A novel biobased plasticizer of epoxidized cardanol glycidyl ether: synthesis and application in soft poly(vinyl chloride) films

Article abstract of DOI:10.1039/c5ra07096a

A novel plasticizer derived from cardanol, and epoxied cardanol glycidyl ether (ECGE), was synthesized and characterized by ¹H-NMR and ¹³C-NMR. The effects of ECGE combined with the commercial plasticizer dioctyl phthalate (DOP), in soft poly(vinyl chloride) (PVC) films, were studied. The mechanical properties of PVC films showed both tensile strength and percent elongation increases with increasing ECGE content. Thermogravimetric analysis (TGA) was performed to characterize the thermal stabilities of the plasticized samples and showed the stability of films increased on increasing the content of ECGE. The properties of volatility, extraction, and exudation resistance of plasticizers were tested and analysis by means of solubility parameters as reported in the literature suggests the ECGE has similar or higher stability for these properties than DOP. FTIR analysis of the films also revealed that ECGE interacted with PVC. Due to its inherent chemical backbone and the modified epoxy groups, ECGE properly balanced the properties and improved the performance of PVC films compared with the neat DOP plasticizer.

Full text of DOI:10.1039/c5ra07096a

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PAPER
A novel biobased plasticizer of epoxidized cardanol
glycidyl ether: synthesis and application in soft
poly(vinyl chloride) films†
Cite this: RSC Adv., 2015, 5, 56171
c
ab
Jie Chen,‡ab Zengshe Liu, Jianchun Jiang,
Xiaoan Nie,ab Yonghong Zhouab
*
*
and Rex E. Murrayc
A novel plasticizer derived from cardanol, and epoxied cardanol glycidyl ether (ECGE), was synthesized and
1
characterized by H-NMR and 13C-NMR. The effects of ECGE combined with the commercial plasticizer
dioctyl phthalate (DOP), in soft poly(vinyl chloride) (PVC) films, were studied. The mechanical properties
of PVC films showed both tensile strength and percent elongation increases with increasing ECGE
content. Thermogravimetric analysis (TGA) was performed to characterize the thermal stabilities of the
plasticized samples and showed the stability of films increased on increasing the content of ECGE. The
properties of volatility, extraction, and exudation resistance of plasticizers were tested and analysis by
means of solubility parameters as reported in the literature suggests the ECGE has similar or higher
stability for these properties than DOP. FTIR analysis of the films also revealed that ECGE interacted with
PVC. Due to its inherent chemical backbone and the modified epoxy groups, ECGE properly balanced
the properties and improved the performance of PVC films compared with the neat DOP plasticizer.
Received 20th April 2015
Accepted 18th June 2015
DOI: 10.1039/c5ra07096a
www.rsc.org/advances
toxic effects on human health and environmental impact.5–10
For this reason, some countries have implemented restrictive
1. Introduction
regulations regarding the use of phthalates in exible PVC
products, especially the products used by children.11 The use of
phthalates is incontrovertibly becoming more limited. Hence,
there is a trend to replace phthalates by alternative plasticizers
and mixtures.12–16 Currently, there is growing interest in the
research and use of natural-based plasticizers which are char-
acterized by low toxicity and low migration levels. They mainly
include modied and epoxidized triglyceride oils from soybean
oil, linseed oil, sunower oil, glycerol monoester, and fatty acid
esters.17–20 As the plastics industry and environmental aware-
ness continues to grow, there is an urgent and unmet need to
develop new natural plasticizers with improved properties and
cost competitiveness.
