Dispersion and Orientation

Many times functionalization is required for improving the homogenization of nanomaterials in the polymer matrix. However, due to surface functional groups, the individual nanomaterials structurally self-assemble 

Tailoring the properties of polymers with the inclusion of nanometric carbon depends on many factors. Among them, the parameters most taken into account are (a) the size, structure and distribution of the nanofiller in the matrix and (b) the interface between the nanofillers and the matrix. This chapter focuses mainly on the effects that functionalization and concentration of nanofillers have in the storage modulus and tribological properties of polymer nanocomposites reinforced with NDs, CNTs and graphene, describing briefly the hardness and scratching performance achieved in these nanocomposites. 

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Once the nanotubes have been characterised and polymer/ nanotubes elaborated, their microstructures have to be precisely determined to understand the relations between the process and the nanocomposites macroscopic properties. It is expected that the microstructural parameters that will play major roles (in addition to the filler geometry) are the nanotube dispersion and orientation... 

Elastomers require, in most applications, to be reinforced by fillers in order to improve their mechanical properties. Carbon black and silica have been used for a long time in the rubber industry to prepare composites with greatly improved properties such as strength, stiffness and wear resistance. These conventional fillers must be used at high loading levels to impart to the material the desired properties (1). The state of filler dispersion and orientation... 

Studies from the composite deformation mechanism and interfacial bonding between nanofillers and the polymer matrix have been performed [46-48]. In these reports, the authors performed straining studies to determine the load transfer between carbon nanotubes and the polymer and observed the phenomena of crack propagation and polymer debonding. In some cases, the mechanical deformation processes were followed over the electrospun composite fibers. Microscopic images revealed information on the dispersion and orientation of nanotubes within the fiber and their impact in the mechanical performance regarding strain at break and stress concentration at the pores of the nanotubes. 

SEM is a fast method for obtaining detailed morphological information for different polyolefins. This method is valuable tool for the analyses of polyolefins, and it is extensively used for the analyses of failure and fracture mechanics, shape and particle size, filler dispersion, and orientation in polymer matrices [90]. A few nanometer spatial resolution and a large depth of field can be obtained by SEM, and it can work up to 100 times that of an optical microscope in some cases. From these feamres, information about topography of the sample surface can be obtained necessary for a deeper understanding of the interaction between the substrate and the surface treatment [91]. 

The incorporation of fillers can induce modifications in the thermal properties of the polymers. Factors that affect the thermal conductivity of composites are the dispersion and orientation of the filler particles, the filler aspect ratio, and the relative ratio of thermal conductivity of the filler and the matrix. The thermal conductivity was found to be increased when the Ti02 volume fraction increases. The measured values of thermal conductivity have been compared to different theoretical models. 

Quantitative predictions of the effects of fillers on the properties of the final product are difficult to make, considering that they also depend on the method of manufacture, which controls the dispersion and orientation of the filler and its distribution in the final part. Short-fiber- and flake-filled thermoplastics are usually anisotropic products with variable aspect ratio distribution and orientation varying across the thickness of a molded part. The situation becomes more complex if one considers anisotropy, not only in the macroscopic composite but also in the matrix (as a result of molecular orientation) and in the filler itself (e.g., graphite and aramid fibers and mica fiakes have directional properties). Thus, thermoplastic composites are not always amenable to rigorous analytical treatments, in contrast to continuous thermoset composites, which usually have controlled macrostructures and reinforcement orientation [8, 17]. 

The extrusion process was conducted below the melting temperature of pure 1,3 2,4-di-p-methylbenzylidene sorbitol, DBS." The reasons were (1) low temperatures were beneficial for avoiding the possible thermooxidative degradation of iPP and decomposition of DBS (2) uniform dispersion and orientation of DBS fibrils in iPP matrix could be realized via extmsion compounding below the melting point of DBS."... 

Polymer composites have attracted a great deal of interest in recent years. In most cases, fillers are used as additives for improAdng the mechanical behavior of the host polymeric matrix. The reinforcement of elastomers by mineral fillers is essential to the rubber industry, because it yields an improvement in the service life of rubber compounds. The state of filler dispersion and orientation in the matrix, the size and aspect ratio of the particles as well as the interfacial interactions between the organic and inorganic phases haw been shown to be crucial parameters in the extent of property improvement [1,2]. 

Optical microscopy is also a technique that can be useful for the characterization of nanocomposites. According to Xie ct al. [27] transmission electron microscopy has been widely used to estimate clay dispersion and orientation in polymer matrices. Although it can provide direct information on clay layers in the real space, the analysis are focused on a very small volume of the sample and may not be representative. However, optical microscopy can be a complementary technique to substitute for analyze the overall dispersion/distribution of day partides at a macroscopic level. It can show, for example, the presence of agglomerate partides that can be related to the degree of exfoliation of clay layers in the matrix. 

The excellent mechanical properties of carbon nanotubes and their high electrical and thermal conductivity make them ideal candidates for a wide range of applications where long carbon fiber-reinforced polymers cannot be employed. The present chapter shows the potential of the CNT as nanofillers in polymers, but also the need of further development for the achievement of optimal dispersion and orientation in order to attain the best possible properties. 

Processing is, of course, crucially important in determining nanotube dispersion and orientation, as well as the more traditional but equally important factors associated with polymer morphology. Polymer nanocomposite fibres may be spun from solution or from the melt, often following an initial dispersion step, as discussed in Section 7.3.1 above. Much of the initial work has been exploratory in nature, and there remains considerable scope for applying the wider understanding of fibre spinning to these systems. 

Although carbon nanotubes show exceptional properties on the nanoscale, the difficulty lies in creating a material that exhibits carbon nanotube properties on the macro-scale. Incorporating the nanotubes as filler into polymer matrices is the most common method currently explored. Similar to other composites made from chopped fiber in a polymer matrix, filler dispersion and orientation are essential to achieve optimal property improvements. Researchers have used many different techniques to attempt to disperse nanotubes in polymer matrices including solution chemistry to... 

The morphology of the PP/nanotube composite samples was observed both qualitatively and quantitatively. The dispersion and orientation of the nanotubes was verified through transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Finally, the polymer crystal structure and orientation was investigated quantitatively through wide-angle X-ray diffraction (WAXD). 

Incorporation of silicate nanolayers in semi-crystalline polymers like polypropylene ean have a two-fold effect on the barrier properties, (1) well oriented large aspeet ratio platelets will increase the tortuosity of the diffusion path and (2) the nanolayers will affect the crystalline order (size and interlamellar spacing) and possibly affect the barrier properties. The extent of orientation is greater in blown film than in extmsion cast film and this leads to similar trends in barrier properties of polypropylene nanocomposites with 7wt.% 1.3 IPS (silated) clay as reported by Qian et al. With cast films, the nanoeomposite had a lower permeability to oxygen by a faetor of 1.5 compared to neat polypropylene. With blown films, the nanocomposite permeability to oxygen was lower by a factor of 2.5 compared to neat polypropylene. However, Ellis and D Angelo were able to prepare only intercalated polypropylene nanocomposites with the same 1.31 PS and obtained no improvement in permeability to a solvent over that for neat polypropylene. This underlines the greater sensitivity of barrier performanee to the level of dispersion and orientation. 

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