Exfoliation of clays within poly(acrylic acid) is the first step towards the development of glass ionomer based dental nanocomposits. Nanocomposites formation generally involves the interaction of silicate nano-plates of clays with the polymer matrix. The reinforcement effects of polymer grade (PG) montmorillonite were evaluated to establish the micro structure, setting chemistry and properties of poly(acrylic acid) which would eventually be used to develop the cements.
Methods:
The poly(acrylic acid)-PG montmorillonite nanocomposites were prepared by dispersing the clay (0.5-8 wt %) into the aqueous solution of poly(acrylic acid) (MW ~100,000, pH 2.0). The mixtures were mechanically stirred for 3 hours before heating at temperature between 85-95 °C for three hours. The low-angle X-rays diffraction (XRD) and X-rays photoelectron spectroscopy (XPS) analysis were carried out to determine the interlayer d-spacing and chemical analysis on the solid residues collected via centrifuge. Transmission electron microscopy (TEM) and fourier transform infrared (FTIR) spectroscopy were performed on liquid samples to study the dispersion, chain conformation and crystallinity in clay containing polymers.
Results:
The introduction of PGV clays within poly(acrylic acid) resulted in the dispersion and exfoliation of silicate plates inside the fully extended chains of polymer. XRD indicated the increase in interlayer d-space from ~13 °A to ~20 °A and XPS showed the release of cations (Na and Fe) from the clay platelets after treatment with poly(acrylic acid). FTIR spectra demonstrated the appearance of new peaks after cross-linking with the nano-plates. Finally, TEM observation confirmed the exfoliated and/or partially exfoliated PGV within the polymer matrix.
Conclusions:
The formation of nanocomposites by the addition of nanoclays in poly(acrylic acid) offers the great potential to disperse these nano-plates in glass ionomer cement after mixing with aluminosilicate glasses. The dispersion of PGV might contribute towards the improvement in materials properties when compared with the conventional glass ionomer cements.