Application
News
Evaluation of Polymer Structure Ratio by FTIR
As noted above, differences in mechanical properties were
observed with and without the advanced recycling process, and
from the decrease in the crystallization start temperature, which
is one thermal property, polymer entanglements are thought to
increase. Based on these two points, it is considered possible
that the microscopic physical structures in the plastic were
altered by the advanced recycling process. In evaluating the
change in the microscopic physical structures, we focused on
the proportion of helical structures, which are considered to be
closely related to polymer entanglements.
The polymer structures of PP are the helical structure and the
parallel structure, and it is possible to detect peaks originating
from these structures by FTIR. Here, ratios of the two structures
with and without the advanced recycling process were
evaluated. Using a microtome, test slices with a thickness of 15
μm were taken from the parallel part of the ISO 527-2 1A test
pieces, and area mapping measurements were carried out by
the transmission method using the infrared mode of the
AIRsight infrared and Raman microscope. Fig. 11 shows the
appearance of the instruments, and Table 8 shows the
measurement conditions.
Fig. 12 shows the spectra of each of the two sample materials
with and without the advanced recycling process. Peaks
originating from the helical structure at 998 cm
-1
and from the
parallel structure at 971 cm
-1
were detected, and chemical
images (Fig. 13) were prepared based on the height ratio
(helical/parallel) of the two peaks. For comparison, the vertical
axes of the chemical images were unified at 0.71 to 0.85 AU. The
results confirmed that the material with the advanced recycling
process had a higher in-plane average value of the
helical/parallel ratio than the material without the process.
Fig. 11 IRXross and AIRsight
Study of Changes in Microscopic Physical
Structure by Multifaceted Evaluation
(1) Verification of increase in tie molecules and intermediate
layers from the macro viewpoint
In this evaluation, improvement of strain at break was not seen,
but differences were observed in the elastic modulus, H
IT
,
crystallization start temperature, and ratio of helical structures.
Although the microscopic physical structures are considered to
be altered by the advanced recycling process, we concluded
that improvement in strain at break was not seen due to the
effect of foreign matter. As in the previous Application News
article mentioned in the Introduction, an increase in tie
molecules is considered as a change in the microscopic physical
structure. The image of the aggregation state of the polymer is
shown in Fig. 14.
Both the elastic modulus and H
IT
decreased as a result of the
advanced recycling process. The cause of this decrease is
considered to be either a decrease in the degree of
crystallization, or an increase in the intermediate layers
containing tie molecules. However, in this evaluation, there was
no difference in the heat of fusion in the DSC measurements,
indicating that there was no difference in the degree of
crystallization with and without the advanced recycling process.
Based on these facts, it can be thought that the intermediate
layers containing tie molecules are increased by the advanced
recycling process.
(2) Consideration of changes in the physical structure from the
micro viewpoint
In this section, we consider the increase in tie molecules from
the microscopic viewpoint, rather than the macroscopic
physical properties of the elastic modulus, H
IT
, and the degree of
cystallization. It is thought that the increase in polymer
entanglements during melting contributes to the formation of
intermediate layers containing tie molecules. Therefore, the
condition of polymer entanglements during melting is
estimated from the polymer structure of the solid state after
molding. In the molding process from the molten state, it is
thought that the polymer is elongated to the parallel structure
when shearing is applied, and the probability that the polymer
will become a helical structure increases as polymer relaxation
proceeds. From the investigation of the ratio of the helical
structures and parallel structures by FTIR, it is found that the
helical structures increased. Based on this, it is thought that
polymer relaxation proceeds when the advanced recycling
process is applied. As mentioned above, based on the fact that
the crystallization start temperature in the cooling process is
decreased by the advanced recycling process in the DSC
measurement, it is thought that polymer entanglements
increase.
From the above, it is thought that polymer entanglements also
increase due to polymer relaxation during melting by the
advanced recycling process in PP without fillers derived from
offcuts in the automobile manufacturing process, and as a result,
the intermediate layers containing tie molecules also increase.
However, unlike the evaluation of the samples of virgin homo
PP with simulated physical degradation, in this study, it is
thought the effect of the increased polymer entanglements on
strain at break was cancelled out by the effect of foreign matter
in the actual recycled plastic.
Instruments : IRXross , AIRsight (infrared mode)
Resolution : 8 cm
-1
Accumulation : 10 times
Apodization
function
: SqrTriangle
Aperture size : 30 μm × 30 μm
Step width : 30 μm
Mapping range : 150 μm × 330 μm (with advanced recycling process)
40 μm × 260 μm (without advanced recycling process)
Detector : T2SL
Table 8 Measurement Conditions
Helical structure
998 cm
-1
Parallel structure
971 cm
-1
Without process_cross section
With process_cross section
Fig. 12 Infrared Spectra of Samples with/without Advanced Recycling Process
Fig. 13 Chemical Images of Test Slices
With Advanced Recycling Process Without Advanced Recycling Process
