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Effect of nanofillers on the properties of natural fiber reinforced polymer composites
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 647–654
www.materialstoday.com/proceedings
ICN3I-2017
Effect of nanofillers on the properties of natural fiber reinforced polymer composites G.L.Devnania*, Shishir Sinhab a,b
Chemical Engineering, IIT Roorkee, Roorkee, 247667, India
Abstract
Nanofillers are bringing exemplary changes in the field of material science and polymer composites. In this sophisticated process a small amount of material is added to a variety of polymers and other materials which can drastically improve the performance and quality of materials including thermal, mechanical, water absorption and flame retardancy etc. Nano fillers can be considered as additives in solid form which can upgrade the various properties of original materials without increasing the density of materials. Now a days researchers are using natural fibers as an alternative reinforcement of synthetic fibers in polymer composites because of their cost effectiveness, biodegradability, lower weight, good mechanical properties and sustainability but the compatibility issue of hydrophobic polymer matrix and hydrophilic fibers is still a concern which ultimately leads to degradation in performance of these composites. Attempts have been made to increase the compatibility between the polymer matrix and the natural fibers with the help of various surface treatments strategies like alkylation, acetylation, maleated coupling etc. Nano particles or nano fillers have tremendous potential to be used as filler material which can improve the properties of polymer composites. Academicians and researchers have used Nano clay, Nano SIO2, carbon nanotubes and many other nanofillers in natural fiber reinforced polymer composites for improvement in properties. Nano clay has shown its potential in decrease in water absorption in sisal fiber reinforced composites which is highly desirable similarly Nano SIO2 has been proven very useful for the improvement in mechanical properties of these composites moreover carbon nano tubes have also exhibited its importance in improvement of mechanical and water absorption properties of bamboo and ramie fiber reinforced polymer composites. Present study provides a review of recent advances on the effect of nanofillers on the properties of natural fiber reinforced polymer composites. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i-2017). Keywords: natural fiber ; hydrophilic ; nanofillers ; polymer composites
* Corresponding author. Tel.: +91-9450333762. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017).
648
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
1. Introduction With the progress in the field of nanotechnology, it is boosting the research in various area like materials, medicines, surface science, semiconductors, energy storage, environment etc. Small amount of nano materials are bringing drastic changes and improving the performance and properties of materials. In recent years lot of emphasis is there to use renewable and environment friendly materials which are sustainable in nature, without compromising the quality of original materials. Natural fiber reinforced polymer composites (NFRC) is one such area where traditional synthetic fibers like glass and carbon are being replaced by natural fibers which are easily available , renewable and biodegradable in nature. A good progress has been made in this field and decent number of review papers are available in this field. Pickering et al. [1] gave an overview of the factors that are essential for the performance of natural fiber reinforced polymer composites. Saba et al. [2] provided the compilation of dynamic mechanical properties of these composites. The effects of waste material is critically reviewed by Vaisanen et al. [3]. All the developments that occurred during 2000-2010 was examined by Faruk et al.[4] , they described about various natural fibers, their availability, treatment methods and about various polymer matrix that had been used. A comprehensive review on the characterization techniques and properties of these composites is done by sanjay et al. [5].Sood and Dwivedi [6] concentrated on flexural properties of these NFRC. Oqla et al [7] reported about conductive polymer composites which fall in the category of natural fiber reinforced composites. Processing and characterisation of natural cellulose fiber in thermoses matrix was explained by Thakur and Thakur [8]. Omrani et al. [9] reviewed the tribological behavior of polymer matrix composites reinforced by these novel materials and evaluated the application of these materials Vaisanen et al.