Different strategies for obtaining high opacity films of MFC with TiO₂ pigments

The present study examines the production and characterization of opaque solid films made with microfibrillated cellulose (MFC) suspension and titanium dioxide (TiO₂) nanoparticles. Three different strategies were investigated: a blend of (1) MFC and TiO₂ (2) a premix in which TiO₂ particles are used to favor the fibrillation step of MFC and (3) a sol–gel strategy in which TiO₂ particles were directly generated onto the surface of MFC. The different process parameters have been optimized both for the production of MFC and the sol–gel reaction. Gel suspensions containing different ratios of TiO₂ were morphologically and chemically characterized. In order to characterize the size and the nature of the particles, diffraction laser scattering, atomic force microscopy were used while the thermo gravimetric analysis and X-ray diffraction were used to investigate the degradation of MFC for all the three strategies. To highlight the level of dispersion of TiO₂ within the MFC network, scanning electron microscopy in BSE mode has been employed. Finally, the transparence and the mechanical properties of solid films were measured by UV spectrophotometry and tensile tests, respectively. Very good TiO₂ dispersion and high opacity MFC films have been achieved with a very low amount of TiO₂. Thus, the best strategy that takes into account the easiest process for making the hybrids and leading to the high level of opacity with the lowest ratio of TiO₂ is the premix strategy.