Near Infrared Raman Spectroscopy System for Real Time Monitoring of Fast Processes: A Resin Composite Photopolymerization Application

Abstract

This work describes the implementation of a technique for data monitoring using dispersive near‐infrared Raman spectroscopy that presents the advantage of non‐invasively being capable to make real time fast measurements. The degree of conversion of an odontological resin composite (A3, Z100^®, 3 M), photopolymerized by an LED (450 nm, 230 mW), was measured as an application of the technique. The Raman system consisted of a 785 nm Ti:Sapphire laser, a Chromex spectrograph with an entrance slit of 200 µm, and a liquid nitrogen cooled CCD detector. The system allowed acquisition of Raman spectra at times as short as 6 s. The progress of the photopolymerization was followed by obtaining Raman spectra every 6 s during 84 s. The intensity of the 1640 cm⁻¹ Raman peak, attributed to the aliphatic carbon double bonds, was chosen to calculate the conversion degree of the resin photopolymerization. Results showed that the degree of conversion presented an exponential growth, reaching a maximum of 50% after 60 s. Findings seem to confirm the trustworthiness of the system.

Keywords:

• Raman spectroscopy
• Real time monitoring
• Fast acquisition
• Resin composite
• Photopolymerization
• Conversion degree

Acknowledgments

The authors gratefully acknowledge the Fundação de Pesquisa do Estado de São Paulo, FAPESP and the Conselho Nacional de Pesquisas, CNPq, for supporting this research.