[10] told about utilization of agricultural and forest industry waste and residues in these NFRC's in his report. Being lignocellulosic these fibers are hydrophilic in nature while the matrix in which they are to be reinforced is a polymeric material which is hydrophobic in nature so the compatibility between these two opposite natured materials is still a challenge. Many surface treatment methods have been experimented [11-14]] to improve the adhesion between polymer matrix and fibers. Kabir et al. [11] emphasized the significance of chemically treated natural fibers for the improvement in the performance of their composites. Li et al [12]. reviewed different chemical treatment methodologies and their mechanism for the property enhancement in the composites. Mohanty et al. [13] described about surface modifications of natural fibers and its effect on their biocomposites . Cruz and Fangueiro[14] also told about surface modifications of these green materials., With the advent of nanotechnology and use of nanofillers in the field of natural fiber reinforced polymer composites researchers and academicians are getting encouraging results [15-16]. Hosseini [15] did a phenomenal review in the use of nanofillers for natural fiber reinforced polymer composites and described about most of the common nanofillers and their effect on the performance of theses composites . Saba also did a [16] very good compilation to evaluate the potentiality of nanofillers/natural fiber in the field of composites 2. Various nano fillers used in natural fiber reinforced polymer composites Nanofillers are considered to be materials which can be added in solid form having different properties like structure and composition from polymer matrix and lignocellulosic fibers. They may be one dimensional in the form of plates and laminas or two dimensional in the form of nano tubes and nano fibers or may be three dimensional in the form of isodimensional nanoparticlea. They generally comprise inorganic substances and some times organic as well. Various nanofillers used in natural fiber reinforced polymer composites are nanoclays primarily montmorillonite ,[17,18, 19, 20,21,22, ] nano SIO2[23,24] , nano TIO2[25], carbon nanotubes [26,27], nanographene, etc [28,29]. Apart from these traditional fillers some other nano fillers like oil palm nano filler has also been tested [30]. The addition of small amount of these fillers can improve the mechanical, thermal and water absorption properties in a significant manner. 3. Effect of nanofillers on properties of natural fiber reinforced polymer composites Ashori and Nouabksh [17] developed polypropylene composites reinforced by wood flour with injection molding process and concluded that at 6% montmorillonite (MMT) clay loading there is a improvement of tensile strength by
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
649
20% and flexural strength by 13% and also lower water absorption at clay loading of 3%.Mohan and Kanny [18] observed the 27% increase in tensile strength and 47% increase in tensile modulus by use of 2 to 5% MMT loading in case of epoxy composites with sisal fibers, they also observed reduction of water absorption by 1/3 in case of 5% nanoclay filled composites. Haq et al. [19] prepared hemp fiber reinforced polyester composites by compression molding and used clay loading from 0 to 1.5% and found that moisture absorption is reduced by 8% but at the same time tensile strength is also reduced by 20% for naoclay filled composites. Han et al. [20] used melt compounding method for the fabrication of bamboo based high density polythene composites and demonstrated that addition of MMT clay led to negative effect on mechanical properties. Ibrahim et al. [21] showed positive effect of MMT clay on polypropylene -sisal composites and noticed best tensile strength in case of composites with 5% coupling agent , 5% nano clay and 40% treated fiber. Venkatraman et al.[22] looked the characteristics of polyester- sisal composites using Garamite nano clay and realized substantial increase in mechanical properties and decrease in water absorption. 25% fiber loading and 3% clay loading was optimum for the improved performance of composites. Hosseini et al [23] used Nano SiO2 filler with 2 and 5% loading for the development of high density polyethylene composites reinforced by bagasse fiber and inspected that there is 71.46% increase in tensile strength in composites filled by nano SiO2. Similar improvement was also observed by Jiang et al. [24] in the wood-urea formaldehyde composites having 1% nano SiO2 as filler. Vilakati et al.[25] experimented 2% TiO2 as filler in bagasse-vinyl acetate composites and revealed that there is 10% up gradation of tensile strength. Another class of nano filler, carbon nano tubes (CNT) was tested by Kushwaha et al [26] in their work. They processed epoxy composites reinforced with bamboo fibers by simple hand lay up method , there findings were 6.67% increase in tensile strength and 5.8% in flexural strength and at the same time reduction in water absorption from 26.28% to 23.18%.Same nano filler CNT was used by Shen et al.[27] in the preparation of epoxy composites reinforced by ramie fibers , they varied the CNT loading from 0 to 0.6% and recognized 34% and 37% increase in flexural strength and modulus respectively. Nano grpahene is also a very important nano filler which is tested by Chaharmahali et al. [28] and Sridharan et al. [29] in bagasse -polypropylene and jute -epoxy composites respectively and observed improvement in tensile flexural and impact properties. Saba et al. utilized oil palm nano filler for the enhancement in the properties of kenaf-epoxy composites. The summary of upgradation and improvement in the properties of natural fiber reinforced polymer composites by addition of nano fillers is described in Table 1
