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Investigations of addition of low fractions of nanoclay/latex nanocomposite on mechanical and morphological properties of cementitious materials
⁎Corresponding author. Hatami@bonabu.ac.ir (Mehdi Hatami)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
In this study, we report the synthesis, characterization and performance of organic-inorganic hybrid (OIH) cementitious nanocomposites. OIH was synthesized by the insertion of polymer latex particles in the structure of clay nanoplates. Polymer latex particles were prepared by the polymerization of three different organic monomer comprising styrene monomer (St), 2-ethyl hexyl acrylate (EHA), and methacrylic acid (MAA). Poly(St/EHA/MAA) was prepared by a semi-continuous emulsion polymerization process. The prepared OIH was used to modify the cement paste properties. For the fabrication of latex structure various composition of methacrylic acid as a functional monomer was examined. The effect of the variety of the percentage of MAA on latex composition, and also the OIH to cement ratios were optimized. The optimum conditions were applied to the fabrication of nanoclay based blends. The effects of OIH onto the cement paste properties were evaluated by measuring of the compressive and flexural strength analyses. The obtained results showed that the best composition in cementitious matrix was related to the sample of OIH namely CP565, in which comprises of five percent nanoclay. Also FT-IR, XRD, and SEM analyses were performed to exactly identify the effects of OIH onto the cementitious matrix properties.
Keywords
Nanocomposite
Nanoclay
Latex
Cement
Characterization
1 Introduction
Concrete is basically comprised of three main components including water, aggregate and Portland cement. Therefore, concrete is a composite material (Sasmal et al., 2017). When aggregates are mixed with Portland cement and water, the slurry is formed. In this process the water and other ingredients react chemically with cement to form an inflexible matrix (Gdoutos et al., 2016). Often, additives are included in the mixture to improve the physical properties of the wet mix or the finished product. Most concretes are filled with reinforcing materials embedded to provide tensile strength, yielding reinforced concrete. Thus, for designing of the cement based composite, the interrelation between fillers and matrix in used process method must be investigated. Over the past decades, polymer-organo modified layered silicate (LS) nanocomposites have attracted great attention from academics to industrial aspects (Faghihi et al., 2017; Ke and Stroeve, 2005). The successful preparation of a fully delaminated construction of LSs and obtaining the good dispersion properties of them in used matrices points to improve in thermal, mechanical, flame resistance and gas barrier properties in combination with light weighting of the final products (Mico-Vicent et al., 2017). The LS showed high aspect ratio and had a width of one nanometer, which ideal candidate as reinforcement agent for different soft and hard matrices (Bertolino et al., 2016). LS showed a very good interaction with functional polymeric structures (Hakamy et al., 2014). Montmorillonite (MMT) is the most widely used LS due to its natural existence and some outstanding properties such as high surface area and also high aspect ratio (Chakrabarty et al., 2015; Kafi, et al., 2016). Modifications of LS as fillers by organic compounds are required for improve the compatibility between organic and inorganic segments. For modification of LSs the cation exchange capacity of them were used by different organic and inorganic moieties. In the most applications the modified LSs as known as organoclays were applied. Due to the large surface area of organoclays, the efficiency of these structures in the dispersed media matrices is very good (Cook et al., 2015; England et al., 2016; Simari et al., 2016). Nevertheless, there are some important drawbacks on cementitious composite materials or concretes such as fluidity, flexural strength, and corrosion properties (Schlumpf et al., 2013). Until now, different macromolecules have been fabricated and investigated in numerous application areas such as sensors, adhesives, and so on (Dastan et al., 2015; Hatami et al., 2015; Hatami, 2017; Karimi-Maleh et al., 2014; Mallakpour et al., 2011; Marandi et al., 2012). Modification of cement by using polymer additives have been attracted the industrial researchers' attention. Numerous kinds of polymer-modified mortars and concretes were introduced such as water-soluble polymer, latex polymer powder, liquid resin, and monomer-modified mortars and concretes (Han et al., 2015; Ohama, 1995). To yield a monolithic matrix phase with a network structure with superior properties, the cement based materials were well mixed with polymer phase. It is very important that both hydration of the cement and coalescence of macromolecule particles were well interpenetrated (Afridi et al., 2003). A co-matrix phase in the macromolecular modified mortar and concrete structure was illustrated by bound the aggregates by polymer/cement ingredients. In spite of the complexity of interactions between cement and polymer, some researchers have explained the mechanisms by which the polymer bonds to the cement ingredients (Li, 2011). The polymeric latexes are the most interested soft materials which have been used to improve the concrete properties. The effects of polymer latex particles on the mechanical