Organosilicone modified styrene-acrylic latex:preparation and application
Xiaoyan Qian • Aiping Zhu • Lijun Ji
Received: 27 May 2012 / Revised: 4 January 2013 / Accepted: 6 March 2013 /
Published online: 15 March 2013
� Springer-Verlag Berlin Heidelberg 2013
Abstract In this paper, organosilicone modified styrene-acrylic (OSA) latexes for
waterproof coating were synthesized through core–shell emulsion polymerization.
The influence of emulsifier type and dosage on the size, size distribution and mor-
phology of the latex was systematically investigated. The water absorbance and
thermal decomposition behavior and the mechanical properties of the waterproof
coating depending on the organosilicone introduced on the latex shell were also
studied. Transmission electron microscopy and dynamic light scattering results indi-
cated that the particles had a regular spherical morphology with different diameters
and distributions. Thermal gravimetric analysis results revealed that the thermal sta-
bility of the latex films was improved with the introduction of organosilicone. The
waterproof property of the OSA latex film was obviously increased as compared to
that of the styrene-acrylic latex film. The tensile strength and fracture elongation of the
elastic waterproof building coating made of the OSA latex and cement powder were
significantly greater than that made of the styrene-acrylic latex and cement powder.
Keywords Organosilicone � Styrene-acrylic latex � Waterproof coating
Introduction
Degradation of cement caused by the penetration of moisture is a serious problem in
building materials. Mixing cement with waterproof latex is an effective strategy to
X. Qian � A. Zhu (&) � L. Ji
College of Chemistry and Chemical Engineering, Yangzhou University,
Yangzhou 225002, People’s Republic of China
e-mail: [email protected]
X. Qian � L. Ji
YAPP Automotive Parts Co., Ltd., Yangzhou 225009,
People’s Republic of China
123
Polym. Bull. (2013) 70:2373–2385
DOI 10.1007/s00289-013-0958-4
prevent or control the degradation of cement [1–3]. In order to prepare cement
composites with excellent waterproofness, weather resistance and high mechanical
properties, waterproof latexes for cement composites must have low water
absorbance and good mechanical properties, and low glass transition temperature
that can endow the composites good elasticity.
Styrene-acrylic (SA) latexes are widely used for paints and adhesives because of
their specific properties such as good film-forming, gloss and transparency and
integrate mechanical properties [4–6], but their complex components and structures
also cause some problems in application. The mechanical properties of SA latex
films are temperature dependent, and their water and weather resistance are highly
influenced by the emulsifiers used in the emulsion polymerization of the SA
latexes. These weaknesses bring about a series of disadvantages when they are
mixed with cements and used as coatings for exterior walls of a building [7]. It has
been confirmed that SA latex-modified gypsum composite has a clear improve-
ment in flexural strength comparing with unmodified gypsum, but the mechanical
properties reduced about 70 % after immersion in water for 7 days [8]. Improving
the integrate properties of SA latexes is important for their applications in building
materials.
The macroscopic properties of SA latex/cement composites depend on the
components and structures of the SA latexes synthesized by emulsion copolymer-
ization and the size distribution and volume fraction of the latexes [9]. For example,
the incorporation of two different emulsifiers can lower the stability of the styrene-
acrylic latexes due to a decrease in the amount of emulsifiers used for stabilizing the
latexes, and cause several problems such as a reduction in water resistance or in
calcium ion stability in film applications [10, 11]. In contrast, organosiloxane/
polymer composite films have excellent water repellency, weather resistance and
thermal stability properties because the hydrolysis and condensation of Si(OR)3
groups result in the formation of a crosslinked silica network [12–15]. Polyacrylate
silicone core–shell particles have been synthesized using hydrophilic acrylic
monomers in the first stage and siloxanes in the second stage of the seeded emulsion
polymerization [16, 17]. It has been confirmed that the integrate performances of the
acrylic latexes can be enhanced by modifying the shells of the latex particles with
polysiloxane [18, 19]. Therefore, modifying the surface of SA latexes with
polysiloxane could be an effective approach to improve their physicochemical
properties.
