- Email: [email protected]
Glass Composites on their Fire Behavior Properties
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 22526–22535
www.materialstoday.com/proceedings
ICASE-2017
Influence of Nanoclays to the Matrix of Vinylester/Glass Composites on their Fire Behavior Properties N. Raghavendra*a, H. N. Narasimha Murthyb, K. R.Vishnu Mahesh c, M. Mylarappa d, D. M. K.Siddeswara e, M. Krishnab a CMRTU, RV College of campus, Bengaluru -560059, Karnataka, India Department of Mechanical Engineering, R V College of Engineering, Bengaluru -560059, Karnataka, India c National Assessment and Accreditation Council, Bangalore -560072, Karnataka, India (An Autonomous Institution of the University Grants Commission) d Research Centre, Department of Chemistry, AMC Engineering College, Bannerghatta Road Bengaluru-560083, Karnataka, India (Affiliated to Tumkur University) e Department of Chemistry, Jyothi Institute of Technology, Bengaluru-560062 b
Abstract This paper presents the influence of dispersing Cloisite-Na and Cloisite-15A Nanoclays in vinylester/glass on their fire retardation behaviour. Cloisite-Na and Cloisite-15A in 1 to 5 wt % was dispersed in vinylester using the combination of ultrasonication and twin screw extrusion. Nanoclay/vinylester/glass specimens were fabricated using hand lay-up technique. XRD results of Nanoclay/vinylester gel coat showed exfoliation of Nanoclay up to 4 wt % loading. Glass transition temperature of Nanoclay /vinylester increased monotonically with increase in Nanoclay loading. Limiting oxygen index of Nanoclay /vinylester/glass specimens decreased monotonically with the addition of Cloisite-Na and Cloisite-15A. TGA study showed that the thermal degradation behavior improved in addition of nanoclay in vinylester. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017. Key words: Nanoclays, Vinylester, XRD, TGA, Fire retardancy.
* Corresponding author. Tel.: +91 9964612672. E-mail address: [email protected] 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017.
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1. Introduction Nanoclays are accepted as effective nano-fillers due to their lower cost and availability. Montmorillonite (MMT) improves the mechanical, thermal, fire and mechanical properties of polymers due to the changes in the interface interaction between MMT and the matrix [1]. Montmorillonite has a high surface area, of the order of 750 m2/g. Property enhancements are obtained due to molecular scale interactions between the polymer and the clay surface. These interactions are greater in exfoliated morphology, where the clay particles present the largest surface area, when they exist as individual platelets. Also, since during exfoliation clay aggregates break up into several nanometer sized individual platelets, very small clay loading can lead to significant property enhancements [2]. Exfoliated MMT imparts superior mechanical and fire properties. These new class of composites have been studied for their applications in structures such as spacecraft’s, airplanes, warships, marine vehicles, etc. which require high stiffness-to-weight ratio [3-6]. MMT platelets dispersed in polymeric resins can drastically increase the stiffness of the polymer [7]. MMT, classified as magnesium aluminum silicate, is a type of naturally occurring smectite clay that can be swollen by small molecules [8]. The presence of MMT in polymer matrix can substantially improve the fire performance [9]. Smectite clays, (Fig.1) such as montmorillonite, are valuable minerals and widely used in many industrial applications because of their high aspect ratio, plate morphology, natural abundance and low cost. They are expandable layered silicates and can be intercalated and/or exfoliated into nanocomposites. Recently, polymer nanocomposites emerged as one of the most promising developments in the area of Fire retardancy, appearing to offer significant advantages over conventional formulations. Much attention was diverted to the use of layered silicates (clay), as a great potential for producing materials characterized by improved Fire retardancy along with superior physical properties [10-14]. Research results, however, swiftly pointed out that clays, while exerting astonishing effects on some fire properties of the polymer, are not sufficient for commercial application, since they fail to act as stand-alone Fire retardants in important regulatory fire tests [15-18]. In order to meet these tests, polymer nanocomposites should therefore be used in conjunction with conventional Fire retardants. In that respect, the aim of this work is to review the scientific and technological advances in the use of clay fillers as fire retardants.
Fig .1 Smectite group
Vinylesters are preferred in marine applications due to their lower moisture absorption and mechanical property degradations than other resins such as epoxy, polyester and iso-polyester which are traditionally used for marine
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vehicles [19]. The dispersion of MMT in vinylester further improves the barrier properties of vinylester [20]. The scientific community has been attempting to tailor the structure and composition of materials at the nanometer scale. The effect of fillers on the composite properties depends on their concentration, particle size and shape of the fillers and their interaction with the matrix as well as compatibility [21]. Vinylester has the combination of superior mechanical properties of epoxy resin and the ease of processing of polyester resin. Vinylester/nanoclay has high potential for marine structural applications because of the inherent advantages of both the constituents. Vinylester has superior barrier properties and nanoclay dispersion in vinylester further improves the diffusion properties as well as fire retardation behaviour. Vinylester resin based nanocomposites should therefore be studied extensively to establish their importance in the world of polymer nanocomposites. The main objective of this research was to study the comparison of two nano clays influence in the vinylester/glass nanocomposites. Nanoclay dispersion studies were undertaken using XRD. Glass transition temperature and thermal degradation were studied using DSC and TGA respectively. Fire retardation was examined based on LOI results. 2. Experimental 2.1. Materials used The specifications of Nanoclays, vinylester, Glass fibre, and curing agents used in the present research are presented in Table 1 . Materials Vinylester resin.
