study on a novel ion-conductive compound plasticizer for soft and antistatic pvc materials
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Study on a Novel Ion-Conductive Compound Plasticizerfor Soft and Antistatic PVC Materials
Jiliang Wang, Wanqing Yang, Jingxin LeiState Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University,Chengdu 610065, China
Ion-conductive plasticizers (ICP) composed of dibutylphthalate (DBP) and butyl 2-poly(ethylene glycol) phthal-ate (BPEGP)/lithium bisoxalato borate (LiBOB) were suc-cessfully synthesized. The composites blended of poly(vinyl chloride) (PVC) and ICP were fabricated in a Haaketorque rheometer. FTIR, surface resistivity measure-ment, and mechanical test were used to investigate thecomprehensive properties of the PVC/ICP composites.The results show that all the synthesized ICP can reducethe surface resistivity of the PVC/ICP composites to105 V sq21 orders of magnitude as the content of ICPreaches 50 phr. The increasing temperature enhancesboth the mobility of PEG molecular chains and the diffu-sion of lithium cations, and thus effectively improves theantistatic ability of the PVC/ICP compounds. With twoexceptions of PVC/ICP compounds which include thosemade of PEG800 and PEG1000, the temperature depend-ence of the surface resistivity of PVC/ICP does not obeythe Arrhenius relationship. The introduction of ICP intoPVC matrix would improve the antistatic ability of thecomposites remarkably. Meanwhile, the mechanicalproperties of the composites are reduced to some rea-sonable extent. POLYM. ENG. SCI., 50:57–60, 2010. ª 2009Society of Plastics Engineers
INTRODUCTION
Poly(vinyl chloride) (PVC) is one of the most common
commodity plastics, which has been widely used in the
automobile, building construction, packaging fields, etc.,
because of its low cost, easy method of preparation, and
the broadening of the properties range [1–3].
The surface resistivity of typical PVC ranges from
1013 to 1016 O sq21, which would limit its large applica-
tions in some special fields, in which the antistatic ability
is required. To enhance the antistatic ability of PVC com-
posites, both antistatic agents, including ionic and non-
ionic surfactants, and conductive fillers such as carbon
blacks, metal fibers, are commonly used [4–6]. Unfortu-
nately, the former cannot endow the compounds with per-
manent antistatic ability, the latter suffers the problem of
filler migration or metal decay in polymer matrix and sur-
face, which would bring about the damage to electronic
devices and reduce the usage of the end products [7].
Moreover, the color of the PVC composites filled with
traditional conductive fillers is too black, and thus it is
difficult to obtain a colorless product by this method.
Dioctyl phthalate and dibutyl phthalate (DBP) are the
most common plasticizers for the preparation of semi-soft
to all-soft PVC composites. However, it seems that a par-
ticular plasticizer with some extent permanent ion-con-
ductive ability (or so-called in situ) has not been previ-
ously reported. In this article, we have developed a novel
transparent ion-conductive plasticizer (ICP) composed of
DBP and butyl 2-poly(ethylene glycol) phthalate
(BPEGP)/lithium bisoxalato borate (LiBOB) with neither
traditional antistatic agents nor conductive fillers. The
synthesized BPEGP owns both the similar molecular
structure with DBP to ensure their compatibility and the
coordination ability to coordinate with lithium cations.
FTIR, surface resistivity measurement, and mechanical
properties of the PVC/ICP composites were studied.
EXPERIMENTAL
Materials
DBP was purchased from Qilu Petrochemical
(Shandong, China), and used without further treatment.
Poly (ethylene glycol) (PEG), supplied by Kelong Chemi-
cal Reagent (Chengdu, China), was dried under vacuum
at 608C for 24 h before use. LiBOB was synthesized by
the method referred in the literature [8]. All the other
chemicals used in this experiment were analytically pure.
PVC (SG-II) and compound stabilizer (Baeropan SMS
318) were provided by Tianyuan (Yibing China) and
Baerlocher (Germany), respectively.
Synthesis of the Ion-Conductive Plasticizer
All the ion-conductive plasticizers (ICP) were synthesized
by the ester-exchange reaction at 1808C under the protection
Correspondence to: Jingxin Lei; e-mail: jxlei@scu.edu.cn
DOI 10.1002/pen.21510
Published online in Wiley InterScience (www.interscience.wiley.com).