Due in part to its versatile chemical structure and low cost,
cardanol can be considered to be a very promising raw-material
to develop new derived materials to be used in environmentally
friendly processes.11,21 Cardanol is an extracted product from
cashew nut shell liquid, which is one of the most commonly
used renewable agricultural resource materials.22 Cardanol and
its derivatives usually have major applications in bio-compos-
ites,23 synthetic resins,24,25 epoxy curing agents,26 and coat-
ings.27–30 Recently, cardanol has been used as a plasticizer in the
polymer and rubber industries, with or without modication,
and has shown signicant plasticizing effects.31,32 Furthermore,
cardanol-based plasticizers have been reported to be a kind of
efficient plasticizer for PVC. Greco et al.11,33 have prepared car-
danol acetate and epoxidated cardanol acetate plasticizers
Poly(vinyl chloride) (PVC) is one of the most important synthetic
resins in terms of consumption. It has been widely used in
various applications from rigid to so products because of its
high versatility, excellent durability and contamination resis-
tance.1,2 Since PVC is rigid, brittle, and has low thermal stability,
it has to be compounded with plasticizers in order to possess
the mechanical properties, process ability, and thermal stability
required for product quality specications. Consequently,
plasticizers have become the most consumable additives in
PVC. During the last decade, the worldwide production of
plasticizers was around 5 million tons per year,3 among which
phthalates play an important role and account for more than
80% due to their good performance and low cost.4 However, in
recent years, phthalates have been criticized for their potentially
aInstitute of Chemical Industry of Forestry Products, Chinese Academy of Forestry,
National Engineering Laboratory for Biomass Chemical Utilization, Key Laboratory
of Biomass Energy and Material, Nanjing, Jiangsu 210042, China. E-mail:
bio-enegry@163.com; Tel: +86 25 85482488
bInstitute of New Technology of Forestry, CAF, Beijing 100091, China
cUSDA, ARS, National Center for Agricultural Utilization Research, Bio-Oils Research
Unit, 1815 N University St, Peoria, IL, 61604, USA. E-mail: kevin.liu@ars.usda.gov;
Fax: +1-309-681-6524; Tel: +1-309-681-6104
† Mention of trade names or commercial products in this publication is solely for
the purpose of providing specic information and does not imply
recommendation or endorsement by the U.S. Department of Agriculture. USDA
is an equal opportunity provider and employer.
‡ Jie Chen is a visiting student at U.S. Department of Agriculture.
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Scheme 1 The compounds used in this study and the conversion of cardanol into ECGE.
through esterication and epoxidation modication. The Germany) at 220–230 ꢀC under 3–5 Torr. The product obtained
results indicated that the epoxidated cardanol acetate showed a was pale yellow in color, which contained 3.6% triene, 62.1%
complete miscibility with PVC, and the cardanol acetate can be diene, 25.7% monoene, and 3.1% saturated compounds.
used as secondary plasticizer of PVC and partially replace Epichlorohydrin (99%), sodium hydroxide (97+%), calcium
DEHP.
oxide (98%), benzyltriethylammonium chloride (97%),
In this study, a novel cardanol derived plasticizer, epoxidized dichloromethane (99%), and DOP (99%) were purchased from
cardanol glycidyl ether (ECGE), was synthesized through the Sigma-Aldrich Co. (St Louis, MO). 3-Chloroperbenzoic acid was
substitution of a hydroxyl group and double bonds in cardanol obtained from Anhui Wotu Chemical Co., Ltd., (Hefei, Anhui,
with a glycidyl ether group and an epoxy group. The rationale China). PVC (DG-1000K) was purchased from the Tianjin Dagu
behind designing ECGE lies in the fact that cardanol provides Chemical Co., Ltd., (Tianjin, China) with average degree of
the main chemical structure of a rigid aromatic core and exible polymerization of 1010–1050, apparent density of 0.57 g mLꢁ1
,
ꢀ
alkyl chains, which is similar to phthalate. It can be modied by volatile of 0.16%, whiteness of 80% (160 C, 10 min), residue
addition of epoxy groups to improve its compatible properties VCM content of 0.2 mg gꢁ1. Calcium stearate and zinc stearate
with PVC (Scheme 1). The ECGE was expected to improve the were supplied by Changzhou Huaren Chemical Co., Ltd.,
plasticizing effect, thermal stability and exudation resistance on (Jiangsu, China).
PVC compounds in a similar manner to commercial phthalate
and epoxy plasticizers. Another consideration is that epoxy
plasticizers are used as secondary plasticizers in so PVC34
because they contain unreacted double bonds. Hydroxyl groups
formed via epoxidation hydrolysis might increase the migration
of the plasticizer from PVC products when used in large
amounts. Therefore, we focused on the effects of the partial
substitution of ECGE for dioctyl phthalate (DOP) in so PVC
lms. Moreover, the mechanical properties, thermal behaviors,
and exudation resistance properties of plasticized PVC lms
were investigated.