properties of the mortar and concrete have been investigated by many researchers. Several parameters, such as polymer/cement ratio, type of cement, polymer functionality, and chemical structure of macromolecule, surfactant type, polymer-glass-transition temperature, and polymer particle size can considerably affect the mortar and concrete properties (Ohama, 1995; Walling and Provis (2016)). Although many scientists have been investigated the effect of polymeric materials onto the cement and concrete properties, less attention has been paid to the use of functionalized polymer latexes, nanoscale fillers and polymer filled with nanoscale particles as nanocomposite additives in this area. Mendoza Realesa et al. (2018) have reported the effects of dispersed multiwall carbon nanotubes (MWCNT)/surfactant on the Portland cement pastes properties. They mentioned that the dispersion of modified MWCNT cause to direct shift to higher yield stress values of cement whereas keeping the viscosity values for measured samples. They concluded that the interaction between MWCNT, surfactant, and cement directs the rheological properties of the cement. Niewiadomski et al. (2017) have reported the production and microstructural analysis of self-compacting concrete by addition of nanoscale fillers. They fabricated the concrete structure with different amounts of silica, titana and alumina nanoparticle as additives. They mentioned that the insertion of nanoparticles in structure of self-compacting concrete improves the microstructure of provided concrete. The study by Xu et al. (2018) displayed that the addition of low dosage of silica and titana nanoparticles in concrete composition could improve the environment resistance of concretes. Bai et al. (2018) reported the enhancement of electrical and mechanical properties of graphene/cement nanocomposite due to the enhancement in distribution of graphene nanosheets by addition of silica fume. Obtained results by this research group revealed that silica fume was capable to aid the distribution of graphene in cement and increase the interfacial strength between graphene and cementitious matrix. According to the reported results from prior studies (Bai et al., 2018; Mendoza Realesa et al., 2018; Niewiadomski et al., 2017; Xu et al., 2018) in the application of nanoscale fillers in cement matrix, it can be understood that the properties of cementitious materials are influenced by various factors, including the size, type, shape, dispersion method and the dosage of nanomaterials. Though previous investigations have proved that the nanostructure fillers have positive effects on physical and mechanical properties of cementitious materials, however, to the best of our knowledge, the application of the polymer filled nanostructures as nanocomposites on the performances of cementitious matrix is not yet accomplished. This research area still needs to be further investigate.
This paper presents the preparation of poly(styrene/2-ethylhexyl acrylate/methacrylic acid), poly(St/EHA/MAA)/LS blend nanocomposite and the dispersion of organic-inorganic hybrid (OIH) nanocomposite as a new admixture in cement composition for the first time. The technique of OIH preparation included both the semi-continuous emulsion polymerization and sonication method. The first step was the preparation of latex-based LS nanocomposite by using physical and chemical approach in order to achieve high degree of exfoliated dispersion, which was followed by the insertion of the prepared OIH into the cement paste. WXRD studies were carried out to visualized the type and degree of clay dispersion in the poly(St/EHA/MAA) matrix. Fourier transform infrared (FT-IR) analysis of polymer structure, OIH and its blend structure also have been carried out to investigate the polymer-clay and OIH- cement interactions. Also, the effects of percentage of functionality of MAA on the poly(St/EHA/MAA) and the presence of organic clay modified latex particles nanocomposite on the cement matrix properties have been extensively investigated. The scanning electron microscopy (SEM) was performed to detect the morphology of fractured surfaces of the polymer and the nanocomposite dispersion in cementitious matrices.
2 Materials and methods
2.1 Materials
All chemical reagents are purchased from Merck chemical company unless otherwise stated. Styrene monomer (St), 2-ethylhexyl acrylate (EHA), and methacrylic acid (MAA) were distillated under vacuum to remove the trace of inhibitor and stored at refrigerator before use. Potassium persulfate (KPS) as initiator and sodium lauryl sulfate (SLS) as ionic surfactant were used. Distilled water used in all experiments was prepared in the author’s laboratory. Portland cement (Type II, Tehran Cement Co.) was used. Nanoclays, Cloisite 20A is an organo-modified montmorillonite with dimethyl dehydrogenated tallow quaternary ammonium (2M2HT) chloride was purchased from Nutrino chemical Co., Iran.
2.2 Characterization
Fourier-transform infrared (FT-IR) spectra of cement paste and modified cement samples were recorded using a FT-IR spectrometer (Nicolet 740) in the frequency range 4000–500 cm−1. Wide angle X-ray diffraction (WXRD) analysis was carried out to study the dispersion of LSs in polymer nanocomposite, and also in cementitious matrix samples. The measurements were performed on Philips PW1140 X-ray diffractometer. The fracture morphology of the neat and OIH modified cement have been studied by means of a scanning electron microscopy (SEM, Philips XL30) apparatus.
