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Effect of Silica on Sherulite Structure andPhoto‑oxidative Degradation Behavior in
Polypropylene/Silica Nanocomposites

Author(s)Asuka, Kazuo; Sumino, Ken‑ichi; Taniike,Toshiaki; Nitta, Koh‑hei; Terano, Minoru

Citation

Journal of Materials Life Society, 19(3): 128‑131

Issue Date

2007‑07

Type

Journal Article

Text version

publisher

URL

http://hdl.handle.net/10119/7931

RightsCopyright (C) 2007 マテリアルライフ学会. Kazuo
Asuka, Ken‑ichi Sumino, Toshiaki Taniike, Koh‑hei
Nitta, Minoru Terano, Journal of Materials LifeSociety, 19(3), 2007, 128‑131.

Description

Japan Advanced Institute of Science and Technology

[ Original Paper)

7T ~ 7 /V7 -{ 7'¥:~tB (Materiaru Raifu GakkaishD, 19 [3J

128~ 131(July 2007)

Effect of Silica on Sherulite Structure and Photo-oxidative
Degradation Behavior in Polypropylene/Silica Nanocomposites
Kazuo ASUKA**I, Ken-ichi SUMINO*\ Toshiaki TANIIKE*1
Koh-hei NITTA *2, Minoru TERANO*1(Received December 21,2006, Accepted January 12,2007)
Abstract
The physico-chemical interaction between hydrophobic polyolefin materials and originally hydrophilic inorganic
nano-particles like surface hydroxylated SiO, has not been well understood up to now. In this study, the influences of particle
size, content of hydrophilic SiO, nanoparticles on the isothermal growth rate of polypropylene (PP) spherulites in various
PP/SiO, nanocomposites were investigated by polarized optical microscope equipped with temperature controlled hot stage.
Moreover, photo-oxidative degradation behavior of the PP/ SiO, nanocomposites were investigated. It is most interesting tonote that the addition of smaller SiO, nanoparticles effectively lowered the growth rate of PP spherulites in the composites
and the spherulite growth rate became zero for the PP/16nm-SiO, nanocomposites with the SiO, content above 2.5 wt%. It
was found that the sample without spherulite morphology is more stable to photo-degradation. Spherulite structure isconsidered to have the influence affect photo-oxidative degradation.
Keywords : Polypropylene/silica nanocomposite, Photo-degradation, Spherulite

understanding of physico-chemical interactions between

1. Introduction

inorganic nano-particles and polymer matrix has been far

Nowadays, the development of various polymer-based

from being achieved. It has been reported that the mechan­. I an d th' 4) -\3) as we II as many oth er
Icaerma ipropertIes

nanocomposites with new properties has become one of theperformances 14 ), IS) could be significantly improved for

key research targets in the field of polymer materials frompolyolefm-based nanocomposites compared with the orig­

both academic and industrial points of view. It is quite

inal polyolefins.

important to develop high performance polymer-based

Environmental durability is a key feature for polyolefm­materials with various outstanding properties. One of thebased nanocomposites in their processing and usage due tomost popular procedures of synthesizing polymer-based

their degradation. There are many factors influencing thenanocomposites is to disperse various nano-sized inorganic

degradation of polyolefm materials, such as photo-irradi­

particles into polymer matrix by melt mixing. Although aation, thermo-degradation, oxidation etc., and their combi­

great number of polymer-based nanocomposites have beennations. Within the various factors, the photo- and thermal­

successfully synthesized up to nowlH\a deep mechanisticoxidation plays an important role. Thus, the study on
photo- and thermal-oxidative degradation of polyolefm"" Corresponding author* I School of Material Science Japan Advanced Instituteof Science and Technology(I-I Asahidai, Nomi, Ishikawa, 923-1292 Japan)*' Department of Chemical Engineering Kanazawa
University(Kakuma, Kanazawa, Ishikawa, 920-1192 Japan)

128materials is always attracting attention in the field ofpolymer degradation and stability.
In this work, correlation of the spherulite structure andphoto-oxidative behavior in terms of the size, content ofsilica particles were investigated.

7T ~ 7 /V7 -{ 7'¥:~tB 2007:¥ 7 jj

Effect of Silica on Sherulite Structure and Photo-oxidative Degradation behavior in Polypropylene/Silica Nanocomposites

2. Experimental

crystallization condition at the temperatures of 339, 403,
and 407K.

2.1 Materials
Isotactic PP pellets with an isotacticity index ( I.I. ) of

2.4 Photo-degradation of PP/Si02 nanocomposites

98% were donated from Japan Polypropylene Corp..

Photo-degradation experiments were conducted in theWeight average molecular weight ( Mw) and molecularweather meter at 35 DC using four 550W xenon lamps. The3

weight distribution (Mw/Mn) are 26 X 10 and 5.6, respec­

oxidative degradation behavior was measured by FT-IR.

tively. AEROSIL@ 200 Si02 with an average particle size
2of 16 nm and surface area of 200m /g was donated from

Carbonyl growth in the region 1500-1800cm -I region ofAerosil Japan Co.. NanoTek@ Si02 with an average par­2
ticle size of 26 nm and surface area of 110 m /g was

the FT-IR spectrum is determined by using carbonyl absor­
bance defmed as follow (see Fig.I).

purchased from Kanto Chemical Co..