2.2 Preparation
2.2.1 Preparation of ECGE. To a 250 mL ask equipped
with a magnetic stirrer, reux condenser and thermometer
were charged: 5.00 g (17 mmol) of CD, 12.25 g (132 mmol) of
epichlorohydrin, and 0.09
triethylammonium chloride. The nal mixture was slowly
g
(0.485 mmol) benzyl-
Table 1 Formulation of the soft PVC films
Formulations
Component
S0
S1
S2
S3
2. Experimental
PVC (g)
ECGE (g)
DOP (g)
Calcium stearate (g)
Zinc stearate (g)
100.00
0.00
40.00
1.50
100.00
4.00
36.00
1.50
100.00
8.00
32.00
1.50
100.00
12.00
28.00
1.50
2.1 Materials
Cardanol was procured from Shanghai Meidong Biological
Materials Co., Ltd. (Shanghai, China) and was puried by
distillation using a Pascal 2105 SD vacuum pump (Asslar,
0.50
0.50
0.50
0.50
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heated to 95 ꢀC and remained at that temperature for 2.5 h.
Hardness of specimens was measured using Rex Gauge H-
Aer the mixture was cooled to 60 ꢀC, 0.66 g (0.017 mmol) 1000-SP Shore A Durometer (Buffalo Grove, IL). Five measures
sodium hydroxide and 1.23 g (0.017 mmol) calcium oxide were were performed to obtain an average value.
ꢀ
added. The reaction was allowed to continue at 60 C for 3 h.
Volatility property was evaluated by placing a PVC sample (20
The excess and unreacted epichlorohydrin, which is moderately mm ꢂ 20 mm ꢂ 1 mm) were placed in a convection oven
toxic, could be recycled and reused by distillation from the (Waltham, MA) at 70 ꢀC for 24 h and cooled to RT in a desiccator
crude product. Therefore even if scale-up the process the for 2 h. The weight changes were measured before and aer the
toxicity of product and environmental pollution could be heating.
reduced. Aer the solids were ltered, 5.22 g cardanol glycidyl
The extraction resistance to water, hexane, NaOH, and acetic
ether (CGE) was obtained. Next, 3.57 g (10 mmol) CGE was acid were measured. The samples (20 mm ꢂ 20 mm ꢂ 1 mm)
added in a 100 mL three-necked round bottom ask equipped were soaked in water, hexane, 5% (w/w) NaOH, and 4% (w/w)
with a magnetic stirrer, thermometer sensor and reux acetic acid at 23 ꢀC for 24 h. Aer being rinsed with owing
condenser. A mixture of 15 g (176 mmol) dichloromethane and water, the samples were dried in a convection oven (Waltham,
ꢀ
2.59 g (15 mmol) 3-chloroperbenzoic acid was added slowly into MA) at 30 C for 24 h. The weight losses before and aer the
the ask. The resultant solution was allowed to react at 30 ꢀC for dipping were measured.
3 h. Aer the reaction was complete, the crude product was
Exudation of the plasticizer was evaluated by placing a
ltered and washed with a saturated solution of sodium sulte, sample (20 mm ꢂ 20 mm ꢂ 1 mm) between two pieces of lter
sodium bicarbonate, and sodium chloride solution, respec- paper. These systems were then placed in a convection oven
tively. Finally, the organic phase was dried with anhydrous (Waltham, MA) at 40 ꢀC for 72 h. The weights of the lms were
magnesium sulfate and then ltered. The ltrate was distilled measured aer washing the surfaces of the lms with acetone
under vacuum to recycle the dichloromethane and 3.29 g and drying at RT. The weight changes before and aer washing
yellowish liquid was obtained (yield: 78% relative to cardanol). were calculated.
