Research method

Development of Silicone Rubber with Ultrahigh TearStrength

X-ray diffraction/scattering

Clarification of behavior of nanosilica filler aggregates

Role of SPring-8

Marked improvement of hardness, tear strength, and independent control of theelongation of silicone rubber
Development of silicone rubber with high tear strength while maintaining
transparency
R&D facility: Sumitomo Bakelite Co., Ltd.
*Silicone rubber: Silicone rubber mainly consists of silicon and contains siloxane bonds (SiO) of alternately bonded silicon and oxygen. It hasvarious characteristics such as resistance to high and low temperatures. Silicone rubber has been widely used as a medical material. The
development of a material that has high transparency, moderate hardness, and a high tear strength is demanded.
**Small-angle X-ray scattering (SAXS): SAXS is a technique for analyzing the nanoscale structure of a target specimen using the scattering
intensity profile obtained by irradiating the specimen with X-rays.
***Ultrasmall-angle X-ray scattering (USAXS): Conventional SAXS can generally identify a structure with a size of 2 – 30 nm. USAXS is a techniquefor measuring and evaluating a mesoscopic structure with a size of 200 – 300 nm using the scattering intensity profile in a range of ultrasmall angles.

X-ray two-dimensional USAXS andSAXS images of silicone rubber withnanosilica filler

USAXS
0.10

0.10

0.10

X-ray

10101
10 010-1
10-2
10-3
10-4
10-510-616SD⊥SD//
USAXSSAXS
λ＝7.2
λ＝6.6
λ＝5.8
λ＝5.0
λ＝4.2
λ＝3.4
λ＝2.8
λ＝1.8
λ＝1.0
λ＝2.8
λ＝2.6
λ＝2.2
λ＝1.8
λ＝1.4
λ＝1.00.01

SAXS

34.1 wt%

34.1 wt%

0 wt%

0.1

0 wt%

10.1

Differences in stress and nonuniformity ofdensity fluctuation depending on tear strength200.2

1Intensity profile in the direction
parallel to elongation of silicone
rubber (filler content, 34.1 wt%;
λ, elongation factor).
A characteristic pattern indicating
the orientation was observed fromthe beginning of elongation. The
state of the aggregation of thefiller elongated in the elongation
direction of the silicone rubber
was clarified.

1510High tearstrength

Low tearstrength1055Low Tear

0Developed silicone rubber with high tear strength

20150.2

λ＝6.62SAXS** and USAXS*** were used to observe
the dispersion state of the filler, including theaggregation structure. The beamline of SPring-8
is appropriate for evaluating structures with awide size range. In situ observation of thehierarchical structure and the behavioral changeof nanosilica aggregates was carried out by SAXS
at SPring-8 while silicone rubber specimens witha dispersed nanosilica filler and different
strengths were elongated using a tensile tester.
The results indicate that when siliconerubber with strong bonding between the filler
and the matrix is elongated, the filler aggregatesare also elongated in the same direction, whichleads to an increase in the tear strength. In
addition, the strength of the interface depends
on the state of the aggregation of the filler. Thisfinding has led to the improvement of theproperty of silicone rubber by controlling thestate of the aggregation.

0.2

λ＝3.4

103

With the advancement of medical care, thedevelopment of medical equipment with higher
performance has been required. Among the various
medical materials, silicone rubber has superior
resistance to high and low temperatures, chemicalstability, electrical insulation, gas permeability,transparency, and a mold release characteristic.
However, the tear strength and tensile strength ofsilicone rubber are inferior to those of other rubbermaterials and the range of its application has beenlimited.
Under such circumstances, the development oftransparent silicone rubber with a high mechanicalstrength has been required. To realize such a rubber, ananosilica filler was dispersed in silicone rubber as areinforcing material and the bonding between thenanosilica filler and the surrounding rubber wasstrengthened to improve the mechanical strength of
the silicone rubber. It was also required to clarify therelationship between the structure of the filler
aggregate and the tear strength upon the elongationof silicone rubber.

λ＝1.0

Drawing machineStress relaxation starts to occur simultaneously when silicone
rubber is elongated. The state of the aggregation of the filler
inside the silicone rubber was observed while the silicone
rubber was extended using a drawing machine with amaximum speed of 1 m/s.

SAXS

ResultsForce（N）

Ultrahigh-speed tensile test andSAXS using BL19B2

Background

13560

High Tear

7Tear strength (N/mm)

Clarification of the change in the hierarchical structure of nanosilica filler
aggregates along with the elongation of silicone rubber*

Nonuniformity ofdensity fluctuation

Achievements

Conventional products
Product with high tear strength50403020100Strain ratio
When the bonding between the filler and the matrix isstrong, the tear strength is high.

Example of product using
silicone as a medical material:
unit for continuous suction ofblood, pus, and effusion fromwounded area after surgery

0050100150200250

Stroke (mm)The surface of the filler was treated to improve the interface strength
between the filler and the silicone on the basis of the observed change
in the state of the aggregation of the nanosilica filler upon elongation.
The research group has succeeded in developing silicone rubber with atear strength that is approximately fivefold (50 N/mm) that ofconventional silicone rubber over a wide range of hardness of 30-70(product name, DuraQ®). It is expected that this ultrahigh-tear-strength
silicone rubber will be used as a material not only in medical equipment
but also in mechanical parts of automobiles and airplanes, clothing,healthcare products, and wearable products.

17