Specifications
Suppliers
Density: 1.07 g/cc,
Naphtha Resins & Chemicals , India
UTS: 70 MPa, E: 3.2 Gpa. Cloisite-Na
Density: 2.86 g/cc Composition: Sodium, Alumino Magnesium Silicates.
Cloisite-15A
Density:1.66 g/cc
Southern Clay Products, USA
Composition Dimethyl, dehydrogenated tallow, quaternary ammonium surface treated alumino magnesium silicates. Glass fibre.
360 gsm, plain-woven fabric
Vetrotex, India.
UTS 1.0 Gpa, Modulus 40 Gpa Density 1.9 g/cc. Density: 0.94 g/cm3. Di-Methyl acetamide as promoter. Empee Corporation, India. Cobalt napthalate as accelerator
Density: 0.98 g/cm3.
Methyl Ethyl Ketone peroxide (MEKP) as catalyst.
Density: 1.17 g/cm3.
Table 1 Specifications of materials used in the research
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2.2. Processing Cloisite-Na and Cloisite-15A vinylester/glass composites Nanoclay loading 1-5 wt % in steps of one wt % was dispersed in vinylester using the combination of ultrasonication and twin screw extrusion. Nanoclay/vinylester gelcoat prepared was mixed with 2 wt % each of DiMethyl acetamide as promoter, Cobalt napthalate as accelerator and methyl ethyl ketone peroxide (MEKP) as catalyst at room temperature to initiate the cross-linking process, which was used to prepare CloisiteNa/vinylester/glass and Cloisite-15A/vinylester/carbon specimens using Hand lay-up technique. The fibre to resin ratio was maintained at 65:35 by wt % respectively and the specimens were cured at room temperature for 24 hours as per the manufacturer’s recommendation for marine applications. The frequency and duration of ultrasonication were 27 KHz and one hour respectively. The twin screw extrusion process was carried out at room temperature (30 0C), at 200 rpm and 10 passes for each sample. 3. Characterization 3.1. X-Ray Diffraction Studies X-Ray diffraction studies of the Nanoclay /vinylester gel coat was carried out using a high resolution X-ray Diffractometer (X’Pert PRO) at a scanning rate of 20 min-1 using CuKα radiation operating at 45 KV and 40 mA. XRD was aimed at studying the dispersion of NANOCLAY in vinylester based on the levels of d-spacing which indicates the exfoliation. 3.2. Atomic Force Microscope Atomic Force Microscope (Nanosurf Easy Scan, Contact mode (static force) with maximum Scan range: 70 µm, Maximum Z-range: 14 µm, drive resolution Z: 0.21 nm) was used to study the dispersion of nanofillers in vinylester resin by compositional mapping. 3.3. DSC and TGA Glass transition temperature, Tg of the 4 wt % Nanoclay/Vinylester specimens was obtained using DSC (Mettler DSC-823e, Temp range: 25 0C to 500 0C). A sample of weight 5 mg sealed in a hermetic aluminum crucible was used for the characterization. For obtaining the curing heat flow pattern of the composite, a dynamic scanning experiment was conducted from 25 0C to 150 0C at a heating rate of 20 C per minute in N2 atmosphere with a flow rate of 20 ml/min. Thermogravimetric Analysis (TGA) was carried out using Universal V4.5A TA Instrument from 250C to 800 0C at a heating rate of 10 0C / min in N2 atmosphere. 3.4. Fire Retardation tests using Limiting Oxygen index As per ASTM D2863 LOI is defined as the measure of minimum amount of oxygen in an environment (O2 + N2) necessary to initiate and support the burning (flame) under specified conditions. The specimen used for LOI test, being 150 mm long, 10 mm wide and 4 mm thick. The apparatus used for LOI was FTT flammability unit from UK. The test sample is positioned vertically in a glass chimney and an oxygen/nitrogen environment is established with a flow from the bottom of the chimney. The top edge of the test sample is ignited and the oxygen concentration in the flow is decreased until the flame is no longer supported. This is a very simple and advantageous method for assessing fire resistance of polymers. The critical amount of oxygen was measured.
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4. Results and Discussion 4.1. X-Ray Diffraction Studies XRD is one of the most useful methods to evaluate the d-spacing between the clay layers which is used to study the degree of dispersion of the nanoplatelets in the polymer matrix. The angle and the d-spacing are related through Bragg’s Law is given. [10]. nλ = 2d sin θ,
............ (1)
Intensity (Counts)
1600 1400 1200 1000 800 600 400 200 0
Intensity (Counts)
Where n is an integer, λ is the wavelength, θ is the angle of incidence, and d is the interplanar spacing of the crystal. XRD patterns of the pristine Cloisite-Na and Cloisite-15A nanoclays are shown in Fig. 2. Pristine CloisiteNa and Cloisite-15A showed d-spacing of 11.2 Å at 2θ = 7.5 and 31.5 Å at 2θ = 3.2. The higher d spacing value is observed in Cloisite-15A. In order to verify whether the resin molecules entered between the clay layers, the diffractograms of the CloisiteNa and Cloisite-15A dispersed vinylester were studied showed in Fig.3 and Fig.4. It was observed that up to 4 wt % loading no significant peaks are observed and at higher clay loading (5 wt %) slight peak was observed this indicates resin molecules could only penetrate in between the clay platelets causing intercalation, and could not delaminate the platelets. Nanocomposites are of two types from the structural stand point. They are intercalated and exfoliated. In intercalated nanoclay, the polymer molecules are inserted within the silicate layers of the clay forming well-ordered multi layers and in exfoliated nanoclay the silicate layers break into single platelets and orient themselves in a random manner [15].