Table1 : Summary of effect of nano fillers on the properties of natural fiber reinforced composites
Matrix
Fiber
Nano filler used
Application of that nano filler
Loading percentage of fiber and clay
Method
Poly propylene
Wood flour
Mont morillonite (MMT) based nanoclay Cloisite 20A
Material applications
30% fiber loading and clay loading is from 0 to 6% and coupling agent
Injection molding
Improve ment in mechanical and water absorption properties property as compare to absence of nanofiller (a)Improveme nt in tensile strength by 20% and flexural strength by 13% (b)
Reference
Ashori and Nourabaksh 2011, [17]
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G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
maleated polypropyl ene from 0 to 7.5%
Epoxy
Sisal
Mont morillonite (MMT) based nanoclay Cloisite 30B
Unsaturated polyester resin partially substituted by epoxi dized soybean oil
Hemp
High density Poly ethylene
Poly propylene
Drug delivery carriers , Material applications Rheology modifiers , Gas absorbents , Nano composites
50% fiber loading and clay loading is from 2 to 5%
Vacuum assisted resin infusion molding
Cloisite 30B
21-22% fiber loading and clay loading is 0 to 1.5%
Compressi on molding
Bamboo
Mont morillonite clay filler
Melt comp ounding
Sisal
Organically modified mont morillonite (MMT) based nanoclay Cloisite 30B
25 to 30% fiber loading and clay loading is from 0 to 5% 10-40% fiber loading and with 5 gram maleic anhydride grafted poly propylene
Comp ression molding
Composites prepared with 3% nanoclay exhibited lower water absorption (a) 27% increase in tensile strength and 47% increase in tensile modulus (b)Uptake in equilibrium water is reduced to one third in case of 5% nanoclay filled composites
Mohan and Kanny 2011,[18]
(a) Decrease in ultimate tensile strength by 20% (b) Moisture absorption reduced by 8% Addition of clay led to negative effect on mechanical properties
Haq et al. 2008 , [19]
(a) Composites with 5% coupling agent, 5% nanoclay, 40% treated fibers showed best tensile strength (b)
Ibrahim et al. 2017, [21]
Han et al. 2008 , [20]
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
Polyester
Sisal
Nanoclay (Garamite)
Rheology modifier
25% fiber loading and 3% clay
Compressi on molding
High density poly ethylene
Bagasse fiber
Nano -SiO2
Improves concrete workability, bio medical applications
40% fiber loading and 2 and 5% Nano -SiO2
Injection molding
Urea Formal dehyde
Wood
Nano -SiO2
Improves concrete workability, bio medical applications
20% wood and 1% nano SiO2
Pressur ized impre gnation
Ethylene covinyl acetate
Sugar cane Bagasse
TiO2
Used in polymers as white pigment,
Melt mixed intercalati on method
Epoxy
Bamboo
Carbon nano tubes (CNT)
Energy storage, Air and water filtration, Biomedical applications
0 to 30% fiber loading and 0 to 2% TiO2 loading -
Hand lay up
Composites with 5% nanoclay has less water absorption but not less as compared to coupling agent alone (a) Substantial increase in mechanical properties (b) Decrease in water absorption (a) 5% nanoSiO2 added samples show 71.46% increase in tensile strength (b) Not significant change in water absorption (a) Most of the properties have been improved (b) Decreased water absorption 10% increased in tensile strength after addition of TiO2 (a) 6.67% increase in tensile strength and 5.8% in flexural strength (b) Water
651
Venkatram et al. 2016, [22]
Hosseini et al. 2014 , [23]
Jiang et al. 2013, [24]
Vilakati et al. 2010, [25]
Kushwaha et al. 2014, [26]
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G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
Epoxy
Ramie
Carbon nano tubes (CNT)
Molecular electronics, Fibers and fabrics
Carbon nano tube addition from 0 to 0.6%
Hand lay up
Poly propylene
Bagasse
Nanographene
Bio medical applications , semi conductors
Fiber loading 15 and 30% Nano graphene 0.1 to 1%
Melt comp ounding
Epoxy
Jute
Graphene
Electronic devices
25% fiber and 0.3,1,3% graphene
Hand lay up
Epoxy
Kenaf
,Mont morillonite
Material applications
3% nano filler
Hand lay up
absorption is reduced from 26.28% to 23.18% Flexural strength and flexural modulus improved by 34% and 37% (a) Composites containing 0.1% NG and 30% bagasse fiber show highest tensile, flexural and impact properties (b) No significant change in water absorption Graphene as nanofiller enhanced the machinability of composite material By addition of oil palm nano filler 24.9% increase in tensile strength and 28.3% increase in impact strength
Shen et al.2014, [27]
Chaharmah ali et al. 2014, [28]
Sridharan et al. 2016 , [29]
Saba et al.2016, [30]
Conclusions The outcome of this review indicates that the mechanical properties of natural fiber reinforced polymer composites improve significantly by the use of nanofillers. The water absorption of these composites also reduces in many of the studies, so the use of nanofillers can be an important aspect in this field but an optimum concentration or loading is very important to keep a balance of properties and at the same time an economic consideration is also very important for the use of these novel materials.