2.2 Preparation of PP/Si02 nanocomposites
Composites were prepared by melt mixing Si02 particles
with different diameters of 16nm, 26nm and 100nm re­I­~spectively. Melt mixing was performed in twin-roller. ThePP pellets were kneaded by mixing rollers at 180 DC for 5min and then a given amount of Si02 was added into theckneaded PP. The mixture was kneaded at 180 DC for anoth­er lOmin. Then, the obtained mixture was pressed into a2flat sheet at 230 DC under a pressure of 100kg/cm for 5 minusing a compression-molding machine. Two kinds of2500 2250 2000 1750 1500 1250 1000

Wavenumber / cmFig. I750

1

Typical FT -rR spectrum of oxidized PP film.

PP/Si02 nanocomposites were prepared at the different
cooling conditions; (a) quenced at 100 DC (spherulites sam­pie), (b) quenched at 0 DC then annealed at 100 DC for 24h

3. Results and discussion

under N2 atmosphere (non-spherulites sample). The contentof Si02 in the PP/Si02 composites was changed from 0wt% to 5.0wt%.

Linear spherulite growth rate for all PP/Si02 nanocom­
posites and neat PP was evaluated by measuring spherulite
radius as a function of time. An example of the measure­

2.3 Spherulite growth behavior of PP/Si02

ment of growth rate in radial direction is shown in Fig.2,

nanocom posites

which makes the time when the growth started as theThe polarizing optical microscope (OLYMPUS, B201)

starting point of the time axis. It was possible to reliably

equipped with a Mettler FP82HT hot stage was used todetermine the growth rates of all the samples because ofexamine the isothermal crystallization processes of neat

the linear relationship between the radius of spherulites andiPP and the composites. An optical polarizing microscope

crystallization time.

was used. The hot stage was held at a steady temperature toGrowth rates measured isothermally at 403K is plotted± 0.2 K by a proportional controller. A thin sample pieceagainst the content of Si02 particles in Fig.3. The spher­were sandwiched between a microscope slide and a coverulite growth rates of PP spherulites decreased significantly

glass, heated to 503K and kept for 10 min to melt com­with increasing the Si02 content. It is interesting to note

pletely the crystallites. Then the samples were rapidlythat the addition of smaller Si02 particles effectively low­quenched to a given crystallization temperature and al­ered the growth rate of PP spherulite in the composites andlowed to crystallize isothermally. The radius of a spherulite

the spherulite growth rate became zero for the PP/16nm­

was measured as a function of time under the isothermal

Si02 nanocomposites with the Si02 content above 2.5wt%.

Materiaru Raifu Gakkaishi, Vo1.l9, No.3129

Kazuo ASUKA, Ken-ichiSUMINO, Toshiaki TANlIKE, Koh-hei NITTA, Minoru TERANO

120o pp•0.51

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Carbonyl adsorption versus degradation timefor PP and various PP/SiO, nanocomposites(SiO, content: 5 wt 'Yo).

03f

PP/26nm-Si01.... PP/16nm-SiO::::J£.

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0.35IeC),

40o pp:i~Fig.4m PPJ100nm-SiO:

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Time / h

The spherulite radius plotted against the crystallization
time for various PP/SiO, nanocomposites(SiO, content: 0.6 wt%).

c::'E,

2025101520
Time / min

12 i i i~I10oIoI

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Fig.3

Effect of the SiO, content on the spherulite
growth rates isothermally measured at 403K.

4060

80100Time/ hFig.5

Carbonyl absorbance versus degradation
time for various PPs.

Consequently, the PP/l6nm-Si02 nanocomposite films has

absorbance plotted against the photo-degradation time innon-spherulite morphology.

the weather meter. It was found that the sample without

Fig.4 shows the carbonyl index plotted against thespherulite morphology is more stable to photo-degradation.

photo-degradation time in the weather meter. The carbonyl

It seems that since the interface of spherulites did not exist

index increases with increasing the Si02 particlesize. Theand diffusion of oxygen was restricted, photo-degradation

addition of smaller Si02 particles effectively improved thestability became high.

degradation stability. The existence of spherulites mor­
phology may have the important role for the phenomena. In

4. Conclusions

addition, influence on photo-degradation for a sample withspherulite morphology and a sample without spherulite

It was found that the addition of smaller Si02 particles

morphology was investigated. Fig.S shows the carbonyl

effectively lowered the growth rate of PP spherulite in the130?T!J 7 /V7 -17~~~ 2007 fp 7 jj

Effect of Silica on Sherulite Structure and Photo-oxidative Degradation behavior in Polypropylene/Silica Nanocomposites

composites and the spherulite growth rate became zero for
the PP/16nm-SiO, nanocomposites with the SiO, content
above 2.5wfllo. Moreover, it was found that the sample
without spherulite morphology is more stable to photo­degradation. Spherulite structure is considered to have theinfluence on photo-oxidative degradation. This result indi­cates the real possibility to develop highly stable PP
materials, which have been eagerly requested from various
application areas.

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