FTIR Analysis of Plastic Parts

SEM Lab, Inc. supports routine FTIR Analysis of plastic parts to compare lot-to-lot variation in the molecular structure of the polymer. FTIR spectra are affected by mix-ratio, degree-of-cure, contamination, and a range of other factors that are important for quality control.

FTIR (Fourier Transform Infrared) analysis provides spectral information that is essentially a molecular fingerprint for organic, polymeric, and in some case inorganic materials. This technique is extremely useful for identifying base polymer compositions and organic contaminants. The FTIR spectrum of the unknown material can be compared for "best matches" with libraries of spectra that have been cataloged for known materials.

An example of an FTIR spectrum for Poly(oxymethylene) or POM or DelrinTM (DuPont trademark) is shown as Fig. A. The x-axis is wave number (cm-1), which is the inverse of wavelength (cm). The y-axis is absorbance normalized on a scale of 0 - 1 where 1 = no absorption and 1 = maximum absorption.

Low Quality fabric
Fig. A - FTIR spectrum for Poly(oxymethylene) or POM or DelrinTM.

The major peak at wave number 903 cm-1 is due to the C-O-C symmetric stretch absorption. The peak at wave number 1097 cm-1 is due to the C-O-C asymmetric stretch. The peak at wave number 2923 cm-1 is due to the CH2-O asymmetric stretch. All of these vibration modes are indications of the specific molecular bonding within the sample and can be used to identify the material.

Routine FTIR testing of plastic parts can flag anomalies before the parts are assembled into products. It will also quickly identify "wrong material" or process changes that might affect the part performance.