2.3 Limitations of process
One of the main difficulties when handing out nanocomposites is the accumulation or agglomeration of nanostructures, which is observed by an inadequate distribution in the provided constructions. To analyze the dispersion quality of nanocomposite in cementitious matrix, in this study the X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were used. The degree of intercalation or exfoliation for clays structures can be considered by XRD (Liu et al., 2006). SEM can be used to distinguish the organization of nanoscale fillers in final clay based products.
2.4 Dispersion quality improvements
The inorganic fillers showed hydrophilic characters and these fillers are consequently not compatible with polymer matrices. Therefore the surface of inorganic fillers can be modified by organic molecules. The purpose of modification of the surface of clay nanostructures is consequently their hydrophobization to improve their compatibility with the polymers with the aim of enable intercalation or exfoliation of the clay structures. For clay structures, the exchange of inorganic surface cations with organic cations has been widely used for surface modifications. For this purpose the embedding of organic molecules or polymeric macromolecular particles between the layers of inorganic silicates can be considered (Liu, 2007; Zare et al., 2017). Also ultrasonic treatment can be used for enhancement of dispersion of nanocomposite. Ultrasonic irradiations can be enhanced the polymer/filler compatibility. There are many studies on the application of ultrasonic waves for synthesis of well dispersed nanocomposite (Hatami, 2018; Hatami and Yazdan Panah, 2017; Mallakpour and Khani, 2018).
2.5 Synthesis of polymer latex
The latex particles were synthesized via a semi-batch emulsion polymerization process according to the reported procedure (Masa et al., 1993). Briefly, the five-neck glass reactor was equipped with a nitrogen inlet, a condenser, and two feeders, and placed in a water bath with a thermostatically temperature controller. The reflux condenser and N2 inlet were considered to prevent evaporating the monomers and to remove the oxygen from the reaction media, respectively. Heidolph overhead stirrer was used to mix the reacting ingredients within the glass reactor. The semi-continuous emulsion polymerization was carried out using the recipes prearranged in Table 1. The feed of the reaction was distributed into two streams. The first was a combination of the monomers (according to the Table 1). The second was an aqueous solution of the initiator and emulsifier (KPS: 1.68 g and SLS: 6.35 g dissolved in 338.70 g of water). The flow rates of these streams were adjusted to complete the insertion process of both streams in 6 h. Then, the polymerization was continued in batch for about 1 h. Eight formulations for polymerization were carried out to examine the effect of the amount of MAA on the final product properties.
Sample
St
(wt%)EHA
(wt%)MAA
(wt%)Tg (°C)
Conversion
MA
55
45
0
16.54
0.94
MA-1
54
44
2
17.26
0.95
MA-2
53
43
4
18.01
0.94
MA-4
52
42
6
19.47
0.95
MA-5
51
41
8
20.23
0.95
MA-6
50
40
10
21.02
0.95
MA-8
49
39
12
22.11
0.94
MA-10
48
38
14
23.02
0.94
2.6 Cement/latex paste and cement/OIH preparation procedures
At given water to cement weight ratio equal to 0.26, the cement to polymer ratios were 1, 3, 5 and 7. The latex was added to the cement/water admixture and stirred by the mechanical stirrer for 5 min at room temperature. The given procedure was used to prepare the nanocomposite based materials (the nanomaterial to cement ratios was 0.01, 0.03, 0.05 and 0.07).
2.7 Investigation of polymer/cement compatibility
The compatibility between cement and polymer latex was examined by using a simple test method. The test was performed in a glass tube with 2 cm in diameters and 28 cm height. The water, latex, and cement were mixed respectively and the amount of supernatant water at determined times were measured.
2.8 Mechanical properties investigation
After mixing water/cement/latex or nanocomposite for 3 min, the polymer or nanocomposite–modified paste specimens were casted into aluminum molds of the size 5 × 32 × 150 mm. The molded specimens were then cured under wet dry condition with 60% humidity. The flexural strength was determined according to ASTM C78 testing method. Each reported value is determined by averaging six test specimens. The compressive strength of cement and polymer-modified cement or nanocomposite-modified cement paste was determined using ASTM C109 protocol test method. For this purposes, the specimens were poured into the rectangular cavities of the mold (2 × 2 × 2 in.3), cured at room temperature under dry condition for 7 and 28 days. Each reported value is determined by averaging six test specimens.
