Surface Modification of Nanoparticle and Natural Fiber Fillers E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Serie: Polymer Nano-, Micro- and Macrocomposites
• Sprache: Englisch

Seitenzahl: 454

Veröffentlichungsjahr: 2015

Beschreibung

A review of the various methodologies for the surface treatment of different types of inorganic spherical and fibrous fillers, describing ball milling, cationic polymerization, vapor phase grafting, plasma treatment and UV irradiation in detail. In addition, the book connects the resulting composite properties to the modified filler surface properties, thus allowing for a purposeful, application-oriented composite design.

Leseprobe

CONTENTS

Cover

Title page

Preface

List of Contributors

1 Surface Modification of Nanomaterials for Application in Polymer Nanocomposites: An Overview

1.1 Introduction

1.2 Types of Nanomaterials

1.3 Synthetic Methodologies of Nanomaterials

1.4 Surface Modification of Nanomaterials and Their Advantages in Polymer Composites

1.5 Method for the Incorporation of Nanomaterials in a Polymer Matrix

1.6 Influence of Surface-Modified Nanomaterials on the Properties of Polymer Nanocomposites

1.7 Conclusion

Abbreviations

References

2 Surface Modification of Boron Carbide for Improved Adhesion to an Epoxy Matrix

2.1 Introduction

2.2 Powder Synthesis

2.3 Ceramic Components

2.4 Composites

2.5 Native Surface Chemistry

2.6 Silane Surface Modification

2.7 Silane-Treated Boron Carbide

2.8 Proposed Mechanism for the Silane Treatment of BC Surface

2.9 Summary

References

3 Surface Modification of Hydroxyapatite for Bone Tissue Engineering

3.1 Introduction

3.2 Surface Modification of HA

3.3 Applications for Bone Tissue Engineering

3.4 Conclusion and Perspective

Acknowledgment

References

4 Influence of Filler Surface Modification on the Properties of PP Composites

4.1 Introduction

4.2 Silica Modification

4.3 Glass

4.4 Silicates

4.5 Mg(OH)

2

and Eggshell Modification

4.6 Cellulose

4.7 Carbon

4.8 Conclusion

References

5 ScCO2 Techniques for Surface Modification of Micro- and Nanoparticles

5.1 Introduction

5.2 Compressed CO

2

and {CO

2

+ Solvent} Properties

5.3 Modification of Particles Using CO

2

as Solvent (Route 1)

5.4 Modification of Particles Using CO

2

as Non-solvent (Route 2)

5.5 Modification of Particles Using CO

2

as Expanding Medium (Route 3)

Acknowledgments

References

6 Surface Treatment of Sepiolite Particles with Polymers

6.1 Introduction

6.2 Surface Properties of Sepiolite

6.3 Interactions of Sepiolite with Polymers

6.4 The Changes in Colloidal Properties of Sepiolite with Polymers

6.5 Thermal Properties

6.6 Structural Changes

6.7 Adsorption Isotherms

References

7 Surface Modification of Aluminum Nitride and Silicon Oxycarbide for Silicone Rubber Composites

7.1 Introduction

7.2 Experimental

7.3 Results and Discussion

7.4 Conclusions

Acknowledgment

References

8 Surface Modification of Natural and Synthetic Polymeric Fibers for TiO2-Based Nanocomposites

8.1 Introduction

8.2 Structure of Titanium Dioxide

8.3 Natural Fibers

8.4 Synthetic Fibers

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Synthetic methodologies of nanomaterials through physical methods.

Table 1.2 Synthetic methodologies of nanomaterials through chemical methods.

Chapter 2

Table 2.1 Experimental and theoretical adhesive contact angle on the BC.

Table 2.2 Thickness of silane layer according to the solution pH and GPS concentrations.

Chapter 4

Table 4.1 Effects of surface modifiers and compatibilizers on the properties of PP–silica composites.

Table 4.2 Effects of surface modifiers and compatibilizers on the properties of PP–glass composites.

Table 4.3 Effects of surface modifiers and compatibilizers on the properties of PP–silicate composites.

Table 4.4 Effects of surface modifiers and compatibilizers on properties of PP–Mg(OH)

2

and PP–eggshell composites.

Table 4.5 Effects of surface modifiers and compatibilizers on the properties of PP–cellulose composites.

Table 4.6 Effects of surface modifiers and compatibilizers on the properties of PP–carbon composites.

Chapter 7

Table 7.1 The atomic ratio of untreated AlN, PSZ/AlN, and SiOC/AlN.

Chapter 8

Table 8.1 Crystal structure data of TiO

2

[18].

Table 8.2 Literature survey of different methodologies for the synthesis of cellulose fibers coated with TiO

2

and respective applications.

Table 8.3 Literature survey of different methodologies for the synthesis of synthetic fibers coated with TiO

2

and respective applications.

List of Illustrations

Chapter 1

Figure 1.1 The modification of nano TiO

2

particles with 3-(trimethoxysilyl) propylmethacrylate (MPS) and the formation of the polystyrene-TiO

2

particles via free radical polymerization [70].

Figure 1.2 The surface modification of alumina nanoparticles with 3-aminopropyltriethoxysilane [73].

Figure 1.3 The surface modification of mesoporous SBA-15 with benzoxazine functional silane [81].

Figure 1.4 Grafting of polymer brushes in BNNTs via surface-initiated ATRP process [98].

Figure 1.5 Dispersion of GO and GO–ODA (20 h) in CHCl

3

/H

2

O mixture [119].

Figure 1.6 Schematic representation of polybenzoxazine–silica hybrid (PBZ–SiO

2

).

Figure 1.7 TEM analysis of 15 wt% of ZrO

2

dispersed in PMMA/ZrO

2

nanocomposite [145].

Figure 1.8 Schematic representation of formation of phenyl dichlorophosphate modified TiO

2

/epoxy nanocomposites [150].

Figure 1.9 Schematic representation of conformational ordering and crystallization of PLLA in the presence of CNTs (a–c) and GNs (d–f) [159].

Figure 1.10 Schematic representation of functionalization of TiO

2

and formation of TiO

2

–PMMA nanocomposite [166].

Figure 1.11 variation of Young's modules (a) and tensile strength (b) with the GO contents of PP nanocomposites.

Figure 1.12 Conductivity as a function of the CB loading in epoxy/bismaleimide composites [173].

Figure 1.13 Effect of f-GO content on the electrical conductivity of rubbery epoxy/graphene composites [179].

Chapter 2

Figure 2.1 Surface charging mechanism of a BC nanoparticle in aqueous solution [24].

Figure 2.2 γ-Glycidyloxypropyl-trimethoxysilane (GPS) molecule structure.

Figure 2.3 SFE terms for the untreated and treated BC with different pH and silane concentrations.

Figure 2.4 Determination of the dispersive and polar SFE fractions of the uncured adhesive.

Figure 2.5 FTIR spectra of the (a) untreated and (c) silanized BC, and of the (b) non-hydrolyzed, and (d) condensed gel form of the silane.

Figure 2.6 High-resolution B1s, C1s, O1s, and Si2p spectra of the untreated and silane-treated BC surfaces with various GPS concentrations in pH 7 solution.

Figure 2.7 High-resolution B1s, C1s, O1s, and Si2p spectra of the silane-treated BC surfaces with 1% GPS in different solution pH values.

Figure 2.8 Elemental composition of (a) silicon, (b) carbon, and (c) oxygen according to the GPS layer coverage percentage (

f

GPS

) on the BC surface.

Figure 2.9 Silicon composition according to solution pH and GPS layer coverage percentage (

f

GPS

) on the BC surface.

