Measuring adhesion forces between model polysaccharide films and PLA bead to mimic molecular interactions in flax/PLA biocomposite

Abstract

International audienceNatural fiber-reinforced polymers or biocomposites are becoming increasingly popular as an environment friendly alternative to traditional glass fiber-reinforced thermoplastics. The mechanical properties of reinforced biocomposites, such as flax/polylactic acid (PLA), are largely governed by the level of interfacial interactions between the two constituents apart from their intrinsic properties. The hierarchical organization of various polysaccharides present in natural fibers results in complex mechanisms at the interface which are still poorly understood and difficult to analyze through a traditional approach that rely on indirect assessments. The possibility of measuring direct adhesion force between individual particles using the colloidal force microscopy has been exploited here by developing an experimental set-up in which a micrometer colloidal PLA bead is brought into close contact with molecularly smooth polysaccharide surfaces that mimic the main constituents of flax fibers, cellulose, hemicellulose, and pectins. Adhesion force measurements performed under ambient and low relative humidity conditions indicate that cellulose/PLA is the weakest interface in the biocomposite. Moreover, the results emphasize the important role of water molecules for the more hydrophilic polymers in flax fibers that takes place in the fundamental forces involved in the adhesion phenomena at the biocomposite interface

Diffusion of macromolecules in self-assembled cellulose/hemicellulose hydrogels

“…4). 42 A change to a less hydrophilic network increases the mobility of fluorescently labelled probes due to repulsion between the probe and the network, similar to observations on systems in which electrostatic repulsion between the probe and the matrix increased the mobility compared to a non-charged reference. The presence of arabinoxylan appears to increase the diffusivity of the dextran probes from the one observed in the cellulose-only hydrogels, especially for the 70 000 g mol À1 FTIC-dextran.…”

Solid-state NMR to quantify surface coverage and chain length of lactic acid modified cellulose nanocrystals, used as fillers in biodegradable composites

“…For example, inhomogeneity and the presence of aggregates in materials produced via solvent casting are often a result of aggregation of CNC already in the organic solvent [2,7]. Another often reported issue is the poor adhesion between cellulose and a PLA matrix [8][9][10][11]. One option for making CNC more compatible with the polymer matrix is to modify the surface of CNC with hydrophobic PLA chains.…”

Controlling water permeability of composite films of polylactide acid, cellulose, and xyloglucan

“…Bioplastic materials can be made from plant, animal, or bacterial sources, and they can be biodegradable or non‐biodegradable. As the cost of fossil fuels increase, bioplastics such as polylactide acid (PLA) become more competitive on the market . Bioplastics can be produced in common processing plants, enabling a relatively simple shift from petro‐plastics to PLA‐plastics.…”

“…These composites have a better plastic storage modulus, which is an advantage both during their processing and in their use for food packaging (e.g., in drinking cups and blister packs) . However, the increased strength in the plastic region gained from the use of a PLA/cellulose composite material is often accompanied by a decrease in the material's elongation, which is related to poor interfacial adhesion between the PLA and the cellulose . Attempts to improve adhesion between PLA and cellulose have included chemical surface treatments of the cellulose fibers or the addition of a compatibilizing agent .…”

“…Routes to increase water permeability have been rarely studied, despite their potential use in applications such as biomedical devices and agriculture . Incorporation of the hydrophilic hemicellulose xyloglucan (XG), in which the water contact angle in films has been measured to 29° (compared with 40° for cellulose films), could be a potential way to control water permeability.…”