Pulp Slurry Enzyme Reining

ISBN : 978-602-17761-0-0 123 © 2013 Published by Center for Pulp and Paper through REPTech2012 A Practical Method to Control Vessel Picking in Uncoated Wood Free Papers Ratna Kumala PT. Riau Andalan Kertas, Pekanbaru-Riau, Indonesia ABSTRACT PT. Riau Andalan Kertas produce Paper One, APRIL’s lagship brand of premium quality uncoated wood free UCWF papers. APRIL operates plantations growing both Acacia and Eucalyptus hardwoods that are processed into ECF bleached hardwood kraft pulp. The naturally occurring vessel cells that transport water within the tree remain inside the pulp where, left untreated, can cause problems as the paper is used in the offset printing process. Vessel picking can become a problem for printers because vessels are weakly bonded within the paper web. For example, when the paper passes through the offset press weakly bonded vessels may be transferred to the blanket creating “voids” in the ink coverage, creating a rectangular shaped spot in the printed image. This paper describes a 6 steps methodology to control the issue of vessel picking in UCWF production : 1 Adjust the pH, temperature and consistency of the hardwood kraft slush pulp within the range that can support enzyme activity and provide homogenous mixing of the enzyme with the slurry. 2 Adding a blend of enzymes that may include [endogluconase, cellulase, and hemicellulase] to the pulp slurry. 3 Controlling the reaction time of the pulp slurry and the enzymes at the requisite temperature and ph to allow the enzymes to begin breaking down the vessels structure. 4 Mechanically reining the slush and enzymes in speciic way to reduce the size of the vessels so they become mechanically entangled in the paper web. 5 Using cassava based cationic starch to assist the bonding of the broken down vessels into the paper web. 6 Heating the paper during the paper drying step to de-activate the enzyme. After processing through the irst 3 steps, the vessels are more lexible and responsive to the mechanical actions of reining so that the vessels become broken down and can be irmly anchored within the paper web by the application of cationic starch. To summarize: vessels cannot be removed in the pulping and bleaching process. If left untreated these vessels tend to pick off the paper surface during printing process. By applying the 6 step method in the paper making process, the vessel picking problem in offset printing can be reduced to zero. Keywords: vessel picking, uncoated wood free, acacia, eucalyptus, hardwood, ECF, kraft pulp 1. Introduction 1.1. Vessel Picking The vessels are composed of single cells. The length of vessel cells is shorter than the ibers and the diameter of vessels are depending on the variety of woods. Generally, there are 3 – 25 vessels per mm2 for the hardwood. Because of the vessels cell is similar with the iber cells, it could not be separated in the pulp making process. The vessel cells will be accumulated in the pulp slurry and it will be carried the paper product. This problem is not only for tropical hardwood but also for Europe’s and Canada’s hardwood. The vessels inluence to the paper properties especially for strength and bonding runnability, surface roughness and surface strength printability. The vessel cells could not bonding well and contribute little to the paper strength. It will cause a problem in the ine paper that is made from hardwood pulp. Some of vessels in the paper surface tend to be picked off by the ink tackiness of the printing press. It will create a small white spots in the solid printed areas.

1.2. Pulp Slurry

Main pulp slurry that is used to make ine paper in APRIL comes from tropical hardwood. For vessel enzyme application, the pulp slurry should be adjusted for supporting the enzyme activity. The pulp slurry in the storage tower has a consistency of 10 ±3 and at the dilution zone the consistency is reduced to 5 ±1 by adding the dilution water. In this step the pH and temperature should be adjusted; The pH of slurry is adjusted by using an alkali donor either NaOH or Na 2 HCO 3 to 6.5 – 7.5. The alkali donor is added to the dilution water prior to the dilution water coming to contact with the pulp slurry. This provides proper mixing and dispersion of the alkali donor. The temperature of slurry is adjusted to 50 - 55 °C by allowing suficient latency time in the high density storage tower prior to the dilution step.

1.3. Enzyme

Additional vessel enzyme is not only solved the vessel problem in the paper surface. The enzyme is derived from the natural sources that apply to bio-reining of hardwood ibers for improving the paper properties and reducing the reining energy consumption. The vessel enzyme is added to the dilution water prior to meeting the pulp slurry to provide proper mixing and homogenous dispersion of the enzyme within the pulp slurry. Enzyme addition is in the range of 0.3 to 0.5 kilogram of enzyme solution per ton of oven dry pulp. The mixture of pulp slurry 124 © 2013 Published by Center for Pulp and Paper through REPTech2012 and enzyme will react in the pulp slurry dump chest with agitation for 2 until 3 hours. The reaction time is controlled by adjustment of level in the dump chest.

1.4. Reining

Reining process is an important role to modiication the characteristics of iber. By reining process the ibers become more lexible. It will give good effect to the paper properties such as stiffness, opacity, tear strength or the paper smoothness. In this study, the pulp slurry is mixed with the vessel enzyme before reined by using conical reiner. The reiner is operated in between 57 to 117 kilometer per revolution for both stator and rotor plates with speed rotation rotor are 360 to 600 rpm. It will consume the reining energy between 50 to 70 kWh per oven dry ton of pulp. The consistency of pulp slurry is 5 ± 0.2 percent. And the pH of slurry is controlled in base condition 7 - 8 by adding Na2HCO3 prior to the reiner.

1.5. Starch Addition