STUDIES ON SOME POTENTIAL NON-WOOD FIBROUS PLANTS FOR PULP & PAPER MAKING

Abstract

The paper industry in India has met the various challanges by adopting itself to the changed conditions. The country has an installed capacity of about 26.0 lakh tonnes producing a large variety of papers from a variety of raw materials. The target set for a paper capacity by the year 2000 A.D. are 42.5 lakh tonnes for paper and 12.9 lakh tonnes of newsprint. It is a well known fact that present forest resources can not meet the demand of raw material even for the existing units leaving aside the additional requirement for the future growth of this industry. The forest based raw materials are in tremendous short supply and can not meet the projected paper capacities. Even with fuller utilization of bagassewheat and rice straws, the supply position will be far from satisfactory for meeting the set target. Further the depleting forest cover and the thrust to, conserve ecological balance will force the industry to look alternative fibrous raw materials other than wood and bamboo. The subject matter of the thesis is broadly divided into six chapters. A summarised account of the results of above mentioned investigations are given as below: The first chapter of the thesis is an account of the various fibrous raw materials viz., hardwood, bamboo, bagasse, wheat & rice straw and other unconventional raw materials, which are being used for pulp and paper making. On the basis of general criteria for choosing a fibrous raw material for pulp and paper making, the following three potential non-wood fibrous raw materials have been chosen for the present investigations: 1. Sesbania aculeata 2. Sesbania sesban 3. Cajanus cajan All these non-wood fibrous raw materials belong to a group which is fast growing in nature and producing soft white wooded plants, having good II characteristics for pulping as well as for paper making. Second chapter of the thesis is an account of the anatomical and chemical studies on S.sesban, S.aculeata and C.cajan non-wood fibrous plants. For morphological characteristics, all these non-wood fibrous plants have been analysed for their density, fibre length, fibre diameter, lumen diameter and cell wall thickness. The morphological characteristics of these non-wood fibrous plants clearly indicated that the plant of S.sesban consist of a large number of vessels, fibres having thick walled with narrow lumen and the plant of S.aculeata consist of less number of vessels and fibres having thin walled with wider lumen while the plant of C.cajan also consist of less number of vessels and fibres having thin walled with wide lumen. The results of proximate chemicals analysis of these non-wood fibrous plants indicated that these are having a high percentage of carbohydrate fraction with low lignin content and the extractives are comparable with bamboo. On the basis of the anatomical and chemical studies, it was concluded that S.aculeata, C.cajan and S.sesban are quite suitable non-wood fibrous raw material for pulp and paper maiking'* Chapter third deals with the studies on carbohydrates of these non-wood fibrous plants. The holocellulose, alpha cellulose, cellulose(by nitration method) and hemicellulose were isolated from those plants. The holocellulose fractions were analysed for ash, Klason lignin, alpha cellulose, pentosan hemicellulose, acetyl content, methoxyl content and uronic anhydride. The alpha cellulose and cellulose were analysed and the results of analysis indicated that the alpha cellulose of these plant are having glucan, mannan, xylan alongwith arab,an, while the cellulose showed the complete absence of arab,an fraction. The cellulose (isolated by nitration method) seems to be more pure cellulose as compared to alpha cellulose, as it was having higher amount of glucan fraction. III The thin,,. longitudinal and transverse sections having thickness about 20 to 30 p.have been cut and these were further delignified and the hemicellulose were also removed from these delignified sections. The infrared spectrums of holocelluloses,alphacelluloses, celluloses, untreated sections, delignified sections and delignified sections after removing hemicellulose, were recorded. The X-ray diffractograms of alpha cellulose and cellulose were also recorded. The hemicelluloses were.analysed by G.L.C. and it indicated the presence of various sugars in different proportion. The hemicelluloses(18% KOH fractions) were also analysed for their ash, pentosan, methoxyl content, acetyl content, and uronic acid content. On the basis of above studies it was•.concluded that the nature of carbohydrate fraction of these plants resembled some what to bamboo and tropical hardwood carbohydrates. Chapter fourth deals with thestudies on lignins, isolated from these plants by different methods. The various types of lignins viz., Klason,-Willstatter, organosolv and thiolignins were isolated. The Klason, Willstatter and organosolv lignins were further subjected to analysis for their molecular weight, C, H and CH30-content and their C9- formulas were also calculated..The thiolignins were also analysed for their sulphur content, Klason lignin, methoxyl and C and H contents. All these lignins were further subjected to alkaline nitrobenzene oxidation to know the various building units of lignins which are present in these non-wood fibrous plants. The infrared and ultra violet spectra of all these lignins were recorded. The result of alkaline nitro benzene oxidations clearly indicated that the lignins of these plants are made,up of guaiacyl-, syringyl-, and p-hydroxyphenyl propane units. On the basis of above studies, it was concluded that the lignins of S.sesban, S.aculeata and C.cajan resembled with bamboo and other tropical hard wood lignins rather than soft wood lignins. Chapter fifth deals with the varoius pulping studies on these non-wood fibrous plants. It is further divided into six sub sections as follows: Iv Section-A, deals with the soda and soda-AQ pulping studies on these plants. The optimization of pulping conditions was made. The results of soda pulping revealed that a temperature of 165°C and 18% active alkali doses for S.sesban, C.cajan and 16% active alkali doses for S.aculeata may be taken as optimum. In alkaline delignification of these non-wood'fibrous plants, two distinct overall.mechanisms with different rate constants, each of which resembled a first order reaction pattern are involved. The Arrhenius activation energy of bulk delignification during