Effect of compatibilizer on the dispersion of untreated silica in a polypropylene matrix

BACKGROUND: A new processing method for polypropylene–untreated precipitated silica (PP/SiO₂) composites based on the incorporation of a second polymer phase of polyamide 6 (PA6) is presented and compared with a more classic one making use of compatibilizers: glycerol monostearate (GMS), ethylene acrylic acid ionomer (IAAZE) and maleic anhydride grafted polypropylene (MA‐graft‐PP). The effects of processing methods and conditions on the microstructure and properties of PP/SiO₂ composites prepared by melt compounding are investigated with a view to reduce the size of aggregates of silica from the micrometre to the nanometre scale and to improve the link between filler and matrix. RESULTS: On the one hand, the presence of GMS and IAAZE compatibilizers significantly improves the dispersion of the silica particles. On the other hand, when using a PA6 second phase, the SiO₂ particles are dispersed in PA6 nodules. Within these nodules, SiO₂ appears dispersed at the nanoscale but with larger particles (‘aggregates’) of about 200 nm. Significant improvements in tensile strength and modulus are obtained using MA‐graft‐PP compatibilizer. An increase in impact strength is observed in the case of GMS compatibilizer. Thermal parameters indicate also that silica plays the role of nucleation agent for PP matrix. All improvements (tensile strength, modulus and impact strength) increase with the addition of compatibilized PA6 second phase. CONCLUSION: By the incorporation of masterbatch of silica in PA6 as a second polymer polar phase, a successful new production method for PP/SiO₂ nanocomposites has been developed. Interestingly, this method does not require any (expensive) pre‐treatment of the silica. Copyright © 2007 Society of Chemical Industry