The book comprises recent innovations and developments in various high performance applications of advanced polymeric materials. It is a compilation of work from eminent academicians and scientists and the chapters provide insight into the effect of tailoring the polymeric systems, blending matrices with nano / micro fillers for improved performance and properties.
The book details the following topics:
* Smart & high performance coatings
* High barrier packaging
* Solar energy harvesting
* Power generation using polymers
* Polymer sensors
* Conducting polymers
* Gas transport membranes
* Smart drug delivery systems
Polymer Nanocomposites and Coatings: The Game Changers
Dr. Shanti Swarup Bhatnagar University Institute of Chemical Engineering and Technology (formerly Department of Chemical Engineering & Technology), Panjab University, Chandigarh, India
Centre for Nanoscience and Nanotechnology (U.I.E.A.S.T), Panjab University, Chandigarh, India
Corresponding author: email@example.com, firstname.lastname@example.org
In recent years, polymer nanocomposites and coatings have caught the attention of the research world due to their versatile properties and widespread applications. The availability of new nanoscale fillers and additives provide polymer scientists with materials and a lot of options to modify the properties of the polymeric matrix and hence widen the ambit of their applications. Increasing usage of polymer nanocomposites and their exploration for more potential applications lead to game-changing solutions to many engineering and technological problems. The issue with nanoscale fillers is their stability and compatibility with polymeric matrix. A lot depends on the processing protocols used for fabricating the nanocomposites. This chapter provides an overview of the structure-property-processing relationship for polymer nanocomposites and coatings.
Keywords: Polymer, nanoscale fillers, structure-property-processing, performance
Polymer nanocomposites are composed of a polymeric matrix and a nanoscale filler which have at least one dimension in the nanometer range (usually 1-100 nm is accepted but nowadays many fillers up to a size of 500 nm have also been considered as nanofiller). The wide variation in shapes and sizes of these nanoscale fillers accounts for wide ranging structural and property modifications of the polymeric matrix, as shown in Figure 1.1. Although polymers themselves are versatile materials and can be easily tailored to imitate metals, natural materials and even biomaterials, the ever widening scope of new materials has yet to catch up with the latest technology, thus requiring constant research and updating.
Figure 1.1 (Top) Different shapes and types of typical nanoparticles (nanoscale fillers) used to reinforce polymeric matrices. (Bottom) Particle shapes and surface area/volume (A/V) versus aspect ratio (a) variation for nanoscale structures which can reinforce polymer matrices .
Depending on how many dimensions of the particles are in nanometer range, nanoparticles are mainly categorized into three types. In the first type, called isodimensional nanoparticles, all dimensions are in the order of nanometers (0D) (e.g., spherical silica nanoparticles, some nanoclusters, etc.). In the second type, called nanotubes or nanowhiskers, two dimensions of the particles are in the nanometer range and the third one is larger, usually forming an elongated structure (1D) (e.g., carbon nanotubes, cellulose nanowhiskers). The third type of nanoparticles is characterized by only one dimension in the order of nano range (2D). In this case the particles are present in the form of sheets one to a few nanometers thick to hundreds to thousands of nanometers long (e.g., layered silicates [LS]).
The 21st century applications are far reaching, as scientists have started to explore more of outer space, planets and other celestial bodies. Aspirations on earth are also much more technologically advanced as compared to a decade ago. Better materials are needed to fabricate new types of automobiles like driverless cars, flying drones or supersonic aircrafts. There are two options for making materials to cater to these needs. One is to invent or discover totally novel materials with distinct properties, new structure and hence new properties. This approach is promising but may not be that helpful as there are shortcomings in a single material. Getting the best property and structural combinations is usually possible by modifying materials. So the second apprxoach is to use nanoscale fillers to tailor materials with better property combinations without compromising their inherent characteristics.
