CELLULOSE CHEMISTRY AND TECHNOLOGY ELEMENTAL CHLORINE FREE BLEACHING OF WHEAT STRAW CHEMIMECHANICAL PULP AHMAD JAHAN LATIBARI,* MOHAMMAD ALI HOSSEIN,* REZA HOSSEINPOUR ** and AJANG TAJDINI * *Department of Wood and Paper Science and Technology, Karadj Branch, Islamic Azad University, Karadj, Iran ** Department of Wood and Paper Science and Technology, Sciences and Research Branch, Islamic Azad University, Tehran, Iran Received October 3, 2012 Production of bleachable CMP pulp from wheat straw using different dosages of NaOH and chemical treatment time was investigated. The yield after chemical treatment varied between 64.6 and 72.7% and the total yield after defiberizing was measured between 53.4% and 62%. The pulp produced applying 10% NaOH, 40 minutes pulping time and 95 °C pulping temperature was selected for bleaching trials. Elemental Chlorine Free (ECF) bleaching sequence was used for bleaching the selected pulp. Applying 3% (based on oven dry weight of the unbleached pulp) chlorine dioxide in D 0EPD1 bleaching sequence (2% in D 0 stage and 1% in D 1 stage) improved the brightness to 62.2% ISO. The kappa number of the ECF bleached pulp was reduced from the value of 40.1 to the final value of 13.4 for bleached pulp. Keywords : wheat straw, CMP, yield, strength, totally chlorine free, elemental chlorine free INTRODUCTION Non-wood fiber resources, such as bamboo development, particularly in regions with limited and reeds, and then straw, were the available and wood supply.1 usable fiber sources for the early production of Regions like Asia and also some countries in paper, when it was invented in China. During the the Middle East concentrated on the utilization of course of paper development through Asia and non-woods as raw material. Even though it seems then Europe, non-woods, such as wheat straw, unrealistic, but it is believed that the non-wood were also utilized. However, the abundant sources pulp production will take the momentum at the of wood in Europe and its easy processing annual rate between 12-15%.2 In this expansion replaced non-woods. Currently, while the path, the share of underdeveloped countries, production and consumption of paper and paper which are facing limitations of wood fiber supply, products is continuously increasing, forest will be greater than that of fiber-rich countries. resources are depleting and the global shortage of Since 1970, globally, the non-wood plant fiber wood has emerged. Therefore, the need to prevent pulping capacities increased two to three times fast deforestation has prevailed. Consequently, faster than the wood pulping capacity.3 It has been paper industry has been forced to look for estimated that the pulp production from wheat alternative sources of fibrous raw material. straw in China will reach almost 13 million tons Countries and regions with limited paper in 2020.4 production are also trying to develop domestic The global interest in non-wood and non- paper production capacities, relying on local, but conventional fiber pulping has attracted attention unconventional raw material. In this situation, worldwide and various groups and organizations non-wood fiber resources appeared as an started research, development, improvement and important alternative to wood for paper industry implementation of non-wood pulping. Such Cellulose Chem . Technol ., 48 (1-2) , 119-125 (2014) AHMAD JAHAN LATIBARI et al . research activities cover a wide range of pulping chemimechanical pulping process to preserve the processes from conventional soda and kraft yield, and to reach suitable pulp properties. The pulping of bagasse and cereal straw, giant reed,1 elemental chlorine free (ECF) bleaching of the high yield pulping of cotton stalks, 5 kenaf,6 flax 7 produced pulp was studied. and chemimechanical pulping of canola straw 8 to non-conventional fibers, such as date palm EXPERIMENTAL residues 9 and oil palm empty fruits.10 Wheat straw Materials has been the major non-wood fiber source and Wheat straw in bales was collected from different pulping processes have been studied.11-12 Agriculture and Natural Resources College Wheat straw alkaline peroxide mechanical Experimental Station, Islamic Azad University, pulping was investigated to develop raw material Karadj Branch. Straw was cleaned and leaves and efficient pulping method 13 and enzyme and hot debris were separated. Then the cleaned straw water treatment of wheat straw was studied to was chopped into 2-4 centimeter length pieces. improve the brightness of the wheat straw pulp.4,14 The chopped straw was dried at ambient For annual plants and wheat straw, mostly temperature and after reaching equilibrium soda pulping has been investigated and applied. moisture, it was stored in plastic bags until used. Soda pulping is a well-established process with a potential for a vast variety of annual plant raw Methods material, but this process presents particular Pulping disadvantages, such as low yield and difficulty in The