2500
D = 1 1 .2 A
0
3 5 0 D = 3 1 .5 A
8
0
C lo is it e -N a
10
13
15
18
20
23
25
C lo is it e - 1 5 A
2000 1500 1000 500 0
0
3
5
8
10
13
15
18
20
23
25
2 D e g re e Fig. 2 XRD patrons of Pristine Cloisite-Na and Cloisite-15A powders
4.2. Atomic Force Microscope (AFM) AFM was used to study the dispersion of nano fillers in vinylester matrix by distributional mapping. The distributional mapping with AFM is often used for observation of multiple phases. The phase contrast is related to the inherent properties of the two phases. The brighter areas in the image can be attributed to the greater force experienced by the cantilever tip when in contact with the filler (tubular or spherical). The matrix is in amorphous state and hence appears red in the images.
N Raghavendra et al./ Materials Today: Proceedings 5 (2018) 22526–22535
Fig.3 XRD Patrons of Different % Cloisite-Na/Vinylester
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Fig.4 XRD Patrons of Different % Cloisite-15A/Vinylester
The nanoclay agglomerates are seen in 4 wt % C-Na/vinylester samples indicated in the micrographs of big bright spotsshown in Fig.5a) and b).Micrographs of 4 wt % C-15A/vinylester samples does not exhibit clay agglomerates as shown by the well scattered small bright spotsshown in Fig.5 c) and d)indicates good dispersion compared to Cloisite Na in Vinylester samples. This is because of the high d-spacing and large surface area of Cloisite 15A clay. a)
b)
c)
d)
Fig.5 AFM images of a) & b) 4% Cloisite-Na/vinylester and c) & d) 4%Cloisite-15A/vinylester
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4.3. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) Differential scanning calorimetry (Fig.6 and Fig.7) was used to determine the glass transition temperature, Tg of the Cloisite-Na and Cloisite-15A dispersed vinylester samples using the measurement of heat flow verses change in temperature. The Tg of the nanocomposites increased with increase in MMT loading, which may be due to the presence of clay platelets leading to better MMT dispersion and exfoliation. Also, the interaction of MMT and the vinylester network restricted the segmental mobility and thus resulted in higher Tg [16]. The increase in Tg in the present study was around 50 % for 4 wt % MMT dispersed vinylester gel coat compared to that of vinylester. The 2 wt % and 4 wt % MMT/vinylester composites were subjected to Thermogravimetric analysis and weight loss verses temperature is shown in Fig.8. The nature of degradation for 2 wt% and 4 wt % MMT/vinylester was similar, but with a significant difference in the residual weight. The residual weight for 2 w t% and 4 wt % MMT/vinylester was observed to be 7.42 % and 9.37 % respectively. This means that addition of MMT resulted in a higher residual weight. The rate of degradation was found to be lower in case of 4 wt % MMT/Vinylester composite. This indicates that MMT dispersed vinylester composite plays an important role in controlling its rate of thermal degradation. The clay platelets present in between the crosslinked resin molecules offered resistance towards their thermal degradation behaviour and, hence, the rate of degradation showed a lowering trend with the increase in MMT content [12].
Fig. 6 Glass Transition Temperature of Different Wt% of Cloisite-Na/Vinylester
4.4. Fire Retardation Behaviour – Horizontal and Vertical Burning rates ASTM D2863 is a method to determine the minimum concentration of oxygen in an oxygen/nitrogen mixture that will support a burning of test specimen. The limiting oxygen index was evaluated for all the composites filled with different weight percentage of fillers. Table 2 represents the limiting oxygen index of filled and unfilled composites. In the present study the values of limiting oxygen index of filled composites are in the range of 20-35. In practice the material is often called self-extinguishing material if LOI is greater than 24.36 Thus the results of the present study are in good agreement with the reported values. The results clearly indicate that the composites of the present study can be used in all fire resistance applications. The composites prepared using fillers give better fire resistance than unfilled composites and also there is increase in fire resistance with the increase in the amount of filler. The fire behavior of polymeric matrices can be improved by adding nanoclays. Tests show that the fire results
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are good with decrease in heat and smoke production during combustion and also decomposition does not release additional toxic gases. Cloisite 15A filled composites having very good thermal stability as compared to other composites and also all filled composites show better thermal stability than unfilled composites. The fire retardation of Cloisite-Na and Cloisite-15A/vinylester and glass fibre reinforced nanocomposites improved monotonically with increase in clay loading from 1 wt % to 5 wt %. The results of LOI are presented in Table 2 and Fig. 9. The 5 wt% Cloisite-Na and Cloisite-15A/vinylester and glass fibre reinforced nanocomposites showed maximum increase in LOI value of about 48 % and 53 % respectively compared to that of vinylester/glass. The formation of a surface layer during pyrolysis of the nanocomposites was usually considered to be the main cause of improved fire retardancy. This is because this layer acts as a heat barrier which preventing heat from transferring into unpyrolysed material. Also it increases the surface re-radiation heat losses with surface temperature. Adding MMT to vinyester/glass reduces the flammability and hence MMT acts as a good flame retardant [14].
