High filler content composites with microfibrillated cellulose

Abstract

The aim of this thesis was to evaluate whether micro fibrillated cellulose (MFC) enables higher filler content in composites. Due to the high filler content exceptional optical properties were anticipated.

The composites consisted of Masuko ground MFC, precipitated calcium carbonate (PCC), unrefined wood pulp and synthetic fiber. The composites were formed by pressure filtration. A membrane was used over a conventional wire in a standard laboratory sheet former. The effect of MFC, fiber and PCC was evaluated in a three component mixture design on different measured properties of the prepared laboratory hand sheets. In all test points a constant amount of 15 w-% of synthetic fibers was added, which was omitted from the model. The data of the results was analysed by stepwise regression using a special cubic model. All results were compared to laboratory or industrial reference as well.

The high surface area of MFC increased the bonding ability of the fibrillated material in the composites and hence increased the strength properties. The tensile index was highest at the highest MFC levels; the test point containing 47 wt.-% MFC had a tensile index of 44 Nm/g. The effect of the three dimensional networking ability of MFC was apparent in the z-directional strength measurements, as the test point with highest amount of MFC was almost three times higher than that of the industrial reference material. Tear strength did not benefit from MFC additions, but the synthetic fiber raised the tear index linearly.

Virtually all optical properties exceeded those of the reference material. Even the wet opacity was higher than the reference, although no titanium dioxide was added to the furnish. The small size of MFC efficiently lowered the porosity of the composites. This did not diminish the water uptake however; all test points were highly hydrophilic and had a water uptake of more than 100 wt.-%, higher than the reference. The regression analyses on optical and strength properties were fairly reliable, since the explanatory degrees (R²-values) were high. For roughness, porosity, water uptake and wet elongation the R² values were lower.

Drainage testing revealed that the membrane in itself already slowed down the process and MFC even more so. Future challenges include faster dewatering times.

In summary, the property space of the composites comprised of highly favourable proportion mixtures, which could be developed to fit industrial applications.