STUDIES ON PULPING AND BLEACHING OF POPLAR DELTOIDES

Abstract

1.0 INTRODUCTION: The demand of paper and paper board is expected to enhance with increasing industrial development and growing literacy rate in our country. Future projection shows that percapita consumption figure would have rise up from 4.3 kg to 5 kg in the next few years. This would call projected annual production of 50 lakhs tons by the turn of century compared to the present demand of 3.7 lakhs tons. The demand for higher production of paper would naturally require more fibrous raw material in future. There is an acute shortage of forest based raw material in our country. Poplar deltoides is a native of North America and can one of the most promising hardwood raw material for Indian pulp and paper industry. P.deltoides is a fast growing tree, raised in close spacing and harvested on short rotation. The biomass obtained from it is good. At present Eucalyptus is the most promising raw material for pulp and paper industry. Due to high transpiration rate of eucalyptus, farmers prefer to grow Poplar trees. Hence it has been planned worthwhile to carry out the detailed investigation on this particular plant with special reference to pulp and paper making. 2.0 STUDIES ON FIBER MORPHOLOGICAL AND PROXIMATE CHEMICAL ANALYSIS OF P.DELTOIDES The detailed investigation includes the anatomical, morphological and proximate chemical analysis studies of P.deltoides. It has been analysed for density, fiber length, fiber diameter, cellwall thickness, lumen diameter and various other derived properties. Further it has been analysed for proximate chemical analysis which includes determination of extractives iii soluble in cold and hot water, alcohol-benzene (1:2v/v) 1% NaOH solubles, lignin, pentosans, hemicellulose, holocellulose, alpha cellulose, beta cellulose, gamma cellulose, ash, content etc. Proximate chemical analysis of P.deltoides is compared to check its suitability vis-à-vis to Eucalyptus, which is the most promising and trusted raw material for pulp and paper industry. Results and Discussion: The results of proximate chemical analysis indicated that the carbohydrate fraction of Poplar is more than that of eucalyptus, which is presently the most promising raw material for pulp and paper making. The Poplar wood has porous structure and lignin content of Poplar has been found to be lower than eucalyptus, which indicates that fewer chemicals will be required for pulping. Hence Poplar can be pulp for higher yield with less chemicals. 3.0 PULPING STUDIES The wood logs of P.deltoides were chipped in the chipper and screened. The chips of the accepted quality were used for pulping studies. The chips of P.deltoides were delignified by various delignification processes. (A) Soda and Soda - AQ process (B) Kraft and Kraft - AQ process (C) Alkaline sulphite and alkaline sulphite - AQ process (D) Polysulphide process. 3 A SODA AND SODA AQ DELIGNIFICATION Since Poplar wood has low density and open structure. It has porous structure, and show good penetration of the cooking liquor and it has been found that it can be conveniently delignified by soda process. During soda delignification process, the various pulping parameter viz., time, temperature and alkali doses were optimised. At optimum delignification conditions, the effect of AQ was iv studied. During soda pulping a cooking temperature of 170°C, cooking time 120 minutes, active alkali dose 16% and liquor to wood ratio of 3:1 may be taken as optimum conditions.The various combinations of AQ and active alkali dosage were used in initial study. These included four levels of AQ dose 0.0, 0.05, 0.1, 0.2 percent on o.d. wood bases each at four active alkali concentration (14,16,18 and 20 percent as Na20) All the cooks were made at the same H factor. Result and Discussion: It has been observed that Poplar has low density and comparatively more open structure. It show good penetration of cooking liquor and found that it can be conveniently delignified by soda process. During soda pulping a cooking temperature of 170°C and time at temperature 120 minutes, active alkali dose of 16% and liquor to wood ratio 3:1 were found to be optimum conditions. Anthraquinone plays an important role in enhancing delignification and stabilization of carbohydrates. The addition of 0.1% AQ (on o.d. wood basis) was found to have beneficially effect on both the aspect of reducing kappa no. along with increase in pulp yield. It has been found that addition of 0.1% AQ increases the yield