Structure-Property Relationships of Thermoset Methacrylate Composites as a Function of Resin Matrices, Nanofillers, and Nanofiller Surface Chemistries
Kristen Wilson O’Brien, Elizabeth Wilder, Joseph Antonucci
Polymers Division, Materials Science and Engineering Laboratory
The goal of this research is to better understand the interactions and relationships between nanoparticle fillers, their surface treatment chemistries, various dental resin matrices, and the resultant properties of these thermoset methacrylate composites. These methacrylate composites are primarily designed for use as restorative and sealant dental materials. For optimal clinical performance, properties such as high strength, facile polymerization, high degrees of vinyl conversion, low polymerization shrinkage, and processable viscosities are desirable. One of the composites of interest was a visible light-curable system containing a 50:50 by mass mixture of 2,2-bis[p-(2’-hydroxy-3’-methacryloxypropoxy)phenyl] propane (Bis-GMA) and tri(ethylene glycol) dimethacrylate filled with 40 nm clustered silica particles that were silanized with various blends of two silane agents, 3-methacryloxypropyltrimethoxysilane (MPTMS - a typical coupling agent for glass-filled, acrylic composites) and n-octyltrimethoxysilane (OTMS). Methacrylate conversion after two minutes of light-irradiation was measured by Near-Infrared spectrometry. Mechanical properties of these nanocomposites 24 h after photopolymerization were measured by three-point bend and biaxial flexural strength tests. In general, it was found that increased concentrations of OTMS and decreased concentrations of MPTMS in the surface treatments of the nanosilica particles lowered the moduli and flexural strengths of the cured composite materials. However, the composites containing silica silanized with a 50:50 mixture of MPTMS and OTMS resulted in slightly higher moduli compared to the other composites.
A second composite system of interest was a bioactive composite capable
of sustained release of calcium and phosphate ions into aqueous environments.
It consisted of an ethoxylated bisphenol-A dimethacrylate matrix filled
with surface-treated amorphous calcium phosphate (ACP) fillers (40 % by
mass fraction), which are clustered nano-sized fillers analogous to the
nanosilica fillers. It was found that adsorption of poly(ethylene glycol)
(PEG), PEG-dimethacrylate, or MPTMS onto ACP particles resulted in small
increases in the moduli and flexural strengths compared to composites filled
with untreated ACP. Ongoing experiments are investigating conversion and
polymerization shrinkage as a function of filler concentration and surface
treatment. Also, atomic force microscopy is being used to probe the microstructure
of these composites; fracture surfaces also are being assessed to determine
the effect of filler types and surface treatments on fracture behavior.
Finally, non-clustered, surface-treated, colloidal silica particles will
be investigated as fillers for the purpose of assessing their effects on
thermoset methacrylate composites.
Presenting Author's information