Polyethylene compounds containing mineral fillers modified by acid coatings. 1: Characterization and processing

Research has been carried out to determine the effect of filler coatings on the processing properties of medium density polyethylene (MDPE) modified by an ultrafine grade of flame-retardant magnesium hydroxide (Mg(OH)(2)) filler. Selected filler coatings were acid-group terminated and were of varying aliphatic chain length. The filler dry-coating process has been optimized by characterizing the reaction between Mg(OH)(2) filler surface and the acid group, using spectroscopic techniques including Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Using immersion calorimetry, the interactions between the fillers and the polyolefin matrix were shown to decrease on the addition of a fatty-acid coating. Compounding torque and specific energy data relate to filler dispersion; qualitative analysis has demonstrated how the coatings provide a reduction in both size and number of particle agglomerates. MDPE compound processability was assessed by capillary rheometry; wall slip was evident in compounds containing uncoated Mg(OH)(2) filler. Consequently, the development of molecular orientation of the polymer during injection mold filling, quantified by a reversion analysis, is modified by the effects of filler coating chain length and addition level, an effect that has important implications to link the mechanical properties of MDPE-Mg(OH)(2) composites to processing history.