Development of bio-based polymers and composites is at the frontline of polymer science and engineering research due to increasing concerns over environment and sustainability. Concerns related to the harmful effects of our disposable consumer lifestyle on the environment, many of them related to synthetic plastics wastes, are growing more and more. To directly address this issue, we are developing a range of eco-friendly plastics and composites made from sustainable crops or agricultural food waste or other bio-sources. So far, our group has gathered extensive expertise in different ways of fabrication of green composites. We use sustainable composite technologies compatible with industrial processes like extrusion or injection molding in order to produce materials that can easily be integrated in the productive chain.
Green and Sustainable Composites
One of the most promising fillers for polymers for the improvement of their physical properties is graphene. Recently, there has been an intense interest in the incorporation of graphene based nanofillers, in a wide range of polymer matrices in order to enhance the polymer performance. Graphene is a two dimensional, sp2-hybridised carbon layer that exhibits unique electrical and thermal transport properties along with mechanical stiffness and chemical stability. By incorporating graphene into a polymer matrix one can harness these extraordinary properties from the composite material, creating a new class of materials suitable for a wide range of applications, from nanoelectronics and biomedical engineering to textile industry.
Materials for Safe Environment
Composite materials are properly tailored by the presence of nano or microfillers in order to be used for the removal/recovery or detection of environmental pollutants. Functional organic compounds, particles, or precursors are used, in order to form, or to functionalize already existing, organic porous materials and films. As a result, smart systems with special surface properties, able to interact efficiently with chemical species are formed. In particular, porous natural or synthetic polymers functionalized with nanoparticles, or organic fillers derived from agricultural wastes, are utilized for the efficient removal of heavy metal ions or for the recovery of precious metals from water. Furthermore, fibrous filters, or foams with tailored surface properties are developed for the efficient separation of oil from oil-polluted water. Concerning the pollutants in gas phase, functional porous films or nanofibers are developed for the detection of organic and inorganic acids and ammonia, upon color change or upon change in the conductivity of the nanocomposite.
Magnetic composites are formed through the mixing and/or the directed assembly of magnetic particles in polymeric matrices. Magnetic particles have sizes in the nano or micro scale, and can be ferromagnetic or superparamagnetic while the matrices can be in the form of polymers or monomer solutions that are subsequently polymerized. Such systems combine the magnetic responsivity with the properties of the polymers utilized. In this way, functional composite films or free standing wires are formed, with anisotropic properties able to respond to an external magnetic field towards a preferential direction. The combination of magnetic particles with other functional fillers can also result in the formation of magnetic composites with special surface properties or with multiple functionalities, such as electrical or thermal conductivity and magnetism at a preferential direction.
Stimuli-induced Nanoparticle Formation into polymers
Nanocomposites are formed in-situ either by photochemical, thermal or chemical reduction of nanoparticle precursors embedded in polymer solid films, aerogels or foams. Depending on the total energy that the external stimulus offers to the system, the density and the size and of the nanoparticles formed in the solid matrix can be tuned. We have developed techniques for the localized formation of the nanofillers at specific areas of the polymers in the bulk or on their surfaces. Combination of precursors, or the appropriate selection of the polymer matrix and its structure leads to the formation of multifunctional films, fibers, foams or aerogels able to be used in diverse applications.
Surface engineering and adhesion
Unwanted wetting of surfaces as well as wet and dry adhesion to technologically important surfaces is known to cause serious problems in many important areas such as power lines, transportation, paper products, textiles, etc. Research in this field has satisfactorily advanced towards designing robust non-wetting surfaces and coatings with tailored adhesion properties. This is the main focus of this research line. Our research is aimed at providing good correlations between liquid repellency of surfaces and their mechanical properties as well as their solid adhesion properties. To this end, we combine our expertise on polymer science, nanoscale structuring as well as composite technology to fabricate novel soft and hard materials in the form of coatings, textile treatments or nanofibers. The right combination of chemistry and morphology can enable repelling of specific liquids with engineered local adhesion properties so that microliter droplets in the form of mist or fog can be manipulated (e.g. fog harvesting applications). Moreover, a similar approach is being developed to engineer surface chemistry in order to control solid-solid adhesion particularly using environmentally benign approaches.
Smart Fabrics and Paper
The activities of this research line deal with the modification of fibrous substrates, like paper or textiles, in order to add to them properties that they lack intrinsically, and in this way expand and optimize their fields of applications. For these modifications are used polymeric nanocomposite materials, that embrace the individual fibers of the substrates with a protective ultrathin layer, that eventually provides the additional properties to the fibrous materials. The modified fibrous substrates can retain their structural characteristics, and thus properties like breathability or mechanical flexibility, but at the same time additional properties are added to them. The principal properties that are added to the treated fibrous materials are water repellency and humidity resistance. The addition of nanoparticles to the polymer coating of the fibers can give further functionalities to the treated materials. Some examples are antibacterial textiles, oil repellent paper, magnetic and fluorescent documents. The treatment of the paper or fabrics is done with methods that can be easily scalable for industrial applications, like spraying or rod coating.
Photochromic and stimuli responsive composites
Photochromic molecules isomerize after an interaction with an external stimulus, such as light irradiation, chemical interaction, temperature etc. changing their structure and color, while are able to recover their initial status after the appropriate treatment (dark storage, thermal treatment). Polymer films, nanofiber mats or foams incorporating photochromic molecules are developed, able to react with organic acid vapors on demand (after irradiation) and reversibly for various functioning cycles. Another interesting application of such systems is their ability to change reversibly the mechanical properties of the polymer matrix in which they are embedded. Furthermore some of them are able to self-assemble on diverse surfaces forming crystalline fibrils introducing thus to the formed system special surface properties which can be tuned by light, in wet or dry conditions. In this research activity the Smart Materials Group also develops composite materials able to respond to external stimuli as light, magnetic or electric field, or heat are developed, such as magnetic and/or conductive nanocomposite films with improved heat conductivity, magnetically actuated films, or films able to expand reversibly upon irradiation.
Materials for regenerative medicine, drug delivery and cosmetics
Materials for medical use have very strict requirements, because of the sensitive environment where they need to operate and the demanding properties that they need to have. Among all the materials adopted, polymers have a good combination of properties to be used in very different context: from drug delivery to prosthesis and scaffolds. Nature itself uses several polymers to build living organisms: cellulose, chitin, collagen and keratin are polymers used to build all plants and animals. These materials are of strong interest to our group since they can degrade in the body with no toxic or harmful by-products and have a safe interaction with the biological environment. Together with our activity of development of innovative materials for scaffolding (photocurable PPF and cyanoacrylates) we study the use of natural polymers such as carbohydrates (cellulose, alginate, pectin) or proteins (silk fibroin and wool keratin) as materials for scaffold, drug delivery and resorbable devices. We also exploit them in combination with other natural products with biological activity like essential oils for application as wound dressing. In this case we focus our research on the control release of the active principles to the human body, for time periods from hours to several days.