Effects of coupling agents on mechanical properties of metal oxide-polymethacrylate composites

The effects of several coupling agents on the mechanical properties of metal oxide-polymethacrylate composites reinforced with titanium dioxide (TiO2), aluminium oxide (Al2O3), silica (SiO2) and zirconium dioxide (ZrO2), as fillers for opaque resins were assessed. The prepared composites consist of 24.75 wt% triethyleneglycol dimethacrylate (TEGDMA), 24.75 wt% 1,6-bis(methacryloxy-2- ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA), 0.5 wt% benzoyl peroxide (BPO) and 50 wt% metal oxide filler. Three methacrylate coupling agents--methoxydiethyleneglycol trimethacryloyl titanate, 3-trimethoxysilylpropyl methacrylate and 2,2-di(allyloxymethyl)butyl trimethacryloyl zirconate--were used for surface treatment of TiO2, SiO2 and ZrO2, respectively, while Al2O3 was treated with 4-methacryloxyethyl trimellitate anhydride (4-META). 4-META was also adopted as a coupler for TiO2, SiO2 and ZrO2 powders. Compressive and transverse strength specimens were prepared with the use of coupled or untreated filler and heat cured at 110 degrees C and 0.5 MPa for 30 min. All coupled metal oxide composites had significantly higher compressive and transverse strengths than did untreated composites after 1 month's immersion in 37 degrees C water. Scanning electron microscopy (SEM) of fractured TiO2 composite surfaces after storage in water for 1 month showed an interface failure between TiO2 filler and matrix resin for untreated TiO2 composite and cohesive failures within the resin for treated specimen. Similar results were observed with silanated SiO2 composite. However, cohesive and interface failures were seen in zirconated ZrO2- and 4-META-coupled Al2O3 composites. Thus, titanated TiO2-polymethacrylate composite may be useful as a composite pigment for opaque resin materials.