soda pulping of S.sesban and C.cajan were found to be 91.90 KJ/mole and 84.14 KJ/mole respectively, while in the case of S.aculeata it was 80.34 KJ/mole. The soda pulps were bleached with conventional CEHH bleaching sequence giving pulps of around 76%(Elrepho) brightness. On the basis of results of pulp evaluation it was concluded that both the bleached and unbleached soda pulps of these plants showed good strength characteristics. An optimum freeness level for these pulps may be considered around 42+2 °SR. The addition of AQ has a favourable influence on both the pulp yields and all the strength properties determined except for brightness. The spent liquors of soda cooks were analysed for their solids, residual alkali, inorganics, organics, pH, viscosity, °TW and calorific values. The calorific value ranges from 11702 KJ/Kg. to 12017 KJ/kg. Section-B, deals with thekraft and kraft-AQ pulping studies on these non-wood fibrous plants. The optimization of pulping condition have been done. On the basis of experiments, it was 'concluded that a temperature of 160°C and 20% sulphidity and 14'% active alkali charge for S.aculeata and 16% active alkali charge for S.sesban and C.cajan, may be taken as optimum for the kraft pulping of these non-wood fibrous species. These results also indicated that the chemical requirement is about 2-3% less than that required for the pulping of bamboo and other tropical hardwoods. Besides the pulping conditions are mild, the total pulp yield is around 44 to 51% in the Kappa no. range of 22-30. The Arrhenius activation energy of bulk delignification in kraft pulping of S.aculeata, V S.sesban and C.cajan were found around 81.59, 86.69 and 90.79 KJ/mole respectively. These pulps showed good response towards bleaching and CEHH bleaching sequence was used to get pulps with a brightness levels of 76-80%(Elrepho). The pulps freeness in the range of 42+2°SR seems to be optimum for the development of strength properties. Both the unbleached and bleached_ -kraft pulps of these non-wood fibrous plants showed good strength properties. The use of AQ in conjunction with kraft process to produce bleachable grade pulps from these non-wood fibrous plants is beneficial in increasing the rate of delignification and enhancing the pulp yields. The total solid contents of the kraft spent liquors of these non-wood fibrousplants are towards little higher side thereby increasing the calorific values. The silica contents were also found to be quite low. The less silica content and higher calorific values of the spent liquors are an advantageous factors towards the energy conservation in chemical recovery process. Section-C, deals with the alkaline sulphite(AS) and AS-AQ pulping on these non-wood fibrous plants. The pulping studies were made using different percentage of sodium sulphite and sodium hydroxide, 10.35% sodium sulphite (as Na20) and 4.65% sodium hydroxide(as Na20) for S.aculeata, 10.8% sodium sulphite (as Na20) and 6.2% sodium hydroxide(as Na20) for S.sesban and C.cajan may be considered as optimum for alkaline sulphite pulping. With increased alkalinity the rate of delignification also increased and approached to that of kraft. The AS unbleached and bleached pulps of these plants showed good strength properties. The tearing strength is largely governed by the alkalinity of the cooking liquor and reaching maximum at a terminal pH of spent liquors in the range of 9-11. These AS pulps showed good response towards optical properties and are having decidedly superior values for both the brightness &ftd opacity. The pulps with a brightness level of about 76-79%(Elrepho) were obtained as a result of CEHH bleaching sequence. The addition of a small amount of AQ during AS pulping showed a significant influence both on pulping characteristic and over all strength properties of these pulps. The AS-AQ pulps showed good response towards VI bleaching and produced more brighter pulps. Section-D, deals with the semi alkaline sulphite(SAS) and SAS-AQ pulping studies on these non-wood fibrous plants. The pulping studies were made using different amounts of Na2SO3 and Na2CO3, in order to. know the optimum alkali ratio. The cookings were also made at different time to know the effect of cooking time during the course of pulping. The results of SAS pulping clearly indicated that the alkali ratio should be in the range of 0.80 - 0.85 to achieve as low Kappa No. as possible. A temperature of 170°C and total alkali charge from 16-20% (as Na20) may be taken as optimum for the SAS pulping of these plants. The AQ has a considerable effect in SAS pulping in reducing both Kappa no. and time at temperature. The pulps with a brightness level of 65-70%(Elrepho) were obtained as a result of CEH bleaching sequence. The pulp brightness were further increased upto a level of 78%(glrepho) by using CEHH bleaching sequence. Both the unbleached and bleached SAS pulps have good bonding ability and thereby showed good values for strength properties.. Section-E, deals with neutral sulphite semichemical(NSSC) pulping studies on these non-wood fibrous. plants. The optimization of sulphite/carbonate ratio was done by varying the ratio of sulphite to carbonate on a molal basis with a:canstent Na20 charge of 6% for S.aculeata and 8% for S.sesban and C.cajan. The cookings were made at a temperature of 160°C using different time at temperature ranging from 30-120 minutes. For high yield NSSC,pulps of short cooking cycle a sulphite/carbonate ratio of (60:40) appeared to be acceptable. The pulps with higher brightness resulted from greater amount of sulphite. The maximum values for strength properties were obtained at sulphite to carbonate ratio of 70:30 and a freeness level of around 42+2°SR. The pulps obtained during NSSC pulping of these plants showed satisfactory strength properties for packaging grades of papers. VII Section-F, deals with the blending studies of kraft pulps of these plants with pine kraft pulp. The present studies revealed that the addition of small quantities of unbleached soft wood pulp(atleast 5 %) in a furnish base having kraft pulps of these non-wood fibrous plant caused a definite improvement in nearly all the strength properties of the paper in comparison with the properties of individual pulps of these plants. The blending studies were conducted by mixing these two pulps after beating them separately. The improvement in tear index was more than the burst and tensile. Chapter six deals with the over all conclusions of the present studies.