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Acknowledgements The author is thankful to Chemical Engineering Department and QIP center IIT Roorkee for the providing resources and financial support for this research. References
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Pickering, K. L., Efendy, M. G. A. & Le, T. M. A review of recent developments in natural fibre composites and their mechanical performance. Compos. Part A Appl. Sci. Manuf. 83, 98–112 (2016). Saba, N., Jawaid, M., Alothman, O. Y. & Paridah, M. T. A review on dynamic mechanical properties of natural fibre reinforced polymer composites. Constr. Build. Mater. 106, 149–159 (2016). Väisänen, T., Das, O. & Tomppo, L. A review on new bio-based constituents for natural fiber-polymer composites. J. Clean. Prod. 149, 582–596 (2017). Faruk, O., Bledzki, A. K., Fink, H. P. & Sain, M. Biocomposites reinforced with natural fibers: 2000-2010. Prog. Polym. Sci. 37, 1552–1596 (2012). Sanjay, M. R. et al. Characterization and properties of natural fiber polymer composites: A comprehensive review. J. Clean. Prod. 172, 566–581 (2018). Sood, M. & Dwivedi, G. Effect of fiber treatment on flexural properties of natural fiber reinforced composites: A review. Egypt. J. Pet. (2017). doi:10.1016/j.ejpe.2017.11.005 Al-Oqla, F. M., Sapuan, S. M., Anwer, T., Jawaid, M. & Hoque, M. E. Natural fiber reinforced conductive polymer composites as functional materials: A review. Synth. Met. 206, 42–54 (2015). Thakur, V. K. & Thakur, M. K. Processing and characterization of natural cellulose fibers/thermoset polymer composites. Carbohydr. Polym. 109, 102–117 (2014). Omrani, E., Menezes, P. L. & Rohatgi, P. K. State of the art on tribological behavior of polymer matrix composites reinforced with natural fibers in the green materials world. Eng. Sci. Technol. an Int. J. 19, 717– 736 (2016). Väisänen, T., Haapala, A., Lappalainen, R. & Tomppo, L. Utilization of agricultural and forest industry waste and residues in natural fiber-polymer composites: A review. Waste Manag. 54, 62–73 (2016). Li, X., Tabil, L. G. & Panigrahi, S. Chemical treatments of natural fiber for use in natural fiber-reinforced composites: A review. J. Polym. Environ. 15, 25–33 (2007). Kabir, M. M., Wang, H., Lau, K. T. & Cardona, F. Chemical treatments on plant-based natural fibre reinforced polymer composites: An overview. Compos. Part B Eng. 43, 2883–2892 (2012). Mohanty, A. K., Misra, M. & Drzal, L. T. Surface modifications of natural fibers and performance of the resulting biocomposites: An overview. Compos. Interfaces 8, 313–343 (2001). Cruz, J. & Fangueiro, R. Surface Modification of Natural Fibers: A Review. Procedia Eng. 155, 285–288 (2016). Hosseini, S. B. A Review: Nanomaterials as a Filler in Natural Fiber Reinforced Composites. J. Nat. Fibers 14, 311–325 (2017). Saba, N., Tahir, P. M. & Jawaid, M. A review on potentiality of nano filler/natural fiber filled polymer hybrid composites. Polymers (Basel). 6, 2247–2273 (2014). Ashori, A. & Nourbakhsh, A. Preparation and characterization of polypropylene/wood flour/nanoclay composites. Eur. J. Wood Wood Prod. 69, 663–666 (2011). Mohan, T. P. & Kanny, K. Water barrier properties of nanoclay filled sisal fibre reinforced epoxy composites. Compos. Part A Appl. Sci. Manuf. 42, 385–393 (2011). Haq, M., Burgueño, R., Mohanty, A. K. & Misra, M. Hybrid bio-based composites from blends of unsaturated polyester and soybean oil reinforced with nanoclay and natural fibers. Compos. Sci. Technol. 68, 3344–3351 (2008). Han, G., Lei, Y., Wu, Q., Kojima, Y. & Suzuki, S. Bamboo-fiber filled high density polyethylene composites: Effect of coupling treatment and nanoclay. J. Polym. Environ. 16, 123–130 (2008). Ibrahim, I. D., Jamiru, T., Sadiku, R. E., Kupolati, W. K. & Agwuncha, S. C. Dependency of the Mechanical Properties of Sisal Fiber Reinforced Recycled Polypropylene Composites on Fiber Surface Treatment, Fiber Content and Nanoclay. J. Polym. Environ. 25, 427–434 (2017).
