Preparation and optimization of a lignin-based pressure-sensitive adhesive.

D-optimal designs were applied to find the best parameters for the preparation of lignin-based pressure-sensitive adhesives (PSA) for sticky notes. Organosolv lignin was directly incorporated into a polycarboxylate polyether (PCE)/water matrix. The independent variables considered in the experimental design were the ratio between PCE, lignin, and water and the curing parameters. The distance traveled by the ball (tack), the peel-off losses and the final water content were the analyzed responses that allowed the optimization of the PSA formulation. The accuracy, the precision and the efficiency of the model were evaluated during the first experimental design for the formulation of the lignin-based adhesive named DES-OL-ADH. This formulation was optimized during the second experimental design abbreviated DES-OL-OPT. The coefficients of determination of the tack, the peel-off losses and the final water content were 0.98, 0.99 and 0.99, respectively. The model was satisfactory which allows the optimization of the PSA formulation. The DES-OL-OPT suggests that lignin-based PSA can be prepared as a sticky note application with 5 wt% of lignin, 84 wt% of PCE and 11 wt% of added water in the oven at 130 °C for 60 min, which shows a higher tackiness and similar peel-off losses than the commercial sticky notes PSAs.•Protocol optimization for the preparation of a green pressure sensitive adhesive (PSA) from PCE polymer, lignin, and water.•Influence of 5 compositional or processing parameters on adhesive performance through a 2-steps d-optimal experimental design.•Development of a new method, based on peel-off losses, to assess the performance of a PSA.

Orienting Cellulose Nanocrystal Functionalities Tunes the Wettability of Water-Cast Films.

Cellulose nanocrystal (CNC)-based materials display apparently erratic wetting behaviors with contact angle (CA) variations as large as 30° from sample to sample. This work hypothesizes that it is the orientation of CNC amphiphilic functionalities at the interface with air that causes the variability in CA. By exploiting relationships with the Hansen solubility parameter theory, a set of surface tension parameters is proposed for both the polar and the non-polar surfaces of cellulose Iß nanocrystals. These coefficients elucidate the wettability of CNC materials by establishing a correlation between the wetting properties of the air/sample interface and its chemical composition in terms of non-polar moieties. Advancing/receding CA experiments suggest that, while spin-coating CNC suspensions yield purely polar films, oven-casting them produces amphiphilic surfaces. We proposed a mechanism where the state of dispersion (individual or agglomerated) in which CNCs reach the air/water interface during casting is the determining factor: while individual nanocrystals find it more stable to orient their non-polar surfaces toward the interface, the aspect ratio of CNC agglomerates favors an orientation of their polar surfaces. This represents the first compelling evidence of CNC orientation at an interface and can be applied to Pickering emulsions and nanocomposites and to the production of CNC materials with tuned wettability.

Self-assembly behaviors of colloidal cellulose nanocrystals: A tale of stabilization mechanisms.

HYPOTHESIS: In solvent casting, colloidal nanocrystal self-assembly patterns are controlled by a mix of cohesive and repulsive interactions that promote destabilization-induced self-assembly (DISA) or evaporation-induced self-assembly (EISA). Tuning the strength and nature of the stabilization mechanisms may allow repulsive interactions to govern self-assembly during the casting of colloidal cellulose nanocrystal (CNC) suspensions. EXPERIMENTS: We propose a tool to classify the level of electrostatic and solvation-induced stabilizations based on two solvent parameters only: dielectric constant, ε, and chemical affinity for CNCs, in terms of Hansen Solubility Parameters, Ra. These criteria are applied to study CNC self-assembly in solvent casting experiments in various media and binary mixtures. FINDINGS: In solvent casting of suspensions stabilized through a combination of electrostatic and solvation effects, the primarily governing mechanism is EISA, which leads to the formation of chiral nematic domains and optically active thin films. In electrostatically-stabilized suspensions, EISA and DISA are in competition and casting may yield anything from a continuous film to a powder. In other suspensions, DISA prevails and evaporation yields a powder of CNC agglomerates. By classifying media according to their stabilization mechanisms, this work establishes that the behavior of CNC suspensions in solvent casting may be predicted from solvent parameters only.

The structural amphiphilicity of cellulose nanocrystals characterized from their cohesion parameters.

Cellulose nanocrystals (CNCs), usually considered as isotropically polar nanoparticles, are sheet-like crystalline assemblies of cellulose chains. Here, we link the anisotropy of the CNC structure to an amphiphilic behavior in suspension. The Hansen solubility parameters (HSP: δD;δP;δH) of wood-based H2SO4-hydrolyzed CNCs were measured from sedimentation tests in a wide set of 59 solvents and binary mixtures. Two sets of cohesion parameters corresponding to a polar surface (18.1; 20.4; 15.3) ±â€¯(0.5; 0.5; 0.4) MPa1/2 and to a mildly non-polar one (17.4; 4.8; 6.5) ±â€¯(0.3; 0.5; 0.6) MPa1/2 were determined, with respective solubility radii of 7.8 and 2.1 MPa1/2. The polar sphere is thought to correspond to the (110) & (11¯0) surfaces of cellulose Iß nanocrystals, while the smaller non-polar sphere is coherent with the exposure of (200) surfaces. The HSP graph provides new insights on the amphiphilic nature of CNCs and a mapping of their chemical affinity for solvents and polymer matrices.