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Hacia los plásticos inteligentes

Towards intelligent plastics

The research into plastic materials shows no sign of slowing down and new applications are constantly being heralded: flexible tablets or mobiles, filaments for 3D printers, biocompatible materials for medical transplants. The scientists at the Repsol Technology Centre are developing plastics that self-repair or that are biodegradable.
The R&D work of the Repsol researchers focuses both on “the improvement of the plastics that we currently manufacture from fossil fuels as raw material”, and “parallel and more emerging lines” in fields such as piezoelectric polymers, bioplastics or self-repairing materials, explains Pilar Lafuente, researcher from the Repsol Technology Centre (CTR). New developments that may revolutionise the use and possibilities of plastics as we know them today and that also seek more efficient alternatives to “recover these materials once used”.

Intelligent materials that self-repair

Plásticos autorreparables
It might sound like science fiction, but the Trainer programme is searching for self-repairing polymers, plastics which, after being damaged, can self-regenerate, without man’s intervention. “We are working to learn how self-repair works and to see what the current technology level is to adapt it to the types of polymers we produce”, states Luis Miguel Méndez Llatas, a CTR researcher working on this project.

One of the alternatives being studied is the creation of ionomers, polymers containing ions, subunits with an electric charge that act as bonding forces and help the plastic to repair fissures . CTR scientists have already performed tests using this principle which show how a projectile perforates a plastic, which then automatically closes after the impact.

“We are also working to introduce microcapsules in polyethylene”, one of the most widely used plastics, “with an adhesive substance which is released after the material breaks and fills the cavity”, continues Méndez Llatas. A third area of study consists of adding a molecule to the structure of that plastic which can make or break chemical bonds with light, “an intelligent material that can be played with depending on the wavelength applied.”

Research at CTR is progressing at a steady rate but self-repair is a “fairly complex” scientific and technological challenge. “The example is always given of living beings: you injure yourself and the skin repairs itself. Reaching that will be very difficult” as natural systems act with highly sophisticated mechanisms. “How long are we talking about? It is going to largely depend on the applications". Some are already on the market, such as paints that self-repair scratches or plastics that can be re-adhered by applying pressure to them. Self-repair systems open up an extensive range of possibilities in sectors such as telecommunications, transport or construction. In the immediate future “the applications will prevail in materials that are difficult to access” such as underwater cables or those found in aircraft that avoid mid-flight short circuits.

New alternatives with bioplastics

CTR also develops ApliCO2 materials, a research to obtain, from alternative carbon sources, new materials such as biopolymers, a catch-all term for different plastics from renewable sources but with different properties. There are natural polymers such as polysaccharides extracted from plants such as potato starch and those that are manufactured, for example, biodegradable plastic bags we find in supermarkets. There are also bioplastics which are not biodegradable and are created from sugarcane, molasses or cereals. “They have the same properties as conventional plastics without consuming fossil fuels, but their final destination is recycling”, explains Pilar Lafuente.

The European regulation stipulating the abolition of non-biodegradable single-use plastic bags, in the case of Spain for 2018, “was the trigger which sparked the research of all sector companies into plastics from renewable sources, which were both biodegradable and compostable”, continues Lafuente. A search for solutions which already have responses such as the development of plastics “easily degradable in sea water” so that “fishing nets or any other plastic items that will inevitably end up in this environment” can be manufactured.

In the short-term, Repsol is assessing the application of bioplastics for food packaging “which, due to their chemical structure, can be sent to composting plants to become organic fertiliser after use”. Also their applications in agriculture, where bioplastics could degrade in the ground and become a source of nutrients.

Medicine is another field where the properties of biopolymers are extremely valuable. The aging of the population means that “we increasingly need more materials that do not form part of our own structure, but also as similar as possible to it and which are biocompatible”, assures Lafuente. Some materials of medical use are obtained from microorganisms which are fed with plant sugars and become molecules with the sufficient length to manufacture biocompatible plastics. These polymers are already used to manufacture artificial prostheses, the encapsulation of ‘intelligent drugs’ or “organ renewal”.
Repsol is assessing the application of bioplastics for food packaging which can be sent to composting plants to become organic fertiliser after use.

The revolution of new materials

Impresión 3D
Among the possibilities open to the new plastic materials, 3D printing is a market under full expansion. In this field, the technologists of the Repsol Technology Centre now study the application of polyacetic acid (PLA) as a raw material for manufacturing plastic filaments which serve as ‘ink’ to these printers. PLA is a plastic which is obtained from corn starch or wheat starch and which has a “very good dimensional stability, which allows you to have in your hands what you see on the screen with no variations”, explains Lafuente.

Other plastic materials with a very promising future are those with piezoelectric possibilities, i.e. an electric field is generated when pressure is applied to them, or, inversely, if an electric field is applied to them they can deform. Researchers are already imagining their use as sensors, for manufacturing electric car batteries or “in what is called ‘energy harvesting’, the harvesting of small quantities of energy present in the environment which can be made use of”, continues Lafuente. These piezoelectric materials could be incorporated, for example, in clothes to turn human movement into sufficient energy to charge a mobile phone.

Electronics is also in the midst of a revolution thanks to progress made in new materials. Plastic microprocessors, folding and transparent screens or graphene supercapacitors, which may replace current batteries and can be charged in mere seconds, are some of the applications in full development. Graphene is undoubtedly a very fashionable material and “is probably going to bring us a great deal of surprises”, thinks Méndez Llatas. Although its industrial-scale production is not yet resolved, it is a resource, which as it is formed by pure carbon, “you have it everywhere: you can obtain it from carbon or ethylene, which comes from oil.”

Lafuente conceives a future scenario where “there will be a coexistence between fossil fuel products, those of renewable sources and also products made from wastes”, something important “as there is a large amount of carbon accumulated in them which can be returned to the use circuit”. Plastic materials will also be decisive in promoting new energies and efficiency improvements. A scenario full of opportunities “where technological development and the imagination we add are going to be vital” concludes Méndez Llatas.
Graphene is undoubtedly a very fashionable material and is probably going to bring us a great deal of surprises.
Last updated: August 2013