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Venkatram, B., Kailasanathan, C., Seenikannan, P. & Paramasamy, S. Study on the evaluation of mechanical and thermal properties of natural sisal fiber/general polymer composites reinforced with nanoclay. Int. J. Polym. Anal. Charact. 21, 647–656 (2016). Hosseini, S. B., Hedjazi, S., Jamalirad, L. & Sukhtesaraie, A. Effect of nano-SiO2 on physical and mechanical properties of fiber reinforced composites (FRCs). J. Indian Acad. Wood Sci. 11, 116–121 (2014). Jiang, Y., Wu, G., Chen, H., Song, S. & Pu, J. Preparation of nano-SiO2 modified urea-formaldehyde performed polymer to enhance wood properties. Rev. Adv. Mater. Sci. 33, 46–50 (2013). Vilakati, G. D., Mishra, A. K., Mishra, S. B., Mamba, B. B. & Thwala, J. M. Influence of TiO 2Modification on the Mechanical and Thermal Properties of Sugarcane Bagasse-EVA Composites. J. Inorg. Organomet. Polym. Mater. 20, 802–808 (2010). Kushwaha, P. K., Pandey, C. N. & Kumar, R. Study on the effect of carbon nanotubes on plastic composite reinforced with natural fiber. J. Indian Acad. Wood Sci. 11, 82–86 (2014). Shen, X., Jia, J., Chen, C., Li, Y. & Kim, J. K. Enhancement of mechanical properties of natural fiber composites via carbon nanotube addition. J. Mater. Sci. 49, 3225–3233 (2014). Chaharmahali, M., Hamzeh, Y., Ebrahimi, G., Ashori, A. & Ghasemi, I. Effects of nano-graphene on the physico-mechanical properties of bagasse/polypropylene composites. Polym. Bull. 71, 337–349 (2014). Sridharan, V., Raja, T. & Muthukrishnan, N. Study of the Effect of Matrix, Fibre Treatment and Graphene on Delamination by Drilling Jute/Epoxy Nanohybrid Composite. Arab. J. Sci. Eng. 41, 1883–1894 (2016). Saba, N., Paridah, M. T., Abdan, K. & Ibrahim, N. A. Effect of oil palm nano filler on mechanical and morphological properties of kenaf reinforced epoxy composites. Constr. Build. Mater. 123, 15–26 (2016). Jeffrey George, Hatsuo Ishida, A review on the very high nanofiller-content nanocomposites: Their preparation methods and properties with high aspect ratio fillers Progress in Polymer Science. 86, 1-39 (2018) C. Forest, P. Chaumont, P. Cassagnau, B. Swoboda, P. Sonntag. Polymer nano-foams for insulating applications prepared from CO2 foaming Progress in Polymer Science, 41, 122-145 (2015)
ScienceDirect Materials Today: Proceedings 18 (2019) 647–654
www.materialstoday.com/proceedings
ICN3I-2017
Effect of nanofillers on the properties of natural fiber reinforced polymer composites G.L.Devnania*, Shishir Sinhab a,b
Chemical Engineering, IIT Roorkee, Roorkee, 247667, India
Abstract
Nanofillers are bringing exemplary changes in the field of material science and polymer composites. In this sophisticated process a small amount of material is added to a variety of polymers and other materials which can drastically improve the performance and quality of materials including thermal, mechanical, water absorption and flame retardancy etc. Nano fillers can be considered as additives in solid form which can upgrade the various properties of original materials without increasing the density of materials. Now a days researchers are using natural fibers as an alternative reinforcement of synthetic fibers in polymer composites because of their cost effectiveness, biodegradability, lower weight, good mechanical properties and sustainability but the compatibility issue of hydrophobic polymer matrix and hydrophilic fibers is still a concern which ultimately leads to degradation in performance of these composites. Attempts have been made to increase the compatibility between the polymer matrix and the natural fibers with the help of various surface treatments strategies like alkylation, acetylation, maleated coupling etc. Nano particles or nano fillers have tremendous potential to be used as filler material which can improve the properties of polymer composites. Academicians and researchers have used Nano clay, Nano SIO2, carbon nanotubes and many other nanofillers in natural fiber reinforced polymer composites for improvement in properties. Nano clay has shown its potential in decrease in water absorption in sisal fiber reinforced composites which is highly desirable similarly Nano SIO2 has been proven very useful for the improvement in mechanical properties of these composites moreover carbon nano tubes have also exhibited its importance in improvement of mechanical and water absorption properties of bamboo and ramie fiber reinforced polymer composites. Present study provides a review of recent advances on the effect of nanofillers on the properties of natural fiber reinforced polymer composites. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i-2017). Keywords: natural fiber ; hydrophilic ; nanofillers ; polymer composites
* Corresponding author. Tel.: +91-9450333762. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017).