at the same kappa no. and decrease the kappa no. at the same yield. It has also been found that the use of AQ decreases the alkali consumption at the same yield of kappa no. 3 B KRAFT AND KRAFT - AQ DELIGNIFICATION. In kraft delignification process the effect of active alkali, sulphidity, time and temperature was studied in order to optimise the pulping conditions. The cooks were made at same H factors. On the basis of experimental results, the effect of alkali change and sulphidity was studied. The experiments were carried out at 165+5°C under a constant reaction time of 1.5 hr at four different active alkali concentration of 14,16, 18 and 20% as Na20 and at different sulphidity levels of 16,18,20% as Na20 alongwith three different levels of AQ dose (0.05, 0.1 and 0.2% AQ on O.D. wood basis) Result and Discussion: Since Poplar has low lignin content and comparatively more open structure , therefore it has been found that the active alkali dose of 16% and sulphidity 20% and time at maximum temperature 90 minutes has been found to be an optimum condition. The use of higher active alkali decreases yield enhancing carbohydrate degradation. The effect on yield is more pronounced at sulphidity value of 15% and there is little increase in pulp yield by increasing sulphidity level from 20-25% The influence of sulphidity on yield seems to be somewhat higher at low active alkali charges. Thus 20% sulphidity may be considered as an optimum dose. Addition of 0.1% AQ under constant condition leads to a significant reduction in kappa no., an addition of 0.2% AQ shows nearly similar result.AQ effectiveness decreases with increasing sulphidity in kraft pulp. The strength properties of kraft —AQ pulp found to be better than kraft pulp. 3 C: ALKALINE SULPHITE AND ALKALINE SULPHITE-AQ PROCESS In alkaline sulphite and alkaline sulphite-AQidelignijfication process, the chips were digested with different proportion of alkali and sodium sulphite doses, at different time and temperature using varing doses of AQ to get the optimum condition. Results and Discussions: On the basis of experimental result the maximum digestion temperature of 180° C time at temperature 150 minutes. Sodium Sulphite dose of 10% as Na20 and NaOH 10% as Na20 was found to be optimum during AS delignification. AS process delignifies at a slower rate than vi kraft process. The yield obtained to be similar to kraft pulp but at higher kappa no.Use of 0.1% AQ in AS process increases the rate of delignification and pulp yield. The strength properties were found to be comparable to kraft pulp. 3 D POLYSULPHIDE PULPING The use of polysulphide (PS), Anthraquinone (AQ) and oxygen delignification are another alternatives for decreasing the kappa number. Under alkaline conditions PS oxidize the aldehyde groups (reducing end) in polysaceharides to carboxylic groups, rendering the polysaccharides in particular glucomarmans stable against the peeling reaction resulting in an increased pulp yield due to the retention of hemicellulose. Results and Discussion : The polysulphide pulp shows an increase in pulp yield an the properties were found slightly better than the kraft pulp. Use of AQ is still improved pulp yield and properties. 4.0 BLEACHING STUDIES The bleaching of P. deltiodes pulps have been done using the following methods (A) Oxygen delignification (B) Conventional bleaching techniques using CEH and CEHH bleaching sequences (C) Chlorine di-oxide based bleaching sequences (D) Elemental chlorine free bleaching sequences (E) Enzymatic bleaching Conventional bleaching techniques using CEH and CEHH bleaching sequences 4A OXYGEN DELIGNIFICATION OF PULP The pulp of Poplar deltoides obtained by the various pulping processes were delignified in a .02m3 electrically heated laboratory digester. In bleaching, oxygen has resulted in significant environmental benefits such as substantial reduction in color. COD and formation of vii chloro-organics. During oxygen delignification the lignin content of the pulp is reduced to 40-50% without sacrificing significantly the strength properties of pulp. Oxygen delignification in turn decreases in the bleach chemical demand alongwith decrease in the pollution load to the tune of around 50%. 4B CONVENTIONAL BLEACHING SEQUENCES The unbleached soda and soda-AQ kraft and kraft-AQ pulps of Poplar deltiodes were bleached using. Conventional CEH and CEHH bleaching sequences. The total chlorine demand applied on pulp is .20 of kappa number. The bleach effluent was analysed for the BOD, COD and other derived characteristics. 