The ECGE has a density of 1.03 g cmꢁ3, epoxy value of 5.87%
Thermogravimetric analysis (TGA) was carried out on a Q500
and acid value of 0.72 mg gꢁ1. The main byproduct of the TGA (TA Instruments, New Castle, DE). Each sample was scan-
epoxidation process was chlorobenzoic acid which is an organic ned from ambient temperature to 400 or 600 ꢀC at a heating rate
intermediate with moderately toxic. The dichloromethane is of 5, 10, 15, 20, and 25 C minꢁ1, respectively. The TGA exper-
ꢀ
low toxicity and can be recycled. Although the epoxidation using iment was performed under a 60 mL minꢁ1 nitrogen ow. The
the 3-chloroperbenzoic acid as oxygen source is efficient and kinetic parameters such as activation energy (Ea, kJ molꢁ1) and
relatively green, more attention should be paid to the safety pre-exponential factor (A) were evaluated by the Kissinger
issue of the 3-chloroperbenzoic acid when scale-up.
equation:
ꢀ
ꢁ
2.2.2 Preparation of plasticized PVC test specimens. A
series of plasticized PVC specimens with different plasticizers
at different concentrations were prepared. The compositions
b
AR Ea
ꢁ
1
ln
¼ ln
(1)
2
Ea
R Tmax
Tmax
are shown in Table 1. First, PVC powder (100 g), plasticizers (40 where R ¼ gas constant (8.314 J molꢁ1 K). Eqn (1) indicates that
g), and thermal stabilizers (2.0 g, Ca soap/Zn soap ¼ 3/1) were ln(b/Tmax2) and 1/Tmax are in a linear correlation. E and A can be
mixed using a mechanical mixer at room temperature (RT) for calculated from the slope (a) and intercept (d) on the curves of
ln(b/Tmax2) change versus 1/Tmax
.
5 min. Second, the mixture was compounded into a homoge-
neous mixture at 160 ꢀC for 5 min by a Plasti-Corder
Lab-Station (South Hackensack, NJ). Finally, the lms were
madꢀe using a Carver 3969 mini hot press (Wabash, IN) at
170 C for 5 min.
Ea ¼ ꢁa$R
(2)
(3)
ꢀ
ꢁ
Ea
R
lnðAÞ ¼ d þ ln
2.3 Characterizations
1H and 13C NMR spectra of the compounds in deuterated
chloroform (CDCl3) were recorded with a Bruker 400 MHz
spectrometer (Bruker, Rheinstetten, Germany) at RT.
3. Results and discussion
3.1 Characterization
1
Fourier transform infrared (FTIR) analysis was conducted Fig. 1 and 2 display the NMR and 13C NMR of cardanol and
using a Thermo Nicolet Nexus 470 spectrometer (Thermo ECGE, respectively. The characteristic peaks at 6.7–7.3 ppm
Scientic, Madison, WI). The samples were scanned from 4000 correspond to the proton on the benzene ring. Compared to the
to 500 cmꢁ1
.
spectrum of cardanol (Fig. 1(a)) and ECGE (Fig. 1(b)), the peaks
Tensile test was measured according to ASTM standard at 5.2–5.5 ppm, corresponding to the proton of –CH]CH– and
D638, type V, using an Instron 4201 equipped with a 1 kN –OH, have almost disappeared. This indicates that the phenolic
electronic load cell. The cross-head speed was set at 10 mm hydroxyl group and unsaturated double bonds on the side chain
minꢁ1. All samples were conditioned at 23 ꢀC and 50% humidity have been converted. Additionally, the new peaks at 2.76, 3.38,
for 1 day prior to tensile testing. Five sample pieces were 4.00, and 4.20 ppm indicate the existence of a glycidyl ester in
prepared from each group to obtain an average value.
