MEMS-based polarized FTIR spectrometer for polymer quality control

Abstract

Polarized Fourier transform infrared FTIR spectroscopy has been used extensively to monitor orientation for polymer quality control and optimized the mechanical properties. In the manufacturing process, using an in-line portable spectrometer would be a great advantage providing near real-time feedback during polymer production processes including temperature, and drawing/stretching. The goal is to let the chains within a polymer disentangle and become more systematic/oriented with predictable properties. In this work, we present a measurement technique using microelectromechanical system (MEMS) based polarization controlled Fourier transform spectrometer in the extended near-infrared used to monitor the polymer quality. The spectrometer is operating in the wavelength range of 1300 nm to 2600 nm (about 3846 cm-1 to 7692 cm-1) with a spectral resolution of 66 cm-1. The polarized-FTIR data were collected for a commercial plastic CD sleeve with thickness of about 1 mm in transmission mode. An ultra-broadband wire grid linear polarizer is used, inserted in the light path and rotated 360 in steps 10. The polarizer orientation is kept in the same position for both background and sample measurements. The dichroic ratios of different absorption bands have been determined with the polarizer oriented parallel and perpendicular to a reference direction. The orientation quality of the polymer can be detected from the dichroic ratio with dichroic ratio equals to one representing an isotropic material. Comparison with a benchtop device is conducted showing good agreement. The presented solution paves the way for a low-cost and portable device for on-line polymer quality control.