648
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
1. Introduction With the progress in the field of nanotechnology, it is boosting the research in various area like materials, medicines, surface science, semiconductors, energy storage, environment etc. Small amount of nano materials are bringing drastic changes and improving the performance and properties of materials. In recent years lot of emphasis is there to use renewable and environment friendly materials which are sustainable in nature, without compromising the quality of original materials. Natural fiber reinforced polymer composites (NFRC) is one such area where traditional synthetic fibers like glass and carbon are being replaced by natural fibers which are easily available , renewable and biodegradable in nature. A good progress has been made in this field and decent number of review papers are available in this field. Pickering et al. [1] gave an overview of the factors that are essential for the performance of natural fiber reinforced polymer composites. Saba et al. [2] provided the compilation of dynamic mechanical properties of these composites. The effects of waste material is critically reviewed by Vaisanen et al. [3]. All the developments that occurred during 2000-2010 was examined by Faruk et al.[4] , they described about various natural fibers, their availability, treatment methods and about various polymer matrix that had been used. A comprehensive review on the characterization techniques and properties of these composites is done by sanjay et al. [5].Sood and Dwivedi [6] concentrated on flexural properties of these NFRC. Oqla et al [7] reported about conductive polymer composites which fall in the category of natural fiber reinforced composites. Processing and characterisation of natural cellulose fiber in thermoses matrix was explained by Thakur and Thakur [8]. Omrani et al. [9] reviewed the tribological behavior of polymer matrix composites reinforced by these novel materials and evaluated the application of these materials Vaisanen et al.[10] told about utilization of agricultural and forest industry waste and residues in these NFRC's in his report. Being lignocellulosic these fibers are hydrophilic in nature while the matrix in which they are to be reinforced is a polymeric material which is hydrophobic in nature so the compatibility between these two opposite natured materials is still a challenge. Many surface treatment methods have been experimented [11-14]] to improve the adhesion between polymer matrix and fibers. Kabir et al. [11] emphasized the significance of chemically treated natural fibers for the improvement in the performance of their composites. Li et al [12]. reviewed different chemical treatment methodologies and their mechanism for the property enhancement in the composites. Mohanty et al. [13] described about surface modifications of natural fibers and its effect on their biocomposites . Cruz and Fangueiro[14] also told about surface modifications of these green materials., With the advent of nanotechnology and use of nanofillers in the field of natural fiber reinforced polymer composites researchers and academicians are getting encouraging results [15-16]. Hosseini [15] did a phenomenal review in the use of nanofillers for natural fiber reinforced polymer composites and described about most of the common nanofillers and their effect on the performance of theses composites . Saba also did a [16] very good compilation to evaluate the potentiality of nanofillers/natural fiber in the field of composites 2. Various nano fillers used in natural fiber reinforced polymer composites Nanofillers are considered to be materials which can be added in solid form having different properties like structure and composition from polymer matrix and lignocellulosic fibers. They may be one dimensional in the form of plates and laminas or two dimensional in the form of nano tubes and nano fibers or may be three dimensional in the form of isodimensional nanoparticlea. They generally comprise inorganic substances and some times organic as well. Various nanofillers used in natural fiber reinforced polymer composites are nanoclays primarily montmorillonite ,[17,18, 19, 20,21,22, ] nano SIO2[23,24] , nano TIO2[25], carbon nanotubes [26,27], nanographene, etc [28,29]. Apart from these traditional fillers some other nano fillers like oil palm nano filler has also been tested [30]. The addition of small amount of these fillers can improve the mechanical, thermal and water absorption properties in a significant manner. 3. Effect of nanofillers on properties of natural fiber reinforced polymer composites Ashori and Nouabksh [17] developed polypropylene composites reinforced by wood flour with injection molding process and concluded that at 6% montmorillonite (MMT) clay loading there is a improvement of tensile strength by