VVC 2009 Society of Plastics Engineers
POLYMER ENGINEERING AND SCIENCE—-2010
of nitrogen, in which 2-ethyl-hexanoic acid tin salt was used
as the catalyst. When the theoretically stoichiometric butanol
was obtained by distillation from the reactor, heating was
stopped for �30 min and then continued to maintain the tem-
perature at around 808C. The sets content of LiBOB and DBP
were added into the reactor under vigorous stirring for 1 h,
the resulting compound was filtered and the slimy filtrate was
used as the end plasticizer. The synthesis route of BPEGP
was shown in Scheme 1.
Preparation of the Antistatic PVC/ICP Composites
PVC (100 phr) powder, synthesized ICP (50 phr), and
the compound stabilizer (5 phr) were mixed in a high-
speed mixing chamber at room temperature for 5 min, the
mixing speed was 1500 rpm. The resulting mixture was
dried at 608C for a given time (more than 2 h) until ICP
penetrated into the PVC matrix sufficiently, and then used
to prepare the PVC/ICP composites in a Haake torque
rheometer equipped with an electrically heated mixing
head and two noninterchangeable rotors. The processing
temperature, rotor speed, and blending time were set at
1608C, 30 rpm, and 8 min, respectively.
Characterization
FTIR Analysis. Pure DBP, synthesized BPEGP, and Liþ
coordinated BPEGP were characterized by using a Nicolet560
FTIR spectrometer with a resolution setting of 4 cm21. The
scanning range was altered from 400 to 4000 cm21.
Conductivity Measurement. A surface resistivity meter
(ZC46A, Shanghai, China) was used to measure the sur-
face resistivity of the PVC/ICP composites at ambient
environment. The surface resistivity was also measured
from 30 to 908C under a low relative humidity (RH) of
12% by using the same instrument. The 1-mm thick
sheets of the PVC/ICP composites were prepared by using
compression molding at 1808C, and then used for the con-
ductivity measurements.
Tensile Tests. The sheets which were prepared for the
surface resistivity measurement were also used for the
tensile tests by using an Instron4302 at a tensile rate of
100 mm min21, and the dimensions 25 mm 3 6 mm 3 1
mm dumbbell samples were prepared for tests.
RESULTS AND DISCUSSION
FTIR Spectroscopy
The ester exchange reaction and the coordination effects
between ethylene oxide (EO) groups and Liþ ions (EO/Li ¼6/1) are confirmed by infrared spectroscopy illustrated in Fig.
1a for pure DBP, and in Fig. 1b and c for the synthesized
BPEGP and Liþ ions coordinated BPEGP compound ICP,
respectively. Figure 1a shows typical DBP spectra without an
absorption band at near 3479 cm21, which is the characteristic
absorption band of the ��OH asymmetric stretching of PEG
end groups. In Fig. 1b, an obvious absorption band at 3479
cm21 is observed. Furthermore, the intensity of the absorption
band at around 1119 cm21 originating from the
��C��O��C�� stretching in PEG ethylene oxide groups
increases. The characteristic features belong to the ��CH2��and ��CH3 groups at near 2870, 2960, and 1459, 1351 cm21
are also observed. The characteristic spectra in Fig. 1b indi-
cate that the ester exchange reactions between DBP and PEG
have taken place successfully.
FTIR analysis is also used to investigate the interac-
tions between polymer molecular chains, having ether (or
ester) oxide groups, and alkali salts [9–11]. The wave
number of the carbonyl stretching is found to remain at
near 1726 cm21 in Fig. 1c, indicating that the Liþ ions
are almost not coordinated with the carbonyl groups of
BPEGP. The changes of absorption bands at about 1351
and 1119 cm21 imply that Liþ ions in this system prefer-
entially coordinate with ether oxygen groups of the PEG
SCHEME 1. Schematic synthesis route of the ionic-conductive plasticizer.
FIG. 1. FTIR of (a) pure DBP, (b) synthesized BPEGP, and (c) BPEGP
coordinated with LiBOB.
58 POLYMER ENGINEERING AND SCIENCE—-2010 DOI 10.1002/pen
molecules, which is in good agreement with the analysis
in the early reported literature [12].
Surface Resistivity Measurement
The effect of molecular weight (MW) of PEG used in
the ester exchange reaction on the surface resistivity of
the PVC/ICP composites are shown in Fig. 2. As can be
seen from Fig. 2, the surface resistivity of the composites
without BPEGP/LiBOB reaches 1013 O sq21 orders of
magnitude. All the synthesized BPEGP/LiBOB plasticiz-
ers with different MWs (400–1000 g/mol) are able to
effectively reduce the surface resistivity of the PVC/ICP
compounds to about 5 3 105 O sq21 at ambient environ-
ment. The surface resistivity of the PVC/ICP composites
ranges from 5.15 to 5.75 3 105 O sq21 as MW of PEG
alters from 400 to 1000 g/mol, revealing that MW of
PEG in BPEGP is not the most important factor affecting
the surface resistivity of the PVC/ICP composites. The
reason behind this is probably accounted for the fact that
the ratio of EO/Li in all ICP samples is a constant (6/1),
and this ratio is not fluctuated with the increase in MW.
