Page 23 - Solutions for Plastic Evaluation

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Orientation Product Evaluation

FTIR

Measurement of Polarized Light of PET Film Using FTIR-ATR Method
When polymers are stretched, the molecules tend to orient longitudinally parallel to the direction they are being stretched. The degree to which
they are oriented in the same direction can be determined from polarized light measurements. Film samples are generally measured using the Plastic Materials Evaluation of
transmission method and polarizers. However, if the film is too thick, the peaks can become saturated, which prevents measurement. In contrast,
the ATR method offers the advantage of being able to measure films regardless of their thickness and obtains information about the sample surface
as well.
Results from measuring the polarized light of unstretched PET film and PET film stretched to 3 times its original length are shown below.
Measurements were performed based on perpendicular polarized light (S), which provides information about vibration perpendicular to the incident
plane (the plane formed by the incident and reflected light). Samples were placed in two orientations. One with the direction of stretching parallel
to the incident plane (lateral orientation) and the other rotated 90 degrees to a perpendicular position (longitudinal orientation). Raw Materials Evaluation of
Direction of
stretching
-POHJUVEJOBM PSJFOUBUJPO
-POHJUVEJOBM PSJFOUBUJPO -POHJUVEJOBM PSJFOUBUJPO
-BUFSBM PSJFOUBUJPO
-BUFSBM PSJFOUBUJPO -BUFSBM PSJFOUBUJPO
-BUFSBM PSJFOUBUJPO
Infrared
light
Direction of perpendicular
polarized light vibration
Lateral Orientation Product Evaluation

Unstretched PET Film Stretched PET Film
Longitudinal Orientation
Longitudinal Orientation
There was almost no difference between the unstretched film spectra and no molecular orientation was observable. However, for the
stretched film, there were clear differences in their spectra, such as in the intensity ratio near 1712 cm (due to C=O stretching vibration) Product Information
-1
and near 1248 cm (due to C-O stretching vibration). C=O stretching vibration was presumably oriented perpendicular to the molecular
-1
axis, whereas the C-O stretching vibration was presumably oriented parallel to the molecular axis. Therefore, these results indicate
that the C=O stretching vibration increased when the sample was placed in the lateral
orientation, so that the stretching direction was parallel to the incident plane. Similarly,
C-O stretching vibration increased when the sample was placed in the longitudinal CH 2 CH 2
orientation, so that stretching was perpendicular to the incident plane. Consequently, n
these results show that the molecules were oriented longitudinally in the stretched film. Structural Formula for Polyethylene Terephthalate
(PET)

Measurement of Polarized Light of PET Film Using ATR Method
Parallel polarized light refers to linear polarized light with an electric field parallel to the incident plane. Conversely, perpendicular
polarized light refers to linear polarized light with an electric field in a plane perpendicular to parallel polarized light. For
perpendicular polarized light, the evanescent wave generated at the reflection point during ATR measurements has a vector
in the X-direction, as shown below. For parallel polarized light, it has vectors in the Y and Z-directions. Therefore, information
about molecular vibration in the X-direction can be obtained using measurements with perpendicular polarized light, whereas
measurements with parallel polarized light provides information about molecular vibrations in the Y and Z-directions.
E
Infrared light Infrared light
Z
Y
E
Ey
X
Ex Ez
Perpendicular polarized light (S) Parallel polarized light (P)
Orientation of Polarized Light and Evanescent Waves

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