ECGE.35 Furthermore, the peaks at 2.9–3.1 ppm corresponding
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Fig. 1 1H NMR spectra of (a) cardanol and (b) ECGE.
to the proton of the –CH–O–CH group have appeared on the 1H PVC molecule, reducing the PVC–PVC interactions at sites
NMR spectrum of ECGE, also indicating the occurrence of where polymer chains could associate37 (as shown in Fig. 3), and
epoxidation. The changed chemical shi of the peaks at 1.2–1.8 increasing the space between polymer molecules. Furthermore,
ppm also supports the production of epoxidized groups aer the motion of long alkyl chains of ECGE will also create more
the epoxidation reaction. The 13C NMR chemical shi peaks at free volume in the polymer. Compared with pure DOP, added
126.44–137.11 ppm are present in Fig. 2(a) but have dis- ECGE will increase the random motion of the PVC chains in the
appeared in the spectrum shown in Fig. 2(b). Likewise, the non-associated regions of the polymer, as well as the volume of
glycidyl ester group and the –CH–O–CH group are distinct the amorphous part of the plasticized exible PVC. Aer adding
between cardanol and ECGE. The chemical shis of the three 10% ECGE, the percent elongation of lm S1 is greatly improved
carbons in the glycidyl ester group occurred at 44.90, 50.24, and to 969.19%, showing 16.48% more exibility when compared to
68.60 ppm, respectively.36 The new peaks at 56.91 ppm corre- pure DOP and PVC. However, continued increasing of the ECGE
spond to the carbons in the –CH–O–CH group.
concentration slightly decreases the percent elongation. This
may be due to a measurement error,38 but still implies that the
inuence of exible alkyl chains might be balanced with that of
the rigidity group when 30% ECGE was added. Hence, it can be
concluded that the ECGE showed higher plasticization effi-
ciency than DOP, and lm S2 showed the highest percent
elongation value of 981.58%. In other words, much less plasti-
cizer of this formulation is needed in order to get the same
elongation value as lm S0.
Young's modulus dropped in lms S1–S3 compared with
that of lm S0, indicating the rigidity decreased with the
introduction of ECGE. It attributed to the higher efficiency of
ECGE on enhancing the free volume of the amorphous part in
the exible product. On the other hand, with the increase of
ECGE content, more rigid groups were present and the Young's
3.2 Mechanical properties
The changes in tensile strength, percent elongation, Young's
modulus and Shore hardness of the obtained plasticized PVC
samples are shown in Table 2. It is observed that almost all the
properties of lms S1–S3 increased with the increasing of ECGE
content. Moreover, compared with lm S0, lms S1–S3 have
better tensile strength, percent elongation, and toughness
properties, but poor Young's modulus properties. These results
might be attributed to the molecular features of the plasti-
cizers.11,37 By having a higher ECGE content, more polar groups
(e.g., epoxy, aromatic ring, terminal glycidyl ether) and longer
alkyl chains are incorporated into the PVC matrix. The polar
groups of the plasticizers interact with the polar parts of the
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Fig. 2 13C NMR spectra of (a) cardanol and (b) ECGE.
modulus relatively increased within lms S1–S3, indicating the mechanical research results suggest that ECGE can endow PVC
high content ECGE can bestow upon the plasticized PVC with a resin with well-balanced properties of exibility, toughness,
relative high level of rigidity.
strength and hardness, and can improve the applicability of the
Table 2 also shows the tensile strength increased with the nished exible product.
increase of ECGE concentration, indicating the enhancement of
the strength of the PVC matrix. Film S3 has the highest tensile
3.3 Material characterization by FTIR
strength of 24.383 MPa, which is 6.46% higher than lm S0.
This result corresponded to Bargellini's report that the tensile
strength is related to the magnitude of the plasticizers
polarity,2,37 which also changed with the plasticizers propor-
tions. It can be concluded that the addition of ECGE provides
not only a signicant improvement in exibility and toughness,
but also an improvement in the strength of PVC compounds.