Fig. 7 Glass Transition Temperature of Different Wt% of Cloisite-Na/Vinylester
Fig.8 TGA of 4Wt% Cloisite-Na and 4Wt% Cloisite-15/Vinylester nanocomposite
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Fig.9 Limiting Oxygen Index of C-Na and C-15A/Vinylester GFRP Composites Table.2 Compositions and fire resistance properties of composites from Vinylester resin. Composite Code
Resin Composition Wt.%
Reinforcement Wt. %
Filler Reinforcement Wt.%
Limiting Oxygen Index
Cloisite Na
Cloisite 15A
VGC-0
100
------
------
------
21
VGC-1
100
-----
1
------
22.8
VGC-2
100
------
2
------
23.2
VGC-3
100
------
3
------
24.1
VGC-4
100
------
4
------
24.9
VGC-5
100
------
5
------
25.2
VGC-6
100
------
------
1
23.2
VGC-7
100
------
------
2
23.9
VGC-8
100
------
------
3
24.8
VGC-9
100
------
------
4
25.5
VGC-10
100
------
------
5
26.2
VGC-11
35
65
------
------
25.3
VGC-12
35
65
1
------
28
VGC-13
35
65
2
------
29
VGC-14
35
65
3
------
30.2
VGC-15
35
65
4
------
31.3
VGC-16
35
65
5
------
32
VGC-17
35
65
------
1
30
VGC-18
35
65
------
2
30.8
VGC-19
35
65
------
3
31.5
VGC-20
35
65
------
4
32.9
VGC-21
35
65
------
5
34
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Acknowledgement The authors gratefully acknowledge University Grants Commission (UGC), New Delhi for the financial support for this research, through NFST, Scholarship for the year 2016-2017 (F1-17.1/2016-17/NFST-2015-17-STKAR90/(SA-III/Website) to complete this research work. References [1] SaminathanK, SelvakumarP, Naresh Bhatnagar, Polymer Testing, 27(3) (2008), 296-307. [2] Dennis H. R., Hunter D. L., Chang D., Kim S., White J. L., Cho J. W., Paul D. R., Polymer, 42, (2001), 9513 - 9522 [3] Schmidt D, Shah D and Giannelis, E.P., Current Opinion in Solid State and Mater. Sci., 6(3) (2002). 205-212. [4] Ray, S.S. and Okamoto M, Prog. Polymer Sci., 28 (2003), 1539–1641. [5] Bhat G., Hegde1 R. R., Kamath M.G., and Deshpande B, J. of Engg. Fibers and Fabrics, 3(3) (2008), 22-34 [6] Alexandre M, Dubois P, Mater. Sci. and Engg., Report 28 (1-2) (2000), 1-63. [7] Arun K Subramaniyan and C.T Sun, J. of Composite Materials, 42(20) (2008), 2111-2122. [8] K Kanny, P.Jawahar, V.K Moodley, Jof Mater. Sci., 43, (2008), 7230-7238. [9] Zhongfu Zhao, Jihua Gou, Stefano Bietto, Christopher Ibeh, David Hui, Composite Sci. and Technol., 69,(2009), 2081-2087. [10] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, J. of Nano Engg. and Nanosys. 229 (2), (2015),55-65. [11] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, Sharma S.C, J. of Front. of Mater. Sci., 7(4), (2013), 396-404. [12] Vishnu Mahesh K. R, Narasimha Murthy H. N, Kumara Swamy B. E, Sridhar R, Ashok Kumar M, Raghavendra N, Raj Kumar G. R, Krishna M and Sherigara B. S, Inter. J. of Sci. Research., 01(01), (2012),06-11. [13] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, J. of Vinyl and Addit., Article first published online: 17 FEB (2015) (DOI: 10.1002/vnl.21463). Online ISSN: 1548-0585. [14] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, J. of Nano Engg. and Nanosys., 2015, (Accepted for Publication). [15] Vishnu MaheshK. R, Narasimha MurthyH. N, RaghavendraN, SridharR, KumaraswamyB. E, KrishnaM, Front. of Chem. in China, 6(2), (2011),153–158. [16] Vishnu MaheshK. R, Narasimha MurthyH. N, KumaraswamyB. E, RaghavendraN, KrishnaM, Key Engg. Mater. 659, (2015), 468-473. [17] Raghavendra N, Narasimha Murthy H N, Vishnu Mahesh K R, Mylarappa M, Ashik K P, Siddeswara D M K, Krishna M, Materials Today: Proceedings, 4 (2017) 12109–12117. [18] Sreejith M, Narasimha MurthyH.N, RaiK.S, KrishnaM., Jeena J.K, Iranian Polymer J, 19(2), (2010), 89-103. [19] Fabienne Samyn, Serge Bourbigot, Charafeddine Jama, Se verine Bellayer, Polymer Degradation and Stability, 93 (2008), 2019–2024. [20] In-Yup Jeon and Jong-Beom Baek, Materials, 3 (2010), 3654-3674. [21] Diparay, Suparna Sengupta, SenguptaS.P, Macromol.Mater.Engg, 291, (2006), 1513–1520.
