| Fly ash is a powdery industrial solid waste generated by coal-fired power plants. Large amount of fly ash has lower utilization rate and causes environmental p ollution and occupation of land. It is the combination of developing novel paper filler and resource utilization of fly ash to use fly ash based porous calcium silicate filler(FACS) as paper filler. In addition, the research on FACS filler has great significance for the conservation of land resources and environmental Protection.In this paper, the physical properties of paper filled with FACS were investigated and compared to paper filled with PCC and GCC. The effect of particle size and filling mode on t he properties of paper filled with FACS was also studied. We had found out that the high paper strength properties kept in high porous structure countributed to the FACS/fiber composite structure gererated in mixed co-refining filling method. We also studi ed the impact of co-refining revolutions and filler/fiber mass ratio on paper properties and FACS/fiber composite structure. Filler/ fines pre-flocculation filling method was studied to strengthen the FACS/fiber composite structure and optimize the pre-flocculation filling process and improve strength properties of paper filled with FACS.Results indicated that FACS revealed a porous honeycomb structure and had smaller density, lower equipment wear than GCC and PCC. At the same filler content, strength prop erties of paper filled with FACS was lower than that of paper filled with PCC about 4%, while the paper bulk was higher than that of paper filled with PCC about 19%. The FACS with different particle size was prepared through grinding. The experimental resu lts showed that paper filled with FACS3(the smallest) had the best strength properties.The effect of filling methods on paper properties was explored. When using mixed co-refining filling mode, paper bulk can be decreased about 0.5cm3/g and paper strength enhanced about 8Nm/g. Optical performance of co-refining paper was improved to some extent. Another filling method, that FACS was pre-flocculated with fine fibers by CPAM, could significantly improve paper strength properties by nearly 10 Nm/g, wh ile reduce bulk of paper less.FACS/fiber composite structure was formed in the meixed co-refining process and beneficial for paper strength. In the composite structure, FACS was wrapped and packaged by fibrils. Raise refining revolutions was co nducive to improving optical and strength properties and promoting the forming of FACS/fiber composite structure. In the optimal revolutions(5000r), paper tensile index, bulk, whiteness and opacity were 31.6Nm/g, 2.28cm3/g, 83.5 %(ISO) and 86.3%, respectively. Droppi ng the filler/fiber mass ratio did good to decreacing particle size and increasing paper tightness, resulting in improving paper optical and strength properties.We also analyzed the formation mechanism of FACS/fiber composite structure. During the proce ss of mixed co-refining, FACS particle size became smaller and fiber fibrillation produced more fibrils, so FACS particles were wrapped and packaged by the fibrils generated freshly, or the fibrils interspersed in the FACS, and then, the FACS/fiber composi te structure was generated. In addition, smaller FACS particles in mixed refining were more likely intertwined by fibrils and form more tightly composite structure. In the FACS/fiber composite body, hydrogen bond between fibers coul d be formed through the fibrils that wrapped FACS particle. Thereby, the FACS/fiber composite structure contributed to paper strength properties improvement.Pre-flocculation filling method was applicated to strengthen the FACS/fiber composite structure. In pre-flocculation ortho gonal experiment, the optimum level for the amount of the fines was 11%, CPAM amount of 0.05% and stirring speed of 300r/min, flocculation time of 5min. Compared with traditional filling, pre-flocculation filling paper had lower bulk about 0.1~0.3cm3/g and higher tensile strength about 4~8 Nm/g. Increasing the amount of fines was beneficial for paper tensile strength, internal bond strength and opacity. While the paper bulk and tear strength showed the trend of increasing first and then decreasing. From the perspective of quantity and quality of the FACS/fine s composite structure, the appropriate amount of the fines was about 6%.In the SEM of paper filled by pre-flocculation, two types of reinforced filler/fine s composite structures were found: one was flocculation group formed by fines and a few of FACS particles with smaller particles size, the other was FACS/fines/long fiber that FACS and long fiber were connected through fines. These two composite structures were tighter than that formed in mixed co-refining filling method, which created more bonding points between long fibers and enhanced strength properties of paper filled with FACS. |
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