Furthermore, Table 2 indicates that the lms contain ECGE
show slightly lower hardness than that of S0, which means they
still have relatively good wettability and long life. All the
FTIR spectra of the PVC lm samples were obtained and are
shown in Fig. 4. The FTIR spectra shied according to chemical
compound and can indicate the interaction between the plas-
ticizers and PVC.39 In the spectrum of lm S0, there are some
characteristic peaks: C]O stretching at 1721, C]C aromatic
stretching at 1599 and 1578 cmꢁ1, CH2–Cl angular deformation
at 1427 cmꢁ1, CH3 and CH2 groups deformation at 1379 and
1331 cmꢁ1, CH–Cl out of plane angular deformation at 1257
cmꢁ1, C–H aromatic deformation at 1270 and 1118 cmꢁ1, C–O
stretching at 1122 and 1073 cmꢁ1, C–H out of plane trans
Table 2 Results obtained from tensile measurements and shore hardness
Tensile strength
Sample
(N mmꢁ2
)
Percent elongation (%)
Young's modulus (MPa)
Shore hardness (HA)
S0
S1
S2
S3
22.90 ꢃ 1.51
22.87 ꢃ 0.46
24.25 ꢃ 0.45
24.38 ꢃ 0.68
832.05 ꢃ 46.29
969.19 ꢃ 21.52
981.58 ꢃ 48.63
981.53 ꢃ 36.32
5.98 ꢃ 0.23
4.99 ꢃ 0.092
5.11 ꢃ 0.125
5.17 ꢃ 0.10
91.4 ꢃ 0.29
91.0 ꢃ 0.51
91.0 ꢃ 0.22
91.1 ꢃ 0.20
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Fig. 3 Possible interaction between ECGE and PVC molecular in the plasticized system.
deformation at 960 cmꢁ1, and C–Cl bond stretching at 833, 694, Second, the absorption frequencies of the glycidyl ether group
and 615 cmꢁ1. These bonds are in accordance with data found and epoxide groups in ECGE shied from 910–855 cmꢁ1 to
in the literature for PVC.40 Aer the incorporation of ECGE into 858 cmꢁ1. This phenomenon can be mainly attributed to the
the formulations, two obvious variations have been found in the formation of the hydrogen bonds between the polar parts of
spectrum of lms S1–S3. First, the characteristic features of the ECGE (benzene ring, glycidyl ether group and epoxy groups) and
CH–Cl gradually shied lower (maximum 3 cmꢁ1 lower) with the PVC (carbon–chloride bond). This is consistent with Fig. 3,
the increase of ECGE content. This result can be explained by therefore, it can be concluded that the mixed plasticizers of
eqn (4) derived from Hooke's law:41
ECGE and DOP can interact with PVC as expected.
rffiffiffiffi
1
k
n ¼
(4)
3.4 Thermal stability and degradation kinetics
2p
m
Fig. 5 shows the TGA curves of the S0, S1, S2, and S3 lms
where v is the vibration frequency, k is the force constant, and m
is the mass. Eqn (4) shows the relationship of force constant to
the wave number (vibration frequency). As the wave number
decreases, the force constant decreased, indicating the inter-
molecular bonding force of PVC–PVC was weakened when the
polar functional groups in ECGE interacted with the PVC.
heated in nitrogen at the rate of 10 C minꢁ1. It was observed
ꢀ
from the TGA curves that all the samples are thermally stable in
nitrogen gas below 190 ꢀC and mainly displayed three-stage
thermal degradation above this temperature. The rst stage
degradation (about 220–340 ꢀC) is the fastest and corresponded
to dechlorination of PVC, with formation and stoichiometric
Fig. 4 FTIR spectra of PVC films with different plasticizers.
56176 | RSC Adv., 2015, 5, 56171–56180
Fig. 5 TGA curves of PVC films at a heating rate of 10 ꢀC minꢁ1
.
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Table 3 The thermal degradation parameters and kinetic parameters for the PVC samples
Ea (kJ molꢁ1
)
ln A
R2
a
a
Sample
Tia (ꢀC)
T10 (ꢀC)
T50 (ꢀC)
Equations
S0
S1
S2
S3
194.01
198.68
199.86
200.03
242.57
251.63
256.24
263.46
291.28
303.03
305.10
308.15
y ¼ 10.22475 ꢁ 11.36278x
y ¼ 12.02394 ꢁ 12.66175x
y ¼ 14.08981 ꢁ 13.60553x
y ¼ 14.84261 ꢁ 14.18513x
94.47
105.27
113.12
117.94
12.66
14.56
16.70
17.49
0.98348
0.98037
0.98985
0.98040
Values of 10 ꢀC minꢁ1. Ti: onset temperature of TGA.
