MAS-NMR spectroscopy studies in the setting reaction of glass ionomer cements.
OBJECTIVE
The main objective is the characterisation of the setting reaction in glass ionomer cements based on experimental ionomer glasses with different fluorine content and a commercial glass ionomer cement liquid by using 13C CP/MAS-NMR, 29Si, 27Al and 31P MAS-NMR spectroscopy in order to receive information specifically about the cross-linking process.


METHODS
Different fluorine containing glass compositions based on 4.5SiO2-3Al2O3-1.5P2O5-(5-z)CaO-zCaF(2) where z=0-3, were mixed with a commercially available polymer liquid to form glass ionomer cements. The cements were subjected to 27Al, 13C CP/MAS, 29Si, and 31P MAS-NMR analysis.


RESULTS
The 27Al spectra showed clearly the formation of six-fold coordinate Al(VI), that may crosslink the carboxyl groups in the poly-acid molecules. A shift towards to more positive values of the carboxyl peak in the 13C CP/MAS-NMR spectra showed clearly the proton dissociation of the carboxyl groups. A shift towards more negative values was observed in the 29Si MAS-NMR spectra, suggesting formation of hydrated silica gel and consequently formation of additional Si-O-Si bonds. 31P MAS-NMR spectra also reflected changes in the coordination state around a PO4(3-) tetrahedron. Increasing the fluorine content of the glasses resulted generally in increased reactivity during setting, due to promoting cross-linking and repolymerisation of the silicate phase, followed by clear changes in the MAS-NMR spectra.


CONCLUSIONS
The cross-linking process during the setting reaction of glass ionomer cements can be followed by MAS-NMR spectroscopy observing the conversion of Al(IV) to Al(VI). The acid base setting reaction is completed in 1 day and no further significant changes in the MAS-NMR spectra can be observed. Further study is required in order to understand the role of phosphorus.
Stamboulis
A
A
School of Engineering, Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. a.stamboulis@bham.ac.uk
Matsuya
S
S
Hill
R G
RG
Law
R V
RV
Udoh
K
K
Nakagawa
M
M
Matsuya
Y
Y
D000535:Aluminum / Q000032:analysis; D017607:Aluminum Compounds / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis; D002626:Chemistry, Pharmaceutical; D003432:Cross-Linking Reagents; D005459:Fluorides / Q000737:chemistry; D005898:Glass / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000138:chemical synthesis / Q000737:chemistry*; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D015394:Molecular Structure; D010759:Phosphorus Isotopes / Q000032:analysis; D012825:Silicon / Q000032:analysis; D017655:Silicon Compounds / Q000737:chemistry
D017607:Aluminum Compounds; D002247:Carbon Isotopes; D003432:Cross-Linking Reagents; D005899:Glass Ionomer Cements; D007554:Isotopes; D010759:Phosphorus Isotopes; D017655:Silicon Compounds; D002245:Carbon Dioxide; C041069:carboxyl radical; D000535:Aluminum; C020328:fluoroaluminum silicate; D005459:Fluorides; D012825:Silicon