Applied Che때S따,
Vo l. 12, No.2, November 2뼈, 285- 7)엉
Influence of thennal curing OD the properties of electrospuD polyca매osilane fiber
Joon-Pyo Jeun , Eun-Jung Kim, Dong-Kwon Seo, Young-Chang Nho, Phil-Hyun Kang*
Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute
Abstract
The effect of thermal curing on the properties of polycarbosilane fiber has been investigated.
Polycarbosilane fibers were fabricated using electrospinning method. Its structure was characterized by Fourier
transformed infrared spectroscopy (FT-IR). The thermal curing beha、 ior was investigated using FT-IR , gel
permeation chromatography (GPC) and thermal stability was characterized by thermogravimetric analysis
(TGA). TG data indicates that thermal stability was improved with increasing the curing time. The molecular
weight and molecular weight distribution were also increased as the thermal oxidation curing time increase
Introduction
Recently, formation of ceramics by the pyrolysis of organometallic polymers has begun to aUract
considerable attention since silicon carbide (SiC) fibers were synthesized from polycarbosilane (PCS).
Organometallic polymers have several advantages for ceramics. One typical example is shown as follows
Organometallic polymers can be easily formed as fibers or films. Then. by heating polymer fibers, ceramics
may be obtained in the original form. In this case, it is possible to have any desired form of ceramics,
impossible by traditional inorganic chemical processes. SiC fiber has been used as reinforcement in advanced
ceramic matrix composites, which are applied in the fields of aerospace, nuclear, and high-temperature
materials, such as gas-turbine engine. In ceramic fiber/ceramic matrix composite, ceramic fibers are demanded
to be fine and strong as possible as they could do, as finer ceramic fibers are more flexible so that it is easy
to make t“ 0- or three-dimensional fabrics. Moreover, it is considered that finer fiber shows higher tensile
strength.
In this study, we reported on the fabrication of PCS fibers as a precursor for SiC fiber and the effect of
thermal oxidation curing of pes fiber. The change of structure was characterized by FT-IR. And the change
of molecular weight and molecular weight distribution were observed by GPe analysis. The thermal properties
were investigated by TGA instrument
Ex perimental
pes (average molecular weight = 1906 g/mol, density = 1.1 g/cm 3
‘NIPUS, Japan) was used as a
precursor polymer SiC fiber. 1,2-Dichroloethane and toluene were used as a solvent“ ithout any further
purification, which were purchased from Aldrich , USA. PCS solution was prepared by dissolving a measured
amount of pes in 1,2-dichroloethane/toluene (50150 wt%). The concentration of the pes solution was 50
wt%. In the electrospinning process, a high electric potential was applied to a droplet of pes solution at the
tip (ID 0.36 mOl) of a syringe needle. The solution was then ejected through a syringe using a syringe flow
pump at feed rate of 0.003 mlimin. applying a voltage of 15 kV and tip-target distance of 120 mOl. The
285
)oon-Pyo )eun' Eun-)ung Kim' Dong-Kwon sea· Young-Chang Nho' Phil-Hyun Kang286
electronspun pes fiber was heated at 10°C/rain over a range of temperatures (190-200°C) in an air gas flow
of 100 ml!min
FT-IR spectra of the thermal cured pes fibers were analyzed using a Bruker Tensor 37 spectrometer
The surface morphology of pes fibers was observed using SE 1'.1 (J SM-6390, lEOL). Specimens “ ere coated
by gold sputtering for 5 min. The working distance of the SEM was 15 mm and the accelerating power was
20 kY. Thermal stability was investigated with a thermogravimetric analyzer (TGA). TGA was conducted 、,v ith
a TA instrument SOT Q600 at a heat rate of 10°C/min, from 50 to looooe ‘ The TGA samples were cut
into small pieces and were machined using a mechanical grinder to maintain sample weights between 9-11
mg. All TGA tests were run in nitrogen gas. The molecular 까 eight distributions were determ ined by gel
permeation chromatography (GPC) using Agilent 1100 series isocratic pump, PL series injector with 100 ul
loop and PLgel_mixed_B (300x7.5mmx2) columns in series (Polymer Laboratories, Shropshire). THF was used
as column eluent and the flow rate of eluent was I mlimin. The column temperature was controlled at 400e.
Results and discussion
The morphology of the pes fibers prepared by electrospinning method was examined by scanning
electron microscopy (SE1'.1). Fig. I shows SEM image of electrospun pes fiber. It can be seen that the fibers
appear to be uniform , smooth, and straight, with a ca. 18-23 urn outer diamete r.
silicon carbide fibe r. The
chemical structures of polycarbosilane by thermal oxidation curing are speculated upon in Fig. 2 by referring
to the polycarbosilane chemical structure mode l. IR spectra of electrospun PCS mat indicated three main
features centered around 2100 cm-I, 1250 cm'l and 2950 em-I. The strong signals of 2100 em-I were
indicated by Si-H stretching. Two other peaks centered at 1250 cm-I (Si-CH3 stretching) and 2950 em -I (C-H
stretching in Si-CH3 stretching) are attributed to the vibration mode for Si-CH3. IR spectra of pes mat
showed the loss of Si-H band, thus it is presumed that curing process results in the formation of Si-Si band
The curing process is necessaη to convert polycarbosilane fibers to
by thermal oxidation of Si-H, Si-CH3.