a
elimination of HCl and a few chlorinated hydrocarbons.36 In the maximum increase of 27.77 ꢀC and 16.87 ꢀC in T10 and T50
second stage of degradation (about 340–420 ꢀC), the weight was respectively. This may be mainly due to the multi epoxy groups
almost stable, which may be associated with the formation of of ECGE which can scavenge for HCl and delay the degradation
aromatic compounds by the cyclization of conjugated polyene events.45–47
sequences.42,43 In the last stage (>420 ꢀC), the third degradation
Fig. 6 shows the TGA and DTG thermograms of the samples
ꢁ1
ꢀ
was shown. It is mainly contributed to the degradation of the heated in nitrogen at several heating rates from 5 C min to
complex structures resulting from aromatization, escaping 25 ꢀC minꢁ1. It can be clearly seen that the thermal degradation
olens and a few HCl.43,44 Furthermore, the TGA characteristic curves of the samples shied to higher temperatures with
temperatures of PVC lms are illustrated in Table 3, including increasing the heating rates. The kinetic parameters calculated
the onset, 10% and 50%, weight loss temperatures (T10 and T50
)
from the Kissinger method48 for the samples are summarized in
for the degradation. Clearly, ECGE improves the thermal Table 3. It was found that the Ea values of different formulations
stability of PVC lms, and an increase in ECGE content gener- followed the order of the samples S3 > S2 > S1 > S0. Generally, a
ally results in a higher increase in thermal stability. Compared higher Ea suggests a higher thermal degradation resistance. The
with sample lm S0, the lms modied by ECGE had a increase in the Ea could be explained by the enhancement of the
Fig. 6 TGA and DTG curves of the PVC films at different heating rates: (a) S0, (b) S1, (c) S2, (d) S3.
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intermolecular distance and chain mobility.49 Hence, ECGE in
small amounts could increase the thermal stability of the PVC
matrix effectively.
Table 4 Solubility parameters for PVC and plasticizers
Items
d (J cmꢁ3 1/2
)
DS (J cmꢁ3 1/2
)
PVC
DOP
ECGE
Mixed plasticizer of S1
Mixed plasticizer of S2
Mixed plasticizer of S3
9.66 (ref. 51)
8.89
9.11
8.91
8.93
—
3.5 Volatility, extraction, and exudation resistance
0.77
0.55
0.75
0.73
0.71
The weight losses of the PVC lms by volatilization, exudation
and extraction in water, hexanes, 5% (w/w) NaOH, and 4% (w/w)
acetic acid are shown in Fig. 7. These properties of the plasti-
cizers from the polymer were strongly dependent on the
molecular weight, solubility, compatibility, and chemical
structure of the plasticizers.29
8.95
In addition, the solubility parameters of mixed plasticizers
can be calculated according to the additivity rule:52
The volatilization loss decreased in the samples in the
following order: S0, S1, S2, and S3. Since the mixed plasticizers
have a similar molecular weight as the pure DOP, the volatili-
zation was mainly effected by the chemical structure of the
plasticizers.50 ECGE has stronger interactions with PVC than
DOP because of the polar functional groups of the glycidyl ether
group and epoxy group on the side chain; therefore, it can be
concluded that the volatilization resistance of PVC lms can be
improved signicantly by substituting ECGE for DOP.
Furthermore, with the substitution of a small amount of
ECGE into DOP, the resistance of extraction by hexanes, 5%
(w/w) NaOH, and 4% (w/w) acetic acid was better than that of
samples using pure DOP, but water resistance was the
opposite. Films S1–S3 exhibited similar exudation resistance
to lm S0. These results can be attributed to the intermo-
lecular interaction and compatibility between mixed plasti-
cizers and PVC, which can be inferred according to the
solubility parameter theory. The solubility parameter of PVC
and plasticizer can be determined using the Small eqn (5),
which is more accurate for plasticizers in low molecular
weight.51
n
X
dmix
¼
Fi; 2di; 2
(6)
i¼1
n
X
Fi; 2 ¼ 1
(7)
i¼1
where d is the solubility parameter, DE is energy of vaporization,
Vi is molar volume, and Fi is the molar attraction constant. r and
M are the density and molecular weight of the plasticizer or
chain unit of the polymer, respectively. Fi,2 and di,2 are the
volume fraction and solubility parameter of the component i,
respectively.