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
649
20% and flexural strength by 13% and also lower water absorption at clay loading of 3%.Mohan and Kanny [18] observed the 27% increase in tensile strength and 47% increase in tensile modulus by use of 2 to 5% MMT loading in case of epoxy composites with sisal fibers, they also observed reduction of water absorption by 1/3 in case of 5% nanoclay filled composites. Haq et al. [19] prepared hemp fiber reinforced polyester composites by compression molding and used clay loading from 0 to 1.5% and found that moisture absorption is reduced by 8% but at the same time tensile strength is also reduced by 20% for naoclay filled composites. Han et al. [20] used melt compounding method for the fabrication of bamboo based high density polythene composites and demonstrated that addition of MMT clay led to negative effect on mechanical properties. Ibrahim et al. [21] showed positive effect of MMT clay on polypropylene -sisal composites and noticed best tensile strength in case of composites with 5% coupling agent , 5% nano clay and 40% treated fiber. Venkatraman et al.[22] looked the characteristics of polyester- sisal composites using Garamite nano clay and realized substantial increase in mechanical properties and decrease in water absorption. 25% fiber loading and 3% clay loading was optimum for the improved performance of composites. Hosseini et al [23] used Nano SiO2 filler with 2 and 5% loading for the development of high density polyethylene composites reinforced by bagasse fiber and inspected that there is 71.46% increase in tensile strength in composites filled by nano SiO2. Similar improvement was also observed by Jiang et al. [24] in the wood-urea formaldehyde composites having 1% nano SiO2 as filler. Vilakati et al.[25] experimented 2% TiO2 as filler in bagasse-vinyl acetate composites and revealed that there is 10% up gradation of tensile strength. Another class of nano filler, carbon nano tubes (CNT) was tested by Kushwaha et al [26] in their work. They processed epoxy composites reinforced with bamboo fibers by simple hand lay up method , there findings were 6.67% increase in tensile strength and 5.8% in flexural strength and at the same time reduction in water absorption from 26.28% to 23.18%.Same nano filler CNT was used by Shen et al.[27] in the preparation of epoxy composites reinforced by ramie fibers , they varied the CNT loading from 0 to 0.6% and recognized 34% and 37% increase in flexural strength and modulus respectively. Nano grpahene is also a very important nano filler which is tested by Chaharmahali et al. [28] and Sridharan et al. [29] in bagasse -polypropylene and jute -epoxy composites respectively and observed improvement in tensile flexural and impact properties. Saba et al. utilized oil palm nano filler for the enhancement in the properties of kenaf-epoxy composites. The summary of upgradation and improvement in the properties of natural fiber reinforced polymer composites by addition of nano fillers is described in Table 1
Table1 : Summary of effect of nano fillers on the properties of natural fiber reinforced composites
Matrix
Fiber
Nano filler used
Application of that nano filler
Loading percentage of fiber and clay
Method
Poly propylene
Wood flour
Mont morillonite (MMT) based nanoclay Cloisite 20A
Material applications
30% fiber loading and clay loading is from 0 to 6% and coupling agent
Injection molding
Improve ment in mechanical and water absorption properties property as compare to absence of nanofiller (a)Improveme nt in tensile strength by 20% and flexural strength by 13% (b)
Reference
Ashori and Nourabaksh 2011, [17]
650
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maleated polypropyl ene from 0 to 7.5%
Epoxy
Sisal
Mont morillonite (MMT) based nanoclay Cloisite 30B
Unsaturated polyester resin partially substituted by epoxi dized soybean oil
Hemp
High density Poly ethylene
Poly propylene