4 C BLEACHING OF PULPS USING CHLORINE DI-OXIDE The use of elemental chlorine free (ECF), Chlorine dioxide substituted bleaching to produce high brightness pulps with low environmental concern is receiving increased attention with respect to the environmental quality of bleach plant effluent. Untreated ECF bleaching effluents have generally been found to exhibit low toxicity. Also the amount of chlorine required for bleaching is being reduced by the application of non elemental free bleaching chemicals like chlorine dioxide(D), oxygen (0), hydrogen-peroxide. Various sequences has been studied and a brightness level of around 90% ISO brightness has been obtained. The bleach effluent is tested for COD and BOD which is found to be very low as compared to conventional bleaching sequence. The following bleaching sequences has been studied CEDED, OCEDED, DEDED, ODEDED, D(EOP)DED, OD(EOP)DED, D(EOP)DP, 0 D(EOP)DP 4D ELEMENTAL CHLORINE FREE BLEACHING The common definition of elemental free bleaching (ECF) of pulps means the pulps bleached without molecular chlorine. This definition implies that the pulp bleached with chlorine viii dioxide, hypochlorite, oxygen, peroxide etc. comes under the category of ECF bleaching. The demand for elemental chlorine free (ECF) bleached pulps and total chlorine-free (TCF) bleached pulps have really forced the pulp and paper producers to stretch the desired technology to meet these tough demands in terms of environmental pollution load. The soda, soda AQ, kraft, and kraft-AQ pulps of poplar deltoides with and without oxygen delignification were bleached using DEDED, D(EOP)DP and D(EOP)DED bleaching sequences. 4 E ENZYMATIC TREATMENT OF PULP Preparation of xylanase The species of thermophillic fungi exhibiting high xylanse activity with greater stability at high temperature and at near about neutral pH value were used for standardization of bio-bleaching process. Phanerochaete chrysosporium was isolated from decaying wood samples and tested for hyperxylanase productions. The strain was inoculated and grown at temp. of 40°C. After desired growth the enzyme is harvested and stored at below 5 °C. The maximum activity of the enzyme was observed to be on 17th day of incubation. Treatment of Pulp. The soda and soda-AQ, kraft and kraft-AQ pulps of Poplar detoides has been treated with enzyme at different dosages, at different time and temperature. The following bleaching sequences studied are XCEHH, XCEDED, OXCEHH, OXCEDED Results and Discussions: The dose of xyanase 10 I.U./gm pulp for 1 hour was found to be the optimum dosage,It has been interesting to note that the xylanase prepared from Phanerochaete chrysosporium has a significant effect of decreasing the kappa number of about 8.10% . It indicates that this enzyme ix may have some amount of liginase also.The enzyme treated pulp was bleached with conventional and non conventional ECF and TCF bleaching sequences. It has been found that the enzyme treatment of pulp may save about 25-30% of bleaching chemicals for the same brightness. 4 E TOTAL CHLORINE FREE BLEACHING Total chlorine free bleaching have been done using enzymatic treatment, oxygen delignification and hydrogen peroxide. The ECF bleaching sequences have been studied are X(EP)P, OX(EP)P X(EOP)P, OX(EOP)P. The brightness of the pulp during these bleaching sequences studied was found to be more than 70% ISO. 5.0 STUDIES ON WET WEB PROPERTIES Wet web properties of pulps directly effect the paper machine runnability which has direct impact on the final production of the paper. The unbleached pulp of poplar and poplar blends with imported softwood and bamboo were chosen for studies. The wet web strength properties were studied at a freeness level of 350+ 10 ml CSF. For the blend pulp, the constituent pulp were separately beaten and blended. These pulps were studied for wet web tensile index, wet web elongation and tensile energy absorption (TEA) using L&W wet web tensile strength tester as per scan C:31:77 method at the dryness values of around 20%. 6.0 BLENDING STUDIES: The blending studies were conducted as follows: a) Blending the chips of Poplar with long fibred raw material in different proportions, followed by joint cooking and further processing of pulps. b) Cook the short fibred and long fibred material separately and blend the pulps before beating in different proportions. c) Cook the short fibred and long fibred material separately, beat them separately and blend the beater pulps in different portions.