Polymer Nanocomposites for Structural Applications

Keywords Polymer composites, nano-reinforcements, structural applications, mechanical properties 

Smita Mohanty et al (eds.) Polymer Nanocomposites Based on Inorganic and Organic Nanomaterials. (505-518) 2015 Scrivener Publishing LLC 

In addition, by scaling the filler size to the nanometer scale, it has been shown that novel material properties can be obtained. Nanoscaled fillers are those having at least one dimension in the range of nanometers ( 100 nm) [3]. When the dimensions of the reinforcement approach the nanometer scale, a number of effects make the properties of the corresponding composites different from those of composites reinforced with micro-scaled fillers. The major influencing factors of the properties of nanocomposites are nanofiller dispersion, dimensions, volume fractions, nature of the matrix material, interfacial properties between filler and matrix, and manufacturing process [4]. 

Furthermore, it is expected that the dispersion of fillers with dimensions in the nanometer level having very large aspect ratio and stiffness in a polymer matrix could lead to even higher mechanical performances. These fillers include layer silicates and carbon nanotubes. Carbon nanotubes have a substantially higher aspect ratio (-1000) in comparison with layered silicates (-200) and they also have very high strain to failure. 

Rigid inorganic nanoparticles with a smaller aspect ratio are also promising reinforcing and/or toughening materials for polymers [2]. Several comprehensive reviews have been already pubHshed in the literature regarding the effect of particle size, interfacial adhesion, and particle content of particulate-polymer composites [5,6]. 

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In this study, in order to clearly understand how the nanoplatelet degree of exfoliation and aspect ratio affect the mechanical properties, systematic investigations on a set of model polymer nanocomposites based on epoxy/a-zirconium phosphate were carried out. The model epoxy nanocomposites allow for systematic control of nanoplatelet dispersion as well as aspect ratio, thus enabling unambiguous study of fundamental structure-property relationship in polymer nanocomposites. The advantage and limitation of polymer nanocomposites for structural applications will be discussed. 

Rajesh, T. Abuja, and D. Kumar, Recent progress in the development of nano-structured conducting polymers/nanocomposites for sensor applications, Sens. Actuators B, 136, 275-286 (2009). 

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs), due to their unique structure and properties, appear to offer quite promising potential for industrial application [236]. As prices decrease, they become increasingly affordable for use in polymer nanocomposites as structural materials in many large scale applications. In fact, three applications of multiwall CNT have been discussed recently first, antistatic or conductive materials [237] second, mechanically reinforced materials [238,239] and third, flame retarded materials [240,241]. The success of CNTs in the field of antistatic or conductive materials is based on the extraordinary electrical properties of CNTs and their special geometry, which enables percolation at very low concentrations of nanotubes in the polymer matrix [242]. 

V. Rangari, Polymer nanocomposite materials for structural applications, in B. Reddy, ed.. Advances in Nanocomposites - Synthesis, Characterization and Industrial Applications, InTech, pp. 61-84,2011. 

With both thermoset and thermoplastic in situ polymerization techniques, there are some fundamentals of polymer nanocomposite synthesis that are weU understood. One fundamental to consider is the interface between polymer and nanoparticle in the final application without a well-designed interface between nanoparticle and polymer, no synthetic technique will yield a good polymer nanocomposite. For in situ polymerization, the focus is on clay nanocomposites, as this field has a wealth of information on structure-property relationships between clay and polymer. Some factors that must be considered include ... 

Synthetic composite materials have passed through intensive progress in the last fifty years. Originally, synthetic polymers were blended with inorganic fillei-s for the sake of price reduction on the other hand, fillers cause considerable change in many physical properties of polymei-s. Later, functional fillers bringing other effects to polymer composites, such as magnetic or electrical properties, bioactivity, reduced flammability, etc., were introduced in the 80 s and 90 s. Nanocomposites can offer both miique properties and multi-functionality, which are well applicable in various fields. Undoubtedly, if one wants to use polymer nanocomposites in specific applications, the structure-property relationships have to be fully understood in these miique materials first. 

To date much of the development of polymer nanocomposites has been for structural applications with current commercial applications such as the step assist for the Chevrolet Astro van introduced by General Motors in 2002. However, there are other composite functions, such as tribological resistance, low friction or fire retardancy which are important in other applications and with nanoscale reinforcements it is possible to mix several different types of reinforcement to generate improvements in a range of properties. The following sections discuss how such properties are improved in nanocomposites. 

The structure-property relationship of a set of model polymer nanocomposite systems has been investigated. The findings suggest that degree of exfoliation and aspeet ratio of nanoplatelets in polymer matrices can greatly influence physical, mechanical and rheological behaviors of polymers. Most importantly, there appears to be a limit to which polymer nanocomposites can be applied for structural applications. 

CNT nanocomposites morphological and structural analysis is often done by TEM but an extensive imaging is required then to ensure a representative view of the material. Moreover, carbon based fillers have very low TEM contrast when embedded in a polymer matrix. The application of microscopy techniques is very useful to control the status of CNTs at any time during the preparation process of CNT/polymer nanocomposites, and moreover, to gain insights on parameters important for a better understanding the performance of the final nanocomposite material based on CNTs. 

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