Micronized wax additives have been used to modify coatings for decades. They can provide a wide range of properties, including surface protection, gloss reduction, water repellency, and texturizing. These additives are typically based on low molecular weight polymeric materials, including polyethylene, polypropylene, carnauba wax, and other synthetic and natural materials. Micronized wax additives can also be used in cosmetics and personal care products, providing properties that include dry binding, thickening, mattifying, and texturizing.
Recent years have witnessed unprecedented growth of research and applications in the area of nanoscience and nanotechnology. Recent leaps in areas such as microscopy have given scientists new tools to understand and take advantage of phenomena that occur naturally when matter is organized at the nanoscale. In essence, these phenomena are based on “quantum effects” and other physical effects such as expanded surface area. In addition, a majority of biological processes occur at the nanoscale which gives scientists models and templates to imagine and construct new processes that can enhance their work in medicine, imaging, computing, printing, chemical catalysis, materials synthesis, and many other fields. Nanotechnology is not simply working at ever smaller dimensions; rather, working at the nanoscale enables scientists to utilize unique physical, chemical, mechanical, and optical properties of materials. In particular, metal nanoparticles exhibit interesting electronic magnetic and catalytic properties that are not present in the bulk metal. These materials offer exciting opportunities to develop smarter, more functional additives.
During the last few years, research on toxicologically relevant properties of engineered nanoparticles has increased tremendously. A number of international research projects and additional activities are ongoing in the EU and the US, nourishing the expectation that more relevant technical and toxicological data will be published. Their widespread use allows for potential exposure to engineered nanoparticles during the whole lifecycle of a variety of products. When looking at possible exposure routes for manufactured nanoparticles, inhalation, dermal and oral exposure are the most obvious, depending on the type or product in which nanoparticles are used. Studies show that nanoparticles can deposit in the respiratory tract after in halation. For a number of nanoparticles, oxidative stress-related inflammatory reactions have been observed. Tumor-related effects have only been observed in rats, and might be related to overload conditions.
There are also a few reports that indicate uptake of nanoparticles in the brain via the olfactory epithelium. Nanoparticle translocation into the systemic circulation may occur after inhalation but conflicting evidence is present on the extent of translocation. These findings urge the need for additional studies to further elucidate these findings and to characterize the physiological impact. There is currently little evidence from skin penetration studies that dermal applications of metal oxide nanoparticles used in sunscreens lead to systemic exposure. However, the question has been raised whether the usual testing with healthy, intact skin will be sufficient. Uptake of nanoparticles in the gastroinstestinal tract after oral uptake is a known phenomenon, of which use is intentionally made in the design of food and pharmacological components.
Only a few specific nanoparticles have been investigated in a limited number of test systems and extrapolation of this data to other materials is not possible. Air pollution studies have generated indirect evidence for the role of combustion derived nanoparticles (CDNP) in driving adverse health effects in susceptible groups. Experimental studies with some bulk nanoparticles (carbon black, titanium dioxide, iron oxides) that have been used for decades suggest various adverse effects. However, engineered nanomaterials with new chemical and physical properties are being produced constantly and the toxicity of these is unknown. Therefore, despite the existing database on nanoparticles, no blanket statements about human toxicity can be given at this time. In addition, limited ecotoxicological data for nanomaterials precludes a systematic assessment of the impact of nanoparticles on ecosystems.
When particle sizes of solid matter in the visible scale are compared to what can be seen in a regular optical microscope, there is little difference in the properties of the particles. But when particles are created with submicron dimensions (especially in the range of 1-100 nanometers where the particles can be “seen” only with powerful specialized microscopes), the materials' properties change significantly from those at larger scales. This is the size of scale where so-called quantum effects rule the behavior and properties of particles. Properties of materials are size-dependent in this scale range. Thus, when particle size is made to be nanoscale, properties such as melting point, fluorescence, electrical conductivity, magnetic permeability, and chemical reactivity change as a function of the size of the particle.
Many benefits of nanotechnology depend on the fact that it is possible to tailor the structures of materials at extremely small scales to achieve specific properties, thus greatly extending the materials science toolkit. Using nanotechnology, materials can effectively be made stronger, lighter, more durable, more reactive, more sieve-like, or better electrical conductors, among many other traits. Many everyday commercial products are currently on the market and in daily use that rely on nanoscale materials and processes.
Nanoscale additives to or surface treatments of fabrics can provide lightweight ballistic energy deflection in personal body armor, or can help them resist wrinkling, staining, and bacterial growth.
Clear nanoscale films on eyeglasses, computer and camera displays, windows, and other surfaces can make them water- and residue-repellent, antireflective, self-cleaning, resistant to ultraviolet or infrared light, antifog, antimicrobial, scratch-resistant, or electrically conductive.
Nanoscale materials are beginning to enable washable, durable “smart fabrics” equipped with flexible nanoscale sensors and electronics with capabilities for health monitoring, solar energy capture, and energy harvesting through movement.
Nano-bioengineering of enzymes as aiming to enable conversion of cellulose from wood chips, corn stalks, unfertilized perennial grasses, etc., into ethanol for fuel. Cellulosic nanomaterials have demonstrated potential applications in a wide array of industrial sectors, including electronics, construction, packaging, food, energy, health care, automotive, and defense. Cellulosic nanomaterials are projected to be less expensive than many other nanomaterials and, among other characteristics, tout an impressive strength-to-weight ratio.
Nano-engineered materials in automotive products include high-power rechargeable battery systems, thermoelectric materials for temperature control, tires with lower rolling resistance, high-efficiency/low-cost sensors and electronics, thin-film smart solar panels, and fuel additives for cleaner exhaust and extended range.