In this paper, organosilicone surface modified styrene-acrylic (OSA) latexes in
the shell structure were synthesized through emulsion polymerization (the synthesis
mechanism of the OSA latexes was shown in Scheme 1), to improve the waterproof
property and the mechanical properties of the SA building materials. To decrease
the negative effect of the emulsifiers on the integrate properties of the SA latexes,
the influences of emulsifier type and dosage on the particle size, size distribution,
particle morphology, viscosity and waterproof property of the latexes were
systematically studied. The OSA latexes were mixed with cement powder and the
tensile strength and fracture elongation were used to evaluate the OSA/cement
building coating.
2374 Polym. Bull. (2013) 70:2373–2385
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Experimental
Materials
Technical grade monomers, wn-butyl acrylate (BA) and styrene (St), were
purchased from Guangzhou Langri Chemical Co., Ltd., China. The monomers
were used without purification. c-Methacryloxypropyltrimethoxysilane (MPS) was
purchased by Shanghai Chemical Reagent Co., Ltd. The emulsifiers [nonyl phenol
polyoxyethylene ether (OP-10) and sodium dodecyl sulfate (SDS)], sodium
bicarbonate (NaHCO3), acrylamide (AM) and ammonia persulfate (APS) were
used as received. Doubly deionized water (DDI water) was used throughout the
work.
Preparation of latexes
The reagents for the preparation of the SA latexes and OSA latexes were given in
Table 1. In a typical synthesis, 0.4 g of SDS, 0.8 g OP-10 and 0.19 g NaHCO3 were
dissolved with 20-mL water in a round-bottom glass flask. Styrene (13.0 g), n-butyl
acrylate (33.0 g) and acrylamide (0.8 g) were added into the round-bottom glass
flask and stirred for 30 min for pre-emulsion. APS (0.35 g) was dissolved in 5-mL
DDI water.
To prepare SA latex, the reaction was carried out in a 250-mL four-necked
round-bottom glass flask, which was equipped with a reflux condenser, a mechanical
Scheme 1 The synthesis mechanism of the OSA latex
Polym. Bull. (2013) 70:2373–2385 2375
123
stirrer, a dropping funnel and a nitrogen gas inlet. NaHCO3 (0.06 g) and 20 mL of
DDI-water were added and stirred. When the NaHCO3 aqueous solution was heated
to 75 �C, 7.0 g pre-emulsion and 1/3 initiator solution were injected into the reactor.
After 10 min, the residual pre-emulsion mixed with the initiator solution was
dropwisely added into the reactor at the same time. After 4 h of feeding, the reaction
system was heated to 90 �C and stirred for another 1 h. The polymerization system
was cooled to 40 �C, and the pH value was adjusted to 7–8. For preparation of OSA
latex, after feeding the residual pre-emulsion and initiator solution for 3 h, MPS was
added into the pre-emulsion. After stirring, the above pre-emulsion was dropped
into the reaction system.
Preparation of OSA latex/cement composites
The OSA latexes or SA latex, cement (YaFei Co., Ltd.) and 400 mesh calcium
carbonate (YaFei Co., Ltd.) were mixed uniformly and casted into a mold. The
sample was dried for 14 days at room temperature. The recipes were shown in
Table 2.