3 Results and discussion
3.1 Preparation of poly(St/EHA/MAA)and clay/poly(St/EHA/MAA) nanocomposites
In this multicomponent system, 2-ethylhexyl acrylate (EHA) was polymerized with styrene (St) and methacrylic acid (MAA) to form the (St/EHA/MAA) polymer particles. Dreher et al. (2003) investigated the properties of poly(St/EHA/MAA) film. Pure terpolymer is able to coalesce at room-temperature condition in the presence of surfactant at the film-air interface. This research group concluded that the presence of ionic species such as calcium hydroxide and ammonium hydroxide does not affect to the stick of the latex structures, but alignment and movement of surfactant may change in this condition. The recipes of the prepared latexes were listed in Table 1. The conversion of the prepared latexes was measured gravimetrically. The solid content of all latexes were in the range of 34–36%. The nanocomposites of poly(St/EHA/MAA) and cloisite 20A were prepared by insertion of polymer latex particles into the LS structure. Therefore by insertion of latex particles in the layered structure of clay, the complete exfoliated structure was provided. This result was confirmed by investigation of crystallinity of clay by XRD analysis. The modification process for the exfoliation structure of nanoclay was illustrated in Fig. 1.
Schematic illustration of exfoliation process during insertion of latex particles in nanocomposite formation step.
3.2 Fabrication and characterization of nano-hybrid cementitious materials
Portland cement is a heterogeneous fine grained solid involves of four main elements, namely Tricalcium Silicate (C3S), Dicalcium Silicate (C2S), Tricalcium Aluminate (C3A), Tetracalcium Alumino Ferrite (C4AF). Chemical composition of used Portland cement was listed in Table 2. In addition, various phases presented in used Portland cement are reported in Table 3.
Oxide
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
LOI
Free CaO
Density
(kg/m3)Blaine fineness (m2/kg)
wt%
22.50
4.15
3.44
63.26
3.50
1.80
0.67
0.24
0.66
0.72
3120
3020
Phase
C3S
C2S
C3A
C4AF
wt%
53.69
24.07
5.18
10.47
The purpose of this part of experiment was to select the best latex composition that is compatible with cement paste environment. Table 4 showed the characteristics of different prepared samples with varies amount of MAA weight percentages. Table 4 indicated the optimum value for cement to polymer ratios. The latexes must be stable when they mixed with cement solution. This performance was due to the chemical structure of SLS. An anionic emulsifier such as the SLS supports electrostatic stabilization effects on to the latex particles, and therefore enhances the chemical stabilization of latex structure in the cementitious matrix.
Sample
Cement to polymer ratio
MAA (%)
Water to cement ratio
C
0
0
0.26
CP50
5
0
0.26
CP51
5
1
0.26
CP52
5
2
0.26
CP54
5
4
0.26
CP55
5
5
0.26
CP56
5
6
0.26
CP58
5
8
0.26
CP510
5
10
0.26
CP16
1
6
0.26
CP36
3
6
0.26
CP56
5
6
0.26
CP76
7
6
0.26
It can be observed visually that the sample namely CP50 (cement to polymer ratio 5: without MAA) is coagulated. In this sample, there is not any carboxylic acid functional group on the structure of polymer and the coagulation phenomenon may be deduced from the lack of functional group of MAA. In order to identify the effect of functional group of MAA monomer, the workability of various samples is examined. Obtained results were reported in Table 5. Results showed that with enhancement in the content of carboxylic acid on matrix structure, the workability of samples is increased from 1 to 6 percent based on methacrylic acid contents and decreased from 10 to 6 percent based on the acidic monomer. Decreasing the workability from CP56 to CP510 is associated in decrement in the pH values of the solution. It can cause the coagulation phenomena in CP58 and CP510 samples. Also, for cited sample, the CP50 faced with coagulation phenomena. It can be inferred that the latex without any carboxylic acid groups is caused to coagulate. It seems that the surfactant adsorbed water was reacted with calcium species to connect the matrix. The relation of spread diameter and workability of the prepared samples were shown in Table 5. It can be deduced that the best percent value for MAA was six.
Sample
Spread diameter (mm)
C
90 ± 1.2
CP50
Coagulation
CP51
94 ± 0.5
CP52
99 ± 10.5
CP54
103 ± 1.1
CP55
105 ± 1.3
CP56
113 ± 2.3
CP58
111 ± 3.1
CP510
109 ± 1.2
The effect of cement to polymer ratio on flexural strength as a comparative study was shown in Table 6. The existence of latex particle has a remarkable effect on the flexural strength of cement paste. Various factors play noticeable roles in mechanical properties of cementitious samples such as curing method, nature of material, surfactant and so forth. In this experiment, the effects of cement to polymer ratio are examined to optimize the best polymer composition. Flexural strength was performed after seven days (one day relative humidity 100%, two days immerged in water, four days relative humidity 60%) and twenty-eight days (one day relative humidity 100%, six days immerged in water, twenty-one days relative humidity 60%) mixed curing for prepared samples. The results indicated that with enhancement from one to seven percent of cement to polymer ratio, the flexural strength reached to peak in six percent. A reciprocal relationship was observed between the polymer content and flexural strength of cement paste. In addition, the internal cohesion was increased due to the presence of latex particles, which was hindered the genesis of cracks and micro cracks in the structure of the final pastes. On the other hand, the value of pH has been decreased for samples CP16 and CP36. The increase in concentration of proton ion or decrease in pH value of the mixture has been affected to the stability of sample of cement paste and the coagulation has been influenced directly by pH value in final samples.