ScienceDirect Materials Today: Proceedings 5 (2018) 22526–22535
www.materialstoday.com/proceedings
ICASE-2017
Influence of Nanoclays to the Matrix of Vinylester/Glass Composites on their Fire Behavior Properties N. Raghavendra*a, H. N. Narasimha Murthyb, K. R.Vishnu Mahesh c, M. Mylarappa d, D. M. K.Siddeswara e, M. Krishnab a CMRTU, RV College of campus, Bengaluru -560059, Karnataka, India Department of Mechanical Engineering, R V College of Engineering, Bengaluru -560059, Karnataka, India c National Assessment and Accreditation Council, Bangalore -560072, Karnataka, India (An Autonomous Institution of the University Grants Commission) d Research Centre, Department of Chemistry, AMC Engineering College, Bannerghatta Road Bengaluru-560083, Karnataka, India (Affiliated to Tumkur University) e Department of Chemistry, Jyothi Institute of Technology, Bengaluru-560062 b
Abstract This paper presents the influence of dispersing Cloisite-Na and Cloisite-15A Nanoclays in vinylester/glass on their fire retardation behaviour. Cloisite-Na and Cloisite-15A in 1 to 5 wt % was dispersed in vinylester using the combination of ultrasonication and twin screw extrusion. Nanoclay/vinylester/glass specimens were fabricated using hand lay-up technique. XRD results of Nanoclay/vinylester gel coat showed exfoliation of Nanoclay up to 4 wt % loading. Glass transition temperature of Nanoclay /vinylester increased monotonically with increase in Nanoclay loading. Limiting oxygen index of Nanoclay /vinylester/glass specimens decreased monotonically with the addition of Cloisite-Na and Cloisite-15A. TGA study showed that the thermal degradation behavior improved in addition of nanoclay in vinylester. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017. Key words: Nanoclays, Vinylester, XRD, TGA, Fire retardancy.
* Corresponding author. Tel.: +91 9964612672. E-mail address: [email protected] 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility ofInternational Conference on Advances in Science & Engineering ICASE - 2017.
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1. Introduction Nanoclays are accepted as effective nano-fillers due to their lower cost and availability. Montmorillonite (MMT) improves the mechanical, thermal, fire and mechanical properties of polymers due to the changes in the interface interaction between MMT and the matrix [1]. Montmorillonite has a high surface area, of the order of 750 m2/g. Property enhancements are obtained due to molecular scale interactions between the polymer and the clay surface. These interactions are greater in exfoliated morphology, where the clay particles present the largest surface area, when they exist as individual platelets. Also, since during exfoliation clay aggregates break up into several nanometer sized individual platelets, very small clay loading can lead to significant property enhancements [2]. Exfoliated MMT imparts superior mechanical and fire properties. These new class of composites have been studied for their applications in structures such as spacecraft’s, airplanes, warships, marine vehicles, etc. which require high stiffness-to-weight ratio [3-6]. MMT platelets dispersed in polymeric resins can drastically increase the stiffness of the polymer [7]. MMT, classified as magnesium aluminum silicate, is a type of naturally occurring smectite clay that can be swollen by small molecules [8]. The presence of MMT in polymer matrix can substantially improve the fire performance [9]. Smectite clays, (Fig.1) such as montmorillonite, are valuable minerals and widely used in many industrial applications because of their high aspect ratio, plate morphology, natural abundance and low cost. They are expandable layered silicates and can be intercalated and/or exfoliated into nanocomposites. Recently, polymer nanocomposites emerged as one of the most promising developments in the area of Fire retardancy, appearing to offer significant advantages over conventional formulations. Much attention was diverted to the use of layered silicates (clay), as a great potential for producing materials characterized by improved Fire retardancy along with superior physical properties [10-14]. Research results, however, swiftly pointed out that clays, while exerting astonishing effects on some fire properties of the polymer, are not sufficient for commercial application, since they fail to act as stand-alone Fire retardants in important regulatory fire tests [15-18]. In order to meet these tests, polymer nanocomposites should therefore be used in conjunction with conventional Fire retardants. In that respect, the aim of this work is to review the scientific and technological advances in the use of clay fillers as fire retardants.
Fig .1 Smectite group
Vinylesters are preferred in marine applications due to their lower moisture absorption and mechanical property degradations than other resins such as epoxy, polyester and iso-polyester which are traditionally used for marine
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vehicles [19]. The dispersion of MMT in vinylester further improves the barrier properties of vinylester [20]. The scientific community has been attempting to tailor the structure and composition of materials at the nanometer scale. The effect of fillers on the composite properties depends on their concentration, particle size and shape of the fillers and their interaction with the matrix as well as compatibility [21]. Vinylester has the combination of superior mechanical properties of epoxy resin and the ease of processing of polyester resin. Vinylester/nanoclay has high potential for marine structural applications because of the inherent advantages of both the constituents. Vinylester has superior barrier properties and nanoclay dispersion in vinylester further improves the diffusion properties as well as fire retardation behaviour. Vinylester resin based nanocomposites should therefore be studied extensively to establish their importance in the world of polymer nanocomposites. The main objective of this research was to study the comparison of two nano clays influence in the vinylester/glass nanocomposites. Nanoclay dispersion studies were undertaken using XRD. Glass transition temperature and thermal degradation were studied using DSC and TGA respectively. Fire retardation was examined based on LOI results. 2. Experimental 2.1. Materials used The specifications of Nanoclays, vinylester, Glass fibre, and curing agents used in the present research are presented in Table 1 . Materials Vinylester resin.