Characterization
FTIR was used to characterize the chemical structures of the OSA latex films
(0.1 mm). A transmission electron microscope (TEM, Tecnai 12–120 kV, Philips)
was used to observe the morphology of OSA latexes. For sample preparation, a drop
Table 1 The synthesis recipes for preparation of the SA and OSA latex
Components SA latex OSA latex
H2O g-1 52 52
NaHCO3 0.25 0.25
ST 15 15
BA 33 33
APS 0.35 0.35
AM 0.8 0.8
SDS 1 1
OP-10 0.5 0.5
MPS / 0.5
Table 2 The recipes for preparation of the elastic building waterproof coatings
Components Emulsion:powder = 1.3:1 (wt.%) Emulsion:powder = 1:1 (wt.%)
Latex 56.50 50.00
Cement 21.75 25.00
400 Mesh calcium carbonate 21.75 25.00
2376 Polym. Bull. (2013) 70:2373–2385
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of sample solution (1 mg mL-1 in distilled water) was placed on a 300-mesh copper
grid coated with carbon. Subsequently, the sample was dried and negatively stained
by a 2 % (w/w) phosphorus tungsten acid solution. Thermal gravimetric analysis
(TGA) measurements were performed on a NETZSCH STA 409PC thermogravi-
metric analyzer under the flow of anhydrous air from 25 to 800 �C at a heating rate
of 10 �C min-1 to measure the silicone content in the SA latex films. The mean
diameter and size distribution of the latexes were measured by a dynamic light
scattering (DLS) system (DLS-5022F). Before measurement, the latex samples were
diluted to an appropriate concentration.
Water absorbance property of the OSA latex film
Static immersion test of a latex film is considered as a standard method for
evaluating waterproof property of films. In brief, film samples were immersed in
distilled water at 25 �C. At specific time intervals, the samples were removed and
blotted with a piece of paper towel to absorb excess water on the surface. The
weight change was calculated by Eq. (1) and expressed as a function of time
Esw ¼We �Wo
Wo
� 100 % ð1Þ
where ESW is the water absorbance ratio of the film, We denotes the weight of the
film at equilibrium state and Wo is the weight of the dried sample.
Mechanical properties of the OSA latex films
The tensile tests were carried out according to ASTM D-256 using a Universal
Testing Machine (Hualong Co., Ltd., P. R. China) at a crosshead speed of
10 mm min-1. All measurements were repeated on at least five nominally identical
samples to obtain a statistical average.
Results and discussion
Characterization of the OSA latex films
Ftir
Figure 1 shows the FTIR spectra of the SA (a) and OSA (b) latex films. In the
spectrum of Fig. 1a, the peaks at 2,952 and 2,854 cm-1 are assigned to the
characteristic vibration of hydro-carbon bond. The peak at 1,735 cm-1 is assigned
to carbonyl (C=O) and the peaks at 761 and 675 cm-1 are attributed to ethyl (CH2),
methyl(CH3) and phenyl groups, respectively. In the spectrum of Fig. 1b, besides
the characteristic peaks of Fig. 1a, the band at 1,021 cm-1 is attributed to the Si–O
stretching modes, whereas the bands at 1,447 and 843 cm-1 are due to the Si–C
rocking normal vibrations [20]. These results suggest that the organosilicone has
been copolymerized onto SA latex through the unsaturated bond.
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TGA and DTA
Figure 2a illustrates the pyrolytic behavior of the SA and OSA latex films. TGA is
widely used for the determination of the composition of inorganic/organic phases. In
order to exclude the formation of non-volatile oxidative degradation products that
may cause some uncertainties in calculations, TGA analysis was carried out in the
flow of anhydrous air. Figure 2 shows the curves of TGA and DTA of SA and OSA
latex film. In the TGA thermograms, the weight loss between 190 and 400 �C
corresponded to the thermal oxidation and pyrolysis of polymer. The silica content
in the composites could be measured to be 1.11 wt.%, which was estimated by the
balance value of 2.31, and 1.20 wt.% for OSA and SA latex film respectively.
The silica content was similar to that of the initial design, suggesting that the
organosilicone has high polymerization conversion. From the DTA curve, the
pyrolytic temperatures were determined to be 403 �C for the SA latex film and
408 �C for the OSA latex film. The increase of the pyrolytic temperature of the OSA
latex film indicated that the thermal stability of the SA latex could be improved
through copolymerization with organosilicone. The hydrolysis and condensation of
Si(OR)3 groups in organosilicone can construct a crosslinked silica network
immobilizing tightly on the surface of the latex particles.