Sample
Flexural strength (MPa)
7 Days
28 Days
C
6.5 ± 0.2
9.3 ± 0.1
CP16
8.5 ± 0.1
9.5 ± 0.15
CP36
8.8 ± 0.2
9.7 ± 0.1
CP56
9.4 ± 0.15
10.7 ± 0.2
CP76
10 ± 0.1
11.5 ± 0.15
The effect of cement to polymer ratio on compressive strength was displayed in Table 7. After curing for samples in 7 and 28 days experiments, the compressive strength of samples were decreased by enhancement in the latex to cement ratio values. The best result for this experiment was related to the sample CP56. The drop of compressive strength with increase in the polymer content is a common phenomenon.
Sample
Compressive strength (MPa)
7 Days
28 Days
C
90 ± 0.2
105 ± 0.1
CP16
65 ± 0.1
89 ± 0.15
CP36
67 ± 0.2
85 ± 0.1
CP56
86 ± 0.15
82 ± 0.2
CP76
80 ± 0.1
84 ± 0.15
The effect of novel nanocomposite admixture containing nanoclay/latex on to the cement flexural strength, and compressive strength were shown in Table 8. After curing for all nanostructured samples with in 7 and 28 days, with increase in the values of cement to nanocomposite ratio, the compressive strength was increased up to 7 percent. The best result of mechanical test was associated to the sample CP567. Flexural strength was performed after seven days and twenty-eight days mixed curing for nanocomposite samples. The results indicated that with enhancement of nanocomposite to cement ratio the flexural strength reached to peak in five percent of nanoclay and after that showed the drop point for sample CP567.
Sample
Clay content
Flexural strength (MPa) after 7 days
Flexural strength (MPa) after 28 days
Compressive strength (MPa) after 7 days
Compressive strength (MPa) after 28 days
CP561
1
9.8 ± 0.1
10.3 ± 0.2
88 ± 0.15
92 ± 0.2
CP563
3
10.3 ± 0.2
11.1 ± 0.15
90 ± 0.1
94 ± 0.1
CP565
5
11.5 ± 0.1
12.4 ± 0.1
93 ± 0.2
98 ± 0.15
CP567
7
10 ± 0.15
10.7 ± 0.15
95 ± 0.1
99 ± 0.1
To recognize the effects of polymer and nanocomposite on micro cracks, it is obligatory to concentrate on micro cracks when the sample in cracked after compressing. As can be seen the sample C (unmodified paste) was fragile than the sample CP565. Also, the less and smaller micro cracks were observed for sample CP565 rather than the sample C. The sample CP565 (cement to polymer ratio 5: MAA percentage 6: nanoclay content: 5) showed the best structure properties relationship. This behavior was related to the effects of polymer nanocomposite on paste properties. Also the presence of layered silicate structure in combination with functional units of polymer helps the admixture to improve the physical and mechanical properties of the prepared samples (Fig. 2). It is related to the strong interaction between cement and nanocomposite functional units or attributed to strong bond between carboxylate anions and calcium cations in exfoliated matrices structure.
Illustration of the nanostructure additive on final product properties; (a) neat sample, (b) sample containing nanostructure CP565 additive.
3.3 FT-IR spectra investigations
Fourier transform infrared (FT-IR) spectroscopy was used to analyzed the nanoclay (a), polymer sample (b), clay-polymer nanocomposite (c), after twenty-eight days mixed curing for two samples, C (d), and CP565 (e) respectively (Fig. 3). The spectrum of C (unmodified cementitious paste) presents some peaks in 3645, 3430, 2923, 1630, 1482, 1450, 1264, 984, 872, 671 and 613 cm−1 which all peaks are illustrated. Major absorption bands in all samples includes 3430 and 1630 cm−1 bands assigned to H—OH stretching and H—O—H bending respectively; 1482–1381 cm−1 associated with calcium carbonate and calcium oxide; 1160 and 985 cm−1 bands assigned to Si—O—Si and Si—O—Al bonds, respectively; and 670 and 520 cm−1 assigned to Si—O bending. For CP565 a peak at 1741 cm−1 was related to the interaction between polymer and ettringite phase or strong bond between carbonyl units of MAA with metal atom or different ions which is produced during the hydration reaction. Generally, for CP565 peak intensity is less than for the C sample. This fact can be concluded that the addition of polymer to cement cause to delay in the hydration reaction. This fact was obviously detected by observing the peak at 3645 cm−1 that is related to hydroxyl stretching vibrations in calcium hydroxide structure. FT-IR spectra of modified LS show some characteristic bands at 3632 and 3388 cm−1 attributed to O—H stretching for the silicate and water fragments respectively. A very strong peak at 1047 cm−1 belongs to the stretching vibration of Si—O—Si from silicate. The latex-LS nanocomposite shows the characteristic band of aluminosilicates and Si—O—Si stretching. The appearance of a carbonyl peak in nanocomposite at around 1727 cm−1 clearly indicates the presence of methacrylate units in chains on the LS nanocomposites. Furthermore, the carbonyl peak of nanocomposite present at lower wavenumber (1724 cm−1) than the carbonyl peak for polymer latex (1727 cm−1) refers to intermolecular interaction between C⚌O group of latex chains and the OH group of LS. Therefore, existence of polymer–nanoclay interaction is observed in the latex nanocomposites.