Figure 2.10 SEM micrographs using back scattering electrons on the failure surface of the (a) untreated and (b) silane-treated PMCs.

Figure 2.11 Reaction mechanism proposed for representation of the possible covalent bonding between GPS and BC surface, through hydrogen-bonding in solution and nucleophilic attack during the drying stage.

Chapter 3

Figure 3.1 Surface modification of HA by oligo-PLLA [14].

Figure 3.2 Synthesis route of AT-grafted HA hybrid materials [15].

Figure 3.3 Reactions for surface-grafting polymerization of CL on the surface of HA particles [19].

Figure 3.4 Grafting of PLLA on the surface of HA.

Figure 3.5 Scheme of surface modification of HA with

L

-lactic acid and subsequent ROP of LA [22].

Figure 3.6 Novel synthesis of HA/PLLA composite via surface-initiating ROP method [23].

Figure 3.7 Schemes of surface modification of HA by grafting polymers containing phosphonic acid groups [38].

Figure 3.8 Surface modification of HA with thermoresponsive PNIPAM [44].

Figure 3.9 Preparation of comb-like PCL on the surface of HA via ATRP and ROP [48].

Figure 3.10 Preparation of polymer-modified HA via radical chain transfer polymerization [39].

Figure 3.11 Illustration of

in situ

synthesis of HA with thiol-functionalized surface [39].

Figure 3.12 Scheme of ROP of BLG NCA on the surface of HA [35].

Figure 3.13 Typical radiographs of radius resection implanted with composites: control (A1&2), PLGA (B1&2), 5 wt% op-HA/PLGA (C1&2), 10 wt% op-HA/PLGA (D1&2), 20 wt% op-HA/PLGA (E1&2), 40 wt% op-HA/PLGA (F1&2), and HA/PLGA (G1&2) taken at 4 (1) or 24 (2) weeks post-surgery [54].

Figure 3.14 Morphological changes of composite fiber membranes after incubation in simulated body fluid (SBF) at 37 °C for 2 (a–c) and 5 weeks (d–f). HA-

g

-PLLA content: 5 wt% (a and d), 10 wt% (b and e), and 20 wt% (c and f) [55].

Figure 3.15 Macroscopic observation of the representative implants of HA-

g

-PLLA/PLGA (left), HA/PLGA (middle), and PLGA (right) scaffolds embedded in rabbit dorsal muscles at 4 (a), 8 (b), 12 (c), or 20 weeks (d) post-surgery. The photos were taken by Fujifilm FinePix S602 Digital Camera with 6× Optical Zoom [56].

Figure 3.16 Morphology of cells cultured on different samples: HA (a), PBLG-

g

-HA12 (b), PBLG-

g

-HA24 (c) and PBLG-

g

-HA72 (d) for 24 h, and HA (e), PBLG-

g

-HA12 (f), PBLG-

g

-HA24 (g), and PBLG-

g

-HA72 (h) for 48 h, respectively [35].

Figure 3.17

In vivo

bone formation after implantation of different samples assessed by μ-computed tomography (CT) [57].

Chapter 5

Figure 5.1 Schematic routes for surface modification, according to the main role of compressed CO

2

: (a) As solvent (Route 1) for guest molecules. (b) As antisolvent (Route 2) for two species initially dissolved in organic solvent (GAS version is presented); one specie can be already present in the solution (precipitation on slurry). (c) As expanding and/or melting medium (Route 3); the PGSS version is presented, in which a suspension is sprayed in a precipitation tower. The alternatives can be (i) melting and depressurization without spraying and (ii) dissolution of species in organic solvent and spraying.

Figure 5.2 Properties of CO

2

as a function of pressure at 25 (liquid–vapor coexisting phases), 45, and 65 °C (monophasic domain). (a) Density and (b) viscosity.

Figure 5.3 Properties of CO

2

-based systems. (a) Liquid–vapor equilibria of CO

2

–acetone mixture at 25, 35, and 45 °C. (b) Viscosity of CO

2

–acetone mixture at 35 and 40 °C. (Data from Ref. [20].) (c) Diffusion coefficient of acetone in CO

2

at 35 and 40 °C.

Figure 5.4 Solubility of (a) low-molecular weight molecule, naproxen, in neat CO

2

as function of pressure and temperature (• 40 °C, ▴50 °C, ▪ 60 °C). Plain symbols: data from Ref. [25].Open symbols: data from Ref. [26]. (b) Solubility of two metal precursors in neat CO

2

as function of pressure and temperature (40 °C, 50 °C, □ 60 °C). Plain symbols: data of Co(acac)

3

from Ref. [27].Open symbols: data of Ni(hfac)

2

·2H

2

O from Ref. [28]. (c) Solubility of naproxen in CO

2

+ acetone at 25 °C and 10 MPa.

Figure 5.5 Mechanism of silanization with octylsilane molecules: (a) Hydrolysis of the alkoxy groups in the organosilane and condensation between organosilane molecules and with the surface silanols forming a self-assembled structure. (b) Possible side reactions of the silanization process carried out in conventional liquid solvents (polycondensation and vertical polymerization).

Figure 5.6 Schematic representation of silica mesoporous matrices and potential aminosilane (3-(methylamino)propyltrimethoxysilane) configurations grafted on the silica surface: (a) one-dimensional channels in MCM-41 and (b) primary silica particles in disordered mesoporous silica gel.

Figure 5.7 Schematic representation of the different mechanisms established for the formation of hyperbranched polyethylenimine from the ring-opening of aziridine under: (a) acid and (b) CO

2

catalysis.

Figure 5.8 Schematic representation of different possible configurations of polyethylenimine on the surface of silica particles: (a) conventionally deposited by electrostatic interactions and (b) supercritically grafted on the silanol groups.

Figure 5.9 Different ship-in-a-bottle synthesis protocols for: (a) pyrylium cation encapsulated in zeolite Y by the diffusion of the diketone precursor and (b) triphenyltrityl cation into aerogel cavities promoted by acid catalytic condensation of benzaldehyde and anisole.

Figure 5.10 Morphologies produced by spraying solutions into scCO

2

by SAS technique. Poly(lactic acid) polymer produced as (a) spheroids below 5 µm and (b) fibers below 10 µm in diameter. Griseofulvine and poly(lactic-

co

-glycolic acid) polymer produced as (c) coated needles below 10 µm in diameter and (d) a network.

Figure 5.11 Formation of naproxen:nicotinamide cocrystals by SAS technique. (a) Mixture of cocrystals and naproxen by optical micrography and (b) precipitation yield and cocrystal content of powders as function of the processed concentration in naproxen.

Figure 5.12 Coating solid particles through GAS/SAS antisolvent technique. (a) Silica of 5 µm coated with PMMA polymer by GAS; (b) silica of 156 nm coated with Gelucire by spraying a suspension (SAS; scale 100 nm); and (c) polyedric crystals coprocessed with silica 5 µm and Eudragit polymer (GAS; scale 20 µm).

Figure 5.13 Decrease of melting points of two lipid mixtures in presence of CO

2

.

Chapter 6

Figure 6.1 Structural model of sepiolite showing the arrangement of tunnels and channels in a cross section of a microfiber [3, 6–8].

Figure 6.2 (a) Transmission electron microscopy (TEM) picture of sepiolite from Eskisehir, Turkey. (b) Scanning electron microscopy (SEM) picture of sepiolite from Eskisehir, Turkey.

Figure 6.3 Diagram illustrating the adsorption of an uncharged linear polymer with trains, loops, and free dangling tails [28].

Figure 6.4 Diagram illustrating the effects of the adsorption of an uncharged polymer on the stability of the sepiolite dispersions.

