coating process has been studied to fully characterise the interaction between Mg(OH)2 filler surface and the acid group. It has been shown using FTIR DRIFT and transmission spectroscopy that the reaction is ongoing, with no unreacted acid present in the system. The temperature and coating cycle time necessary to produce a full reaction between acid group and filler surface has been determined for each coating type. XPS analysis carried out on the coated fillers has shown that the coating thickness is of the same order as the calculable fully extended chain length, demonstrating that the aliphatic chains are normal to the surface of the filler. [Continues.]