Polymers with high and finely tunable dielectric permittivity are of great scientific interest due to their wide application potential, ranging from transducers and capacitors to Li-ion batteries.[1] However, how much can the permittivity be increased, and how does this increase affect other properties? To answer these questions, we have modified the polysiloxanes with different types and amounts of polar groups and investigated how these chemical modifications affect different properties.[2] We also explore the impact of filler addition on the properties of our polar silicones, focusing on enhancing the processability and functionality of thin films.[3] The most promising polar silicone elastomers have also been investigated as dielectrics in actuators[1,3], sensors, energy harvesters, capacitive light-emitting de-vices,[4] and electrolytes in solid-state Li-ion batteries[5] and thus demonstrated their functionality.

Piezoelectric polymers are bound to play a crucial role in the advancement of responsible electronics, as they offer benefits over ceramics that cannot satisfy the increasing demand of flexible smart devices. A main line of research is the development of polymer-based hybrid composites formed by inorganic fillers within polymer matrix. Most works resorted to PVDF-TrFE, a fuel-based, non-biodegradable polymer with associated environmental concern, while poly-L-lactide (PLLA) has emerged as a potential alternative due to its biobased and biodegradable character, as well as biocompatibility. In this context, we are investigating the suitability of biobased PLLA as piezoelectric matrix with imbedded inorganic ZnO and KNN piezoelectric perovskites, as non-toxic metal oxides, and the use of innovative approaches towards 3D-printing technologies. The control of the printing parameters has been key to obtain high chain orientation and crystallinity, thus allowing piezoelectric response of the matrix to be tailored. Commercial PLLA has been used and large shear piezoelectric coefficients d14 approaching 10 pC/N were achieved on thin and flexible cantilevers adaptable to complex structures. An in-depth characterization of the dielectric and piezoelectric properties is here presented, and used to discuss and validate the performance of energy harvesters based on these hybrid composites. A key point addressed is the challenge of adequately characterizing the voltage piezoelectric response of polymer-based materials, so differences between open-circuit and short-circuit measurements are discussed and related to contributions from each composite component.

Grants PID2021-122708OB-C33 and PID2023-152475OB-100, funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe by the “European Union”.

The thermoelectric potential of single-wall carbon nanotubes (SWCNT) has been well-attested in the literature¹, with performance dependent on the chirality and purity of the nanotubes. When incorporated into composites, the Seebeck coefficients and power factors can vary significantly based on the chemical nature of the polymer matrix². Cellulose is one of the most widely available bio-polymer materials, and a good candidate for more sustainable functional materials³.
Filterpaper-derived cellulose was functionalized in three different processes with citric acid (CA), 3-trimethoxysilylpropyl methacrylate (TMSPMA), and 4,4'-diphenylmethane diisocyanate (MDI) in a solvent-based chemical modification. The composites were prepared with a combination of high-shear processing and ultrasonication, with subsequent casting, without the use of any surfactants. Two series of paper composites were then prepared with each type of cellulose (neat, CA, TMSPMA, MDI) in order to determine the thermoelectric properties (at around 10-90 wt.% SWCNT) and the electrical percolation threshold and vapor solvent sensitivity (at around 0.1-1 wt.% SWCNT).
The functionalization of cellulose was evaluated using Fourier-transform infrared spectroscopy, the buckypaper morphology using scanning electron microscopy. Composite electrical conductivity was measured in a test-fixture in combination with a multimeter and thermoelectric properties using custom measurement devices developed at IPF⁴. The composites with functionalized cellulose displayed enhanced P-type thermoelectric properties compared to neat SWCNT buckypaper and cellulose-SWCNT composites, reaching Seebeck coefficients of up to 70.42 ± 1.37 [(µV)/K]. Additionally, composites near the percolation threshold show reversible changes in electrical resistivity depending on solvent vapor (water or acetone) and time of exposure.

The depletion of fossil resources and growing environmental concerns drive the development of bio-based and biodegradable plastics as sustainable alternatives to conventional polymers. However, the susceptibility of these plastics to oxidative degradation compromises their durability and performance. Natural antioxidants, such as phenolic compounds extracted from plants or agro-food waste, offer a sustainable alternative to synthetic stabilizers by enhancing the thermo-oxidative stability of polymers like poly(lactic acid), poly(butylene succinate) (PBS), poly(butylene succinate-adipate) (PBSA), poly(butylene adipate-co-terephthalate) (PBAT), poly(hydroxyalkanoate) (PHA)1,2. Despite this, their sensitivity to environmental factors limits their industrial applications. Encapsulation techniques provide an innovative solution by improving the stability of antioxidants and enabling controlled release.
In this study, we incorporated a hybrid system based on layered double hydroxides (LDH), functionalized with rosmarinic acid (RA), into a PLA/PBSA 60/40 wt/wt blend, characterized by renewability, high ductility, and toughness3. The resulting composites (PLA/PBSA/LDH-RA) also exhibit additional antioxidant and antimicrobial properties4. We analyzed their structural, thermal, and water vapor permeability characteristics and the release kinetics of active molecules. Furthermore, the composite material underwent multiple extrusion and injection molding cycles without significant degradation or loss of mechanical properties. Structural and thermal analyses confirmed a reduction in the fragmentation and branching of PBSA chains, which was attributed to the antioxidant effect of the LDH-RA additive. Preliminary biodegradation tests indicated that the composite and the pure blend exhibit comparable degradation kinetics. These findings suggest that, like traditional petroleum-based polymers, this bio-based material can undergo mechanical recycling before composting, maximizing its lifecycle while preserving its compostability.