FT-IR spectra of (a) Cloisite 20A, (b) clay in polymer matrix as a novel nanocomposite, (c) Polymer matrix, (d) cement, and (e) cementitious matrix containing nanostructure CP565 nanocomposite.
3.4 X-Ray diffraction analysis
The wide angle XRD patterns (WXRD) of the Cloisite 20A (a), and latex nanocomposite (b) with 3 wt% of inorganic content are presented in Fig. 4. The WXRD graphs (2θ = 2–10°) of Cloisite 20A exhibited intensive peaks at around 2θ = 3.1 corresponding to a basal plane spacing d (0 0 1) of 2.7 nm. The pattern of the nanocomposites latex/20A, has a diffraction peak at around 2θ region of 2.7, 4.7, and 7.1, respectively. The increased d-spacing of nanocomposite latex/20A to an appreciable level over the pristine Cloisite 20A indicates a successful and effective complete exfoliation structure. Form the WXRD analysis from 2θ = 10–70° (Fig. 5) for clay and nanocomposite sample, an extremely broad peak was observed for nanocomposite sample in the range 2θ = 10–30°. Such a broad peak is understood to be due to the amorphous nature of latex particles.
(a) WXRD pattern of Cloisite 20A, form 2θ = 1–10°, and (b) WXRD pattern of nanocomposite, form 2θ = 1–10°.
WXRD pattern of Cloisite 20A, form 2θ = 10–70°, and (b) WXRD pattern of nanocomposite, form 2θ = 10–70°.
Hydrated phase was produced by the reaction of different cement phases and water. X-ray diffraction pattern (Fig. 6) showed the important peaks related to the different phases existed in the structure. The outstanding stability of nanocomposite was attributed to the carboxylate functional units of polymer structure, steric interaction forces and van der Waals forces. Due to the little or no holes in the structure of nanocomposite, it can be concluded that, good interfacial adhesion between modified LS and latex particles were existed. It is clear that the addition of the polymeric nanocomposite into cement causes to decrease the peaks intensities. This was attributed to delay in hydration reaction in polymer contain samples. Also detected phases in WXRD analysis were listed in Table 9.
WXRD patterns of cement sample (red), and cement containing nanostructure CP565 nanocomposite (green), form 2θ = 10–70°.
Symbol
Component
A
Ca(OH)2
B
CaSiO5H2
C
Ca2SiO5H2
D
CaCO3
E
Ca6Al2S3O48H66
F
Ca3Fe2OH12
N
Not assigned
3.5 Morphological investigation by scanning electron microscopy
Morphological features of latex polymer, latex/nanoclay nanocomposite, cement, and cement nanocomposite modified paste were inspected in order to find out the state of spreading of LS platelets in the matrix, and finally at cement structures, which is the most important factor for projecting the mechanical properties of cement based nanocomposites. The microstructures of the samples were investigated by SEM observations (Fig. 7(a–d)). The SEM analyses were carried out at the age of 28 days to detect the morphological difference between composites. The morphological observation of the polymer modified cement samples (CP36, and CP56) was studied by SEM analysis. Fig. 7(c) and (d) shows that the morphology of polymer/cement blend for sample CP56 becomes better than the sample CP36 (Fig. 7(a and b)). The matrix is islanded with interconnecting parts. However, increasing the latex content to the cement leads to a decrease on the number and the size of these parts. These morphological changes can be attributed to the better network constructions of the cement ingredients.
SEM micrographs of polymer/cement blend for sample CP36 (a and b) and sample CP56 (c and d).
