PULPING STUDIES OF EUCALYPTUS TERETICORNIS AND DENDROCALAMUS STRICTUS

Abstract

The growth of the Indian pulp and paper industry may come up to the global standards only by addressing the core issues like availability of the raw materials, technology, energy and environment and competition with overseas market. The global concerns related to preservation of forests from pulping and bleaching processes have led us towards exploration of alternate cellulosic fibrous resources other than wood and new pulping and bleaching processes that are compatible with the environment without sacrificing product quality. Now-a-days, public awareness about environmental hazards compel the government to make more stringent laws against pollution generating industries. Therefore, the present investigation aimed at developing an environmental benign technology for the production of pulp using short and long fiber lengths fibrous raw materials i.e. Eucalyptus tereticornis and Dendrocalamus stictus. The study was focused to mitigate pulp kappa number before bleaching by putting a separate pre-bleaching stage i.e. oxygen delignification, enzyme treatment stage and using different digester additives and to investigate their impact on pulp kappa number, pulp yield and mechanical strength properties. The kraft pulp was subjected to conventional, elemental chlorine free and total chlorine free bleaching sequences to produce high brightness pulp and observe its effect on paper properties and pollution load generated during bleaching. The detailed morphological and anatomical features of E. tereticornis and D. stictus were conducted and chemical characterization of the two raw materials was carried out in order to assess their suitability for pulp and papermaking. E. tereticornis revealed that it was diffused porous and vessels were solitary which were surrounded by parenchyma and lignified sclerenchyma cells. The fibers of E. tereticornis were non-septet with distinctly bordered pits and thick-walled. Being thin walled and highly perforated, the vessel cells were present during pulping process. On the other hand, D. strictus has a strong sheath of sclerenchyma cells encircling the conductive tissues and xylem and phloem cells made the characteristic shape of the vascular bundle. Both the raw materials were subjected to proximate chemical analysis assessing their suitability for pulp and paper making. Proximate chemicals indicated that both the raw materials required extreme cooking conditions owing to higher lignin content for producing bleachable grade pulp. E. tereticornis could be stored for a longer period, compared to D. strictus. Kraft process was used to produce pulp of E. tereticornis and D. stictus. The various operating process variables like maximum cooking temperature, cooking time and active alkali dose and sulphidity were optimized for kraft process and effect of anthraquinone and surfactant II individually and in combination were then observed. An active alkali dose of 18% (as Na2O), sulphidity 20% and cooking time of 90 min at a maximum cooking temperature 1650C respectively for E. tereticornis and D. stictus were found optimum for kraft pulping. AQ (0.05%) as a pulping additive accelerated the delignification rates along with improvement in screened pulp yield and decreased the pulp reject. An introduction of AQ (0.05%) and surfactant (0.05%) individually and in combination at optimum cooking condition enhanced pulp yield and reduced the pulp kappa number and pulp reject for E. tereticornis and D. strictus. Both the raw materials showed optimum mechanical strength properties at a beating level of 40±1 0SR. Also, all the mechanical strength properties such as burst index, tensile index, and double fold improved with increasing alkali doses at each beating level. The maximum strength properties were obtained at an alkali dose of 18% (as Na2O) because of the removal of lignin and exposure of cellulose for bonding. Oxygen treatment reduced kappa number by 33.6 and 36.2% and screened pulp yield by 4.6 and 3.3% in case of E. tereticornis and D. strictus compared to kraft pulp. The enzymatic extraction pretreatment of E. tereticornis and D. strictus kraft pulps mitigated the total chlorine demand by 1.05 and 1.24% for CEpH1H2 bleaching sequence, for achieving high degree of brightness, bleached pulp yield, pulp viscosity, and low post color in comparison to their respective controls. The mechanical strength properties of E. tereticornis and D. strictus XECEpH1H2 bleached pulps decreased except porosity and apparent density compared to their respective controls. The enzymatic pretreatment stage also reduced the AOX formation in bleach effluents of E. tereticornis and D. strictus by 9.43 and 16.9% respectively compared to CEpH1H2 bleaching sequence. The introduction of oxygen pre-bleaching stage before D0EpD1 sequence showed an improvement in pulp brightness by 2.9 and 3.2% for E. tereticornis and D. strictus respectively compared to their respective controls. The final bleached pulp viscosity of OD0EpD1 bleached pulps decreased by 9.34% for E. tereticornis and 3.84% for D. strictus compared to their respective controls. The decrease in post color number for OD0EpD1 bleached pulps were 44.7 and 53.3% for E. tereticornis and D. strictus respectively compared to their respective controls. All the mechanical strength properties of OD0EpD1 bleached pulps of E. tereticornis and D. strictus like burst index, tensile index, tear index and folding endurance except porosity and apparent density decreased compared to their respective controls. Similarly, AOX in combined effluent generated during OD0EpD1 bleaching sequence of E. tereticornis and D. strictus reduced by 38.7 and 23.4% compared to their respective controls. III Oxygen delignified pulp followed by AZD0EpD1 bleaching sequence improved pulp brightness by 1.8 and 2.9% for E. tereticornis and D. strictus respectively compared to their respective controls. Pulp viscosity of OAZD0EpD1 bleached pulps decreased by 12.0% for E. tereticornis and 3.24% for D. strictus compared to their respective control. The post color number of E. tereticornis and D. strictus bleached pulps decreased by 35.9 and 33.3% respectively compared to their respective controls. Oxygen bleached pulp showed a reduction in burst index by 4.94%, tensile index 19.5%, tear index 14.5% and folding endurance 12.7% for E. tereticornis and burst index 4.86%, tensile index 19.2%, tear index 5.71% and folding endurance 11.7% for D. strictus compared to their respective controls. The oxygen bleached pulps of E. tereticornis and D. strictus also showed a reduction in AOX by 63.0 and 59.8% respectively compared to their respective controls. The kraft pulps of E. tereticornis and D. strictus were bleached by two different TCF bleaching sequences i.e. OA(EP)QP1P2 and OAZ(PO)P. It was observed that the pulp yield, brightness, viscosity and post color number were reduced by 0.20, 0.50, 6.70 and 57.1% for E. tereticornis and 0.40, 0.20, 8.92, and 43.2% for D. strictus respectively compared to another TCF bleaching sequence i.e. OAZ(PO)P. The mechanical strength properties of bleached pulps of OA(EP)QP1P2 of E. tereticornis and D. strictus stood on a better position compared to bleaching sequence OAZ(PO)P at a fixed beating level of 40±1 0SR. It might be due to carbohydrate degradation during pressurized oxygen stage in OAZ(PO)P bleaching sequence. It was further validated by increase in COD and color of combined effluent of E. tereticornis and D. strictus generated during OAZ(PO)P sequence.