There is an increasing interest in structuring lignin under the form of spherical micro and nano-particles. Spherical lignin particles can bring several advantages, for example in coatings, emulsions, and composite materials. In the present work we used, for the first time, lignin particles to synthesize structured layers via evaporation-induced self-assembly, into coatings and films.<br/>It is known that the vertical distribution of particles in drying waterborne systems involves a balance of timescales for evaporation, diffusion and sedimentation. In our polydisperse system, a colloidal threshold of 300 nm in size was calculated by using the shift produced by Brownian motion and that of settling. Particle size measurements along cross section analyses (SEM) allowed identification of the diffusion effects upon drying. The sedimentation can be neglected if the size of the particles is in the colloidal range. In this case, evaporation and Brownian diffusion remain as the two competing processes. Using the Peclet formalisms we revealed the formation of coating layers driven by evaporation rather than diffusion. We explored the origins of our observations and propose that the colloidal, polydisperse fraction enables an optimal drying rate for maximal particular size segregation. Remarkably, the particle packing analysis revealed the possibility of dense and highly packed structures.<br/>However, the produced films were non-cohesive structures, losing their structure upon contact with water. With the aim at obtaining mechanically-resistant, self-standing films we used cellulose nanofibers (CNF). Experiments revealed that films with a CNF content of only 8% were crack free, homogeneous, and self-standing. SEM imaging revealed film’s morphology, showing structures in which CNF were embedded within lignin particles.<br/>Our results offer a first insight on the possibilities of using polydisperse organic-based systems for several applications, where it is possible to control material transport and mechanical performance depending on particle structuring.<br/>

Stratification of lignin particles in waterborne systems via evaporation-induced self-assembly

2019 Spring National Meeting

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