47 Figure 5-1: Effect of CBH I pretreatment and specific refining energy on CSF for BHKP. 53 Figure 5-3: Effect of CBH I pretreatment and mechanical refining on (a) tensile index, (b) burst index, and (c) tear index for BHKP relative to CSF. 59 Figure 5-5: Effect of CBH I pretreatment and mechanical refining in the dark for BHKP relative to CSF.
61 Figure 5-6: Effect of CBH I pretreatment and specific refining energy on CSF for FBSW pulp.
INTRODUCTION
- Background and motivation
- Problem statement
- Research aim and objectives
- Aim
- Objectives
- Dissertation outline
Enzymes allow for energy savings without compromising pulp strength properties (Bajpai et al., 2006; Gil et al., 2009). Xylanases, cellulases, laccases, pectinases and manganese peroxidase are some of the enzymes typically used to aid the refining process (Hyoung-Jin et al., 2006; Torres et al. Excessive enzyme treatment can degrade the inherent strength of the fiber and degrade the strength properties of the pulp (Znidarsic - Plazl et al., 2009).
As a result, mechanical pulp refining accounts for approximately 18 to 25% of total production costs (Pathak et al., 2017).
LITERATURE REVIEW
Papermaking process overview
Consequently, the resulting pulp is rich in cellulose, which is the main ingredient required for paper production. After pulping, the pulp is washed to remove any impurities as well as spent liquor. Consequently, the pulp is first bleached to increase the brightness of the pulp as well as to remove any remaining lignin, which would cause a yellow discoloration of the paper over time (Bajpai, 2010).
After bleaching, the pulp is further cleaned and washed to remove bleaching chemicals and solubilized pulp components (Biermann, 1996).
Refining
- Refining mechanism
- Specific edge load refining theory
- The effect of refining on the fibre morphology
- Variables that affect the refining process
- The effect of refining on handsheet properties
The second step gives rise to fibrillation and increased flexibility of the fibers to improve fiber properties (Torres et al., 2012). The fibers are subjected to a significant refining impact in this phase and the majority of the water in the fiber is compressed. Tensile strength is one of the basic strength properties tested on handsheets in the pulp and paper sector.
Tensile strength is dependent on the inter-fibre bonds, the strength of the fibers and the conditions used to make the handsheet (Fisevora et al., 2009; Welch, 1999).
Hardwoods and softwoods pulp fibres
- Differences between hardwood and softwood fibre morphology
- Refining of hardwood and softwood pulps
The porosity of paper is defined as the voids in the sheet that are not occupied by fibers, also referred to as the air volume in the sheet (Ek et al., 2009a). The difference between HW and SW pulp fibers is also attributed to the different environmental and climatic conditions in which the trees grow (Pokhrel, 2010). Softwood and hardwood pulp fibers respond differently to the refining process and therefore require different refining conditions due to their fiber morphological differences (Bajpai, 2005; Finn, 1991).
Regardless of the pulp fibers used during refining, the refining process is a high energy consuming process.
Enzymes
- Overview of cellulases
- Application of cellulase in the pulp and paper industry
Therefore, these organisms have an enzymatic system that enables them to easily degrade cellulose (Singh et al., 2016). The combination of these three primary forms of cellulases ensures complete hydrolysis of the cellulose chain (Figure 2-13) (Torres et al., 2012). Initial reports suggested that both CBH I and CBH II act on the non-reducing ends of the cellulose chain (Teeri et al., 1998).
A reduction in the time spent in the drying section reduces the energy consumption and thus reduces the investment costs (Pathak et al., 2016).
Future prospect of enzymes in refining
Process conditions such as temperature, pH, reaction, consistency and enzyme dosage should be optimized before refinement (Pathak et al., 2016; Singh & Bhardwaj, 2010). Currently, enzymes are applied only in specific mill applications in the pulp and paper industry. Refinement enzymes currently used include cellulases, xylanases, laccases, amylases, proteases and pectinases (Manorma, 2015; Torres et al., 2012).