Specifications
Suppliers
Density: 1.07 g/cc,
Naphtha Resins & Chemicals , India
UTS: 70 MPa, E: 3.2 Gpa. Cloisite-Na
Density: 2.86 g/cc Composition: Sodium, Alumino Magnesium Silicates.
Cloisite-15A
Density:1.66 g/cc
Southern Clay Products, USA
Composition Dimethyl, dehydrogenated tallow, quaternary ammonium surface treated alumino magnesium silicates. Glass fibre.
360 gsm, plain-woven fabric
Vetrotex, India.
UTS 1.0 Gpa, Modulus 40 Gpa Density 1.9 g/cc. Density: 0.94 g/cm3. Di-Methyl acetamide as promoter. Empee Corporation, India. Cobalt napthalate as accelerator
Density: 0.98 g/cm3.
Methyl Ethyl Ketone peroxide (MEKP) as catalyst.
Density: 1.17 g/cm3.
Table 1 Specifications of materials used in the research
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2.2. Processing Cloisite-Na and Cloisite-15A vinylester/glass composites Nanoclay loading 1-5 wt % in steps of one wt % was dispersed in vinylester using the combination of ultrasonication and twin screw extrusion. Nanoclay/vinylester gelcoat prepared was mixed with 2 wt % each of DiMethyl acetamide as promoter, Cobalt napthalate as accelerator and methyl ethyl ketone peroxide (MEKP) as catalyst at room temperature to initiate the cross-linking process, which was used to prepare CloisiteNa/vinylester/glass and Cloisite-15A/vinylester/carbon specimens using Hand lay-up technique. The fibre to resin ratio was maintained at 65:35 by wt % respectively and the specimens were cured at room temperature for 24 hours as per the manufacturer’s recommendation for marine applications. The frequency and duration of ultrasonication were 27 KHz and one hour respectively. The twin screw extrusion process was carried out at room temperature (30 0C), at 200 rpm and 10 passes for each sample. 3. Characterization 3.1. X-Ray Diffraction Studies X-Ray diffraction studies of the Nanoclay /vinylester gel coat was carried out using a high resolution X-ray Diffractometer (X’Pert PRO) at a scanning rate of 20 min-1 using CuKα radiation operating at 45 KV and 40 mA. XRD was aimed at studying the dispersion of NANOCLAY in vinylester based on the levels of d-spacing which indicates the exfoliation. 3.2. Atomic Force Microscope Atomic Force Microscope (Nanosurf Easy Scan, Contact mode (static force) with maximum Scan range: 70 µm, Maximum Z-range: 14 µm, drive resolution Z: 0.21 nm) was used to study the dispersion of nanofillers in vinylester resin by compositional mapping. 3.3. DSC and TGA Glass transition temperature, Tg of the 4 wt % Nanoclay/Vinylester specimens was obtained using DSC (Mettler DSC-823e, Temp range: 25 0C to 500 0C). A sample of weight 5 mg sealed in a hermetic aluminum crucible was used for the characterization. For obtaining the curing heat flow pattern of the composite, a dynamic scanning experiment was conducted from 25 0C to 150 0C at a heating rate of 20 C per minute in N2 atmosphere with a flow rate of 20 ml/min. Thermogravimetric Analysis (TGA) was carried out using Universal V4.5A TA Instrument from 250C to 800 0C at a heating rate of 10 0C / min in N2 atmosphere. 3.4. Fire Retardation tests using Limiting Oxygen index As per ASTM D2863 LOI is defined as the measure of minimum amount of oxygen in an environment (O2 + N2) necessary to initiate and support the burning (flame) under specified conditions. The specimen used for LOI test, being 150 mm long, 10 mm wide and 4 mm thick. The apparatus used for LOI was FTT flammability unit from UK. The test sample is positioned vertically in a glass chimney and an oxygen/nitrogen environment is established with a flow from the bottom of the chimney. The top edge of the test sample is ignited and the oxygen concentration in the flow is decreased until the flame is no longer supported. This is a very simple and advantageous method for assessing fire resistance of polymers. The critical amount of oxygen was measured.
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4. Results and Discussion 4.1. X-Ray Diffraction Studies XRD is one of the most useful methods to evaluate the d-spacing between the clay layers which is used to study the degree of dispersion of the nanoplatelets in the polymer matrix. The angle and the d-spacing are related through Bragg’s Law is given. [10]. nλ = 2d sin θ,
............ (1)
Intensity (Counts)
1600 1400 1200 1000 800 600 400 200 0
Intensity (Counts)
Where n is an integer, λ is the wavelength, θ is the angle of incidence, and d is the interplanar spacing of the crystal. XRD patterns of the pristine Cloisite-Na and Cloisite-15A nanoclays are shown in Fig. 2. Pristine CloisiteNa and Cloisite-15A showed d-spacing of 11.2 Å at 2θ = 7.5 and 31.5 Å at 2θ = 3.2. The higher d spacing value is observed in Cloisite-15A. In order to verify whether the resin molecules entered between the clay layers, the diffractograms of the CloisiteNa and Cloisite-15A dispersed vinylester were studied showed in Fig.3 and Fig.4. It was observed that up to 4 wt % loading no significant peaks are observed and at higher clay loading (5 wt %) slight peak was observed this indicates resin molecules could only penetrate in between the clay platelets causing intercalation, and could not delaminate the platelets. Nanocomposites are of two types from the structural stand point. They are intercalated and exfoliated. In intercalated nanoclay, the polymer molecules are inserted within the silicate layers of the clay forming well-ordered multi layers and in exfoliated nanoclay the silicate layers break into single platelets and orient themselves in a random manner [15].
