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Plasticized starch (PLS) nanocomposite films using glycerol and reinforced with graphene (G) and graphene oxide (GO) were prepared by solvent casting procedure. On one hand, the influence of adding different G contents into the PLS matrix was analyzed. In order to improve the stability of G nanoflakes in water, Salvia extracts were added as surfactants. The resulting nanocomposites presented improved mechanical properties. A maximum increase of 287 % in Young's modulus and 57 % in tensile strength was achieved for nanocomposites with 5 wt% of G. However, it seemed that Salvia acted as co-plasticizer for the PLS. Moreover, the addition of the highest G content led to an improvement of the electrical conductivity close to 5 × 10-6 S/m compared to the matrix. On the other hand, GO was also incorporated as nanofiller to prepare nanocomposites. Thus, the effect of increasing the GO content in the final behavior of the PLS nanocomposites was evaluated. The characterization of GO containing PLS nanocomposites showed that strong starch/GO interactions and a good dispersion of the nanofiller were achieved. Moreover, the acidic treatment applied for the reduction of the GO was found to be effective, since the electrical conductivity was 150 times bigger than its G containing counterpart.

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Full harnessing of grape pomace (GP) agricultural waste for the preparation of antioxidant Pickering emulsions is presented herein. Bacterial cellulose (BC) and polyphenolic extract (GPPE) were both prepared from GP. Rod-like BC nanocrystals up to 1.5 µm in length and 5-30 nm in width were obtained through enzymatic hydrolysis (EH). The GPPE obtained through ultrasound-assisted hydroalcoholic solvent extraction presented excellent antioxidant properties assessed using DPPH, ABTS and TPC assays. The BCNC-GPPE complex formation improved the colloidal stability of BCNC aqueous dispersions by decreasing the Z potential value up to -35 mV and prolonged the antioxidant half-life of GPPE up to 2.5 times. The antioxidant activity of the complex was demonstrated by the decrease in conjugate diene (CD) formation in olive oil-in-water emulsions, whereas the measured emulsification ratio (ER) and droplet mean size of hexadecane-in-water emulsions confirmed the physical stability improvement in all cases. The synergistic effect between nanocellulose and GPPE resulted in promising novel emulsions with prolonged physical and oxidative stability.

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Starch-based tablets with tailored releases were prepared by 3D printing using a hydrophobic drug. The importance of the origin of the excipient in the inks and tablets was analyzed. Besides, the effect of the geometry of the tablet on the drug release profile was also evaluated. The rheological properties of the inks was influenced by the botanic origin of the starch. Consequently, tablets presented different microporous structure and particular compression and swelling behaviors. Normal maize starch showed a non-well-defined porous morphology, not being able to form a stable structure whereas, waxy maize and potato starches exhibited a well-defined porous structure and were both able to maintain their integrity after long time immersion. Finally, tablets combining different starches and geometries were printed tailoring the drug release from 10 min to 6 h and designing two-steps profiles. The applicability of the developed 3D printed drug release systems in personalized therapies was demonstrated.

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Starch-based nanocomposite hydrogels were successfully prepared by the Diels-Alder click cross-linking reaction between furan-functionalized starch derivative and a water-soluble tetrafunctional maleimide compound, adding cellulose nanocrystals (CNC) as nanoreinforcement. The effect of increasing the CNC content on rheological and swelling properties as well as on the morphology of the hydrogels was analyzed. Besides, in order to evaluate the applicability of the as-prepared hydrogels as delivery systems, drug release measurements and in vitro cytotoxicity assays were also performed. It was found that the prepared nanocomposite hydrogels presented higher stiffness as the CNC content increased. The incorporation of the nanocrystals modified the internal porous microstructure of the hydrogels, affecting consequently both the swelling capacity and the drug-delivery kinetics. Moreover, the prepared nanocomposite hydrogels showed non-toxic behavior, demonstrating their potential applicability in the biomedical field, especially as sustained drug delivery systems.

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Starch-based hydrogels were performed by Diels-Alder cross-linking reactions between furan-modified starch and a water soluble bismaleimide, with improving conducting properties by using graphene layers as active nanofillers. The characterization results demonstrated that the Diels-Alder reaction and the corresponding conditions for the hydrogel formation were appropriate. The effect of increasing the furan/maleimide ratio on the architecture of the hydrogels and on the morphological, rheological and swelling properties were thoroughly evaluated. Effective network structure was obtained by increasing the cross-linker content leading to decreasing pore size and increasing storage modulus value of the final material. It was shown that the swelling behavior of hydrogels was mainly governed by the hydrophilic character of bismaleimide. Graphene nanosheets were added for the synthesis of nanocomposite hydrogel and it was characterized in terms of rheological properties, electrical conductivity and antimicrobial activity. The nanocomposite hydrogel presented enhanced mechanical performance, antimicrobial activity and increased conductivity values, up to a decade, indicating that conductive and active hydrogels could be satisfactory obtained, for a large range of potential applications such as biomed.

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Electrospinning offers the possibility of obtaining fibers mats from polymer solutions. The use of environmentally-friendly waterborne polyurethane (WBPU) allows obtaining electrospun polyurethane mats in water medium. Furthermore, the incorporation of water dispersible nanoentities, like renewable cellulose nanocrystals (CNC), is facilitated. Therefore, in this work, a WBPU was synthesized and CNC were isolated for preparing WBPU-CNC dispersions nanocomposites with 1 and 3wt% of CNC following both the classical mixing by sonication, and the innovative in-situ route. The dispersions were used for obtaining electrospun mats assisted by poly(ethylene oxide) (PEO) as polymer template. Moreover, the extraction of PEO with water resulted in continuous WBPU-CNC mats, showing different properties respect to WBPU-CNC mats containing PEO. The effective addition of CNC led to more defined cylindrical morphologies and the two alternative incorporation routes induced to different CNC dispositions in the matrix, which modified fibers diameters, and thus, mats final properties.

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In the present work, thermoplastic maize starch based bionanocomposites were prepared as transparent films, plasticized with 35% of glycerol and reinforced with both waxy starch (WSNC) and cellulose nanocrystals (CNC), previously extracted by acidic hydrolysis. The influence of the nanofiller content was evaluated at 1 wt.%, 2.5 wt.% and 5 wt.% of WSNC. The effect of adding the two different nanoparticles at 1 wt.% was also investigated. As determined by tensile measurements, mechanical properties were improved at any composition of WSNC. Water vapour permeance values maintained constant, whereas barrier properties to oxygen reduced in a 70%, indicating the effectiveness of hydrogen bonding at the interphase. The use of CNC or CNC and WSNC upgraded mechanical results, but no significant differences in barrier properties were obtained. A homogeneous distribution of the nanofillers was demonstrated by atomic force microscopy, and a shift of the two relaxation peaks to higher temperatures was detected by dynamic mechanical analysis.

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