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Cellulose nanocrystals (CNCs) based microfiltration membranes for water purification
The CNCs enhanced mechanical properties, low defects, high surface area to volume ratio; CNCs have been successfully added to a wide variety of microfiltration membranes for water purification. Additionally, CNCs are particularly attractive nanoparticles because they have low environmental, health and safety risks, are inherently renewable, sustainable and have the potential to be processed in industrial-scale quantities at low costs. Cao et al. reported robust poly acrylonitrile nanofibrous membrane reinforced with jute cellulose nanowhiskers for water purification. They developed a novel double layer of poly acrylonitrile (PAN) electrospun nanofibrous membranes (with an average fibre diameter of 173 nm) reinforced with TEMPO (2,2,6,6- tetra methyl piperdine-1-oxyl radical) selectively oxidized jute cellulose nanowhiskers (with a diameter in the range of 3-10 nm). They showed that the introduction of cellulose whiskers into the composite membrane had improved the mechanical properties, such as tensile strength increased to 10 MPa for single layer composite membrane and 14 MPa for double layer composite membrane, shown in figure 1.14. This can interpreted by the strong hydrogen bonding of cellulose nanowhiskers network formed on the surface of PAN nanofibrous electrospun membrane.
EMI Shielding as a global challenge for future and intrinsically conducting polymers based on cellulose nanopapers as an advanced solution
Widespread use of electric and electronic systems for household, industrial, communication and other application makes it necessary for circuits to operate in close proximity of each other. Often these circuits affect performance of other near or far region electromagnetic fields. This interference is thus called electromagnetic interference (EMI), and is emerging to be a major problem for circuit designers. In addition the use of integrated circuits are being put in less space close to each other, thereby increasing the problem of interference [56]. EMI which can cause unacceptable deterioration of equipment performance due to the unwanted radiated signals [57]. If these issues are left unattended, it may cause severe damage to communication system and safety operation of many electronic devices. More over the EMI also causes a lot of health issues such as symptoms of languidness, insomnia; nervousness and headache on exposure to electromagnetic waves [58-60]. In the operation of microprocessor controlled devices the use of high frequency signals may be transmitted out of the device to the surrounding environment can severely affect the functioning of nearby equipment. So in order to prevent this, an electronic devices must be shielded in such a way that both incoming and outgoing interferences should be filtered [61].
ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tuneable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Intrinsically conducting polymers (ICPs) are attractive alternative materials for EMI shielding.
EMI Shielding Theory
Shielding effectiveness is the ratio of impinging energy to the residual energy. When an electromagnetic wave pass through a shield, absorption and reflection takes place. Residual energy is part of the remaining energy that is neither reflected nor absorbed by the shield but it is emerged out from the shield. All electromagnetic waves consist of two essential components, a magnetic field (H) and an electric field (E) as shown in figure 1.17. These two fields are perpendicular to each other and the direction of wave propagation is at right angles to the plane containing the two components. The relative magnitude depends upon the waveform and its source. The ratio of E to H is called wave impedance. EMI shielding consists of two regions, the near field shielding region and far field shielding region. When the distance between the radiation source and the shield is larger than λ/2π (where λ is the wavelength of the source), it is in the far field shielding region. The electromagnetic plane wave theory is generally applied for EMI shielding in this region. When the distance is less than λ/2π, it is in the near field shielding and the theory based on the contribution of electric and magnetic dipoles is used for EMI shielding [62].
Polymers as EMI shielding material
Generally polymers are natural insulators and do not reflect or absorb EMI. Most of the energy waves are not obstructed by polymers and enter or leave the housing rapidly which causes interference problems. In order to shield EMI, several technical approaches have been extensively used to improve the electrical conductivity of polymers by the way of 1) Conductive coating of plastics, 2) Compounding with conductive fillers and 3) Intrinsically conducting polymers.
Table of contents :
General Introduction
Chapter 1: Bibliographical Review
1. Introduction
1.1 Cellulose , its sources, chemical composition and physical properties
1.2 Cellulose nanofibers (CNFs) and Cellulose nanocrystals (CNCs)
1.3 Isolation and Extraction techniques for cellulose nanofibers ( CNFs)
1.3.1 High pressure homogenization
1.3.2 Grinding
1.3.3 Cryocrushing
1.3.4 High Intensity ultrasonication
1.3.5 Steam explosion coupled with mild acid hydrolysis
1.3.6 Electrospinning
1.3.7 Enzymatic pre-treatments
1.4 Surface chemistries on Nanocellulose
1.4.1 TEMPO oxidation
1.4.2 Acetylation
1.4.3 Silyation
1.4.4 Esterification
1.4.5 Polymer Grafting
1.4.6 Catonization Nanocellulose Based Functional Constructs for Clean water and Microwave Suppression Deepu Ambika Gopakumar 2017
1.5. Water purification as a comprehensive challenge for future and electrospun nanofibers as an advanced solution
1.5.1. Next Generation filtration media: electrospun fibers
1.5.2 Nanocellulose as a sustainable solution for water purification
1.5.2.1. Cellulose nanofibers (CNFs) based microfiltration membrane for Water purification
1.5.2.2 Cellulose nanocrystals (CNCs) based Microfiltration membrane for Water Purification
1.6 EMI Shielding as a global challenge for future and Intrinsically conducting polymers based on cellulose nanopapers as an advanced solution