Drug delivery carriers , Material applications Rheology modifiers , Gas absorbents , Nano composites
50% fiber loading and clay loading is from 2 to 5%
Vacuum assisted resin infusion molding
Cloisite 30B
21-22% fiber loading and clay loading is 0 to 1.5%
Compressi on molding
Bamboo
Mont morillonite clay filler
Melt comp ounding
Sisal
Organically modified mont morillonite (MMT) based nanoclay Cloisite 30B
25 to 30% fiber loading and clay loading is from 0 to 5% 10-40% fiber loading and with 5 gram maleic anhydride grafted poly propylene
Comp ression molding
Composites prepared with 3% nanoclay exhibited lower water absorption (a) 27% increase in tensile strength and 47% increase in tensile modulus (b)Uptake in equilibrium water is reduced to one third in case of 5% nanoclay filled composites
Mohan and Kanny 2011,[18]
(a) Decrease in ultimate tensile strength by 20% (b) Moisture absorption reduced by 8% Addition of clay led to negative effect on mechanical properties
Haq et al. 2008 , [19]
(a) Composites with 5% coupling agent, 5% nanoclay, 40% treated fibers showed best tensile strength (b)
Ibrahim et al. 2017, [21]
Han et al. 2008 , [20]
G.L. Devnani and S. Sinha / Materials Today: Proceedings 18 (2019) 647–654
Polyester
Sisal
Nanoclay (Garamite)
Rheology modifier
25% fiber loading and 3% clay
Compressi on molding
High density poly ethylene
Bagasse fiber
Nano -SiO2
Improves concrete workability, bio medical applications
40% fiber loading and 2 and 5% Nano -SiO2
Injection molding
Urea Formal dehyde
Wood
Nano -SiO2
Improves concrete workability, bio medical applications
20% wood and 1% nano SiO2
Pressur ized impre gnation
Ethylene covinyl acetate
Sugar cane Bagasse
TiO2
Used in polymers as white pigment,
Melt mixed intercalati on method
Epoxy
Bamboo
Carbon nano tubes (CNT)
Energy storage, Air and water filtration, Biomedical applications
0 to 30% fiber loading and 0 to 2% TiO2 loading -
Hand lay up
Composites with 5% nanoclay has less water absorption but not less as compared to coupling agent alone (a) Substantial increase in mechanical properties (b) Decrease in water absorption (a) 5% nanoSiO2 added samples show 71.46% increase in tensile strength (b) Not significant change in water absorption (a) Most of the properties have been improved (b) Decreased water absorption 10% increased in tensile strength after addition of TiO2 (a) 6.67% increase in tensile strength and 5.8% in flexural strength (b) Water
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Venkatram et al. 2016, [22]
Hosseini et al. 2014 , [23]
Jiang et al. 2013, [24]
Vilakati et al. 2010, [25]
Kushwaha et al. 2014, [26]
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Epoxy
Ramie
Carbon nano tubes (CNT)
Molecular electronics, Fibers and fabrics
Carbon nano tube addition from 0 to 0.6%
Hand lay up
Poly propylene
Bagasse
Nanographene
Bio medical applications , semi conductors
Fiber loading 15 and 30% Nano graphene 0.1 to 1%
Melt comp ounding
Epoxy
Jute
Graphene
Electronic devices
25% fiber and 0.3,1,3% graphene
Hand lay up
Epoxy
Kenaf
,Mont morillonite
Material applications
3% nano filler
Hand lay up
absorption is reduced from 26.28% to 23.18% Flexural strength and flexural modulus improved by 34% and 37% (a) Composites containing 0.1% NG and 30% bagasse fiber show highest tensile, flexural and impact properties (b) No significant change in water absorption Graphene as nanofiller enhanced the machinability of composite material By addition of oil palm nano filler 24.9% increase in tensile strength and 28.3% increase in impact strength
Shen et al.2014, [27]
Chaharmah ali et al. 2014, [28]
Sridharan et al. 2016 , [29]
Saba et al.2016, [30]
Conclusions The outcome of this review indicates that the mechanical properties of natural fiber reinforced polymer composites improve significantly by the use of nanofillers. The water absorption of these composites also reduces in many of the studies, so the use of nanofillers can be an important aspect in this field but an optimum concentration or loading is very important to keep a balance of properties and at the same time an economic consideration is also very important for the use of these novel materials.
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Acknowledgements The author is thankful to Chemical Engineering Department and QIP center IIT Roorkee for the providing resources and financial support for this research. References
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