Olive Stones as Filler for Polymer-Based Composites: A Review.

Olives' consumption produces copious agricultural byproducts that have accompanied humanity for millennia, but the increasing worldwide production complicates its management. Most wastes are generated during olive oil production in form of olive stones and other lignocellulosic derivatives. Industrial processes of chemical or physical nature to recover economically compounds from biomass residues are costly, difficult, and non-environmentally friendly. Cellulose, hemicellulose, and lignin biopolymers are the principal components of olive stones, which present interesting qualities as lignocellulosic fillers in polymeric composites. This review will summarize examples of composites based on thermoplastic polymers, such as polystyrene (PS), polylactide (PLA), polyvinyl chloride (PVC), polypropylene (PP), and polycaprolactone (PCL); thermosetting resins (phenol-formaldehyde, unsaturated polyesters, and epoxy) and acrylonitrile butadiene rubber/devulcanized waste rubber (NBR/DWR) blends focusing on the fabrication procedures, characterization, and possible applications. Finally, thanks to the wide disparity in polymer matrix types, the variability in applications is important, from adsorption to mechanical enhancement, showing the easiness and benefit of olive stone integration in many materials.

Electroactive γ-Phase, Enhanced Thermal and Mechanical Properties and High Ionic Conductivity Response of Poly (Vinylidene Fluoride)/Cellulose Nanocrystal Hybrid Nanocomposites.

Cellulose nanocrystals (CNCs) were incorporated into poly (vinylidene fluoride) (PVDF) to tailor the mechanical and dielectric properties of this electroactive polymer. PVDF/CNC nanocomposites with concentrations up to 15 wt.% were prepared by solvent-casting followed by quick vacuum drying in order to ensure the formation of the electroactive γ-phase. The changes induced by the presence of CNCs on the morphology of PVDF and its crystalline structure, thermal properties, mechanical performance and dielectric behavior are explored. The results suggest a relevant role of the CNC surface -OH groups, which interact with PVDF fluorine atoms. The real dielectric constant ε' of nanocomposites at 200 Hz was found to increase by 3.6 times up to 47 for the 15 wt.% CNC nanocomposite due to an enhanced ionic conductivity provided by CNCs. The approach reported here in order to boost the formation of the γ-phase of PVDF upon the incorporation of CNCs serves to further develop cellulose-based multifunctional materials.

Enhanced charge-transfer emission in polyimides by cyano-groups doping.

Conjugated polyimides (PI) are successfully synthesized by chemical imidization through in situ silylation of diamines by the alteration of different donor-acceptor monomers. A detailed photophysical characterization is performed in the monomers and different polymers in tetrahydrofuran solutions. The emission spectra of the related donor-acceptor polymers with electron withdrawing cyano groups showed broader and more intense fluorescence bands in comparison to the polymer without -CN groups. The new emission band results from the contribution of two different charge-transfer (CT) pathways: (i) An intramolecular CT (ICT) state in the donor monomers due to the presence of strong electron withdrawing CN groups, and (ii) a intramolecular CT complex (CTC) in the PI polymer between the donor-acceptor monomers, which is red-shifted and shows longer lifetime respect to the ICT of the diamine monomers. The very wide emission band is a very interesting feature for obtaining white light from UV light.