RESUMEN
In this work, stability of dispersions and foams containing CaCO3-based pigments and cellulose nanofibrils (CNF) was evaluated with the aim to reveal the mechanisms contributing to the overall stability of the selected systems. The utmost interest lies in the recently developed hydrocolloid hybrid CaCO3 pigments and their potential to form bionanocomposite structures when incorporated with CNF. These pigments possess a polyelectrolyte layer deposited on the surface of the particle which is expected to enhance the compatibility between inorganic and organic components. Stability assessment of both dispersions and foams was conducted using turbidity profile scanning. In dispersions, CNF provides stability due to its ability to form a firm percolation network. If surface-modified pigments are introduced, the favourable surface interactions between the pigments and CNF positively influence the stability behaviour and even large macro-size pigments do not interfere with the stability of either dispersions or foams. In foams, the stability can be enhanced due to the synergistic actions brought by CNF and particles with suitable size, shape and wetting characteristics resulting in a condition where the stability mechanism is defined by the formation of a continuous plateau border incorporating a CNF network which is able to trap the inorganic particles uniformly.
RESUMEN
Flow properties of the calcite/poly(vinyl alcohol) (PVOH) system were studied and related to the microstructure of the suspension. Adsorption of PVOH on calcite was confirmed, and it results in a shift of the slipping plane out from the surface. The charge density at the surface is assumed to remain unchanged. Since the PVOH used is only partially hydrolyzed, the most likely adsorption conformation consists of residual acetate groups adsorbed to the surface and vinylalcohol groups extending outward from the surface as loops and tails. The microstructure and flow properties of the calcite/PVOH system was found to go through several different stages as a function of PVOH concentration. At low PVOH concentrations a gradual weakening of the initially formed floc network is observed as a function of PVOH concentration. Further addition of PVOH eventually leads to breakdown of the flocs which results in a sterically stabilized suspension with a very low viscosity. This state persists for a narrow concentration range of PVOH, and increasing the PVOH concentration over a certain limit leads to a second gradual increase in viscosity. The system is believed not to undergo reflocculation at high PVOH concentrations as judged from the nonelastic nature of the suspensions. Instead, the polymers form a viscous matrix in the solution while the particles remain well-dispersed. At high enough PVOH concentration, the free volume available for the particles is greatly reduced, and the viscosity increases sharply.
