Phase selective localization of silica filler in Polymenthyl mMhacrylate/ethylene Vinly Acetate (PMMA/EVA) composites

Filler dispersion in polymer composites depends on the interfacial tension of filler and polymer matrix, especially for composites using a thermoplastic elastomer blend (TPE). Both interfacial tensions, filler and thermoplastic as well as filler and elastomer, caused different distribution and dispersion of the filler in each polymer phase. The filler will select and locate in the polymer phase having low interfacial tension with; this is called as phase selective localization (PSL) of filler in TPE composites. This research concerned about PSL of silica filler in PMMA/EVA composite; which in turn decided the characteristics and properties of PMMA/EVA/Si composites. There are three interfacial tensions in PMMA/EVA/Si composite such as interfacial tensions of PMMA/EVA, PMMA/Si, and EVA/Si; based on Wu's equation, it was calculated as 7.18 mN/m, 47.99 mN/m, and 41.24 mN/m, respectively. It indicated that silica selects to locate in EVA phase because of their lower interfacial tension compared to PMMA/Si. In addition, silica and EVA also have similar polarity values. In order to maximize the effect of PSL of Si in PMMA/Si composite, three different compounding methods were implemented for each formula of PMMA/EVA/Si composite. The first method followed conventional compounding by addition of silica into melt PMMA/EVA blend (notated as CON). The second was pre-dispersion of silica into PMMA phase (Si/M), which was further blended with extruded EVA to get the final composite (notated as Si/M-EVA). The third was pre-dispersion of silica into EVA phase (Si/E) and followed by blending Si/E with extruded PMMA to get the final composite (notated as Si/E-PMMA). The investigation was focused on two PMMA/EVA blend ratios and different silica contents. PSL was examined by correlating the practical viscosity (obtained by capillary rheometer) and theoretical viscosities (Model Conventional, Model EVA, and Model PMMA). All melting compounding were conducted by using a twin-screw extruder. The samples for mechanical and DMA testing were prepared by using injection moulding. PSL of Si to EVA was proven from the well-matching of both practical and theoretical viscosity of Si/E-PMMA. The fact of PSL of Si to EVA was evident in both blend ratios: 50/50 PMMA/EVA equivalent blend and 70/30 PMMA/EVA of PMMA dominion. Moreover, migration of silica in the PMMA phase to EVA phase in Si/M-EVA composite was also detected from the EDX results. It confirmed that PSL of silica is EVA phase versus PMMA phase. Therefore, the Si/E-PMMA composite exhibited the best mechanical, thermal, and dynamic mechanical properties for the equivalent blend composites. For PMMA dominion blend of 70/30 PMMA/EVA/Si composites, Si/E-PMMA exhibited the best thermal properties while Si/M-EVA exhibited the best mechanical properties. The most interesting finding was both composites of pre-dispersion silica in PMMA or EVA, had exhibited better properties compared to the conventional composite. This proved that PSL of silica was very essential as it controlled the properties of PMMA/EVA/Si composites.