experimental conditions for chemical recovery.13 Mechanical pulping has been chemimechanical pulping (CMP) of wheat straw developed to reach higher yield and more efficient to reach optimum pulping conditions were set as use of raw material. However, the strength described below. properties of this pulp are inferior to normal soda Combinations of one of the four levels of pulp. Therefore, to overcome such deficiencies, active alkali (10, 12, 14, and 16% NaOH based on various measures, including enzyme treatment of oven dry weight of the straw), and one of the raw material,4 as well as mild chemical three chemical treatment times (20, 30 and 40 treatment,7-8 have been foreseen. minutes after reaching the pulping temperature) The environmental concerns of paper were studied. Pulping temperature and liquor to manufacture and the consumer demands related to straw ratio were constant at 95 °C and 8/1, conventional chlorine based bleaching have respectively. For each combination of variables, directed the paper industry toward the application three replica pulps were prepared. of new approaches to reduce its adverse All cooks were performed in a 4 liter rotating ecological impact. Both totally chlorine free digester, Ghomes Wood and Paper Equipment (TCF) and elemental chlorine free (ECF) Manufacturing Co., using 100 grams of wheat bleaching sequences have been utilized mostly for straw (dry basis). At the end of each cooking, the the bleaching of wood chemical pulps with low content of the cylinder was discharged on a 200 kappa numbers.15-20 However, parallel to the mesh screen and the cooked material was washed development of non-wood alkaline peroxide using hot water and the remaining liquor was mechanical pulping, chemimechanical pulping of separated by hand pressing the cooked material. non-woods has been investigated and in this Spent liquor was collected and used for residual respect TCF bleaching was studied.4,14,21 Although alkali (NaOH) measurement. The residual NaOH ECF bleaching is currently in general use to was determined by titration with dilute H 2SO 4. bleach wood chemical pulps, but by far the The cooked material was then defibered using a literature on the application of ECF sequences to 25 cm laboratory single disc refiner, Ghomes bleach non-wood chemical pulps is limited and Wood and Paper Equipment Manufacturing Co., only few reports are observed.17-18 and the pulp was screened using a set of two In this investigation, our attempts were screens, a 14-mesh screen on top of 200 mesh concentrated on the development of a simple screens. The material retained on the 14 mesh pulping process for wheat straw suitable for screen was considered as rejected and the fibers small-scale production to be utilized as that passed the 14 mesh screen and retained on the supplementary pulp in fine paper production. We 200 mesh screen were considered as accepted concentrated on the modification of the pulp (screened yield). 120 Wheat straw The selected CMP pulps from the pulping can be erected.13,23-24 Soda pulping has been trials were refined to reach the freeness level of applied on wheat straw to produce pulps suitable about 350 mL CSF and then the strength for further conventional chlorine (CEH) bleaching properties of the handsheets produced from the of the pulp to produce writing and printing papers. refined pulps were measured, using relevant This pulping process requires the application of Tappi test methods. high temperatures in the range of 175 °C and consequently, the equipments are under higher Bleaching pressure. Irrespective of such limitation and The selected CMP pulp with the kappa number shortcoming, wheat straw has been used for pulp of 40.1 from the pulping trials and after the and paper production for a long time and it strength evaluation was used for bleaching remains as one of the major raw materials in experiments applying Elemental Chlorine Free many developing countries. The utilization of (ECF) bleaching. For ECF bleaching, the D 0EpD1 non-woods in general and wheat straw in sequence was used, applying one of the three particular for pulp and paper production provides charges of 2.5, 3 or 3.5% chlorine dioxide (ClO 2). some benefits, but it imposes some problems too. Two thirds of the ClO 2 were used in the D0 stage During the alkaline delignification process, the and the rest was used in the final D 1 stage. silica present in the raw material dissolves into Hydrogen peroxide reinforced extraction stage the pulping liquor, which will lead to difficulty in (E p) was used between D 0 and D 1 using 1% H 2O2 the chemical recovery. Even though, this and 2.5% NaOH (based on the oven dry weight of difficulty has been overcome to some extent by the unbleached sample). The bleaching the alkaline-sulfite process,12 the other temperatures in D 0, E p and D 1 were 60, 70 and 80 deficiencies of chemical pulping, especially the °C, and the relevant times in the bleaching stages low yield, still exist.