Fig. 8 shows the SEM picture of the pure Cloisite 20A, and exfoliated clay/latex particles. In the case of Cloisite 20A, the degree of crystallinity of the pristine clay is very high. The particle size is less than 100 nm as it was observed in SEM images (a–c). After modification with latex, the degree of crystallinity is reduced but one can still observe small crystals corresponding to Cloisite 20A. The SEM pictures of exfoliated Cloisite 20A showed how strong morphological changes were occurred. Parts (d–f), and (g–i) of Fig. 8 showed the SEM pictures of the samples CP563, and CP565 respectively. In the case of modified LSs by organic latex modifier (Fig. 8(d–i)) the interaction domination between the nanoplates and the polymer matrix was not obvious because the cloisite particles were treated by organic molecules and due to the compatible nature of organic modified clay and polymer particles, the interaction domains appeared clean with little discontinuity. However, the unique structure of latex was not damaged by clay structure. From these images, clay particles in the range of 54–86 nm were embedded in polymer nearly met the requirements of nano-materials. Besides, fine particles could be detected in the matrix. In Fig. 8(d), the diameters of observed particles are ranging from 54 nm to 90 nm. By comparing Fig. 8(d) with (g), the size of observed particles increases as the content of clay is enriched. It arises from the existence of immense —OH on the surface of clay, which is favorable to form particles with large dimensions. Usually for particles reinforced polymeric materials the improvement result is primarily related to the size of the particles because the larger diameter particles create the stress concentration source. The latex carboxylic acid functional units could induce hydrogen bond with modified clays; hence, treatment of clays by latex could reduce the amount of agglomerated particles and make the exfoliated structure for clay.
SEM micrographs of nanoclay (a–c), nanocomposites samples CP563 (d–f), and CP565 (g–i).
Also the micro scale dispersion in cement matrix for CP565 sample is considered with SEM and illustrated in Fig. 9. Parts (a and b), (c and d), and (e and f) of Fig. 9 were related to the 2, 7, and 28 days hardening of CP565 sample respectively. It is clear to observe that there is some ribbon structures were observed in the pictures of the CP565 in 7 days experiment. One of the main reasons for this fact is related to changes in rheological properties regarded to the addition of latex to paste composition. Although, the rheological properties of cement were improved by the addition of the nanocomposite to cement ratio, but the increase in the ratio of polymeric nanocomposite to cement caused to produce the cavities in the structure of CP565/cement matrix due to the presence of additional segments from 28 days.
SEM micrographs of morphology of cementitious nanocomposites CP565, after 2 days (a and b), 7 days (c and d), and 28 days (e and f).
4 Conclusion
The synthetic nanocomposite structure, poly(St/EHA/MAA)/nanoclay nanocomposite was prepared and introduce into the cement composition in order to increase the process characteristics of organic-inorganic nanocomposites with unique properties. As a result, the interaction of the organic functional units of prepared polymeric nanocomposite introduced into the cement paste has an important effect on properties of the subsequent hybrid structures. Morphological examinations by using SEM showed the perfect joining of cement to nanocomposite in the structure of final product. The FT-IR spectra showed the existence of the nanoclay and carbonyl functional units of latex in the structure of modified pastes. Obtained results confirmed that the sample CP565 showed the better characteristics in comparison with other prepared samples.
Acknowledgments
We wish to express our thankfulness to the Research Affairs Division Islamic Azad University, Mahshahr and Miyaneh branches. Also we wish to express our gratitude to the Research Affairs Division University of Bonab, Bonab for partial financial support. Further financial support from Iran Nanotechnology Initiative Council (INIC) is appreciatively acknowledged.
References
- Development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars. Cem. Concr. Res.. 2003;33:1715-1721.
- [Google Scholar]
- Enhancement of mechanical and electrical properties of graphene/cement composite due to improved dispersion of graphene by addition of silica fume. Constr. Build. Mater.. 2018;164:433-441.
- [Google Scholar]
- Effect of the biopolymer charge and the nanoclay morphology on nanocomposite materials. Ind. Eng. Chem. Res.. 2016;55:7373-7380.
- [Google Scholar]
- Tailor-made fluorinated copolymer/clay nanocomposite by cationic RAFT assisted pickering miniemulsion polymerization. Langmuir. 2015;31:12472-12480.
- [Google Scholar]
- Highly ordered self-assembling polymer/clay nanocomposite barrier film. ACS Appl. Mater. Interfaces. 2015;7:10915-10919.
- [Google Scholar]
- Studies on electrical properties of hybrid polymeric gate dielectric for field effect transistors. Macromol. Symp.. 2015;347:81-86.
- [Google Scholar]
- Styrene/2-ethylhexyl acrylate/methacrylic acid (Sty/EHA/MAA) coalescence and response-driven mobility of sodium dodecyl sulfate (SDS) in colloidal films. 22. A spectroscopic study. Macromolecules. 2003;36:1228-1234.
- [Google Scholar]
- Anti-fogging/self-healing properties of clay-containing transparent nanocomposite thin films. ACS Appl. Mater. Interfaces. 2016;8:4318-4322.
- [Google Scholar]
- New poly(ether-amide-imide) reinforced layer silicate nanocomposite: synthesis and properties. Arab. J. Chem.. 2017;10:s651-s656.
