Why pulp consistency is one of the main factors in the pulp refining?4 answersPulp consistency is a crucial factor in pulp refining due to its significant impact on refining efficiency, power consumption, and ultimately pulp quality. Studies have shown that varying pulp consistencies influence the power consumption and refining efficiency in both low-consistency (LC) and high-consistency (HC) refining processes. In LC refining, power consumption is directly affected by pulp consistency, with higher consistencies leading to increased net power and refining efficiency. On the other hand, in HC refining, optimal operation conditions are closely tied to pulp consistency, as deviations from the optimal point can rapidly deteriorate pulp quality due to reduced fiber length and strength. Therefore, controlling and optimizing pulp consistency during refining processes is essential for achieving desired pulp quality while managing energy consumption effectively.
How the pulp mass moves in the refining zone?5 answersThe movement of pulp mass in the refining zone is facilitated by various mechanisms. In a high-consistency conical pulp refiner, forces acting on the pulp are analyzed to understand the flow dynamics along the plate, considering both flat and conical refining zones. Pulp slurry in a pulp refiner undergoes a screw pump action due to the spiral pattern of grooves and lands on the refiner members, creating a pinching action on pulp fibers. Additionally, in an apparatus for refining pulp stock, centrifugal force accelerates the pulp radially towards the grinding zone through sector-shaped channels between rotating disc members. Moreover, a chemical refining process involves passing pulp in turbulent flow through an elongated reaction zone under specific conditions to achieve chemical modification without excessive mechanical working. These combined mechanisms ensure efficient movement and treatment of pulp mass in the refining zone.
How can fiber surfaces be physically modified?4 answersFiber surfaces can be physically modified through various methods. One approach is the use of physical treatments such as low- and high-energy radiative methods, electrical discharges, and UV treatments. These treatments can cause cleaning, purification, defibrillation, and chemical modification of the fiber surface, resulting in improved wettability and compatibility with polymers in composite formulations. Another method involves the grafting of carbon nanotubes onto the surface of carbon fibers using a reactive polymer, which enhances the bonding between the fibers and nanotubes and improves the mechanical properties of the composite. Additionally, the surface of natural fibers can be altered through chemical, physical, and biological methods, with physical treatments including ionizing radiations, e-beams, and vacuum UV treatments. Furthermore, the surface of carbon fibers can be modified by growing a conductive polymer on their surface, resulting in improved tensile strength, modulus, and interfacial adhesion in composite materials.
What are the different methods for extracting bast long fibers?5 answersDifferent methods for extracting bast long fibers include water retting, dew retting, chemical extraction, micro-organism techniques, and degumming. Water retting and dew retting are traditional methods that involve soaking the fibers in water or exposing them to dew for a specific period of time. Chemical extraction methods involve the use of chemicals to separate cellulose and non-cellulose parts of the fibers. Micro-organism techniques, such as fungi and bacteria formation, can be used to degrade lignin and pectin materials in the fibers, increasing the cellulose content. Degumming is a necessary step to separate cellulose and non-cellulose parts of the fibers, and degumming methods are being developed to be more environmentally friendly and efficient.
What are the different curing periods for fiber glass?4 answersThe different curing periods for fiber glass mentioned in the abstracts are as follows: In the study by Canbaz et al., the concrete cubes were cured for 3, 7, and 28 days using standard curing in the water tank and for 4 and 8 hours using steam curing. Sharma et al. conducted curing studies on fiber reinforced epoxy nanocomposites at different cure temperatures (70 °C, 80 °C, 85 °C, 95 °C) and for different curing time periods (7 h and 10 h). Meng and Zhang investigated the curing time of glass fiber/urethane composites at temperatures of 150 °C, 160 °C, and 170 °C, and found that the resin system cured within 8-10 min at 150 °C and 160 °C, and within 5 min at 170 °C. Madhukar et al. conducted tests on single fiber glass-epoxy and graphite-epoxy composites and observed significant tensile stresses in the fibers when the temperature was raised from the first to the second dwell period during curing. Overton and Ling proposed a method for curing a coated fiber with two curing stages separated by a cooling stage or a distinct time interval.
What is the reason for the decrease of tensile strength after the optimum amount of fibre reinforced concrete?4 answersThe decrease in tensile strength after the optimum amount of fiber reinforced concrete is due to the high volume of fibers causing difficulty in concrete compaction and lowering its workability. When the fiber content exceeds the optimum amount, the concrete becomes less cohesive, leading to a reduction in strength. Additionally, an increase in fiber dosage in the concrete mix leads to a decrease in its density and an increase in water absorption percentage. This is because the increase in fiber content creates more air voids in the concrete, reducing its density and increasing its water absorption. Therefore, beyond the optimum fiber content, the concrete loses its strength and workability, resulting in a decrease in tensile strength.