ENZYMATIC DEINKING OF PHOTOCOPIER WASTE PAPERS

Abstract

In response to increasing environmental awareness and regulatory pressures, the paper industry expects to recover and recycle all major grades of paper. Due to inadequate availability of indigenous waste papers, Indian mills rely heavily on imported waste paper to meet the raw material demand of recycled fibres. To minimize the import of costly papers, relatively little attention has been given to develop novel methods for the recycling of indigenous waste papers such as photocopier and laser printed papers having good quality chemical pulp but hard to deink toner ink. Toner ink contains styrene and acrylate in its chemical composition and gets thermally fused with the fibre surface. Conventional chemical treatment is not effective to detach this ink from the fibre surface. Therefore, it is important to induce suitable methods, which can increase the deinking efficiency for efficient recycling of this new source of waste papers to manufacture paper products. Consequently, the present research work aims to develop an effective, ecofriendly enzymatic deinking process for photocopier waste papers. In this regard, mainly cellulase and xylanase enzymes have been reported for the efficient ink dislodgement from the fibre surface by peeling off mechanism. The enzymatic treatment has been reported to improve as well as deteriorate the strength properties with enhanced drainage of recycled fibres. Therefore, there is an intense need to find the suitable enzyme preparations, which are able to improve the deinking efficiency (DE) and drainage, without affecting the strength properties. For this reason, this study aims to produce crude enzyme preparations, containing high activity for cellulase and xylanase enzymes from the isolated fungi and subsequently, to investigate their potential to deink photocopier waste papers in comparison to commercial enzyme and conventional chemicals. This research work has been distributed into five chapters.  The first chapter deals with the introductory literature review of global and Indian scenario of waste papers utilization and enzyme industry. This part also covers basic information and literature review about the fungi, enzymes, fermentation and deinking.  The second chapter describes the materials and methodology for the enzyme production and deinking experiments. Different environmental factors (Inoculum size, incubation days, incubation temperature, initial pH of the fermentation medium, particle size of the selected LCW) and nutritional factors (Carbon sources: different LCW and their combinations, nitrogen sources: different doses of soluble inorganic, soluble complex organic and insoluble plant based, surfactants) were analyzed for enzyme production by both the fungal isolates individually. Various additives like sugars, vitamins, amino acids, metal ions and chelators were evaluated. A wide range of pH and temperature values was used for the determination of their optima for the enzymatic activity. Crude enzyme Abstract ii supernatant was pre-incubated at optimum pH and temperature for various times to determine the pH and thermal stability, respectively. Different parameters for deinking of photocopier waste papers were optimized using chemicals, commercial enzyme and crude enzyme of the isolated fungal strains. The deinking performance of the crude enzymes (from the isolated fungal strains) were compared with chemical and enzyme treated pulp/handsheets in terms of deinking efficiency, residual ink, yield, freeness, drainage time, optical (brightness and opacity) strength properties (tensile, burst, tear and folding endurance) dirt count and effluent load using standard tests methods. Characterization of the pulps has been done using different techniques like Scanning electron microscope (SEM), Fourier transform infrared spectroscope (FT-IR) and X-ray diffractometer (XRD).  In the third chapter, the efforts have been made to find the optimum fermentation conditions for the enhanced production of industrially important cellulase and xylanase by the two newly isolated fungal strains i.e. Trichoderma harzianum PPDDN-10 NFCCI- 2925 and Coprinopsis cinerea PPHRI-4 NFCCI-3027. This study also supports that solidstate fermentation (SSF) process is suitable for these lignocellulosic enzyme production. In the present study, T. harzianum and C. cinerea both are reported to utilize effectively cheap wheat bran (WB) as carbon source, which stimulate the production of both cellulase and xylanase. The combinations of the WB with other lignocellulosic wastes (LCWs) did not improve enzyme production. T. harzianum is able to produce the maximum enzyme production using ferrous ammonium sulphate (as nitrogen source) in just 4 d at 34 °C. For C. cinerea, mycological peptone is used as nitrogen source to produce the cellulase and xylanase enzyme in 8 d at 34 °C. The particle size of the WB has shown positive as well as negative effect on the enzyme production, but WBas such (with mix particle sizes) has shown the comparable results with the optimum particle size. Alkali pretreatment of WB has resulted in the reduced enzyme production. The addition of sugars except cellobiose acts as repressor towards enzyme production for both the fungi. The additives (vitamins, amino acids, metal ions and chelators) have influenced the enzyme production significantly. Characterization of the crude enzyme of both the fungi shows the maximum activities at optimum pH 5.5 and temperature 55–60 °C with good stability (even up to 6 h).  Fourth chapter covers the deinking studies of photocopier waste papers. This study deals with the deinkability potential as well as pulp quality evaluation of photocopier waste paper using conventional chemicals, commercial enzyme (cellulase) and lab produced crude enzyme preparation containing cellulase and xylanase from isolated fungal strains. The chemical deinking is not able to improve DE beyond 75.9%. Different operational parameters are optimized such as point of enzyme addition, enzyme dose, Abstract iii pulp consistency and reaction time to achieve the maximum possible deinking efficiency without affecting the paper strength properties. The enzymatic deinking experiments are performed in acidic range because of enzyme‘s optimum pH. Commercial cellulase and lab-produced enzymes have shown the maximum DE of around 93.9-95.2% under different optimum conditions. The addition of these enzymes at hydrapulping stage at medium pulp consistency is found to improve the DE. It is observed that lab produced crude enzymes are responsible for the increase in the brightness. The results have indicated that the enzymes have the potential to maintain or improve the strength properties by promoting the fibrillation, if they are used in optimized conditions of dose and time. The higher dose and longer reaction time than the optimum value found to be detrimental to the fibre surface. Commercial cellulase and crude enzymes from the isolated fungal strains have improved ink removal efficiency by 23.6 to 25.4% and freeness by 19.6 to 21.6%, with the reduction in drainage time by 11.5 to 17.3% than chemical deinking. The strength properties like tensile and burst indices are observed to improve by 2.7 to 6.7% and 13.4 to 23.9%, respectively. The folding endurance is also 10.3 to 15.9% higher with respect to chemical treatment.The tear index is reduced by 7.6 to 21.9% in all the enzymatic treatment. The ISO brightness is improved by 3.2 to 5.2% when using crude cellulase and xylanase of the isolated fungal strains, while commercial enzyme reduces 2.1% ISO brightness than the chemical deinking.The results of deinking efficiency and freeness are comparable with commercial cellulase, but the strength properties significantly improved. The ISO brightness of crude cellulase and xylanase treated pulps are higher than the commerical cellulase treated. BOD/COD ratios of effluent from enzymatic deinking with crude enzymes (0.59 and 0.55) have been observed to be higher than that of chemical deinking (0.45) but almost equal to commercial cellulase (0.57). Characterization of the enzymatic deinked pulps has shown better fibrillation than chemical treated (SEM analysis) thus exposing more hydroxyl groups (FT-IR analysis). The crystallinity indices are found to be higher for the enzymatic treated pulp than chemical treated pulps (XRD analysis). The lower effluent load during the enzymatic treatments makes the process ecofriendly.  The final chapter concludes that isolated fungi T. harzianum PPDDN-10 NFCCI-2925 and C. cinerea PPHRI-4 NFCCI-3027 are capable to produce the cellulase and xylanase production to deink the photocopier waste papers. These crude enzymes and commercial cellulase have the potential to replace the conventional chemicals used to deink the photocopier waste papers without deteriorating the handsheet strength properties after the improvement in the freeness.