LOW CONSISTENCY REFINING OF MIXTURES OF SOFTWOOD & HARDWOOD

(ABSTRACT) The effect of refining energy on the measured properties of pulp and paper was investigated based on different ratios of softwood and hardwood chemical pulps in corefined blends. A mix of 70-80% lodgepole pine, 20-30% white spruce and 5% sub alpine fir was used as softwood and the eucalyptus as hardwood. The mixtures studied were 0/100, 25/75, 50/50, 75/25 and 100/0 hardwood/softwood at 3.5 % consistency. In the experiment studied here mixtures of hardwood and softwood bleached pulps were refined in a single disk refiner. The plate used had a BEL of 2.74 km/rev and the refiner speed was 1200 RPM. Gap size between plates was measured using a sensor connected to a LabVIEW interface. The different refining energy values were created by changing the gap size between plates at constant flow rate. The refining flow rate was 200 l/m. Refining hardwood and softwood together enhanced the paper properties such as tensile, burst strength, paper density and drainability, but reduced the tear strength, sheet thickness and light scattering coefficient. In order to significantly reduce the refining power, the ratio of hardwood must be 50% at least. We expect that the energy was put into the softwood pulp and resulted in a higher specific refining energy in the softwood fraction. No-load power did not vary with the % hardwood content. Fibre length weighted was reduced after refining due to fibre cutting and fines generation. (Conclusions) This research was carried out to determine the effects of mixing softwood and hardwood in low consistency refining for the purpose of making fine paper. The results can be summarized as below: 1. Decreasing softwood content in the mixture makes the pulp quality similar to hardwood quality. 2. As expected, refining hardwood and softwood together improved tensile and burst strength, increased paper density and improved drainability by decreasing the freeness. Refining also reduced tear strength, sheet thickness and light scattering coefficient. 3. As softwood content increased, the refiner was able to reach higher peak power and specific energy. With 100% and 75% softwood, we could reach 80 ±1 kW, with 25% we could reach 46.74 kW, while almost no power could be obtained with 100% HW. 4. The best tensile performance was obtained with 100% softwood pulps and 25% softwood pulps. We expect that the energy was put into the softwood pulp and resulted in a higher specific refining energy in the softwood fraction. 5. No-load power did not vary with % hardwood content. 6. The higher the hardwood content, the smaller the critical gap was. 7. Fibre length weighted was reduced after refining due to fibre cutting and fines generation. In 100% softwood, the fibres were 2.25 mm – 4.15 mm long. This initial length was reduced by 14.31%, while fines in the range of 0.2 mm – 0.4 mm long increased almost 39.53%. 8. The refiner plate with a BEL of 2.74 km/rev (bar width 1.6 mm) gave a better refining response to fibres with length > 1.6 mm. For that reason it is better for fibres with length > 1.6 mm to be refined with plate > 2.74 km/rev. Dimas DP Nugroho (August 2012)