Figure 6.5 Diagram showing to (a) the steric and (b) electric/electrosteric stabilization.

Figure 6.6 TG-DTA curves of sepiolite from Eskisehir, Turkey [57].

Figure 6.7 FTIR spectra of sepiolite from Eskisehir, Turkey.

Figure 6.8 XRD diagram of sepiolite from Eskisehir/Turkey.

Figure 6.9 Examples of the different types of the adsorption isotherms.

Chapter 7

Scheme 7.1 Schematic illustration of preparation of polysilazane- and silicon oxycarbide-coated aluminum nitride particles and proposed chemical structure of PSZ during moisture-crosslinking and heat treatment at 700 °C in air.

Figure 7.1 FTIR spectra of (a) untreated AlN, (b) PSZ/AlN, and (c) SiOC/AlN.

Figure 7.2 XPS spectra of (a) Al2p, (b) N1s, and (c) Si2p of untreated AlN, PSZ/AlN, SiOC/AlN, and untreated AlN at 700 °C.

Figure 7.3 Surface morphology of (a) untreated AlN, (b) PSZ/AlN, and (c) SiOC/AlN.

Figure 7.4 XRD spectra of (a) untreated AlN, (b) PSZ/AlN, (c) SiOC/AlN, (d) PSZ, and (e) SiOC.

Figure 7.5 XRD spectra of (a) untreated AlN and PSZ/AlN and (b) untreated AlN and SiOC/AlN at the intensity ranging from 10 to 100 au.

Figure 7.6 SEM cross-sectional images of silicone rubber filled (a) untreated AlN, (b) PSZ/AlN, and (c) SiOC/AlN at the filler content of 30 vol%.

Figure 7.7 Thermal conductivity of silicone rubber filled with (▪) untreated AlN, (•) PSZ/AlN, and (▴) SiOC/AlN at various filler contents.

Figure 7.8 AFM images and section analysis of (a) PSZ film and (b) SiOC film on sapphire substrate.

Figure 7.9 (a) Degradation temperature (

T

d

) and (b) tensile strength and elongation at break of silicone rubber filled with untreated AlN, PSZ/AlN, and SiOC/AlN at filler content of 30%.

Chapter 8

Figure 8.1 Schematic diagram representing the formation of photogenerated charge carriers (hole and electron) upon absorption of ultraviolet (UV) light.

Figure 8.2 SEM (Scanning Electron Microscopy) micrographs of TiO

2

/cellulose nanocomposite prepared by the titanyl sulfate hydrolysis in acidic medium (a) and with TiCl

4

hydrolysis in the presence of urea (b).

Figure 8.3 The TiO

2

-coated nanocellulose aerogel (a–c) showing pore network and structures at several length scales, leading to a contact angle of about 140° and promoting high water absorption under UV illumination. (d) TiO

2

-coated filter paper with predominantly microscale roughness showing a water contact angle of 129°. (e) TiO

2

-coated nanocellulose film showing a water contact angle of 90° due to the smooth surface. (Reproduced with permission [55]. Copyright 2011, John Wiley and Sons.)

Figure 8.4 (a) Schematic representation of the preparation processes. (b) SEM images demonstrating effect of the different drying methods. (c) Photographs of the aerogel samples: (1) liquid propane freeze-dried aerogel of 2 mm thickness; (2) supercritically dried sample with about 12 mm diameter and 10 mm height; and (3) atmospherically dried sample, which has collapsed completely. Wet dimensions were the same as in the supercritically dried sample. (4) Supercritically dried aerogel after ALD shows a slight yellow color on the surface. (Reproduced with permission [54] Copyright 2011, American Chemical Society.)

Figure 8.5 SEM photographs of PET fiber fabric subjected to NaOH treatment, titania, and HCl treatments and then soaked in SBF for 3 days. (Reproduced with permission [90]. Copyright 2007, Elsevier.)

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Polymer Nano-, Micro- & Macrocomposite Series

Mittal, V. (ed.)

Surface Modification of Nanotube Fillers

Series: Polymer Nano-, Micro- & Macromolecular (Volume 1)

2011

Print ISBN: 978-3-527-32878-9

Mittal, V. (ed.)

In-situ Synthesis of Polymer Nanocomposites

Series: Polymer Nano-, Micro- & Macromolecular (Volume 2)

2012

Print ISBN: 978-3-527-32879-6

Mittal, V. (ed.)

Characterization Techniques for Polymer Nanocomposites

Series: Polymer Nano-, Micro- & Macromolecular (Volume 3)

2012

Print ISBN: 978-3-527-33148-2

Mittal, V. (ed.)

Modeling and Prediction of Polymer Nanocomposite Properties

Series: Polymer Nano-, Micro- & Macromolecular (Volume 4)

2013

Print ISBN: 978-3-527-33150-5

Mittal, V.

Thermoset Nanocomposites

Series: Polymer Nano-, Micro- & Macromolecular (Volume 5)

2013

Print ISBN: 978-3-527-33301-1

Mittal, V.

Synthesis Techniques for Polymer Nanocomposites

Series: Polymer Nano-, Micro- & Macromolecular (Volume 6)

2015

Print ISBN: 978-3-527-33455-1

Edited by Vikas Mittal

Surface Modification of Nanoparticle and Natural Fiber Fillers

The Editor

Dr. Vikas MittalThe Petroleum InstituteChemical Engineering DepartmentBu Hasa Building, Room 22042533 Abu DhabiUAE

Cover:The cover image was kindly supplied by Pascale Subra-Paternault and Conception Domingo, chapter 5, figure 5.10.

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Preface

Nanocomposites are high-value nanomaterials with applications in diverse fields. Owing to the requirement of dispersion of the filler at nanoscale (<100 nm), a large number of synthesis routes have been developed. In addition to the synthesis routes, compatibilization of the organic and inorganic phases is of prime importance. Filler surface modification is a very useful route to achieve such compatibilization, which ultimately results in nanoscale dispersion of the filler in the polymer matrix. The book reviews some advances in the surface modification technologies of specific filler materials useful to generate polymer nanocomposites.

Chapter 1 reviews the modification of various nanoparticles and fibrous fillers in order to achieve their uniform dispersion in polymer matrices. Chapter 2 reports the effect of silane treatment on the surface properties of boron carbide and adhesion to an epoxy matrix. The authors also propose a mechanism for the silane treatment on boron carbide surface. Chapter 3 presents the recent advances in the surface modification of hydroxyapatite nanoparticles. In addition, some of their applications in bone tissue engineering are also introduced. Chapter 4 reviews the surface modifications specific to various fillers (such as silica, glass, silicates, magnesium hydroxide, eggshells, cellulose, and carbon) and their effects on composite properties. Chapter 5 highlights the use of scCO2 as solvent, non-solvent, or expanding medium to prepare composites for various applications: dyeing textiles, chemical grafting of nanometric silica or aerogels, deposition of metals in polymer substrates or carbon nanotubes, preparation of drug delivery systems, formation of cocrystals, encapsulation of magnetic nanoparticles, or preparation of janus-type particles. In a similar study, Chapter 6 reviews the surface treatment of sepiolite particles with polymers. Chapter 7 reports the surface modification of aluminum nitride and silicon oxycarbide for silicone rubber composites. Chapter 8 presents the surface modification of natural and synthetic polymeric fibers for TiO2-based nanocomposites.