Nanostructured ceramic coatings exhibit much greater toughness than conventional wear-resistant coatings for machine parts. Nanotechnology-enabled lubricants and engine oils also significantly reduce wear and tear, which can significantly extend the lifetimes of moving parts in everything from power tools to industrial machinery.
Nanoparticles are used increasingly in catalysis to boost chemical reactions. This reduces the quantity of catalytic materials necessary to produce desired results, saving money and reducing pollutants. Two big applications are in petroleum refining and in automotive catalytic converters.
Nano-engineered materials make superior household products such as degreasers and stain removers, environmental sensors, air purifiers, and filters, antibacterial cleansers, and specialized paints and sealing products, such a self-cleaning house paints that resist dirt and marks.
Nanoscale materials are also being incorporated into a variety of personal care products to improve performance. Nanoscale titanium dioxide and zinc oxide have been used for years in sunscreen to provide protection from the sun while appearing invisible on the skin.
It is evident from these many examples that the power of nanoscale materials presents many opportunities to create innovative products. The challenge is to harness the power of the nanoparticle in such a way that the shortcomings of these novel materials are avoided.
Nanoparticles, having an extremely high surface areas, are very difficult to disperse or otherwise incorporate into a liquid system, whether it's water based, solvent based, oil based, or other. Nanoparticles are difficult to handle in both laboratory and industrial processes, as they can create fine clouds of dust when conveyed, dispensed, or otherwise incorporated into a product. Nanoparticles are still not fully understood with regards to potential risks to human health on exposure including, but not limited to inhalation and skin absorption. Nanoparticles can abrade, wear, or otherwise degrade manufacturing, processing, and filling equipment.
Submicron particles (including nanoparticles) can be classified into different types according to the size, morphology, physical and chemical properties. Some of them are carbon-based particles, ceramic particles, metal particles, semiconductor particles, and polymeric particles.
Carbon-based nanoparticles include two main materials: carbon nanotubes (CNTs) and fullerenes. CNTs are nothing but graphene sheets rolled into a tube. These materials are mainly used for the structural reinforcement as they are 100 times stronger than steel. CNTs can be classified into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). CNTs are unique in a way as they are thermally conductive along the length and non-conductive across the tube. Fullerenes are the allotropes of carbon having a structure of hollow cage of sixty or more carbon atoms. The structure of C-60 is called Buckminsterfullerene, and looks like a hollow football. The carbon units in these structures have a pentagonal and hexagonal arrangement. These have commercial applications due to their electrical conductivity, structure, high strength, and electron affinity. Graphene particles are known to provide benefits that include corrosion resistance and electrostatic dissipation (ESD).
Ceramic particles are inorganic solids made up of oxides, carbides, carbonates and phosphates. These submicron particles and/or nanoparticles have high heat resistance and chemical inertness. They have applications in photocatalysis, photodegradation of dyes, drug delivery, and imaging. By controlling some of the characteristics of ceramic nanoparticles like size, surface area, porosity, surface to volume ratio, etc, they perform as a good drug delivery agent. These nanoparticles have been used effectively as a drug delivery system for a number of diseases like bacterial infections, glaucoma, cancer, etc.
Metal particles are prepared from metal precursors. These submicron particles and/or nanoparticles can be synthesized by chemical, electrochemical, or photochemical methods. Metal nanoparticles, such as aluminum oxide, are also highly effective at improving surface durability properties (scratch resistance, abrasion resistance, etc.) in coatings.
Inorganic particles can include titanium dioxide submicron and/or nanoparticles, which can impart a self-cleaning effect to glass and solid exterior surfaces. Zinc oxide particles have been found to have superior UV blocking properties compared to its bulk substitute.
Semiconductor nanoparticles have properties like those of metals and non-metals. They are found in the periodic table in groups II-VI, III-V, or IV-VI. These particles have wide bandgaps, which on tuning shows different properties. They are used in photocatalysis, electronics devices, photo-optics and water splitting applications. Some examples of semiconductor nanoparticles are GaN, GaP, InP from group III-V, ZnO, ZnS, CdS, CdSe, CdTe are II-VI semiconducts and silicon and germanium are from group IV.
Polymeric submicron and/or nanoparticles are organic based particles. Depending upon the method of preparation, these can have structures shaped like nanocapsular or nanospheres. A nanosphere particle has a matrix-like structure whereas the nanocapsular particle has core-shell morphology. In the former, the active compounds and the polymer are uniformly dispersed whereas in the latter the active compounds are confined and surrounded by a polymer shell. Some of the merits of polymeric nanoparticles are controlled release, protection of drug molecules, ability to combine therapy and imaging, specific targeting and many more. They have applications in drug delivery and diagnostics. The drug deliveries with polymeric nanoparticles are highly biodegradable and biocompatible.
A limitation of the commercial industrial use of submicron particles is that they are highly difficult to disperse. These powders have very high surface areas, and it is challenging to use these powders in additives without preliminary processing. This could include chemical surface modification, to stabilize the particle in a liquid media, and wet phase agitation bead milling, to separate, wet, and disperse the powder into its primary particle size. When wet processing is used, the choice of processing media limits the versatility of the modified powder. For example, nanoparticles can be dispersed with sufficient time and energy into a solvent based polyurethane medium, but the resulting dispersion would not be suitable for end uses in water based, energy curable, or 100% solids applications. Other processing aids such as surfactants and dispersants may need to be incorporated, further limiting the versatility of the dispersion.
Therefore, it would be desirable to find a way to deliver the performance of these submicron particles in a dry matrix that is readily dispersible into a wide variety of end systems without the use of a solvent, using much easier and common mixing technology. It would be further desirable to develop a composition containing submicron particles that are safe to handle.
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