’’”3센센젠시낀μμ“시센,‘
이‘
‘‘--,‘””센μElι써‘
--control120 min290 min
.' ‘ 420 min600min
Fig. 2. FT-IR spectra of thermally cured pes
10002500 2000 1500
Wavenumber (cm ’)30003500
Fig. I. SEM image of electrospun PCS fibers
웅용화학, 제 12 권 제 2 호, 2뼈
Influence of thermal curing on the properties of electrospun polycar뼈ilane fiber 287
fibers.
The weight losses for the electrospun pes fibers and thermal cured pes fibers are reported in Fig ‘
3. The weight loss of electrospun pes fibers is veη 10“ up to 280eC. Then it reaches 23% at 800ee and
remains stable above this temperature. The weight loss for the thermal cured PCS fibers for 600 min is very
low up to 6000e and reaches only about 11% at 8000 e. This thermal stability is increased with increasing the
thermal curing time.
Table I. and Fig. 4 show the molecular weight distributions of various thermal curd pes fibers. The
electrospun pes had a 10、、 molecular weight ‘ i.e. Mn=I ,900 g/mol, I\1 w=6,289 g!mol, but aftcr thεrmal curing
for 120 min , Mnand Mw increased to 2‘ 192 and 8,774 gimol , respectively, and for 600 min these reached
2,485 and 20.953 gimol, respectively. The polydispercsity also increased to 4.00 and 8.43. respectively. The
GPC results ‘ which prove the curing of PCS. are in good agreement with FT-IR spectra, ‘.vhich show the
dehydrocoupling of Si-H led to the formation of Si-Si and Si-CH 3 bonds under thermal oxidation
10030。
~ 90se.r:;.2'
응80
m
m
i@1드
@〉--umt@α
--control_._..- 120min- 300min--_.. 420min•••• OCKl min
control
70o 200 400 600 800
Temperature (oC)1000 13 14 15 10 17 18 1Q 20
EhAion time (min)
Fig. 3. TGA diagram of thermally cured pes fibers. Fig. 4. GPe curves of thermally cured pes fibers.
Table I Characteristics of thermal cured pes fibers
Mn l)
GPC results
Mw 2) PDI3)
6,289 3.3 I
8,774 4.00
11 ,548 5.01
14,418 5.90
20,953 8.43
Thermal curing time
(min)
o 1,900
120 2,192
300 2,303
420 2,441
600 2,485
I) The number average molecular weight (gimo l)
~) The weight average molecular weight (g!mol)
3) Pl)ly dispersity index (M 까1M 띠
Applied Chemistry, Vol. 12, No.2, 2α%
288 Joon-Pyo Jeun' Eun-Jung Kim· Dong-Kwon Sea' Young-Chang Nho' Phil-Hyun Kang
Conclusion
The PCS fibers prepared using electrospinning method ‘,vere successfully crosslinked by thermal
oxidation reaction , The electrospun PCS fibers appear to be uniform. smooth with average fiber diameter
range from 18 to 23 um , FT-IR pro、 ed the gradual formation of Si-Si and Si-CH) bonds due to the
dehydrocoupling of Si-H under thermal oxidation. With increasing the thermal curing time. the thermal
stability of the pes fibers was improved ‘ and the molecular weight and molecular weight distribution were
also increased.
Acknowlegement
This present work was supported by the Nuclear R&D program from the Ministry of Education
Science and Technology, Korea
References
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Masayoshi Itoh ‘ (200 I), Application of electron beam curing for silicon carbide fiber synthesis from blend
polymer of polycarbosilane and polyvinylsilane, Radiation Physics and Chemistry, Volume 60(4-5) ‘ 483-487.
3. Kentaro Suzuya, Kaoru Shibata, Kiyohito Okamura, Kenji Suzuki, (1992), The polycarbosilane-to-SixC I-x
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4. O. Delverdier, M. Monthioux, D. Mocaer, R. Pailler, (1993), Thermal behavior of polymer-derived
ceramics. I. Si-C and Si-C-O systems from both commercial and ne、v p이ycarbosilane (PCS) precursors,
Journal of the European Ceramic Society, Volume 12( I), 27-4 1.
5. Siobhiil1 Matthews ‘ Mohan J. Edirisinghe, Michael 1. Folkes, (1999), Effect of pre-pyrolysis heat treatment
on the preparation of silicon carbide from a polycarbosilane precursor, Ceram ics International, Volume
25( I), 49-60
웅용화학, 제 12 권 제 2 호, 2008
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