Abu DhabiApril 2015

Vikas Mittal

List of Contributors

Nuno A.F. AlmeidaUniversity of AveiroCampus Universitário deSantiagoCentre for Mechanical Technology and Automation (TEMA)3810-193, AveiroPortugal

Devrim Balköseİzmir Institute of TechnologyDepartment of Chemical EngineeringGulbahce 35430, UrlaIzmirTurkey

James G. BroughtonOxford Brookes UniversityDepartment of Mechanical Engineering and Mathematical Sciences (MEMS)Joining Technology Research CentreWheatley Campus, WheatleyOxfordshire, OX33 1HXUK

Xuesi ChenChinese Academy of SciencesKey Laboratory of Polymer EcomaterialsChangchun Institute of Applied Chemistry5625 Renmin StreetChangchun 130022P. R. China

Hsien Tang ChiuNational Taiwan University of Science and TechnologyDepartment of Material Science and EngineeringNo. 43, Sec. 4, Keelung Rd.,Da’an Dist.Taipei 106Taiwan

Jianxun DingChinese Academy of SciencesKey Laboratory of Polymer EcomaterialsChangchun Institute of Applied Chemistry5625 Renmin StreetChangchun 130022P. R. China

Conception DomingoICMAB CSICInstitut de Ciencia de Materialesde BarcelonaCampus UAB s/n, 08193BellaterraSpain

Gil A.B. GonçalvesUniversity of AveiroCampus Universitário de SantiagoCentre for Mechanical Technology and Automation (TEMA)3810-193, AveiroPortugal

Sevim IsciIstanbul Technical UniversityDepartment of PhysicsMaslak, 34469IstanbulTurkey

Lan LiaoNanchang UniversitySchool of Stomatology999 Xuefu AvenueNanchang 330031P. R. China

Paula A.A.P. MarquesUniversity of AveiroCampus Universitário de SantiagoCentre for Mechanical Technology and Automation (TEMA)3810-193, AveiroPortugal

Vikas MittalThe Petroleum InstituteDepartment of Chemical EngineeringBu Hasa Building, Room 22042533 Abu DhabiUAE

David D. RodriguesOxford Brookes UniversityDepartment of Mechanical Engineering and Mathematical Sciences (MEMS)Joining Technology Research CentreWheatley Campus, WheatleyOxfordshire, OX33 1HXUK

Patrícia R. da SilvaUniversity of AveiroCampus Universitário de SantiagoCentre for Mechanical Technology and Automation (TEMA)3810-193, AveiroPortugal

Pascale Subra-PaternaultLaboratoire de Chimie etBiologie des Membranes et NanoobjetsCBMN UMR 5248Bâtiment 14B Allée GeoffroySaint Hilaire33600 PessacFrance

Tanapon SukachonmakulNational Taiwan University of Science and TechnologyDepartment of Material Science and EngineeringNo. 43, Sec. 4, Keelung Rd.Taipei 106Taiwan

Muthukumaraswamy Rangaraj VengatesanThe Petroleum InstituteDepartment of Chemical EngineeringBu Hasa Building, Room 22042533 Abu DhabiUAE

Junchao WeiNanchang UniversityDepartment of Chemistry999 Xuefu AvenueNanchang 330031P. R. China

Xiuli ZhuangChinese Academy of SciencesKey Laboratory of Polymer EcomaterialsChangchun Institute of Applied Chemistry5625 Renmin StreetChangchun 130022P. R. China

1Surface Modification of Nanomaterials for Application in Polymer Nanocomposites: An Overview

Muthukumaraswamy Rangaraj Vengatesan and Vikas Mittal

1.1 Introduction

In recent years, advanced nanocomposite materials have been widely used in a large number of commercially valuable industrial applications such as in automobile, marine coatings, aerospace, and construction industries. The nanocomposites are made up of organic polymers and inorganic nanomaterials using different processing techniques. For example, metal, metal oxide, and carbon-based nanomaterials have been widely used in the preparation of hybrid polymer nanocomposites. The nanocomposites are a new class of advanced materials exhibiting excellent properties compared to those of virgin polymers [1]. Nanomaterials have the ability to improve the properties of polymeric materials. In order to avoid agglomeration and insufficient dispersion of nanomaterials in polymer matrices, the surfaces of the nanomaterials are modified with some organic functionalities. Without surface modification, the unmodified nanomaterials reduce the properties of polymer nanocomposites [2, 3].

Owing to the excellent interfacial interaction between the surface of the nanomaterials and polymers, Surface-modified nanomaterials (SMNs) have attracted a great deal of attention compared to unmodified nanomaterials [4]. The surface functionalization of nanomaterials is carried out with a variety of organic functional groups such as alcohols, thiols, sulfonic, carboxylic acids, and amines. Numerous methods have been employed in the process of surface modification of nanomaterials, which is based on (i) copolymerization of functional organosilanes, macromonomers, and metal alkoxides, (ii) functionalization of organic components within sol–gel-derived silica or metallic oxides, (iii) organic functionalization of nanotubes, nanoclays, or other compounds with lamellar structures, and so on [5].

SMNs that have been reinforced into polymer matrices result superior hybrid nanocomposites, which possess light weight and high strength. The SMNs enhance the mechanical, rheological, optical, electrical, thermal, and flame retardancy properties of the polymer matrices [6, 7]. SMN-reinforced polymeric nanocomposites are widely used in the form of photonic crystals, coatings, adhesives, pharmaceutical, biomedical, and cosmetic formulations [8–14].

This review is focused on SMNs for the application of polymer nanocomposites. The synthesis, classification, and surface modification of nanomaterials have been summarized and the effects of SMNs on the properties of the polymer matrices are also discussed.

1.2 Types of Nanomaterials

Nanomaterials can be classified on the basis of the number of dimensions, but this is not confined to the nanoscale range. The nanomaterial can be classified into following types:

Zero-dimensional (0D) nanomaterial

One-dimensional (1D) nanomaterial

Two-dimensional (2D) nanomaterial

Three-dimensional (3D) nanomaterial.

1.2.1 Zero-Dimensional (0D) Nanomaterial

The dimension of the material is measured within a nanoscale range, that is, less than 100 nm, which has no dimension. The 0D nanomaterials are commonly represented as nanoparticles. Recently, numerous physical and chemical methods have been adopted for the fabrication of 0D nanomaterials. A lot of research work has been focused on the synthesis of well-controlled dimension of 0D nanomaterials such as quantum dots [15, 16], hollow spheres [17], core–shell nanospheres [18, 19], and nanocluster [20, 21]. The 0D nanomaterials have been synthesized from metal, metal oxides, and carbon-based materials, and are widely used in applications of nanomedicine [20, 21], display [22], energy [23], and so on.

1.2.2 One-Dimensional (1D) Nanomaterials

The 1D nanomaterials have two physical dimensions in the range of 1–100 nm and lead to a needle-like structure. These materials have been focus of intense interest in both academic research and industrial applications because of their potential as building blocks for other structures [24]. Researchers have classified 1D nanomaterials into four types: nanotubes [25], nanowires [26], nanorods [27], and nanobelts [28], all of which are widely used for the fabrication of electronic and optoelectronic devices in nanoscale dimensions. 1D nanomaterials have a significant impact on applications in electronics, display and devices, composite materials, catalysis, and energy [29–35].

1.2.3 Two-Dimensional (2D) Nanomaterials

The 2D nanomaterials have two dimensions beyond the nanometric size in range and are not confined to the nanoscale [36]. They exhibit plate-like shapes such as nanodisks [37], nanoplatelets [38], nanowalls [39], nanoprisms [40], and nanosheets [41]. These nanomaterials are widely used in applications in the fields of energy [39], sensors [40], and catalysis [41].