Academic and industrial institutions are conducting the necessary research, and recently designed techniques are expected to significantly reduce the cost of enzyme production, while also improving the properties of these enzymes (Bajpai, 2005; Pathak et al., 2016; Tripathi et al., 2008). ).
MATERIALS AND METHODS
Raw materials
- Enzyme
- Pulps
Methods
- CBH I characterisation
- Bijective studies on pilot refiner
- Pulp quality evaluation
- Computational modelling
- Optimisation of pilot refining parameters
- Scanning electron micrographs analysis
CBH I CHARACTERISATION
Analysis of CBH I characterisation data
- Results
- Discussion
BIJECTIVE STUDIES ON THE PILOT REFINER
Pilot refining bijective study for the BHKP
- Effect of CBH I pre-treatment and refining on the CSF drop
- Effect of CBH I pre-treatment and refining on the fibre morphology
- Effect of CBH I pre-treatment and refining on the handsheet properties
- Recommended bijective refining run for the BHKP
Pilot Refining bijective study for the FBSW pulp
- Effect of CBH I pre-treatment and refining on the CSF drop
- Effect of CBH I pre-treatment and refining on the fibre morphology
- Effect of CBH I pre-treatment and refining on the handsheet properties
- Recommended bijective refining run for the FBSW pulp
Pilot refining bijective study for the UBSW pulp
- Effect of CBH I pre-treatment and refining on the CSF drop
- Effect of CBH I pre-treatment and refining on the fibre morphology
- Effect of CBH I pre-treatment and refining on the handsheet properties
- Recommended bijective refining run for the UBSW pulp
Refining bijective studies discussion and concluding remarks
OPTIMISATION OF REFINING PARAMETERS
- BHKP optimisation
- BHKP computational modelling
- Analysis of BHKP pilot refiner optimisation results
- FBSW optimisation
- FBSW computational modelling
- Analysis of FBSW pilot refiner optimisation results
- UBSW optimisation
- UBSW computational modelling
- Analysis of UBSW pilot refiner optimisation results
- Analysis of scanning electron micrographs
Finally, SEM micrographs of the fiber morphology of the optimal run and two runs with and without CBH I are presented.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
In the second phase, the effect of CBH I as a refining enzyme was investigated using the byective diagram technique. In addition, CBH I pretreatment led to an improvement in macrofibrillation, which enhanced the tensile and burst strength developments. In contrast, with the unbleached pulp, the fiber length was preserved, leading to an improvement in the tear strength development.
This suggests that high intensity combined with the enzyme treatment lowers the fiber's intrinsic strength. The pulps responded better to the lower intensity run (SEL-); this type of treatment resulted in fiber strength preservation. In addition, the low-intensity treatment combined with the enzyme pretreatment improved the macro-fibrillation compared to the REF runs.
For FBSW cellulose, both GA and GC treatments improved fiber development, leading to improved board strength properties compared to the enzyme-treated reference batch. BHKP and UBSW had the REF plate design as the optimal refining plate. Scanning electron micrographs revealed that the enzyme-treated reference fiber mesh had better fibrillation and low mass, leading to improved strength properties compared to the untreated reference series.
Overall, considering all the data, the CBH I enzyme has the potential to transform the refining process towards a more environmentally friendly, cost-effective and efficient operation compared to the conventional method. However, more research is still required before the enzyme can be made commercially available to the pulp and paper industry.
Recommendations for future work
The impact of Pinus patula chemical and physical properties on pulp and strength properties. Application Of Enzyme For Improving The Acacia APMP Pulping And Mixed Pulp Refining For Printing Paper Making In Vietnam. Low consistency refining of mechanical pulp: the relationship between plate pattern, operational variables and pulp properties.
Effect of cellulase refining on the properties of dried and never dried eucalyptus pulp. Production of cellulases and use of cellulases and auxiliary enzymes in the pulp and paper industry: a review. Strength properties of paper made from a mixture of softwood kraft pulp and pulp, reinforcement and stratification of sheets.