DLS
Figure 3 and Table 3 show the diameters and size distributions of the SA and OSA
latexes depending on the organosilicone introduction and the ratio of the anionic to
non-ionic emulsifier with fixed total emulsifier amount. As shown in Fig. 3a, b, the
average diameters of the SA and the OSA latexes are 78.4 nm with a polydispersity
index of 0.015 and 89.3 nm with a polydispersity index of 0.029, respectively. This
result suggests that copolymerizing organosilicone on the shell of SA latex can
Fig. 1 ATR–FTIR spectra of the SA and OSA latex films. a SA, b OSA latex film
2378 Polym. Bull. (2013) 70:2373–2385
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increase the size of the latex. The low value of the polydispersity indexes confirms
that the latex particles are dispersed uniformly. Figure 3b–d indicates that the latex
sizes increase and their distributions broaden with the decrease of the ratio of
anionic to non-ionic emulsifier. These results suggest that the type and quantity of
the emulsifiers can influence the size and distribution of the latexes.
TEM
Typical TEM micrographs of the SA and the OSA latexes depending on the ratio of
anionic to non-ionic emulsifier are shown in Fig. 4. Both the SA and the OSA latexes have
regular spherical morphology and uniform size distributions (Fig. 4a [anionic:nonionic
(wt.%) = 2:1, SA] and b [anionic:nonionic (wt.%) = 2:1, OSA]), but the size increased
and the size distributions became broaden when the ratio of the anionic to non-ionic
0 100 200 300 400 500 600 700 800 900
0
20
40
60
80
100
Temperature /
Mas
s/%
OSA SA 2.31
1.32
a
340 360 380 400 420 440 460
-30
-25
-20
-15
-10
-5
0
DT
G/(
%/m
in)
Temperature /
OSA SA
403
408
b
Fig. 2 TGA and DTA curves of the SA and OSA latex films. a TGA, b DTA
Polym. Bull. (2013) 70:2373–2385 2379
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emulsifier decreased (Fig. 4c [anionic:nonionic (wt.%) = 1:1, SA] and d [anionic:non-
ionic (wt.%) = 1:1, OSA]), which was consistent with the DLS results (Table 3).
Rheology
Viscosity of the SA latexes is an important factor for their applications in building
materials. The variation of the steady state viscosity (g) as a function of the shear
rate ð _cÞ is presented in Fig. 5. The viscosity of the OSA latex evidently decreased
when the relative amount of the non-ionic emulsifier increased. It suggests that
latexes with bigger size and broaden size distribution have much lower viscosity
a b
c d
Fig. 3 Diameters and diameter distributions of the SA and OSA latexes. a Anionic:non-ionic(wt.%) = 2:1, SA latex; b anionic:non-ionic (wt.%) = 2:1, OSA latex; c anionic:non-ionic (wt.%) = 1:1,OSA latex; d anionic:non-ionic (wt.%) = 1:2, OSA latex
Table 3 Results of DLS analysis
Ratio of emulsifiers Mean diameter PDI
Anionic:non-ionic (wt.%)
2:1 (a) 78.4 0.015
2:1 (b) 89.3 0.029
1:1 (c) 130.7 0.093
1:2 (d) 315.2 0.240
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according to the TEM and DLS results. The viscosity of the OSA latex decreased
only a little under throughout shear rate when comparing with that of the SA latex
with the same ratio of anionic to non-ionic emulsifier. These results suggest that the
components of the emulsifiers have more significant influence on the viscosity of the
latexes than the components and structure of the latexes.
Formation mechanism of the OSA latex
The formation mechanism of the OSA with silica-containing shell is a size
controlled core–shell seed emulsion polymerization (Scheme 1). It is proposed that
the seed latexes are initially formed via the formation of the SA copolymers. After
that styrene and acrylic diffuse into the seed latexes and polymerize on the seed
latex surface to form SA core before organosiloxane (MPS) addition. When MPS is
added into the pre-emulsion, polymerization takes place on the surface of the SA
Fig. 4 TEM morphologies of the SA and OSA latexes. a Anionic:non-ionic (wt.%) = 2:1, SA latex;b anionic:non-ionic (wt.%) = 2:1, OSA latex; c anionic:non-ionic (wt.%) = 1:1, OSA latex;d anionic:non-ionic (wt.%) = 1:2, OSA latex
Polym. Bull. (2013) 70:2373–2385 2381
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core, forming organosilicone modified SA shells. Hydrolysis and condensation of
the Si(OR)3 groups in the organosilicone happen simultaneously and form
crosslinked silica network in the shells [21], which can improve the thermal
stability, water resistant property and toughness of the latex film. This core–shell
emulsion polymerization provides a novel material with outstanding performance
combining the unique properties of both SA and organosiloxane materials.
