3D printable fully biomass-based composite using poly(furfuryl alcohol) as binder and cellulose as a filler.

Nowadays, composite materials are widely used in different sectors owing to their improved mechanical and functional properties compared to bulk materials and efficient manufacturing processes. Nevertheless, the majority of these materials are still petroleum-based, which is incompatible with the recent environmental awareness. As a result, in the current study, a fully biomass-based composite material was produced employing poly(furfuryl alcohol) (PFA) as a bio-based matrix coupled with cellulose powder as fillers and processing aid agent. The addition of cellulose powder increased the viscosity of the uncured composite paste and conferred it a shear-thinning thixotropic making it suitable for 3D printing using the liquid deposition modeling technique (LDM). After curing, the combination of these raw materials yields a renewable and cost-effective composite for additive manufacturing by the LDM technique with high interlayer and interfilament adhesion, good mechanical performances, and adequate shape fidelity.

A fibrous cellulose paste formulation to manufacture structural parts using 3D printing by extrusion.

An optimized paste based on short natural cellulose fibers combined with carboxymethyl cellulose at a high dry content (42 wt.%) was implemented as a bio-based material for 3D printing by extrusion. The homogeneous paste exhibited a pronounced thinning behavior and yield stress; it was extruded using a screw extrusion-based direct ink writing system and could easily flow through a small nozzle. The optimized formulation enabled accurate additive manufacturing of parts using a natural air-drying process with or without an ethanol bath. We characterized the anisotropic shrinkage that occurred during the drying of 3D printed parts and proposed a compensation method to account for it. The obtained results emphasized that cellulose had a strong potential to be used as a raw material for 3D printing of cheap, lightweight, robust, and recyclable parts.

Fabrication of 3D conductive circuits: print quality evaluation of a direct ink writing process.

The use of conductive inks and direct writing techniques for the fabrication of electronic circuits on complex substrates is attracting ever increasing interest. However, the existing knowledge is only focused on the electrical performances of the produced smart objects with no direct correlation with the conductive paths morphology and printing conditions. In order to evaluate the printing quality of a direct writing process using an eccentric screw dispenser, a printing device for the deposition of silver paste on 3D objects was developed. Lines of different widths were printed on flat PC + ABS substrates by means of the developed printing device and a conventional screen printing process. The developed process permitted printing lines as thin as possible with screen printing but with a better regularity of their edges. However unlike screen printed lines, the thickness of the lines was dependent on their width. Finally, the possibility to print on 3D objects was demonstrated.

On the halt of spontaneous capillary flows in diverging open channels.

Due to their compactness and independence of exterior energy sources, capillary microsystems are increasingly used in many different scientific domains, from biotechnology to medicine and biology, chemistry, energy and space. Obtaining a capillary flow depends on channel geometry and contact angle. A general condition for the establishment of a spontaneous capillary flow in a uniform cross section channel has already been derived from Gibbs free energy. In this work, we consider spontaneous capillary flows (SCF) in diverging open rectangular channels and suspended channels, and we show that they do not flow indefinitely but stop at some location in the channel. In the case of linearly diverging open channels, we derive the expression that determines the location where the flow stops. The theoretical approach is verified by using the Surface Evolver numerical program and is checked by experiments. The approach is extended to sudden enlargements, and it is shown that the enlargements can act as stop and trigger valves.

Laccase-based biocathodes: Comparison of chitosan and Nafion.

Chitosan and Nafion(®) are both reported as interesting polymers to be integrated into the structure of 3D electrodes for biofuel cells. Their advantage is mainly related to their chemical properties, which have a positive impact on the stability of electrodes such as the laccase-based biocathode. For optimal function in implantable applications the biocathode requires coating with a biocompatible semi-permeable membrane that is designed to prevent the loss of enzyme activity and to protect the structure of the biocathode. Since such membranes are integrated into the electrodes ultimately implanted, they must be fully characterized to demonstrate that there is no interference with the performance of the electrode. In the present study, we demonstrate that chitosan provides superior stability compared with Nafion(®) and should be considered as an optimum solution to enhance the biocompatibility and the stability of 3D bioelectrodes.

Laccase wiring on free-standing electrospun carbon nanofibres using a mediator plug.

Electrospun carbon nanofibres (CNFs) containing CNTs were produced by electrospinning and subsequent thermal treatment. This material was evaluated as a bioelectrode for biofuel cell applications after covalent grafting of laccase. Bis-pyrene-modified ABTS was used as a plug to wire laccase to the nanofibres leading to a maximum current density of 100 µA cm(-2).

Photoluminescence of 2,7-poly(9,9-dialkylfluorene-co-fluorenone) nanoparticles: effect of particle size and inert polymer addition.

Stable nanoparticle dispersions of 2,7-poly(9,9-dialkylfluorene-co-fluorenone) (PFFO) and of PFFO/cellulose acetate butyrate (CAB) mixtures with particle size ranging between 5 and 500 nm were prepared by miniemulsification in the presence of a cationic surfactant. Photoluminescence spectra of nanoparticle dispersions showed that the decrease of particle size and of the PFFO/CAB mass ratio induced the progressive suppression of the PFFO excimer emission band at 535 nm. This behavior was associated with the limited ordered structure and π-stacking arrangement of PFFO molecules when confined within nanoparticles smaller than 150 nm or in the presence of CAB molecules. All nanoparticle dispersions displayed high dimensional stability; however, the relative intensity of the excimer emission band increased upon aging reflecting excimer formation due to the high mobility of PFFO chains (T(g) -20 °C) or fluorene moiety oxidation.

Surfactant (TTAB) role in the preparation of 2,7-Poly(9,9-dialkylfluorene-co-fluorenone) nanoparticles by miniemulsion.

The role of tetradecyltrimethylammonium bromide (TTAB) and its partition between water, chloroform, and the chloroform/water interface during the miniemulsification of a photoluminescent polymer was investigated by indirect interfacial tension/elasticity measurements. Dynamic interfacial tension and elasticity measurements showed the presence of a gas-liquid phase transition at the chloroform/water interface and the formation of a rigid interface, which was supposed to promote emulsion stability. The parameters of the adsorption isotherms and the TTAB partition coefficient were obtained from surface tension isotherms. Dynamic surface tension measurements performed after TTAB water/chloroform extraction were used to compute TTAB partition between water, chloroform, and the chloroform/water interface. Model calculations allowed identifying (for the tested conditions) the minimum size of emulsion droplets before the onset of instability and the segregation of a sizable amount of TTAB in the final polymer nanoparticles, which induced a shift in the 2,7-poly(9,9-dialkylfluorene-co-fluorenone) (PF) photoluminescence emission band. The size of the emulsion droplets of the final polymer particles and the amount of segregated TTAB were in good agreement with the corresponding experimental values.