1.2.4 Three-Dimensional (3D) Nanomaterials

The 3D materials are the bulk nanomaterials which are not confined to be nanoscale in any dimension. These materials thus possess three arbitrary dimensions above 100 nm and have nanocrystalline structures. The bulk nanomaterials have a multiple arrangement of nanosize crystals with different orientations. The 3D nanomaterials can contain dispersions of nanoparticles, bundles of nanowires, and nanotubes as well as multiple nanolayers. It is well known that the application of 3D nanomaterials mainly depends on sizes, shapes, dimensionality, and morphologies [36]. The 3D nanomaterials are mainly used in applications in the fields of catalysis [42], biomedicine [43], and energy [44].

1.3 Synthetic Methodologies of Nanomaterials

Nanomaterials are prepared via physical or chemical methods. A variety of physical and chemical methods are available for synthesis and fabrication of 0D, 1D, 2D, and 3D nanomaterials. The synthetic methodologies for the preparation of nanomaterials are presented in Tables 1.1 and 1.2.

Table 1.1 Synthetic methodologies of nanomaterials through physical methods.

S. No.

Types of nanomaterials

Method

Examples with reference

1.

Nanoparticle (0D)

Sputter deposition

(i) Ag nanoparticles in TiO

2

matrix [45]

(ii) Sintered TiO

2

[46]

2.

Quantum dots (0D)

Evaporation

Self-assembled ZnO nanodots are grown by electron beam evaporation [47]

3.

Nanoclusters (0D)

Ultra-high vacuum ion beam evaporation

Ge nanoclusters embedded in Al

2

O

3

and ZrO

2

/Al

2

O

3

matrix [48]

4.

Nanowires (1D)

Thermal evaporation

Silver nanowires [49]

5.

Nanorods (1D)

Radiofrequency magnetron sputtering

ZnS nanorods [50]

6.

Nanotubes (1D)

Thermal chemical vapor deposition

Carbon nanotubes [51]

7.

Nanoplatelets (2D)

Spray pyrolysis

ZnO nanoplatelets [52]

8.

Nanodiscs (2D)

Thermal evaporation

ZnO nanodiscs [53]

9.

Nanowalls (2D)

Chemical vapor deposition

Carbon nanowall [54]

10.

Nanoflower (3D)

Thermal evaporation

ZnO nanoflowers [55]

11.

Aligned nanocluster (3D)

Thermal evaporation

Aligned Cu nanocluster on Si substrate [56]

Table 1.2 Synthetic methodologies of nanomaterials through chemical methods.

S. No.

Types of nano materials

Method

Examples with reference

1.

Nanoparticle (0D)

(i) Chemical reduction

(i) Ag nanoparticle [57]

(ii) Sol–gel

(ii) ZnO nanoparticle [58]

2.

Quantum dots (0D)

Wet chemical synthesis

CdS quantum dots [59]

3.

Nanoclusters (0D)

Hydrothermal

Silver nanocluster [60]

4.

Nanowires (1D)

Wet chemical synthesis

Silver nanowires [61]

5.

Nanorods (1D)

Solvothermal

TiO

2

nanorods [62]

6.

Nanotubes (1D)

Electrochemical

TiO

2

nanotubes [63]

7.

Nanoplatelets (2D)

Wet chemical synthesis

Amphiphilic graphene platelets [64]

8.

Nanosheets (2D)

Solvothermal

ZnO nanosheets [65]

9.

Nanodiscs (2D)

Hydrothermal

Fe

3

O

4

nanodiscs [66]

10.

Nanoflower (3D)

Solvothermal

CuS flower-like nanostructure [67]

11.

Hierarchical (3D)

Hydrothermal

Anatase TiO

2

hierarchical [68]

1.4 Surface Modification of Nanomaterials and Their Advantages in Polymer Composites

Numerous methods have been employed for the surface modification of nanomaterials. Among these, the silane grafting, polymer grafting, and surfactant-assisted modification methods are the more predominant and effective methods for functionalization of nanomaterials.

1.4.1 Silane Grafting

Silane is a very useful coupling agent for the modification of a variety of nanomaterials. The polar surfaces of the inorganic nanomaterials are modified by grafting silane coupling agents to improve dispersion ability in various organic media. Plueddemann et al. [69] first reported the surface modification of nanoparticles using silane coupling agents. They found that the SMN improves the compatibility of particle and polymer surfaces, which subsequently improves the properties of composite materials. Rong et al. [70] modified the surface of TiO2 nanoparticles using 3-(trimethoxysilyl)propylmethacrylate (MPS) (Figure 1.1) and carried out the in situ polymerization of styrene with modified TiO2 nanoparticles. Tuan et al. [71] functionalized the surface of TiO2 by using 3-glycidoxypropyltrimethoxysilane (GPS), which they used as a nanofiller for the high-density polyethylene (HDPE) composites. Prabakaran et al. [72] synthesized amine-functionalized TiO2 using 3-aminopropyltrimethoxysilane (APTMS) and TiO2 nanoparticles and studied the influence of amine-functionalized TiO2 on the dielectric properties of polyvinylidene fluoride-co-hexaflouropropylene (PVDF) composites. Duraibabu et al. [73] modified the surface of alumina nanoparticles using APTMS (Figure 1.2) and the modified alumina nanoparticles reinforced into epoxy matrix. Mandhakini et al. [74] studied the tribological properties on the influence of surface-modified alumina in bismaleimide/epoxy blend. The surface of alumina was modified using GPS. Chena et al. [75] developed a colloidal silica through sol–gel process and the surface of silica was modified using different types of silane coupling agents such as methyltriethoxysilane (MTES), octyltriethoxysilane (OTES), vinyltriethoxysilane (VTES), and methacryloxypropyltrimethoxysilane (MATMS). They studied the surface effect of silica nanoparticle on the properties of acrylic-based polyurethane/silica composites. Ariraman et al. [76] synthesized the zirconia (ZrO2) nanoparticle through sol–gel process and the surface of the nanoparticle was modified with GPS. They incorporated the modified ZrO2 into cyanate ester/azomethine blends and studied the effect of nanoparticles on the dielectric constant of the nanocomposites. Kanimozhi et al. [77] modified the surface of mullite fibers using GPS and studied the effect of surface-modified mullite fibers on the properties of epoxy nanocomposites. Selvi et al. [35] modified the multiwalled carbon nanotubes (CNTs) using benzoxazine functional silane. They developed multiwalled carbon/polybenzoxazine (PBZ) nanocomposites using modified CNTs. Yu et al. [78] functionalized the graphene nanosheets (GNs) using 3-mercaptopropyl trimethoxysilane (MTS) and developed graphene nanocomposites through thiol-ene photo polymerization method. Iqbal et al. [79] carried out edge functionalization on thermally reduced graphene oxide (TRG) using APTMS and studied the solvent effect for the silane grafting on the TRG. They found that the organic solvent increases the grafting yield of silane in TRG. Wang et al. [80] prepared amine-functionalized GNs using graphene oxide (GO) with 3-aminopropyl triethoxysilane (APTES) and used amine-functionalized GNs as a nanofiller for the epoxy composites. Vengatesan et al. [81] grafted the benzoxazine functional silane on to SBA-15 and developed the PBZ/SBA-15 nanocomposite. They found that the benzoxazine functional silane was perfectly grafted on the walls of the SBA-15 (Figure 1.3) and resulted in a homogenous dispersion into the PBZ matrix. Devaraju et al. [82] prepared glycidyl functional SBA-15 using GPS through simple post-grafting method. The glycidyl-modified SBA-15 has been used as nanofiller for the development of cyanate ester nanocomposites. Ariraman et al. [83] modified the surface of FMCM-41 silica using GPS via post-grafting method and used this as nanofiller for the preparation of cyanate ester silica nanocomposites.

Figure 1.1 The modification of nano TiO2 particles with 3-(trimethoxysilyl) propylmethacrylate (MPS) and the formation of the polystyrene-TiO2 particles via free radical polymerization [70].