Using nanoscale fillers to modify conventional materials like polymers is an up-and-coming and very promising technique. By using only a very small quantity of nanoscale fillers like less than 10 weight percent, huge property benefits can be achieved. In comparison to conventional microscale filled composites, the reduction in weight percentage of the filler used is about 10 times or more, while the property improvements almost double. Sometimes the properties which couldn't be imbibed in conventional composites (Figure 1.2) can now be easily induced in nanocomposites. These advantages and other structural, morphological and physical improvements have led to increased interest in scientific and commercial communities. The only issue facing the use of nanocomposites is the ultimate control over nanofiller size, which still needs to be attained. Processing of nanocomposites, especially coatings, is also a far cry from realization; hence; the objective of this chapter is to instigate the research world into formalizing the processing protocols. By using examples of polymer-based nanocomposites and coatings, this chapter presents useful information on structure-property-processing of nanocomposites. Some of their applications will also be briefly discussed.
Figure 1.2 Types of composites.
1.2 Polymer Nanocomposites
1.2.1 Types of Polymer Nanocomposites: Processing
The possibility of combining nanoscale fillers with polymers is enormous, as polymers themselves are a huge class of materials with versatility in their chemistry and physical structure. The tunability of polymeric structures results in various forms like hard plastics, soft foams, coatings and even cellular structures and biomaterials. Inspired by many natural structures and composites like bone, teeth and nacre, many hierarchical structures of polymer nanocomposites have been built. Depending upon the use of either thermoplastic or thermosetting polymers, various processing techniques are adopted to fabricate these materials. For example, commercially developed large-scale thermoplastic composites of polymers can be processed using melt processing mechanical methods like extrusion and injection molding (Figure 1.3). Composite processing machines ranging from lab-scale customized extruders to pressurized plunger-type injection-molding machines are sometimes well suited for thermoplastic polymer and 1D nanofillers like nanotubes and nanofibers. Although these nanofibers/nanotubes significantly depend on their orientation in the shear developed during melt processing, many times a solution or solvent precasting with polymer is done for blending them with certain matrices. Shear is generated through twin-screw extruding for some matrices like polyether ether ketone (PEEK) in some cases to disperse nanofibers up to 1 weight percent (wt%) [2, 3]. The intrinsic viscosity of thermoplastic polymers contributes to the high shear which is generated inside the barrel during processing and helps in dispersing the carbon nanotubes/carbon nanofibers (CNTs/CNFs). The orientation of the fibers can be an issue when using such techniques. Certain composites may require directional properties, others might not. Depending upon the requirement of the product, the suitability of the technique may be decided. Some scientists have also used preprocessing or a precursor technique like ball milling or sonication prior to final or intermediate processing to achieve better aspect ratio of the nanofillers .
Figure 1.3 Processing of thermoplastic nanocomposites.
Thermosetting polymers like epoxy and polyurethane and their variants have to undego a solution/solvent-based processing protocol when reinforced with nanofillers like carbon nanotubes (CNTs) (Figure 1.4). Solvent-based processing requires separate dispersion or dissolution of CNTs directly in polymer mixture and then casting into a given mold, unlike thermoplastic processing techniques of extrusion, where in-situ mixing of nanofillers are carried out.
Figure 1.4 Processing of thermosetting nanocomposites.
But the new nanoscale fillers demand greater technological advancements for dispersing and homogenizing them into polymer matrices. As needs have changed, an upgrade of conventional processing equipment used in the polymer and rubber industries is required. Parameters like stability and control over shape, particle size and surface area can only be attained if the equipment in use caters to their manipulation and alteration. New designs may soon be entering the industry for commercialization and large-scale production of polymer nanocomposites. Till that time, small batches may be produced with prototypes being used at laboratory and research scale. Shown in Figures 1.5-1.7 are three such essential types of equipment used by our laboratory to produce polyurethane-clay nanocomposite coatings [5-10].
Figure 1.5 (a) View of ultrasonic bath used for sonication with time control. (b) Schematic representation of the deagglomeration of particles by sonication with the help of cavitation.
Figure 1.6 (a) Oblique and (b) front view of high shear homogenizer and (c) its stator-rotor.
Figure 1.7 (a,b) Stator-rotor system. (c,d) Action of high...