The waterproof properties of the OSA latex film
Water uptake
The water absorbance and the water contact angle of the OSA latex film are shown
in Fig. 6 and Table 4. The water absorbance of the SA and the OSA latex films after
48 h were 5.63 % ± 0.11 (w/w) and 1.70 % ± 0.09 (w/w), and increased to
9.15 % ± 0.89 (w/w) and 3.5 % ± 0.07 (w/w) after 7 days (Fig. 6; Table 4). The
water contact angles were 60.3 ± 0.5� and 73.7 ± 0.3� for the SA and OSA latex
films, respectively. Generally, the surface water contact angle of measurements is
surface-sensitive, responding to the outermost monolayer of surface. The increase of
contact angle could be attributed to the low-energy of organosiloxane. The OSA
latex film has much lower water absorbance than the SA film due to the formation of
cross-linked structure with the shell layer modified with organosiloxane (KH-570),
thus much better waterproof property.
Mechanical properties
The tested values of the tensile strength and elongation of the silicone–styrene acrylic
elastic building coatings are listed in Table 5. rb and d represent the tensile strength
and the elongation of the elastic building coating material (latex:powder = 1.3:1
w/w), respectively; rb* and d* the values of the elastic building coating material
Fig. 5 The viscosity of the SA and OSA latexes
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(latex:powder = 1:1 w/w), respectively. From Table 5, it can be found that the
tensile strength and the elongation of the OSA elastic building coating material are
better than those of the SA elastic building coating material and meet the China
Industry Standard (JC/T894-2001). This could be due to the enhancement of the
compatibility on the interface between the OSA latex and the cement powder
according to the ‘‘similar dissolve mutually’’ theory.
Conclusions
In this study, OSA latexes with shell containing organosilicone for waterproof
coating were successfully prepared by core–shell emulsion polymerization. The size
Fig. 6 The water absorbance of the SA and OSA latex films
Table 4 The water absorbance of the SA and OSA latexes [anionic:non-ionic (wt.%) = 1:2]
Sample After 48 h After 7 days Water contact angle
SA latex film 5.63 ± 0.11 % 9.15 ± 0.89 % 60.3 ± 0.5
OSA latex film 1.70 ± 0.09 % 3.5 ± 0.07 % 73.7 ± 0.3
Table 5 Tensile strength and elongation of the elastic waterproof building coating made from SA or
OSA latex and cement powder [anionic:non-ionic (wt.%) = 1:2]
Sample SA latex OSA latex
Tensile strength, rb (MPa) 1.01 2.9
Elongation, r (%) 185 202.0
Tensile strength, rbł (Mpa) 0.9 3.8
Elongation, rł (%) 74.5 94.0
rb and d Emulsion: powder = 1.3:1 (w/w)
rbł and dł Emulsion: powder = 1:1 (w/w)
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and its distribution can be well controlled by emulsifier type and dosage, affecting
the viscosity of the resulting latex. The OSA latex film has higher water contact
angle and lower water absorbance in comparison with the SA latex film, suggesting
better waterproof property. The building coating made of the OSA latex and cement
powder has better tensile strength and fracture elongation than that made of the SA
latex and cement powder. This enhancement could be due to the formation of the
silica network in the shells of the latexes and the improvement of the compatibility
between the latexes and the cement powder.
Acknowledgments This research was supported by a National Natural Science Foundation of China
(No. 51073133), a China Jiangsu Provincial Natural and Scientific Grant (Project SBK200930208), China
Jiangsu Provincial Innovative Grant (Project SBC200910282), and was supported by Jiangsu Province,
Project No. 08KJA430003 (China).
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