Figure 1.2 The surface modification of alumina nanoparticles with 3-aminopropyltriethoxysilane [73].

Figure 1.3 The surface modification of mesoporous SBA-15 with benzoxazine functional silane [81].

1.4.2 Polymer Grafting

The grafting of polymers for the surface modification of nanomaterials can be done in two ways, namely, (i) grafting of the end-functionalized polymers, which react with the appropriate surface and (ii) by growing polymer chains from an initiator-terminated, self-assembled monolayer. A high yield of grafting percentage of polymer-grafted nanomaterial has been obtained by initiating the graft polymerization from the surface of the nanomaterials with polymer initiating groups [84–86]. The polymerization process consists of radical, anionic, and cationic polymerization methods, involving propagation of the grafted polymers from the surface of the particle [87]. Zhang et al. [88] successfully modified the surface of zinc oxide nanoparticles with methyl methylacrylate acetate (ZnMAAc) and developed ZnO/poly (methyl methacrylate) (ZnO/PMMA) nanocomposite films via free-radical polymerization between methyl methacrylate (MMA) and ZnMAAc. Arrachart et al. [89] functionalized the surface of TiO2 nanoparticles with undecenylphosphonic acid and prepared TiO2/PMMA nanocomposite using modified TiO2 and MMA via in situ bulk copolymerization. Fresnais et al. [90] modified the surface of iron nanoparticles with polyacrylic acid via a H-bonding interaction and studied the coating properties of the nanoparticles for the applications of pollutant dye removal. Kos et al. [91] developed PMMA/ZnO nanocomposites by the hydrolysis of Zn precursor. They prepared PMMA-block-PMMA-co-(zinc methacrylate acetate), as a polymeric precursor for the formation of ZnO nanoparticles through the reversible addition fragmentation chain transfer (RAFT) polymerization process. Hojjati et al. [92] coated the PMMA chains on TiO2 spherical surfaces by RAFT polymerization using supercritical carbon dioxide (scCO2) as the green solvent. Hu et al. [93] modified the surface of zirconia using MMA and prepared transparent PMMA/ZrO2 nanocomposites using MMA-grafted ZrO2 and MMA through in situ bulk polymerization. Wu et al. [94] successfully modified the surface of iron oxide (Fe3O4) nanoparticles with maleimide and prepared PBZ magnetic nanocomposite using modified iron oxide nanoparticles and benzoxazine through in situ Diels–Alder polymerization. Ou et al. [95] functionalized the surface of TiO2 nanoparticles with toluene-2,4-diisocyanate (TDI) and used this as a nanofiller for the polypropylene/polyamide blend. Wu et al. [96] modified the surface of TiO2 nanotubes using phenyl dichloro phosphate and incorporated this into the polystyrene (PSt) matrix through in situ bulk polymerization. Zhou et al. [97] developed a core–shell nanostructure using single-crystalline lanthanum hydroxide nanowires and a soft shell of PSt brushes. The PSt brush was grown on the surface of lanthanum hydroxide nanowires using atom transfer radical polymerization (ATRP). Ejaz et al. [98] grafted polyglycidyl methacrylate (PGMA) and PSt on the surface of boron nitride nanotubes (BNNTs) through the surface-initiated ATRP method (Figure 1.4). Gu et al. [99] modified the active surface of phosphazene nanotubes using epichlorohydrin. The epoxy-modified phosphazene nanotubes were used as nanofiller for the epoxy resin. Zhang et al. [100] carried out the covalent modification of GO with polynorbornene by surface-initiated ring-opening metathesis polymerization. Kumar et al. [101] grafted PMMA onto the surface of high-density functionalized GO through controlled radical polymerization (CRP). Mamaqani et al. [102] successfully grafted PSt on the surface of graphene platelets with various graft densities via the ATRP method from the edge of carboxyl groups. Gonçalves et al. [103] modified the surface of GO with PMMA via the ATRP method and used PMMA-g-GO as a nanofiller for the PMMA matrix. Cheng et al. [104] grafted the poly(vinyl)alcohol (PVA) on the surface of GO via a simple condensation reaction and used this as a nanofiller for the PVA matrix. They found that the mechanical properties of PVA were significantly improved by incorporation of PVA-g-GO. Fang et al. [105] modified the surface of graphene platelets using PSt chains via diazonium addition followed by the ATRP method. They found that the functionalized graphene platelets resulted in a 15 °C increase in the glass transition temperature of PSt compared to the pure polymer. Yang et al. [106] grafted poly(N-isopropyl acrylamide) (PNIPAM) on the surface of the mesoporous silica (MSN) through the ATRP method. They found that MSN@PNIPAM materials can be applied in biological systems for cellular imaging or as biosensors. Lia et al. [107] modified the outer surface of MSN nanoparticles using light-responsive polymers and studied the drug delivery application using surface-modified MSN. Hong et al. [108] developed a novel core–shell nanostructure with a mesoporous core and a polymer nanoshell by grafting the PSt chain on the exterior surface of MSNs. They reported that the thickness of the nanoshell increased with an increase in the time of polymerization. Pasetto et al. [109] grafted the polymer chains on the surface of ordered mesoporous silica (OMS) particles via surface-initiated atom transfer radical polymerization (SI-ATRP) using MMA or styrene. They studied and discussed the influence of the polymerization conditions on the OMS particle structure.

Figure 1.4 Grafting of polymer brushes in BNNTs via surface-initiated ATRP process [98].

1.4.3 Surface Modification of Nanomaterials Using Surfactants

Physical modification of nanomaterials is usually performed with the help of surfactants or macromolecules. The polar groups in the surfactants are selectively adsorbed on nanoparticle surface as a result of electrostatic interactions. The surfactant reduces the physical forces between the nanomaterials which decrease the inter particle interaction and controlling the agglomeration, therefore the surfactant-modified nanomaterials can be used as a nanofiller for polymer matrices [110]. Zhu et al. [111] modified the surface of SiO2 with oleic acid and used this as a nanofiller for the polylactide matrix. Nakayama and Hayashi fabricated poly(l-lactic acid)/TiO2 nanocomposite films by incorporating surface-modified TiO2 nanoparticles into the poly(l-lactic acid) matrix. The surface of TiO2 nanoparticles was modified by using carboxylic acid and long-chain alkyl amine [112]. Rahmani et al. [113] modified the surface of calcium carbonate (CaCO3) with steric acid and incorporated this into polypropylene matrix. They found that influence of the surface modification was to improve the distribution and dispersion of CaCO3 into the PP matrix. Zhong et al. [114] prepared ferroferric supermagnetic nanoparticles by the coprecipitation method and the surface of the nanoparticles was modified with oleic acid. The modified nanoparticles were incorporated into PSt by facile bulk polymerization and showed a uniform distribution. Mallakpour and Mani [115] modified the surface of ZrO2 using 2, 3, 4, 5-tetrabromo-6-[(4-hydroxyphenyl)carbamoyl] benzoic acid as the flame-retardant material and used this as a nanofiller for poly (amide-imide) matrix. Kiskan et al. [116] coated the surface of iron nanoparticles with carboxylic acid functional benzoxazine monomer via the post-coating method. They developed nanomagnetite PBZ thermosets by thermally activated ring-opening copolymerization of benzoxazine group-coated nanomagnetite with bare benzoxazine. Hana et al. [117] improved the lipophilicity of graphene by the addition of steric acid. They incorporated steric acid-modified graphene into a low-density polyethylene (LDPE) matrix and studied its thermal and mechanical properties. Lin et al. [118] modified graphene platelets with steric and oleic acid and used this as an additive for the lubricant oil. They studied the wear resistance and load-carrying capacity of the lubricant oil with the reinforcing effect of modified graphene platelets. Li et al. [119] carried out a simultaneous surface functionalization and reduction of GO using octadecylamine (ODA) without the use of any other reducing agents. The ODA-modified GO is well dispersed in organic solvents (Figure 1.5). They incorporated the ODA-g-GO into a PSt matrix and studied its thermal and electrical properties.

