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First Edition: Jul. 2025 01-00868-EN
Study of Changes in Microscopic Physical
Structure by Multifaceted Evaluation
DUH, AGX, HITS, TRAPEZIUM, IRXross, AIRsight, SPM-Nanoa, and Nano 3D Mapping are trademarks of Shimadzu Corporation or its affiliated companies in Japan
and/or other countries.
(1) Verification of increase in tie molecules and an intermediate
layers from the macro viewpoint
First, this section considers the existence of intermediate layers
containing tie molecules, which are expected to have a strong
influence on the improvement of the impact property and
strain at break of plastics. Both the elastic modulus and H
IT
were
reduced by the advanced recycling process. The cause of this
change is considered to be either a decrease in the degree of
crystallization, or an increase in the intermediate layers
containing tie molecules. In this evaluation, the DSC analysis
showed that there was no difference in the heat of fusion,
confirming that there is 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. The image of the tie molecules and
intermediate layers is shown in Fig.17.
(2) Consideration of changes in the physical structure from the
micro viewpoint
In the section, the increase in tie molecules is considered,
changing the perspective from the macroscopic physical
properties of the elastic modulus, H
IT
, and the degree of
crystallization to the microscopic viewpoint. It is suggested that
the increase in polymer entanglements during melting in the
advanced recycling process contributes to the formation of
intermediate layers containing tie molecules. The condition of
polymer entanglements during melting is estimated from the
polymer structure in 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.
When the ratio of the parallel structure and the helical structure
was investigated by FTIR, it was found that the helical structures
had increased. Based on this, it is thought that relaxation
proceeds as a result of the advanced recycling process.
Moreover, the evaluation of the orientation in the micro region
by SPM showed that the distribution becomes more uniform as
a result of the advanced recycling process, which also supports
the conclusion that the effect of shearing was moderated by the
advanced recycling process. As mentioned previously, the
crystallization start temperature during cooling in the DSC
measurements decreased as a result of the advanced recycling
process, which also suggests that polymer entanglements
increased.
Based on the multifaceted evaluation described above, it is
though that relaxation of the polymer during melting was
promoted by the advanced recycling process, leading to an
increase in polymer entanglements and an accompanying
increase in the intermediate layers containing tie molecules,
and as a result, the impact property and strain at break of the
recycled plastic improved.
<Reference>
1) Present and future of waste plastics: plastic resource circulation
in sustainable society, The Japan Institute of Energy, p. 147
<Acknowledgement>
The authors wish to express their heartfelt gratitude to Mr. Kaga, Mr.
Fujioka, and Mr. Hisaizumi of ISONO Co., Ltd. for their guidance in
the preparation of this report.
Conclusion
It was found that the impact property and strain at break of PP
were improved by the advanced recycling process.
This study also demonstrated that the multifaceted evaluation
described in this article is an effective tool for evaluating
changes in the microscopic physical structure.
Reference: Image of Entaglements during
Melting of Polymers and Crystal Structure
after Cooling
1)
As reference, the following diagram shows the image of the
aggregation state of polymers explained in the main text. If
entanglements of the molecules are increased by heat
treatment in the advanced recycling process, the number of tie
molecules after crystallization will increase.
Crystals
Molten
condition
Few polymer
entanglements
Many polymer
entanglements
Cooling
Many
intermediate
layers with tie
molecules
Few tie
molecules
With advanced
recycling process
Without advanced
recycling process
Fig. 17 Image of Aggregation State of Polymers
