Nanomaterials charge ahead
It starts with a clever mix
In its raw state, a polymer does not generally have the qualities required for its intended application. This is why additives are added to the mix, at less than 5%, or adjuvants likely to change its properties above 5%. The properties that can be modified include: appearance, elasticity, mechanical or thermal resistance, durability, etc.
Although reserved for thermosetting resins until the 1950s, the use of additives became commonplace in the plastics industry as new types of plastics were created. Some additives, such as plasticisers, chemically modify polymer chains, while others such as pigments, reinforcing fillers and gases, are inert compounds that reduce the plastic's transparency or modify its mechanical strength, or even transform it into a foam.
The art of plastic processing resides in developing the perfect formula by combining the basic polymer(s) with the appropriate additives in order to obtain the best interactions. And given the large amount of candidates in the various families of plastics, there are almost unlimited combinations.
A giant leap towards the infinitesimally small
Until the end of the last century, most additives used in plastic processing were particles measuring over one micron. But the use of scanning tunnelling microscopes invented by Gerd Binnig and Heinrich Roeher, two 1986 Nobel Prize-winners, changed the landscape. Not only did their discovery provide high resolution nanoscale 3D images, it also enabled atoms and molecules to be manipulated. It was now possible to see, at this scale, that the materials had very different behaviours than those usually noted.
The reason for this is simple. By fractionating a cubic centimetre of material into a billion fragments, the material's contact surface is multiplied by 10 million. Where a single atom out of 10 million was previously on the surface of the initial cube, almost 80% of the atoms become accessible on a cubic nanometre of material. This makes them much more reactive. A little like powdered sugar melting faster than sugar cubes.
Exploiting the surface phenomena of nanomaterials is a real boon for plastics processors who are always on the lookout for the most efficient combinations of polymers and additives.
They are now able to select from a wide range of mineral, organic, metallic or hybrid nanomaterials which can be placed in three categories: lamellars such as clays, talcs or graphite, nanofibres such as nanotubes of silica and carbon, and nodular particles mainly comprised of silica, metal oxides or carbon blacks.
Chi va nano va sano!
The plastics industry first sought to exploit the nanoscale effects of its conventional additives. For instance, instead of using titanium dioxide as a simple pigment, in the form of a 1 to 2 micron powder, it now uses its photocatalytic properties which, at the nanoscale, served to oxidise organic matter using UV radiation. Adding nano-titanium dioxide to coatings and polymer fibres provides them with self-cleaning properties, which make it easier to remove grease or volatile organic compounds.
One of the most innovative applications in this regard is the recent development of luminous synthetic textiles impregnated with titanium dioxide. Placing LED-powered optical fibres into the weft of the material considerably increases the biofilm effect of photocatalysis. Besides the aesthetic value of the lighting effect, this process, christened UVtex, paves the way for a wide range of applications beyond asepsis in the medical sector. It could also be used, for instance, to decontaminate pesticide or hydrocarbon residues present in the environment.
Silver has no odour
Silver has long been known for its germicidal properties, which is likely the reason for the popularity of silverware. Its use as nanoparticles in a colloidal suspension has seen uninterrupted growth since the late 1990s.
The medical implements sector, a major consumer, integrates nanosilver into the polymers used to manufacture dressings, surgical masks, catheters, etc. Certain PMMA (methyl methacrylate) based bone cements also contain such nanoparticles.
he technical textiles sector leverages the purifying properties of nanosilver in anti-odour sports clothing and equipment, among others. In the electronics and household appliances industries, silver nanoparticles are incorporated into the plastic coatings that come into contact with putrescible materials, like the canisters of vacuum cleaners, computer keyboards, the walls of washing machines, fridges and air conditioning units, among others. At this scale, silver may not bring good fortune but it does protect health.
Biobased plastics for high-safety packaging
The biocidal properties of nanosilver are also used in packaging, to extend food shelf life. When associated with silica nanoparticles, in many polymers, its effect is further strengthened.
Speaking of innovative combinations, the grand prize goes to the European Dibbiopack project. Currently being mass-produced after three years of development, it brought together around twenty industrial and scientific partners to develop biobased packaging based on polylactic acid for food, cosmetic and pharmaceutical use.
This biodegradable plastic is generally not permitted to be used for such applications because of its poor barrier properties. Combining it with many nano-additives helped to solve this problem. Four nano-additives were used simply to increase the PLA matrix's mechanical strength, its inertia and impermeability: two types of nanoclays, lamellar graphene and magnesium nanoparticles coated with oleic acid. A nano-silicone-based antimicrobial varnish was then added on top. And the cherry, on this nanotechnology cake, was a plastic micro-sensor loaded with nanoparticles that change the packaging's colour when it detects over 2% of oxygen inside the container.
Teflon nanoparticles to fight pollution
Oil pollution is one of the plagues of the aquatic environment. Although extremely serious when it occurs following a maritime accident, it also causes problems, at a smaller scale, in the river systems and port areas. To fight this problem, researchers at the Smart Materials project of the Italian Institute of Technology in Genoa have come up with a novel solution: a sponge that can be controlled through magnetic fields and which absorbs oils by separating them from the water.
Oil pollution is one of the plagues of the aquatic environment. Although extremely serious when it occurs following a maritime accident, it also causes problems, at a smaller scale, in the river systems and port areas. To fight this problem, researchers at the Smart Materials project of the Italian Institute of Technology in Genoa have come up with a novel solution: a sponge that can be controlled through magnetic fields and which absorbs oils by separating them from the water.
After it has been treated in this way, the sponge acquires magnetic, oleophilic and hydrophobic properties. It is then able to absorb thirteen times its weight in oil.
The nanoparticles incorporated into the foam can be recovered to be re-used. The cleanup process therefore relies on an innovative, smart and recyclable material.