Figure 1.5 Dispersion of GO and GO–ODA (20 h) in CHCl3/H2O mixture [119].

1.5 Method for the Incorporation of Nanomaterials in a Polymer Matrix

The incorporation of nanomaterials into a polymer matrix has been carried out at the nanoscale level through in situ polymerization, reactive blending method, and sol–gel method.

1.5.1 Sol–Gel Method

In this method, the nanomaterials incorporated into the inside of the polymer matrix in aqueous solution medium results in an interpenetration network formation between the inorganic and organic phases at mild temperatures. This method helps to improve a strong interfacial adhesion between the phases. This is very facile method for the preparation of SiO2, Al2O3, ZrO2, ZnO, and TiO2-based polymer nanocomposites at a nanoscale level [120]. In this method, metal alkoxides, coupling agents, and polymer precursors have been employed for the preparation of hybrid polymer nanocomposites. Jothibasu et al. [121] prepared a transparent PSt–silica hybrid using maleimide-grafted PSt, tetraethoxysilane (TEOS), and APTES via in situ sol–gel process and utilizing the Michael-addition reaction. Selvi et al. [122] developed PBZ–SiO2–TiO2 hybrid nanocomposites using dimethylol-functional benzoxazine monomer (4HBA-BZ), TEOS, 3-(isocyanatopropyl) triethoxysilane (ICPTS), and titaniumisopropoxide (TIPO) through an in situ sol–gel process followed by thermal polymerization. They found that the hybrid PBZ nanocomposites possess higher surface energy than that of pure PBZ. Devaraju et al. [123] prepared polybenzoxazine–silica (PBZ–SiO2) hybrid nanocomposite via in situ sol–gel process followed by thermal polymerization (Figure 1.6). Ivanković et al. [124] carried out a simultaneous polymerization and sol–gel reaction using GPS, MMA, and poly (oxypropylene)diamine. Their results showed that the hybrids have much better thermal stability than PMMA and the surface of hybrids are more hydrophilic than PMMA. Zhang et al. [125] developed zinc oxide quantum dots (ZnO QDs)–PMMA nanocomposite films by incorporating ZnO QDs into a transparent PMMA matrix. The results showed that 3-(trimethoxysilyl)propylmethacrylate (TPM) used as a coupling agent which bound to the surface of ZnO QDs inhibited the agglomeration of QDs and promoted the compatibility between ZnO QDs and PMMA matrix. Jung et al. [126] developed polyimide–organosilicate hybrids via hydrolysis and polycondensation of aminosilane with alkyl-bridged silane. Jena et al. [127] prepared hyperbranched waterborne polyurethane-urea/silica hybrid coating material using 3-aminopropyltriethoxysilane as a coupling agent with SiO2 as a crosslinker.

Figure 1.6 Schematic representation of polybenzoxazine–silica hybrid (PBZ–SiO2).

1.5.2 Blending Method

The incorporation of nanomaterial into the polymer matrix has been carried out by melt blending or solution blending. This method is more convenient and simple for the preparation of polymer hybrid nanocomposites in bulk scale. The SMN has reactive and nonreactive sites and it reacts or interacts with the polymer matrix, resulting in perfect hybrid polymer nanocomposites. In this method, the SMN has the advantage that it avoids agglomeration in the polymer nanocomposites.

1.5.2.1 Solution Blending Method

Charpentier et al. [128] prepared polyurethane/TiO2 composite via the solution blending method and studied its antibacterial; self-healing properties. Selvi et al. [129] used solution blending of surface-modified carbon black with benzoxazine. They obtained the PBZ/carbon black composite by simple solvent evaporation followed by thermal annealing. Vengatesan et al. [81] utilized the solution blending method for the preparation of SBA-15/PBZ nanocomposites using benzoxazine functional silane and benzoxazine monomer. The nanocomposites were prepared by solvent evaporation followed by thermal annealing. Sasikala et al. [130] synthesized a PSt hybrid silica sphere composite using vinyl and amine-functionalized silica sphere and PSt through the solution blending method. Devaraju et al. [131] prepared cyanate ester-polyhedral oligomeric silsesquioxane (POSS) composites via the solution blending method. Vengatesan et al. [132] used the solution blending method for the preparation of PBZ–POSS nanocomposites using benzoxazine monomer and POSS derivative. Gu et al. [99] prepared phosphazene/epoxy nanocomposites through the solution blending method. Cao et al. [133] developed polyolefin–graphene nanocomposites through the solution blending method. Zeng et al. [134] prepared PMMA/graphene composites via a simple solution blending method. Joshi et al. [135] utilized the solution blending method for preparation of polyaniline-coated graphene epoxy composites [135].

1.5.2.2 Melt Blending

In this method, the SMNs are well dispersed into the polymer matrix using extrusion, internal mixing, and two-roll milling at elevated temperature. This method is more convenient and common method for the preparation of polymer hybrid nanocomposites on a large scale. Wong et al. [136] used melt extrusion for the preparation of ZnO QDs/PMMA nanocomposites. Murariu et al. [137] developed high-performance polylactide/ZnO nanocomposites using surface-modified ZnO and unmodified ZnO via the melt blending method. They found that the silane-treated ZnO nanoparticle-reinforced nanocomposites have good mechanical properties compared to those of unmodified nanoparticles. Ou and Li [138] prepared nanocomposites by incorporating the TDI-functionalized TiO2 nanoparticles into the PP/PA6 blend via the melt blending method. Xu et al. [139] developed polyamide 6/SiO2 nanocomposite by melt mixing of polyamide 6 and surface-modified SiO2. They found that crystallization temperature and crystallization rate of PA6/SiO2 nanocomposites were lower than that of neat polyamide 6. Reddy and Das [140] prepared high-pressure low-density polyethylene (HPLDPE)/organic functionalized SiO2 nanocomposites using the melt blending method. They reported that the organic modification onto the SiO2 surface led to an increase in thermal stability, elastic modulus, and toughness of the nanocomposite. Zubair et al. [141] prepared poly(styrene-co-MMA)/graphene nanocomposites via the melt blending method and irradiated the nanocomposites using microwave at different time intervals. Ryu and Shanmugharaj [142] prepared polypropylene-modified GO nanocomposites via the melt blending method and studied its crystallization, mechanical, and electrical properties.

1.5.3 In Situ Polymerization

In this method, nanoparticle dispersion and polymerization occurs simultaneously. Abdul Kaleel et al. [143] synthesized polyethylene (PE)/TiO2 nanocomposites using ethylene, metallocene catalysts, and titanium (IV) oxide through in situ polymerization. Rong et al. [70] developed PSt/TiO2 nanocomposites using styrene monomer and MPS-modified TiO2in situ radical polymerization. Liu and Su [144] successfully prepared PMMA/ZnO nanocomposites using MMA and oleic acid–modified ZnO nanoparticles (OA-ZnO) with 2,2′-azobis(isobutyronitrile) through in situ solution radical polymerization. Hu et al. [145] prepared PMMA/ZrO2 nanocomposites using MMA-functionalized ZrO2 nanoparticles and MMA via in situ bulk polymerization. Transmission Electron Microscopy (TEM) analysis results show that the nanoparticles are well dispersed in PMMA matrix (Figure 1.7). Milani et al. [146] prepared isotactic polypropylene (iPP)/GNs nanocomposites by the in situ polymerization method using metallocene complex (rac-Me2Si(Ind)2ZrCl2) and methylaluminoxane (MAO) as cocatalyst. Huang et al. [147] developed highly conductive polypropylene/graphene composites via in situ Ziegler–Natta polymerization.

