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First Edition: Oct. 2023 01-00590-EN
Measurement of Changes in Molecular
Structure
Conclusion
AGX, TRAPEZIUM, DUH, IRTracer, and QATR are trademarks of Shimadzu Corporation or its affiliated companies in Japan and/or other countries.
In the results in the previous sections, differences in yellowness
and breaking elongation were seen in Sample A and Sample B.
These differences were assumed to occur due to changes in the
chemical structure of the resin caused by the difference in the
kneading condition. To confirm this assumption, the differences
in the molecular structures of the two specimens were
measured with a matrix assisted laser desorption/ionization
time of flight mass spectrometer (MALDI-TOF MS). The results
are shown in Fig. 14.
In this evaluation, there were no differences in the
compositional homogeneity, tensile strength, elastic modulus,
hardness, or glass transition temperature of the specimens
prepared under the different kneading conditions. Thus, no
effect of kneading on these properties was observed. On the
other hand, when kneading treatment was conducted,
deterioration of the yellowness index and breaking elongation
properties could be seen, and progress of changes in the
molecular structure due to kneading treatment was also
confirmed. Multifaceted evaluation like that introduced here
can provide a detailed understanding of the changes in material
properties that occur as a result of differences in overall molding
conditions, not limited simply to kneading. Therefore, this is
considered to be an effective approach for study of the
optimum molding conditions.
Fig. 13 MALDI-8020
Fig. 14 Comparison by MALDI-TOF MS
A) Without kneading, B) With kneading, C) PC
: New signal due to kneading
: Characteristic signal due to blending (molding)
Cyclic; (n)
Both-end capped; –(n)–
One-end hydroxyl group; HO(n)–
Fig. 15 End Terminal Structures of Polycarbonate (PC)
Table 10 Measurement Conditions
Instrument : MALDI-8020
Laser source : Solid-state laser (λ = 355 nm)
Matrix : DCTB, Nal (cationization agent)
Mass range : m/z 1-5000
Detection ion : Positive ion mode
Flight mode : Linear mode
Delayed extraction condition : m/z 2500
Changes in the signal originating from PC in the blended
product were observed, regardless of whether the material was
treated with the kneading machine or not. In comparison with
virgin PC, there was a relative decrease in both-end capped
molecules in both Samples A and B, and the number of
molecules having one end capped with a hydroxyl group
increased. Furthermore, the number having a hydroxyl group at
one end decreased in the specimen treated with the kneading
machine. Although the chemical structure could not be
estimated, new characteristic signals appeared, as indicated by
the yellow arrows in Fig. 14. The possibility that the origin of
these signals may be some type of reaction with the one-end
hydroxyl groups due to the extended kneading time is
conceivable.
A precise analysis extending to the cause of the changes in
yellowness and breaking elongation was not possible. However,
it was at least possible to confirm that changes occur in the end
groups of PC as a result of a chemical reaction during kneading.
Thus, in addition to analytical methods to understand the
physical properties of the material, such as strength, analysis of
chemical structure at the molecular level is considered to be
effective for ensuring proper molding.
