Résumé
The addition of some biofillers like lignocellulosic biomass is an effective way to improve polylacticacid (PLA) properties and to extend its range of applications. Lignin, in powder form, has a wide set ofapplications as filler in composites, such as UV blocker, antioxydant, charring agent in flameretardancy, mechanical reinforcement or surfactant [1]. However, the strong polar nature of lignin, dueto the presence of hydroxyl groups, makes it incompatible with the non-polar PLA matrix, resulting ina poor interfacial filler-matrix adhesion. Acetylation and phosphorylation are two lignin chemicalmodifications used to enhance the mechanical and thermal properties of lignin/PLA compositesrespectively. These properties are strongly related with the interfacial adhesion between fillers and PLA[2].To characterize the interfacial adhesion, the determination of lignin and PLA surface energycomponents is required. Surface energy is an intrinsic property of each liquid and solid material and,for a solid, it is obtained by means of equilibrium contact angle measurements. However, for powdersor porous materials more issues arise, notably due to the imbibition of the liquid into the medium. Anapparent contact angle can be obtained using wicking tests and the well-known modified Washburnequation for porous materials. However this method, that theoretically allows the determination ofapparent advancing contact angles, does not always give reliable results due to the Washburnhypotheses that are not respected or no longer valid. A new simple method using a modified Jurin lawfor porous media is proposed here in order to determine reliable apparent equilibrium contact anglesand obtain surface energy of fillers [3]. An experimental protocol based on capillary wicking (Figure1) and coupled to the modified Jurin law was set and applied to lignin particles used as reinforcementin PLA. Some treatments were performed on lignin to improve the adhesion with PLA and themodifications due to the treatments were characterized. Reliable surface energy and dispersive andpolar components of untreated and treated lignin were obtained revealing the efficiency of the proposedmethod. Lignins were then used as reinforcements for PLA. The microstructure of the biocompositeswas characterized to highlight the modification of adhesion at the filler/matrix interface due to themodification of fillers surface properties [3].[1] Duval et al., A review on lignin-based polymeric, micro- and nano-structured materials. Reactive& Functional Polymers 85 (2014) 78–96.[2] Guo et al., The influence of compatibility on the structure and properties of PLA/ligninbiocomposites by chemical modification. Polymers (2020), 12(1), 56.[3] Carretier et al. An efficient solution to determine surface energy of powders and porous media:application to untreated and treated lignin. Applied Surface Science (2021)https://doi.org/10.1016/j.apsusc.2021.152159.