- [Google Scholar]
- Portland cement mortar nanocomposites at low carbon nanotube and carbon nanofiber content: a fracture mechanics experimental study. Cem. Concr. Compos.. 2016;70:110-118.
- [Google Scholar]
- Thermal and mechanical properties of hemp fabric-reinforced nanoclay–cement nanocomposites. J. Mater. Sci.. 2014;49:1684-1694.
- [Google Scholar]
- Cementitious composites containing nanosilica and styrene butadiene latex polymer. Int. J. Polym. Sci.. 2015;2015:1-9.
- [Google Scholar]
- Production and morphological characterization of low resistance polyimide/silver nanowire nanocomposites: potential application in nanoconductive adhesives. J. Mater. Sci.: Mater. Electron.. 2017;28:3897-3908.
- [Google Scholar]
- Production of polyimide ceria nanocomposites by development of molecular hook technology in nano-sonochemistry. Ultrason. Sonochem.. 2018;44:261-271.
- [Google Scholar]
- Ultrasonic assisted synthesis of nanocomposite materials based on resole resin and surface modified nano CeO2: chemical and morphological aspects. Ultrason. Sonochem.. 2017;39:160-173.
- [Google Scholar]
- Morphological investigation of synthetic poly(amic acid)/cerium oxide nanostructures. Polym. Eng. Sci.. 2015;55:2339-2348.
- [Google Scholar]
- Microstructural characterization and mechanical properties of cementitious mortar containing montmorillonite nanoparticles. J. Mater. Civ. Eng.. 2016;28:040161551-0401615510.
- [Google Scholar]
- Voltammetric determination of captopril using a novel ferrocene-based polyamide as a mediator and multi-wall carbon nanotubes as a sensor. J. Anal. Chem.. 2014;69:162-168.
- [Google Scholar]
- Polymer-Layered Silicate and Silica Nanocomposites (first ed.). Amsterdam: Elsevier; 2005.
- Advanced Concrete Technology. New Jersey: Wiley; 2011.
- Intercalation and exfoliation: a review on morphology of polymer nanocomposites reinforced by inorganic layer structures. Mater. Manuf. Process.. 2006;21:143-151.
- [Google Scholar]
- Surface modified SiO2 nanoparticles by thiamine and ultrasonication synthesis of PCL/SiO2-VB1 NCs: morphology, thermal, mechanical and bioactivity investigations. Ultrason. Sonochem.. 2018;41:527-537.
- [Google Scholar]
- An electrochemical investigation of novel optically active poly(amide-imide)s based on natural amino acids using multi-wall carbon nanotubes paste electrode. J. Solid State Electrochem.. 2011;15:2053-2061.
- [Google Scholar]
- Kinetic modeling of photocatalytic degradation of an azo dye using nano-TiO2/polyester. Environ. Eng. Sci.. 2012;29:957-963.
- [Google Scholar]
- High-solids-content seeded semicontinuous emulsion terpolymerization of styrene, 2-ethylhexyl acrylate and methacrylic acid. Polymer. 1993;34:2853-2859.
- [Google Scholar]
- Influence of MWCNT/surfactant dispersions on the rheology of portland cement pastes. Cem. Concr. Res.. 2018;107:101-109.
- [Google Scholar]
- A combination of three surface modifiers for the optimal generation and application of natural hybrid nanopigments in a biodegradable resin. J. Mater. Sci.. 2017;52:889-898.
- [Google Scholar]
- Microstructural analysis of self-compacting concrete modified with the addition of nanoparticles. Procedia Eng.. 2017;172:776-783.
- [Google Scholar]
- Handbook of Polymer-Modified Concrete and Mortars (first ed.). Amsterdam: Elsevier; 1995.
- Synthesis, characterisation and performance of piezo-resistive cementitious nanocomposites. Cem. Concr. Compos.. 2017;75:10-21.
- [Google Scholar]
- Schlumpf, J., Bicher, B., Schwoon, O., 2013. Sika Concrete Handbook, Sika AG.
- Clay-carbon nanotubes hybrid materials for nanocomposite membranes: Advantages of branched structure for proton transport under low humidity conditions in PEMFCs. J. Phys. Chem. C. 2016;120:2574-2584.
- [Google Scholar]
- Magnesia-based cements: a journey of 150 years, and cements for the future? Chem. Rev.. 2016;116:4170-4204.
- [Google Scholar]
- Environmental resistance of cement concrete modified with low dosage nano particles. Constr. Build. Mater.. 2018;164:535-553.
- [Google Scholar]
- Efficiency of stress transfer between polymer matrix and nanoplatelets in clay/polymer nanocomposites. Appl. Clay Sci.. 2017;143:265-272.
- [Google Scholar]