2500
D = 1 1 .2 A
0
3 5 0 D = 3 1 .5 A
8
0
C lo is it e -N a
10
13
15
18
20
23
25
C lo is it e - 1 5 A
2000 1500 1000 500 0
0
3
5
8
10
13
15
18
20
23
25
2 D e g re e Fig. 2 XRD patrons of Pristine Cloisite-Na and Cloisite-15A powders
4.2. Atomic Force Microscope (AFM) AFM was used to study the dispersion of nano fillers in vinylester matrix by distributional mapping. The distributional mapping with AFM is often used for observation of multiple phases. The phase contrast is related to the inherent properties of the two phases. The brighter areas in the image can be attributed to the greater force experienced by the cantilever tip when in contact with the filler (tubular or spherical). The matrix is in amorphous state and hence appears red in the images.
N Raghavendra et al./ Materials Today: Proceedings 5 (2018) 22526–22535
Fig.3 XRD Patrons of Different % Cloisite-Na/Vinylester
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Fig.4 XRD Patrons of Different % Cloisite-15A/Vinylester
The nanoclay agglomerates are seen in 4 wt % C-Na/vinylester samples indicated in the micrographs of big bright spotsshown in Fig.5a) and b).Micrographs of 4 wt % C-15A/vinylester samples does not exhibit clay agglomerates as shown by the well scattered small bright spotsshown in Fig.5 c) and d)indicates good dispersion compared to Cloisite Na in Vinylester samples. This is because of the high d-spacing and large surface area of Cloisite 15A clay. a)
b)
c)
d)
Fig.5 AFM images of a) & b) 4% Cloisite-Na/vinylester and c) & d) 4%Cloisite-15A/vinylester
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4.3. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) Differential scanning calorimetry (Fig.6 and Fig.7) was used to determine the glass transition temperature, Tg of the Cloisite-Na and Cloisite-15A dispersed vinylester samples using the measurement of heat flow verses change in temperature. The Tg of the nanocomposites increased with increase in MMT loading, which may be due to the presence of clay platelets leading to better MMT dispersion and exfoliation. Also, the interaction of MMT and the vinylester network restricted the segmental mobility and thus resulted in higher Tg [16]. The increase in Tg in the present study was around 50 % for 4 wt % MMT dispersed vinylester gel coat compared to that of vinylester. The 2 wt % and 4 wt % MMT/vinylester composites were subjected to Thermogravimetric analysis and weight loss verses temperature is shown in Fig.8. The nature of degradation for 2 wt% and 4 wt % MMT/vinylester was similar, but with a significant difference in the residual weight. The residual weight for 2 w t% and 4 wt % MMT/vinylester was observed to be 7.42 % and 9.37 % respectively. This means that addition of MMT resulted in a higher residual weight. The rate of degradation was found to be lower in case of 4 wt % MMT/Vinylester composite. This indicates that MMT dispersed vinylester composite plays an important role in controlling its rate of thermal degradation. The clay platelets present in between the crosslinked resin molecules offered resistance towards their thermal degradation behaviour and, hence, the rate of degradation showed a lowering trend with the increase in MMT content [12].
Fig. 6 Glass Transition Temperature of Different Wt% of Cloisite-Na/Vinylester
4.4. Fire Retardation Behaviour – Horizontal and Vertical Burning rates ASTM D2863 is a method to determine the minimum concentration of oxygen in an oxygen/nitrogen mixture that will support a burning of test specimen. The limiting oxygen index was evaluated for all the composites filled with different weight percentage of fillers. Table 2 represents the limiting oxygen index of filled and unfilled composites. In the present study the values of limiting oxygen index of filled composites are in the range of 20-35. In practice the material is often called self-extinguishing material if LOI is greater than 24.36 Thus the results of the present study are in good agreement with the reported values. The results clearly indicate that the composites of the present study can be used in all fire resistance applications. The composites prepared using fillers give better fire resistance than unfilled composites and also there is increase in fire resistance with the increase in the amount of filler. The fire behavior of polymeric matrices can be improved by adding nanoclays. Tests show that the fire results
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are good with decrease in heat and smoke production during combustion and also decomposition does not release additional toxic gases. Cloisite 15A filled composites having very good thermal stability as compared to other composites and also all filled composites show better thermal stability than unfilled composites. The fire retardation of Cloisite-Na and Cloisite-15A/vinylester and glass fibre reinforced nanocomposites improved monotonically with increase in clay loading from 1 wt % to 5 wt %. The results of LOI are presented in Table 2 and Fig. 9. The 5 wt% Cloisite-Na and Cloisite-15A/vinylester and glass fibre reinforced nanocomposites showed maximum increase in LOI value of about 48 % and 53 % respectively compared to that of vinylester/glass. The formation of a surface layer during pyrolysis of the nanocomposites was usually considered to be the main cause of improved fire retardancy. This is because this layer acts as a heat barrier which preventing heat from transferring into unpyrolysed material. Also it increases the surface re-radiation heat losses with surface temperature. Adding MMT to vinyester/glass reduces the flammability and hence MMT acts as a good flame retardant [14].
