Difference analysis of fiber morphology and strength properties between recycled pulp and high yield pulp

1. Experimental methods

Using domestic waste paper, American waste 12# imported waste pulp and high yield pulp as raw materials, the microscopic morphology of fibers was compared and analyzed by optical microscope and fiber quality analyzer. The strength, morphology and shape of the fibers were compared by means of zero-range tensile strength meter, X-ray diffractometer, polarizing microscope and fiber mass analyzer. The paper properties of three kinds of pulp were compared and analyzed by the changes of physical strength of paper under multiple reuse times.

2. Fiber microscopic morphology analysis

High yield pulp and domestic waste paper fiber shape distribution is similar (see Figure 1), the content of medium fiber component is more, long fiber component is less, but the fiber length is shorter, the content of fine fiber is higher (see Table 1). American waste 12# pulp has more long fiber components, accounting for nearly 50%, and the fiber length is longer (see Table 2). High yield pulp and domestic waste paper have certain similarities in fiber length distribution and spinning. In order to achieve the paper performance of domestic waste paper, the fiber should be fully moistened by chemical pretreatment to reduce the damage to fiber length, improve fiber length distribution and reduce the fine fiber components, so as to improve its papermaking performance.

3. Fiber strength analysis

As can be seen from Table 3, the dry-zero distance tensile index of the three kinds of pulp is not much different, and the wet-zero distance tensile index of the US waste 12# is slightly better, but the wet-zero distance tensile index of the high-yield pulp and domestic waste paper is lower than that of the US waste 12# (about 21% lower). Compared with the strength properties of the three kinds of fiber raw materials, the strength properties of the US waste 12# fiber are better. Domestic waste paper and high yield pulp can not reach the replacement of imported waste paper.

As can be seen from Table 4, American waste 12# pulp has the highest water retention value, and high yield pulp is slightly higher than domestic waste pulp. The ash content of domestic waste pulp is nearly 3 times that of American waste 12#. After ICP-OES analysis, domestic waste paper contains more calcium and silicon elements, which may be because domestic waste pulp contains non-wood raw materials and calcium carbonate fillers.

4, paper performance analysis

With the increase of The Times of reuse, the strength properties of the paper showed a decreasing trend. Both kinds of recycled pulp showed a large decline trend of paper strength after 1 reuse, and a gentle decline trend of 2~4 reuse. The strength properties of high yield pulp showed a gentle decreasing trend. After repeated reuse, compared with domestic waste pulp, the high yield pulp still maintained better ring compression strength and rupture resistance, as shown in Figure 2.

conclusion

✅ The shape distribution of high yield pulp was similar to that of domestic waste paper, but the fiber length was shorter and the content of fine fiber was higher. The dry and wet zero-distance tensile strength properties are close, indicating that the two fibers have little difference in self-strength, but there is a big gap with the American waste 12#, in which the wet-zero-distance tensile index is 21% lower than the American waste 12#. The crystallization indices of domestic waste paper, American waste 12# and high yield pulp were 76%, 72% and 68%, respectively.

✅ The ash content of domestic waste paper is about 3 times that of American waste 12#, and the Ca and Si contents of ash are higher than those of American waste 12#. The higher ash content affects the recycling performance of waste paper; The ash content of high yield pulp without actual papermaking process is 0.6%.

✅ In terms of the reuse performance of pulp, the paper strength properties of American waste 12# and domestic waste paper pulp showed a large decrease after reuse, and the decrease rate of high yield pulp was small. After repeated reuse, compared with domestic waste pulp, the high yield pulp still maintains better annular compressive strength and rupture resistance.

Wan Jinquan, second-level professor, doctoral supervisor, Academician of International Wood Academy of Sciences (IAWS), expert enjoying the special allowance of The State Council, national outstanding scientific and technological worker, outstanding talent of Guangdong "Special Support Plan", He has won the May 1st Labor Medal of Guangdong Province, the Outstanding Patent Inventor Award of Guangdong Province, the Dingying Science and Technology Award of Guangdong Province, and the Ten outstanding returnees of Guangzhou City. He is the director of Guangdong Plant Fiber High-Value Clean Utilization Technology Research Center of South China University of Technology, the deputy director of the Key Laboratory of Pollution Control and Ecological Restoration in Industrial Populated Areas of the Ministry of Education, the deputy director of the recycled fiber Special Committee of China Paper Society, the deputy director of the Environmental Protection Special committee of China Paper Association, and the member of the Water Treatment and Response Professional Committee of China Environmental Society.

Professor Wan Jinquan's research group is affiliated to the State Key Laboratory of Pulp and Paper Engineering of South China University of Technology and the Engineering Technology Research Center of High-Value Clean Utilization of Plant Fiber of Guangdong Province. Under the leadership of Professor Wan Jinquan, he has been engaged in the research of new clean production technologies for pulp and paper making for a long time. He has put forward a whole set of new theories and technologies for short-range and low-consumption advanced treatment and resource utilization of papermaking wastewater, and established the first project application of PS acid-free advanced oxidation treatment for thousand-ton paper industry wastewater at home and abroad. For the first time, the engineering application of accurate, real-time, fast and intelligent soft sensing of the water quality index of papermaking wastewater and the intelligent, efficient and stable operation of the wastewater treatment process were realized, and the relationship between the ultrastructure of plant fiber cell wall pores, crystal state and surface chemical groups and their macro recycling papermaking properties was clarified. Clean production theories such as "closed circulation of paper waste water and recycling of fine fiber resources" and "carbon accounting and incremental sink method of paper industry" have been widely recognized by the academic community.

The team has won 13 science and technology awards above provincial and ministerial level, such as the second prize of National Science and Technology Progress, the first prize of Science and Technology of Guangdong Province, and the first prize of Technology invention of China Light Industry Federation.