Figure 1.7 TEM analysis of 15 wt% of ZrO2 dispersed in PMMA/ZrO2 nanocomposite [145].

1.6 Influence of Surface-Modified Nanomaterials on the Properties of Polymer Nanocomposites

1.6.1 Thermal and Flame-Retardant Properties

The incorporation of SMNs into the polymer matrix, results in a large influence on the crystallization behavior and glass transition temperature of the resultant composite material. The SMNs improves the thermal stability and flame-retardant property of the polymer matrix by acting as a superior thermal insulator and as a mass transport barrier to the volatile products generated during decomposition [148]. Patra et al. [149] studied the thermal degradation behavior of oleic acid-capped TiO2 nanorods/PMMA nanocomposites. They reported that the thermal stability of the nanocomposites improved with increasing in filler loading and the nanorods prevent rapid heat diffusion and limit further degradation of the PMMA matrix. Wu et al. [150] fabricated TiO2 nanotube–epoxy composites using phenyl dichlorophosphate–modified TiO2 nanotubes (Figure 1.8) and epoxy resin. They found that the modified TiO2 nanotubes were able to improve the thermal stability and combustion behavior of the epoxy matrix due to their flame-retardant behavior. Gao et al. [151] studied the intumescent flame-retardant behavior of polypropylene (IFR-PP) with the reinforcing effect of polysiloxane and silane-modified SiO2. They found that the polysiloxane more effectively enhances the thermal stability of the IFR-PP at high temperature and increases the char residue and markedly reduces the flammability parameters of PP. Ash et al. [152] studied the glass transition behavior of alumina/PMMA nanocomposites. They reported that the 0.5 wt% of surface-modified alumina reduces the glass transition temperature of PMMA by 25 °C. Nikje and Tehrani [153] prepared polyurethane rigid foam/modified nanosilica composite. They found that the functional groups on the nanosilica affected the stoichiometry and reduced the hard phase formation in bulk polymer and also decreased the glass transition temperature. Selvi et al. [154] developed cyclophosphazene nanotube (PZT) reinforced poly (benzoxazine-co-e-caprolactum) nanocomposites and studied its thermal and flame-retardant behaviors. They reported that 1.5 wt% of PZT nanocomposites show a low oxygen index (LOI) value of 31.4. Baoqing et al. [155] studied the effect of oleic acid–modified CaCO3 on the crystallization behavior of PP. They found that the addition of modified CaCO3 nanoparticles significantly increased the crystallization temperature, crystallization degree, and crystallization rate of PP and also led to the formation of β-crystal PP. Wu et al. [96] studied the thermal and combustion behavior of surface-modified TiO2-reinforced PSt nanocomposites. They observed that the addition of nanotube reduces the heat release rate and improves the thermal stability of the PSt matrix. Mallakpour and Zeraatpisheh [156] developed ZrO2-reinforced chlorinated poly(amide-imide) nanocomposites and studied their flame-retardant behavior. The surface of the ZrO2 was modified with APTES. They reported that the addition of ZrO2 nanoparticles enhances the thermal stability and flame-retardant behavior of the polymer matrix. Jose et al. [157] studied the nucleation and nonisothermal crystallization kinetics in cross-linked PE/ZnO nanocomposites with the aid of theoretical estimation. The surface of the ZnO was modified with trimethoxyoctyl-silane. They found that the addition of surface-modified ZnO accelerates the overall crystallization process and possesses a heterogeneous nucleating ability in the cross-linked PE matrix. Shehzad et al. [158] synthesized HDPE/graphene nanocomposites via in situ polymerization using metallocene catalyst and MAO as cocatalyst. They studied the nonisothermal crystallization behavior of the nanocomposites and found that the graphene nucleates the crystallization of HDPE in addition to increasing the crystallization onset temperature (Ton). Xu et al. [159] carried out a comparative study of isothermal crystallization behavior of poly(l-lactide) (PLLA) with GNs and CNTs. They observed that both the CNTs and GNs could serve as nucleating agents that accelerate the crystallization kinetics of PLLA. They found that the crystallization ability of CNT is stronger than that of GNs (Figure 1.9). Liao et al. [160] prepared a flame-retardant reduced graphene oxide (rGO) via in situ reduction and functionalization on the surface of GO using 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The DOPO-functionalized reduced GO (DOPO-rGO) was used as nanofiller for epoxy matrix. They studied the flame-retardant behavior of the epoxy nanocomposites and reported that 10 wt% of DOPO-rGO significantly increases the char yield and LOI value of epoxy nanocomposites.

Figure 1.8 Schematic representation of formation of phenyl dichlorophosphate modified TiO2/epoxy nanocomposites [150].

Figure 1.9 Schematic representation of conformational ordering and crystallization of PLLA in the presence of CNTs (a–c) and GNs (d–f) [159].

1.6.2 Mechanical Properties

The mechanical properties of polymeric materials are an important parameter for advanced industrial and engineering applications. Virgin polymer materials have relatively low mechanical properties compared to hybrid polymer nanocomposites. The polymeric materials are hybridized with SMNs to enhance the mechanical properties via reinforcement mechanisms [2]. Ma and Zhang [161] studied the mechanical properties of waterborne polyurethane nanocomposites using surface-modified flower-like ZnO nanowhiskers (f-ZnO). They found that the tensile strength of composite films increased significantly with increase in f-ZnO up to the optimum value (1.0 wt%). Gao et al. [162] developed the rubbery block copolymer–grafted SiO2 nanoparticle-toughened epoxy nanocomposites and studied its mechanical properties with the effect of grafting density and molecular weight of the polymer in SiO2 nanoparticle. They found that the ductility (maximum 60% improvement), fracture toughness (maximum 300% improvement), and fatigue crack growth resistance of the epoxy matrix enhanced with the incorporation of copolymer-grafted SiO2 nanoparticles. They also reported that the nanocomposites with SiO2 containing lower graft density and larger molecular weight of the polyhexylmethacrylate (PHMA) block show simultaneous improvements in fracture toughness and tensile modulus. Shukla et al. [163] prepared epoxy/alumina composites using surface-modified and unmodified alumina and studied their mechanical and fracture properties. They reported that unmodified alumina platelets increase the elastic modulus and fracture toughness of epoxy nanocomposites and decrease the tensile strength at higher volume. They observed that the surface-modified alumina platelets enhanced the tensile strength of epoxy nanocomposites, also retaining the improvements in elastic modulus and fracture toughness. Palimi et al. [164] studied the mechanical properties of polyurethane/Fe2O3 nanocomposites. They reported that surface-modified nanoparticles show a significant improvement in the mechanical properties of the polyurethane coating. Zhou et al. [165] prepared surface-modified silica-hybridized CdTe QDs/PMMA hybrid nancomposite film and studied its mechanical properties. They observed the loading of 0.2 wt% of modified QDs improved the Young's modulus, and elongation at break of about 46, 74, and 6%, respectively. Khaled et al. [166] synthesized TiO2/PMMA nanocomposite via bulk polymerization using methacrylic acid (MA)-functionalized TiO2 nanofibers and MMA (Figure 1.10). They studied the mechanical properties of the composites and reported that the functionalized TiO2 nanofibers increases the dynamic Young's moduli of PMMA composites in the range from 5.1 to 7.8 GPa. Zhang et al