Fig. 7 Glass Transition Temperature of Different Wt% of Cloisite-Na/Vinylester
Fig.8 TGA of 4Wt% Cloisite-Na and 4Wt% Cloisite-15/Vinylester nanocomposite
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Fig.9 Limiting Oxygen Index of C-Na and C-15A/Vinylester GFRP Composites Table.2 Compositions and fire resistance properties of composites from Vinylester resin. Composite Code
Resin Composition Wt.%
Reinforcement Wt. %
Filler Reinforcement Wt.%
Limiting Oxygen Index
Cloisite Na
Cloisite 15A
VGC-0
100
------
------
------
21
VGC-1
100
-----
1
------
22.8
VGC-2
100
------
2
------
23.2
VGC-3
100
------
3
------
24.1
VGC-4
100
------
4
------
24.9
VGC-5
100
------
5
------
25.2
VGC-6
100
------
------
1
23.2
VGC-7
100
------
------
2
23.9
VGC-8
100
------
------
3
24.8
VGC-9
100
------
------
4
25.5
VGC-10
100
------
------
5
26.2
VGC-11
35
65
------
------
25.3
VGC-12
35
65
1
------
28
VGC-13
35
65
2
------
29
VGC-14
35
65
3
------
30.2
VGC-15
35
65
4
------
31.3
VGC-16
35
65
5
------
32
VGC-17
35
65
------
1
30
VGC-18
35
65
------
2
30.8
VGC-19
35
65
------
3
31.5
VGC-20
35
65
------
4
32.9
VGC-21
35
65
------
5
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Acknowledgement The authors gratefully acknowledge University Grants Commission (UGC), New Delhi for the financial support for this research, through NFST, Scholarship for the year 2016-2017 (F1-17.1/2016-17/NFST-2015-17-STKAR90/(SA-III/Website) to complete this research work. References [1] SaminathanK, SelvakumarP, Naresh Bhatnagar, Polymer Testing, 27(3) (2008), 296-307. [2] Dennis H. R., Hunter D. L., Chang D., Kim S., White J. L., Cho J. W., Paul D. R., Polymer, 42, (2001), 9513 - 9522 [3] Schmidt D, Shah D and Giannelis, E.P., Current Opinion in Solid State and Mater. Sci., 6(3) (2002). 205-212. [4] Ray, S.S. and Okamoto M, Prog. Polymer Sci., 28 (2003), 1539–1641. [5] Bhat G., Hegde1 R. R., Kamath M.G., and Deshpande B, J. of Engg. Fibers and Fabrics, 3(3) (2008), 22-34 [6] Alexandre M, Dubois P, Mater. Sci. and Engg., Report 28 (1-2) (2000), 1-63. [7] Arun K Subramaniyan and C.T Sun, J. of Composite Materials, 42(20) (2008), 2111-2122. [8] K Kanny, P.Jawahar, V.K Moodley, Jof Mater. Sci., 43, (2008), 7230-7238. [9] Zhongfu Zhao, Jihua Gou, Stefano Bietto, Christopher Ibeh, David Hui, Composite Sci. and Technol., 69,(2009), 2081-2087. [10] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, J. of Nano Engg. and Nanosys. 229 (2), (2015),55-65. [11] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, Sharma S.C, J. of Front. of Mater. Sci., 7(4), (2013), 396-404. [12] Vishnu Mahesh K. R, Narasimha Murthy H. N, Kumara Swamy B. E, Sridhar R, Ashok Kumar M, Raghavendra N, Raj Kumar G. R, Krishna M and Sherigara B. S, Inter. J. of Sci. Research., 01(01), (2012),06-11. [13] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, J. of Vinyl and Addit., Article first published online: 17 FEB (2015) (DOI: 10.1002/vnl.21463). Online ISSN: 1548-0585. [14] Raghavendra N, Narasimha Murthy H.N, Vishnu Mahesh K.R, Sridhar R, Krishna M, Gangadhar Angadi, Salim Firdosh, J. of Nano Engg. and Nanosys., 2015, (Accepted for Publication). [15] Vishnu MaheshK. R, Narasimha MurthyH. N, RaghavendraN, SridharR, KumaraswamyB. E, KrishnaM, Front. of Chem. in China, 6(2), (2011),153–158. [16] Vishnu MaheshK. R, Narasimha MurthyH. N, KumaraswamyB. E, RaghavendraN, KrishnaM, Key Engg. Mater. 659, (2015), 468-473. [17] Raghavendra N, Narasimha Murthy H N, Vishnu Mahesh K R, Mylarappa M, Ashik K P, Siddeswara D M K, Krishna M, Materials Today: Proceedings, 4 (2017) 12109–12117. [18] Sreejith M, Narasimha MurthyH.N, RaiK.S, KrishnaM., Jeena J.K, Iranian Polymer J, 19(2), (2010), 89-103. [19] Fabienne Samyn, Serge Bourbigot, Charafeddine Jama, Se verine Bellayer, Polymer Degradation and Stability, 93 (2008), 2019–2024. [20] In-Yup Jeon and Jong-Beom Baek, Materials, 3 (2010), 3654-3674. [21] Diparay, Suparna Sengupta, SenguptaS.P, Macromol.Mater.Engg, 291, (2006), 1513–1520.