EFFECTS OF LIQUOR COMPOSITION ON THE PROPERTIES OF HARDWOOD ULTRA-HIGH-YIELD PULPS

Ultra-high-yield pulps from aspen and white birch were produced using an alkaline pretreatment at low temperature (< 100-degrees-C) of chips followed by an atmospheric refining and an interstage peroxide bleach ing prior to a secondary atmospheric refining. By using 3% NaOH charge in chip pretreatment, 5% hydrogen peroxide in interstage bleaching, a nd 5 mJ/kg refining energy (CSF 200 mL) one could produce hardwood pul ps with excellent strength properties (tensile index 4.5-5 N.m2/g; tea r index 6.5-7 mN.m2/g) and brightness (78-80% ISO). The use of Na2CO3 and Na2SO3 in chip pretreatment considerably improved pulp brightness, but had poor effect on strength improvement. Using Na2CO3 Instead of NaOH in peroxide bleaching gave higher brightness for pulps produced f rom chips pretreated with Na2CO3, but this chemical formulation yielde d poor mechanical properties.