Figure 3 demonstrates the effect of temperature on the
surface resistivity of different PVC/ICP blends under a
RH of 12%. The experimental data indicate that the sur-
face resistivity of all samples apparently decreases with
increasing temperature. It can be attributed to the fact that
both the mobility of PEG molecular chains and the diffu-
sion of lithium salts enhance with temperature, which will
be greatly favorable to the enhancement of the antistatic
ability. Figure 3 also reveals that with two exceptions of
PVC/ICP compounds which include those made of
PEG800 and PEG1000, the relationship between tempera-
ture and the surface resistivity of PVC/ICP does not obey
the Arrhenius equation. Moreover, over the whole
testing temperature range, it is evident that the surface
resistivity of the PVC/ICP composites prepared by using
PEG1000 based ICP is higher than that prepared by
PEG800 based ICP.
Tensile Strength and Elongation at Break Results
To find out the effect of MW of PEG on the mechani-
cal properties of the PVC/ICP composites, the tensile
strength and elongation at break tests were carried out at
ambient environment. As can be seen from Fig. 4, when
the MW of PEG is lower than 800, the increasing MW
decreases the tensile strength of the PVC/ICP compounds
from 22 to 11 MPa. The tensile strength of all samples
except for BPEGP prepared by PEG400 is lower than that
of the pure DBP-plasticized PVC material whose tensile
strength approaches 19.8 MPa. On the other hand, the
elongation at break of all PVC/ICP samples blended of
different MWs of PEG is not so good in comparison with
that of the PVC/DBP (100 phr/50 phr) compounds. The
elongation at break of the composites increases from
109.23 to 155.49% when the MW of PEG increases from
400 to 1000 g/mol. The probable reasons behind the me-
chanical properties reduction mentioned earlier are prob-
ably accounted for:
FIG. 2. Effect of the molecular weight of PEG on the surface resistiv-
ity of the PVC/ICP composites.
FIG. 3. Effect of temperature on the surface resistivity of the PVC/ICP
composites.
FIG. 4. Effect of molecular weight on the mechanical properties of the
PVC/ICP composites.
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2010 59
1. The content of ICP which includes pure DBP and
BPEGP/LiBOB is too large to maintain an optimum
mechanical property of the PVC/ICP blend.
2. The existence of a concentrated alkali salt (EO/Li
¼ 6/1) may weaken the interactions between the
plasticizer and the PVC polymeric matrix, which will
also influence the mechanical properties remarkably.
The relevant mechanism of that can be illustrated in
Scheme 2.
CONCLUSIONS
BPEGP can be successfully synthesized by ester
exchange reaction of DBP and PEG with different molec-
ular weights. ICPs blended of DBP and the synthesized
BPEGP/LiBOB are able to efficiently reduce the surface
resistivity of the PVC/ICP composites to 105 O sq21
orders of magnitude as BPEGP/LiBOB reaches 25 phr.
The surface resistivity of the PVC/ICP compounds having
an ion-conductive ability is able to be reduced 1 or 2
orders of magnitude as the temperature ranges from 30 to
908C. The introduction of the ion-conductive plasticizer
(i.e., BPEGP/LiBOB) to PVC matrix leads to the reduc-
tion of the mechanical properties of the composites. How-
ever, such ICPs are able to be used for the preparation of
many soft PVC products, especially, which need the per-
sistent antistatic ability and good appearances of the end
manufactures. Furthermore, we are endeavoring to over-
come the mechanical properties reduction of the PVC/ICP
composites by using more suitable molecular design and
selecting a moderate salt concentration. And we have al-
ready developed a superior PVC/ICP (100 phr/60 phr)
compound with both lower surface resistivity (about 107
O sq21) and excellent mechanical properties which almost
obtain the level of pure DBP-plasticized PVC composites.
The relevant details will be reported later.
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SCHEME 2. Schematic interactions among lithium cations, DBP, and
BPEGP.
60 POLYMER ENGINEERING AND SCIENCE—-2010 DOI 10.1002/pen
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