1.6.1 EMI Shielding Theory
1.6.2 Polymers as EMI shielding material
1.6.3 Conductive coating of plastics
1.6.4 Compounding with conductive fillers
1.6.5 Intrinsically conducting polymers (ICPs)
1.6.6 EMI shielding with PANI
1.6.7 Cellulose nanopapers derived from bio-mass as an effective substrate for EMI Shielding applications.
1.7 Objectives of research
1.8 References
Chapter 2: Materials and methods
2.1 Introduction
2.2 Materials
2.3 Methods of Fabrication Nanocellulose Based Functional Constructs for Clean water
2.3.1 Extraction of Cellulose nanofibers via steam explosion coupled with Mild acid hydrolysis
2.3.2 Surface modification of CNFs using Meldrum’s acid
2.3.3 Preparation of electrospun PVDF microfiltration membranes
2.3.4 Fabrication of PVDF/Meldrum modified CNFs based Nanofibrous Microfiltration Membranes
2.3.5 In-situ Polymerization of aniline on cellulose nanofibers
2.3.6 Fabrication of PANI/CNF flexible conductive papers
2.4 Characterization techniques
2.4.1 Transmission electron microscopy (TEM)
2.4.2 Scanning electron microscopy (SEM)
2.4.3 X-ray diffraction analysis (XRD)
2.4.4 Thermogravimetric Analysis (TGA)
2.4.5 Conductimetic titration
2.4.6 Fourier Transform Infrared Spectroscopy (FTIR)
2.4.7 Water Contact angle studies
2.4.8 BET measurements
2.4.9 UV- Visible Spectrophotometer
2.4.10 Dye adsorption studies
2.4.11 Microfiltration performance of the nanofibrous MF membranes
2.4.12 Electrical conductivity measurements
2.4.13 Dielectric studies
2.4.14 EMI shielding performance
2.5 Conclusion
2.6 References Nanocellulose Based Functional Constructs for Clean water and Microwave Suppression Deepu Ambika Gopakumar 2017
Chapter 3: Surface modification of cellulose nanofibers via non solvent assisted procedure using Meldrum’s acid- a unique methodology
3.1 Introduction
3.2 Morphology of cellulose nanofibers (CNFs)
3.3 Characterization of Meldrum’s acid modified CNFs.
3.3.1 FTIR spectroscopy studies
3.3.2 XRD studies
3.3.3 Morphology of the Meldrum’s acid modified CNF
3.3.4 Thermogravimetric Analysis
3.3.5 Determination of the amount of carboxyl groups in the Meldrum’s acid modified CNFs
3.4 Conclusion
3.5 References
Chapter 4: Meldrum’s Acid modified cellulose nanofiber based PVDF nanofibrous Microfiltration membrane for dye water treatment and nanoparticle removal
4.1 Introduction
4.2 Morphology of cellulose nanofibers and PVDF electrospun membrane
4.3 Morphology of Modified CNFs based PVDF nanofibrous MF membrane
4.4 Surface area of nanofibrous MF membrane
4.5 Contact angle studies
4.6 Evaluation of adsorption capacity of nanofibrous membrane against crystal violet dye
4.7 Microfiltration performance of nanofibrous MF membrane against nanoparticles Nanocellulose Based Functional Constructs for Clean water and Microwave Suppression Deepu Ambika Gopakumar 2017
4.8 Conclusion
4.9 References
Chapter 5: Strategy and fabrication of in-situ polymerized PANI/CNF Nanopaper
5.1 Introduction
5.2 Strategy for the in-situ polymerization of aniline monomers onto cellulose nanofibers
5.3 Characterization of the Fabricated PANI/CNF composite paper
5.3.1 FTIR studies
5.3.2 XRD studies
5.3.3 Morphological Studies of PANI/CNF flexible composite papers
5.3.4 DC Conductivity of the fabricated PANI/CNF paper.
5.3.5 Dielectric properties of the PANI/CNF composite paper
5.4 Conclusion
5.5 References
Chapter 6: Electromagnetic wave Attenuation performance of PANI/CNF Nanopapers
6.1 Introduction
6.2 EMI shielding of fabricated conductive PANI/CNF paper
6.3 Conclusion
6.4 References
Chapter 7: Conclusions and Perspectives
