The use of microfibrillated cellulose produced from kraft pulp as strength enhancer in TMP paper

The effect oil the physical properties of TMP handsheets by adding microfibrillated cellulose (MFC) is investigated. 26 TMP handsheet series were made with 4% addition of MFC produced by grinding or homogenization. Analysis of particle size distribution of the MFC showed that homogenization yields a bimodal distribution Curve, while grinding gives a log normal distribution. The produced MFC had hydrodynamic particle sizes in the range 30-150 mu m, and homogenization produced MFC with the largest particles. Addition of MFC to handsheets increased the tensile index and air resistance. MFC made by homogenization had a larger effect on the tensile index than MFC made by grinding (7-21% and 11-34% strength increase respectively), suggesting that the strengthening mechanisms of the two MFC qualities are different. The addition of MFC reduced the light scattering coefficient (a loss of 8% for the worst case), opacity and brightness of the sheets. Theoretical consideration regarding addition of fillers to maintain the optical properties showed that one still may get a 10% increase in tensile index. The use of MFC as strength enhancer in commercially produced paper is discussed.