実験番号：2022P1007

熱可塑性ウレタンエラストマーの永久ひずみ低減
Elucidation of the Cause of Permanent Strain Reduction in
Thermoplastic Urethane Elastomers
YAMASHITA Yoshihiro1，TASHIRO Kohji2
1

University of Fukui，2 Aichi Synchrotron Radiation Center

Keywords：Thermoplastic polyurethane, permanent strain，SAXS，WAXD
1．Date of measurement
2022/11/17 BL8S3 （2 shift）
2022/11/18 BL8S3 （2 shift）
2. Abstracts.
Thermoplastic elastomers are rapidly replacing conventional natural rubber materials because of theirrecyclability. For example, their disposal has become a major social problem in automobile tires. In this study, wefocused on polyurethane, a representative thermoplastic elastomer. Although it has excellent strength and elasticmodulus, it has a drawback that its permanent strain is larger than that of natural rubber. SAXS and WAXD
investigations revealed that the cause is due to the crystallization of soft segments and rearrangement of hard
segments caused by elongation of the rubber.
3. Background and research objectives
The molecular structure of polyurethane elastomer (TPU) is shown in Figure 1. Permanent strain ismainly due to the crystallinity of the soft segment corresponding to R2. Therefore, it is important to reduce thecrystallinity of the R2 portion. However, along with that, the structure of the hard segment including isocyanate
bonds is also affected. In this study, we used SAXS
to investigate the effect of soft segments consistingof different R2 on the structure of hard segments.
R24．Experimental
Experiments were performed with SAXS and WAXD simultaneousFig.1 polyerethane elastomer

measurements, camera length 1958.830 mm, wavelength 1.5 Å, and PILATUS. The samples used were BASF
(hardness 70 and 80).
5．Result and discussion(a) polybutylene adipate terephthalate (b) ethylene glycol(c) ethylene glycol copolymer-1

SAXS measurements of TPU with
polybutylene adipate terephthalate
as the soft segment with the R2component are shown in Figure2(a); results with the R2 component
replaced with an amorphous ester
component are shown in Figure2(b)~(e). These results indicate thatelongational deformation changes
the structure of the hard segment.

(d) ethylene glycol copolymer-2 (e) Same soft segment as (a) with alarger proportion of hard segment
Fig.2 SAXS profiles of TPU

We compared the long period in the undeformed state with that at 0% strain after 300% elongation. First,
the original polybutylene adipate terephthalate soft segment (a) showed an increase in long period, but the lengthof the long period did not change in elongation. However, the length of the long period did not change withelongation, but the hard segments were oriented in the direction of stretching. When the soft segments in (b) and(c) were made more similar to rubber elasticity, the distance between the hard segments widened when the strain
was returned to 0% after 300% elongation. This may be due to the fact that the hard segments remained slightlyaligned by stretching. In case (d), where the soft segments were brought closer to the rubber elasticity, thestructure of the hard segments became less visible than in the case of stretching. This may be due to the fact thatthe hard segments have a smaller cohesive structure than in (a)~(c), or that the structure has collapsed due tostretching. When the strain in sample (d) was returned to 0%, the distance between the hard segments recovered toalmost the same position as in the unstretched sample. This sample (d) also had the lowest permanent strain.
When the percentage of hard segments in (e) was increased from that in (a), the change in the long-period distance
was also smaller.
From these results, it can be considered that the orientation of hard segments caused by elongation is not
maintained after strain recovery, but returns to the undeformed state, which contributes to the reduction ofpermanent strain.
6. Future Issues
Since the rate of structural change due to stretching seems to be very fast, time-resolved SAXS
measurements at an acquisition rate of less than 1 second while stretching with a stretcher attached are necessary.

(a) polybutylene adipate terephthalate(b) ethylene glycol(c) ethylene glycol copolymer-1

(d) ethylene glycol copolymer-2e) Same soft segment as (a) with a larger proportion of hard segment
Fig.3 SAXS patterns in all ring directions of TPU
7. References
1．Furukawa M., J. Society of Rubber Sci. &Tech., Japan, Vol.783(2010), pp 278-283