Addition of polyvinylamine in chemi-thermomechanical pulp and kraft pulp and the effects on dewatering, strength, and air permeance

The addition of polyvinylamine (PVAm) in the wet-end of the papermaking process was investigated. The changes in pulp drainage, vacuum dewatering, tensile strength, and air permeance were measured with and without PVAm. Both chemi-thermomechanical pulp (CTMP) and bleached kraft pulp were used. The dewatering and drainage abilities of the different pulps was examined by measuring the dewatering resistance (°SR), the water retention value (g/g), and the vacuum dewatering. The tensile strength and air permeance values were tested on paper sheets. The results showed that the initial dewatering was faster for pulps with PVAm, and this effect was greater for the CTMP and at higher basis weights. The strength increased when PVAm was added but only if the pulp was washed before sheet forming. The unwashed pulp with PVAm had worse formation, which resulted in lower tensile strength values. The air permeance of the sheets was higher with the addition of PVAm, primarily as a result of higher flocculation. Adding PVAm to the stock suspension in the wet-end of the paper machine has great potential for end-products that require high air permeance and tensile strength properties. PVAm could also act as a dewatering enhancing agent, but caution must be taken regarding the potential of formation problems.