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Polymer composites and nanocomposites
Polymer composites
Although polymers are being employed more and more as structural materials, their use is often limited by their relatively low levels of stiffness and strength compared, for example, with metals. Because of the need for light, stiff and strong materials for applications as diverse as aerospace structures and sporting goods, polymer composites with a specific combination of properties beyond those obtainable from a single material have been developed over recent years. Junior (2002) defines a composite as « a multiphase material made artificially in contrast with material that occurs or is formed naturally. In addition, the constituent phases must be chemically different and must be separated by a distinct interface ». Also according to Junior (2002), in general, a composite may be considered as any multiphase material that exhibits a significant proportion of the properties of the constitute phases.
Polymer composites can be obtained through the use of copolymers or blends, but the specific aspect that characterizes composite materials is that they are made up of distinct phases with very different physical properties. They are often, but not exclusively, found to consist of a relatively soft flexible matrix reinforced by a stiffer component. Sometimes, however, a softer phase is used to improve impact properties. An example is the addition o rubber particles to a rigid polymer to yield a rubber-toughened material. In some cases, a second phase is added to a polymer to improve properties other than just mechanical behaviour. The need for property improvement is not the only reason for the development of composite materials. For instance, polymers are often employed in low-cost high-volume applications where the addition of an inexpensive inert mineral filler may reduce the quantity of relatively expensive of the polymer used with no sacrifice in mechanical properties.
Historically, the first type of synthetic polymer composites developed were formaldehydebased resins filled with mineral particles or sawdust (Young and Lovell, 2011). The most well-known polymer composites in industry are those filled with synthetic or natural inorganic compounds (commonly called conventional fillers). Conventional fillers are materials in the form of particles (e.g. calcium carbonate), fibres (e.g. glass fibres) or plateshaped particles (e.g. mica). However, although conventionally filled or reinforced polymeric materials are widely used in various fields, it is often reported that the addition of these fillers imparts drawbacks to the resulting materials. The disadvantages include weight increase, brittleness and opacity.
Polymer nanocomposites
“A nanocomposite refers to every material that combines one or more separate components in order to improve performance properties, for which at least one dimension of the dispersed particles is in the nanometer range” (Kumar et al., 2009). Alexandre and Dubois (2000) defined it more narrowly stating that polymer nanocomposites are a new class of composites that are particle-filled polymers for which at least one dimension of the dispersed particles is in the nanometer range.
Fillers with at least one nanoscale dimension (nanoparticles) have proportionally larger surface area than their microscale counterparts, which favours the filler–matrix interactions and the performance of the resulting material. A uniform dispersion of nanoparticles leads to a very large matrix/filler interfacial area, which changes the molecular mobility, the relaxation behaviour and the consequent thermal and mechanical properties of the material.
The interest of scientists in applying nanoscale fillers with a high aspect ratio (i.e., high specific surface area) into polymer matrices is the attainment of potentially unique properties.
In addition, to the effects of the nano-reinforcements themselves, an interphase region of altered mobility surrounding each nanoparticle is induced by the well-dispersed nanoparticles. This results in a percolating interphase network in the composite that plays an important role in improving the polymer nanocomposite properties (Kumar et al., 2009, Tjong, 2006, De Azeredo, 2009).
In fact, it is well established that dramatic improvements in physical properties, such as heat resistance, stiffness, strength, toughness, impact resistance, barrier properties, rheological properties, flame retardancy, etc., can be achieved by adding just a small fraction of clay nanoparticles to a polymer matrix, without impairing the optical homogeneity of the material. Since the weight fraction of the inorganic additive is typically well below 10%, the materials are also lighter than most conventional composites (Kiliaris and Papaspyrides, 2010, de Sousa Rodrigues et al., 2013, Arora and Padua, 2010, Utracki, 2008, de Paiva et al., 2008, LeBaron et al., 1999). The unique properties pointed out here make polymer nanocomposites ideal materials for products ranging from high-barrier packaging for food and electronics to strong, heat-resistant automotive components.
Among the various applications of polymer nanocomposites, automotive parts, packaging and electronics are the main nanocomposite applications on a worldwide basis. In 2013 for example, the automotive industry absorbed 51.4%, packaging industry with 22.5% and finally electronics with 13.8% of the market. By 2019, automotive parts’ share is expected to drop to 40.6%, while electronics’ share may drop to 8% (BCC Research).
1. GENERAL INTRODUCTION
1.1. Background
1.2. Research objectives .
1.3. Methodology
CHAPTER 2
2. LITERATURE SURVEY
2.1. Clays and clay minerals
2.2. Smectites
2.2.1. Location and geology setting of Boane bentonite used in the study
2.3. Vermiculite
2.3.1. Exfoliation and delamination of vermiculite.
2.3.2. Location and geology setting of Palabora vermiculite
2.4. Sepiolite
2.5. Clay surface modification
2.5.1. Organomodified clays for polymer nanocomposite technology
2.5.2. Organomodified clay structure
2.5.3. Characterization of modified clays
2.6. Generalities about polymers.
2.6.1. Macromolecule polymer chains
2.6.2. Skeletal structure of polymers
2.6.3. Classification of polymers .
2.6.4. Biopolymers .
2.6.5. Dimer fatty acid-based polyamides – Preparation routes and main applications .
2.6.6. Polyamide 11 – Preparation routes and main applications
2.7. Polymer composites and nanocomposites
2.7.1. Polymer composites
2.7.2. Polymer nanocomposites
2.7.3. Polyamide bio-nanocomposites
2.8. Clay-polymer composite – Preparation methods
2.8.1. In situ polymerization process .
2.8.2. Melt intercalation proces
2.8.3. Solvent intercalation process
2.9. Clay-polymer nanocomposite structure
2.10. Clay-polymer composite – Properties and characterization
2.10.1. Physical properties
2.10.2. Chemical properties .
CHAPTER 3 EXPERIMENTAL
3.1. Materials
3.1.1. Clay samples .
3.1.2. Chemicals
3.1.3. Polymer matrices
3.2. Methods
3.2.1. General description of the “novel method” used in the present stud
3.3. Samples preparation
3.4. Samples characterization
CHAPTER 4 RESULTS AND DISCUSSIONS
4.1. Clay characterization
4.2. Composites characterization
4.3. NH4+-MMT/bio-nanocomposites based on DAPA
4.4. VMT (exfoliated by thermal shock and H2O2 treatment and/or sonication)/bio-nanocomposites
based on DAPA.
4.5. Melt compounded VMT and PGS9/bio-nanocomposites based on PA-11
CHAPTER 5 GENERAL CONCLUSIONS