Furthermore, according to van Krevelen,52 good solubility
between polymer and plasticizers occurs when the difference in
value of the solubility parameter (eqn (8)) is as small as possible:
DS ¼ dPVC ꢁ dPlasticizer
(8)
where dPVC and dPlasticizer denotes the solubility parameter of the
polymer and plasticizer, respectively.
X
X
ꢂ
ꢃ
The value of different terms calculated according to eqn (5),
(6) and (8) are reported in Table 4. It can be seen that the DS of
ECGE is lower than that of pure DOP and mixed plasticizers,
indicating a good miscibility between ECGE and PVC due to the
high polar group content for ECGE. The substitution of DOP
with ECGE leads to a decrease of the polar group contribution.
Consequently, the solubility parameters of mixed plasticizers
are lower than that of ECGE, although higher than that of DOP.
This explains why the weight loss of extraction by organic
solvent and acid–base solvent, as well as the volatilization of
plasticized PVC, were improved with the substitution of a small
amount of ECGE into DOP. Furthermore, since the DS values of
lms S1–S3 and pure DOP did not vary signicantly, the
exudation resistances of all the samples were at similar levels.
1=2
Fi
r
Fi
DE
1=2
d ¼ ðCEDÞ
¼
¼
¼
Vi
Vi
M
X
X
X
x1
F1 þ x2
F2 þ .xn
x1V1 þ x2V2 þ .xnVn
Fn
¼
(5)
4. Conclusions
In the present study, a novel natural plasticizer, epoxidized
cardanol glycidyl ether (ECGE), was synthesized from cardanol
and incorporated into so PVC lms to evaluate its effects on
partially replacing the commercial plasticizer DOP. The plasti-
cizing performance of ECGE modied PVC lms was mainly
evaluated by the analysis of exibility, toughness, strength,
thermal stability, and compatibility compared with those of
Fig. 7 Weight losses of PVC films after volatilization, extraction and
exudation testing.
56178 | RSC Adv., 2015, 5, 56171–56180
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DOP. The mechanical properties revealed that the incorpora- 18 D. Yang, X. Peng, L. Zhong, X. Cao, W. Chen, X. Zhang, S. Liu
tion of ECGE could signicantly increase the exibility and and R. Sun, Carbohydr. Polym., 2014, 103, 198–206.
toughen the PVC lms. The results of TGA showed the thermal 19 O. Fenollar, D. Garcıa, L. Sanchez, J. Lopez and R. Balart, Eur.
stability of PVC lms increased with increasing the content of Polym. J., 2009, 45, 2674–2684.
ECGE. The volatility, extraction and exudation resistance tests 20 B. Garg, T. Bisht and Y.-C. Ling, RSC Adv., 2014, 4, 57297–
suggested the ECGE has similar or higher stability on those 57307.
properties than that of DOP. Thus, it can be concluded that the 21 C. Voirin, S. Caillol, N. V. Sadavarte, B. V. Tawade,
´
´
´
ECGE can partially replace DOP in so PVC lm formulations,
and could allow the production of highly effective, lower cost,
and more eco-friendly products.
B. Boutevin and P. P. Wadgaonkar, Polym. Chem., 2014, 5,
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22 B. Rao and A. Palanisamy, Eur. Polym. J., 2013, 49, 2365–2376.
23 A. Barreto, D. Rosa, P. Fechine and S. Mazzetto, Composites,
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Acknowledgements
24 R. Yadav and D. Srivastava, Eur. Polym. J., 2009, 45, 946–952.
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The authors are grateful for the nancial support from basic
research funding earmarked for the National Commonwealth
Research Institute, Chinese Academy of Forestry (Grant
number: CAFINT2014C12), and the National “Twelh Five-
Year” Plan for Science and Technology Support (Grant number:
2014BAD02B02). The authors also gratefully acknowledge Mr
Daniel Knetzer for help in DMA and TGA analysis and Mrs Kathy
Hornback for help in preparing PVC test specimens.
28 M. Kathalewar and A. Sabnis, J. Coat. Technol. Res., 2014, 11,
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