Cellulase-assisted refining of chemical pulps: Impact of enzymatic loading and refining intensity on energy consumption and pulp quality. Low consistency refining of softwood-hardwood bleached kraft blends: effects of refining power. The effect of low-consistency refining of eucalyptus species on the fiber morphology and strength properties of the pulp Durban: University of Kwazulu Natal.
Evaluation of cell wall modifying enzymes for improved pulp refining of two eucalyptus species. The beatability-enhancing effect of crude cellulase from Aspergillus niger on bleached Simao Pine Kraft pulp and its mechanism of action.
Procedure for pulp consistency determination
Procedure for pulp CSF determination
Place the drainage chamber on the higher support bracket, close the lower cover and open the upper cover and air valve. Set up a container to collect the discharge from the bottom opening and a graduated cylinder of freedom to accept the discharge from the side opening. To obtain a uniform solution, stir the stock thoroughly in the 2.5 L, then properly measure 1000 ml into a clean 1 L cylinder.
After about 5 seconds have passed since adding the stock, fully open the air valve in one motion. When the side discharge has stopped, test the temperature of the filtrate with a thermometer and record the volume discharged from the side vent in milliliters (freedom) to the nearest 10 ml. Combine the pulp from the chamber in a large enough plastic cup with drainage from the side and bottom vents.
Using the TAPPI Standard Technique correction tables, calculate the corrected freedom based on the measured temperature and consistency.
Procedure for handsheet formation
Make sure the dryer temperature is 93±4°C and place one hand sheet at a time in the dryer. Remove the handsheet from the dryer and immediately weigh it using a calibrated and verified laboratory scale. Make sure the handsheet weight is within the specified range for the targeted gram weight.
Procedure for handsheet testing
Adjust the clamping mechanism to provide enough clamping pressure to prevent the hand sheet from slipping out of the clamps. Insert the test piece (consisting of six rectangular sheets) between the two clamps and fasten the clamps. If the pointer is fitted, gently catch the pendulum on its return swing with your hand without changing the position of the pointer.
Change the switch to 'open', insert the test piece into the measurement gap, then change the switch to close. Allow the pressure plane to hold the test piece by allowing the pressure plane to move gradually and gently towards the anvil at a speed less than 3 mm/s, so that any punching effect is avoided. At the end of the 1 s to 2 s dwell time, record the thickness of the micrometer reading.
Make sure that the temperature of the corrugation rolls is 175 °C ± 8 °C, then insert the test strip into the corrugation rolls with its length perpendicular to the gap. Place the comb over the ribbed test strip on the rack, making sure it is firmly pressed against the valleys of the rack. The adhesive tape must be long enough that it is in contact with the ends of the corrugated test strip.
After rebuilding, perform the test by placing the corrugated tape down in the center of the pressure tester's bottom plate. Cut test strips 70 mm long and 15 mm ± 0.1 mm wide from the central region of the hand sheet.
The effect of temperature on CBH I activity
To determine the activity, a conversion to standard concentration units of IU/mL was performed using Microsoft Excel, the results are in Table C-2. The individual activities of glucose and cellobiose in UI/mL were then combined to give the total CBH I activity.
The effect of pH on CBH I activity
The concentration of glucose and cellobiose was then converted to standard units of IU/mL from mg/mL to calculate CBH I activity (Table C-5). The individual concentration of glucose and cellobiose were then combined to give the total CBH I activity (Table C-6).
Thermostability profile for CBH I
Time (min) mg/mL μmol/mL μmol/mL/s nkat/mL x DF IU/mL Residual activity. The individual activities of glucose and cellobiose were combined to obtain the total activity and total residual activity of CBH I, the results are shown in Table C-9. This section presents the raw data obtained for two-way refining runs performed on the 12-inch pilot refiner for each pulp during Phase 2.
CSF raw data
Handsheet and fibre properties raw data
132 Table D-7: Sheet property results obtained for six bilateral refining processes performed for BHKP. Refining data obtained for the pilot bijective refining studies were modeled using custom modeling software to determine the optimal refining parameters for each pulp.
Optimisation of refining parameters raw data
The green shaded column indicates the optimum refinement point as indicated by the custom bijective modeling software.
One-way ANOVA statistical analysis raw data
