Preparation of SiO₂-PMMA Composite with a Nanoscale Dual-network Structure

Objectives: Composite resins for computer-aided design/computer-aided manufacturing (CAD/CAM) systems are generally divided into two groups in terms of their microstructure. One is dispersed filler (DF) structure which micro- or nano-fillers dispersed in a polymer matrix. The other is dual-network (DN) structure which is composed of co-continuous phases of ceramic skeleton and infiltrated resin. Mechanical properties of the DN structure composite is similar to those of human enamel. However, practical DN structure composites are limited to micro-structural types. Purpose of this study is to develop new type of DN structural composite with nano-scale complex structure by using a porous silica and an infiltrated poly(methyl methacrylate) (MMA).
Methods: A nano-porous silica block was fabricated by sintering a silica-polymer based precursor. The obtained porous silica block was treated by a silane coupling agent and then immersed in MMA with benzoyl peroxide. This process allow that the MMA infiltrated into the continuous pores of the porous silica block. The MMA infiltrated silica block was heat-treated at 60–80°C. Consequently, a SiO₂-PMMA composite block was obtained. Nano-structure of the resultant SiO₂-PMMA was examined by a nitrogen sorption porosimeter and field emission scanning electron microscopy(FE-SEM). Mechanical properties of the composite were characterized by Vickers hardness, elastic modulus and flexural strength.
Results: The pore size measurements and FE-SEM observations reveals that the SiO₂-PMMA composite had a DF structure composed of a nanosized silica-skeleton and PMMA continuous phase. Vickers hardness and elastic modulus of the composite increased with increasing silica content. Above 80 wt% of silica content, Vickers hardness of the composite was close to that of human enamel. On the other hand, the elastic modulus of the composite was little less than that of human enamel.
Conclusions: The nano-dual-network structure of SiO₂-PMMA composite with a compatible hardness to enamel can be prepared successfully.