Sustainable and High Performing Biocomposites with Chitosan/Sepiolite Layer-by-Layer Nanoengineered Interphases

Biocomposites encompassing biopolymers and natural fibers represent potential candidates for the replacement of fossil-based polymers in many application fields. However, due to poor matrix/fiber interphase produces insufficient mechanical properties for practical application. In this Letter, we use the Layer-by-Layer assembly technique in order to modify the surface of natural fibers and produce a nanostructured interphase capable of improving the mechanical properties of poly­(3-hydroxybutyrate-<i>co</i>-3-hydroxyhexanoate)/hemp fibers biocomposites. Chitosan and sepiolite nanorods have been selected as interphase constituents. When assembled on hemp fibers, this chitosan/sepiolite system conformally coats every fiber yielding a nanostructured coating that subsequently becomes the matrix/fiber interphase during composite preparation. Thanks to the LbL assembled interphase, the biocomposites achieve impressive mechanical properties with elastic moduli up to 2.6 GPa, which is 70% and 30% better of the neat matrix and the composite prepared with unmodified fibers, respectively. The achieved performances would allow for the use of these LbL engineered biocomposites in load bearing applications, thus opening up new opportunities for the exploitation of biobased resources

Nanostructured Wood Hybrids for Fire-Retardancy Prepared by Clay Impregnation into the Cell Wall

Eco-friendly materials need “green” fire-retardancy treatments, which offer opportunity for new wood nanotechnologies. Balsa wood (Ochroma pyramidale) was delignified to form a hierarchically structured and nanoporous scaffold mainly composed of cellulose nanofibrils. This nanocellulosic wood scaffold was impregnated with colloidal montmorillonite clay to form a nanostructured wood hybrid with high flame-retardancy. The nanoporous scaffold was characterized by scanning electron microscopy and gas adsorption. Flame-retardancy was evaluated by cone calorimetry, whereas thermal and thermo-oxidative stabilities were assessed by thermogravimetry. The location of well-distributed clay nanoplatelets inside the cell walls was confirmed by energy-dispersive X-ray analysis. This unique nanostructure dramatically increased the thermal stability because of thermal insulation, oxygen depletion, and catalytic charring effects. A coherent organic/inorganic charred residue was formed during combustion, leading to a strongly reduced heat release rate peak and reduced smoke generation

Efficient Gas and Water Vapor Barrier Properties of Thin Poly(lactic acid) Packaging Films: Functionalization with Moisture Resistant Nafion and Clay Multilayers

Poly­(lactic acid) (PLA) represents one of the most promising and attractive biobased polymer for the industrial development of environmentally sustainable packaging. However, oxygen and water barrier properties of PLA based films cannot compete with those of commercially available composite multilayers. To fill this gap, we used the layer-by-layer deposition technique on commercially used PLA thin films (30 μm thick) in order to increase their barrier properties to oxygen and water vapor. Nanometric films were grown by alternating branched poly­(ethylene imine) (BPEI), hydrophobic fluorinated polymer (Nafion), and montmorillonite clay (MMT) layers with the aim of obtaining low gas permeability in both dry and moist conditions as well as low water vapor permeability. Two different kinds of architectures were designed and successfully prepared, based on a 4 layer repeating unit (BPEI/MMT/BPEI/Nafion), represented here as quadlayer (QL), and on a 6 layer repeating-unit ((BPEI/Nafion)₂/BPEI/MMT), hexalayer (HL). Reduction in oxygen and water permeabilities is observed for films based on both types of repeat units. The reduction of the permeabilities increases with the number of quad and hexalayers achieving reductions in terms of oxygen permeability in both dry and humid conditions up to 98% and 97% respectively for 10 HL and QL. Furthermore, a reduction of 78% of water vapor transmission rate through the functionalized film was obtained for these films. As far as oxygen permeability is concerned, HL films are more efficient than QL films for smaller numbers of deposition units. These properties are shown to result from the complementarity between the presence of BPEI/Nafion and MMT layers