Paper engineered with cellulosic additives: effect of length scale

Composites of cellulose fibers were made with paper-making technology. Two types of microfibrillated cellulose (MFC), obtained by with either homogenization or ball milling, were blended with hardwood fibers to give composites having high strength and low air permeability. The strengthening effects of the MFCs were compared with strengthening by cellulose microparticles (CMPs) made by cryogenic milling, with and without polyamideamine-epichlorohydrin addition. The MFC from homogenization was fully retained on the fiber web due to a broad size distribution; in contrast, the retention ratio for MFC produced by ball milling was lower than 50 % because of its smaller particle size. The small size caused the resulting paper to display a more compact and denser structure. The main distinction between the papers made with the two types of MFC was the elongation at break under wet conditions, suggesting that they reinforce the paper in different ways. On the other hand, CMPs act as mechanical debonders and could find application in tissue paper, increasing paper bulk and decreasing the density and thus improve tissue softness.