pulp fiber raw material research Bamboo

September 13, 2023

Pulp and paper industry value chain: pulp fiber raw material research (2) Bamboo

Source: Huwei Wei pulp and paper enterprise management

1. Bamboo resources

 China is the country with the most abundant bamboo resources in the world, with more than 530 species of bamboo plants in 39 genera, covering an area of 6.8 million hectares, accounting for 1 / 3 of the world's bamboo forest resources. Among them, 4.7 million hectares of bamboo forests and 2.1 million hectares of other bamboo forests. It is mainly distributed in Fujian, Jiangxi, Sichuan, Hunan, Zhejiang and Guangdong, with six provinces accounting for 77.6% of the national bamboo resources. Hubei, Yunnan, Shaanxi, Chongqing, Guizhou and other provinces and cities also have bamboo forest resources distribution, but the proportion is relatively low, all less than 4%. There are altogether 16 major bamboo-producing provinces in China. Bamboo is the main forest area, in which Jiangxi, Fujian, Hunan and Zhejiang provinces account for about 80% of the national bamboo forest area. In recent years, a number of excellent and efficient bamboo species such as thunder bamboo, hemp bamboo, green bamboo and square bamboo have been cultivated and developed in a large area, and then a new pattern of comprehensive development of scattered bamboo, overgrown bamboo, large bamboo, small and medium bamboo, native bamboo, introduced bamboo species, ecological bamboo forest and economic bamboo forest has been formed.

 Bamboo grows rapidly, grows quickly and has a high yield. Like a mild climate, loose soil and humid places, planting 5 years can be a forest. The general annual yield of bamboo per mu can reach 600~900 kg, and the growth is particularly good. The annual yield per mu can reach 1500~2000 kg. A planting can be sustainable use, more and more paper industry enterprises began to turn their eyes to bamboo pulp. The pulp raw material structure in China is in the conversion period, and the tight supply and demand of pulp leads to high import dependence. The import of pulp is about 30 million tons every year.

The used area of bamboo pulp in India is the largest in the world, with bamboo accounting for 50-55% of the pulp raw materials, and 100% bamboo paper has been used for bamboo pulp.

2. Bamboo pulp fiber

1. Suitable performance of bamboo pulp

1) In 2022, China's bamboo forest output is about 4.25 billion roots, bamboo pulp output of about 2.92 million tons. The fiber shape and content of bamboo are similar to that of conifers, high cellulose content, fiber slender and strong, good plasticity, fiber length is between broad-leaved wood and coniferous wood, fine and soft.

2) Bamboo pulp with bamboo, bamboo, bamboo and other bamboo as raw materials, using chemical method, mechanical method or a combination of the two methods to make plant fiber raw materials into natural pulp and bleached pulp. Bamboo pulp and paper loose thickness, high tear degree, low breaking resistance strength and tensile strength, easy to apply glue, has a high mechanical strength.

3) The paper made of bamboo fiber, the body and bones are firm and "sound". Bleached bamboo pulp is used to make all kinds of cultural paper, and natural bamboo pulp is used to make household paper, packaging paper, kraft paper, insulating paper, food packaging paper, industrial paper and special paper, etc. The wool pulp produced by bamboo is still a high quality filling material for sanitary napkins, with superior water absorption and adsorption performance. "Zhukun" is bacteriostasis and disinfection, and is a high quality filling material for sanitary products.

2. Bamboo characteristics

1) Bamboo belongs to monocot Poaceae and the subfamily.

2) Bamboo fiber cells account for about 60%~70% of the total cell area ratio, lower than conifers and higher than general grass. The bamboo fiber is slender, spindle-like, and sharp at both ends. Its average length is generally between 1.5 and 2.1 mm, and the average width is generally about 15 microns. Its aspect ratio is from about 120 to 200, which is better than broad-leaved wood. The bamboo fiber wall is about 5 microns thick, the inner and outer walls are smooth, the cell wall is very thick, and the cell cavity is small. There are also some short and wide fibers, pure pointed ends, large cell cavity, such fibers grow in the node. The fiber is thin, the wall thick cavity is small, larger, harder than the fiber, high transparency.

3) The cellulose content of bamboo is generally 50%~60%, somewhere between conifers and broad-leaved timber. It is 10%~15% higher than reed and wheat grass. The lignin content of bamboo is generally 19%~25%, a few in more than 25%, relatively close to the broad-leaved wood.

4) The polypentose content of bamboo is generally 19%~24%, a few as high as 27%~28%, close to broad-leaved wood and grass raw materials, much higher than conifers (about 12%).

5) Bamboo 1%NaOH extract is generally 25%~30%, a few as high as 30%, about twice higher than wood, lower than the general grass.

6) The ash content of bamboo is generally 1%~2%, which is about three times higher than wood, but lower than grass, only 10%~14% of the ash content of straw.

7) The ash of bamboo is mainly concentrated in the skin and section. The joint ash content was 2.09%, the cortex content was as high as 27.64%, and the SiO2 content in the ash accounted for 97.7%.

8) Paper bamboo, 2~3 years of better, less bamboo spring, high fiber content, less ash.

9) The ratio of bamboo raw materials is significant, generally from 0.6 to 0.8. Needle wood 0.4, hardwood 0.43~0.64, bamboo in the pulp steaming fashion pot quantity is higher than wood and grass raw materials.

3. Bamboo fiber structure

1) Bamboo fiber has two kinds of cell wall structures, one is multilayer structure, the fiber wall is composed of alternating wide layer and narrow layer, wide layer and narrow layer are about 4 ~5 layers each, wide layer color is lighter, indicating that low lignin density; the narrow layer is deep and lignin density is higher. This type of fiber is mainly found in the peripheral parts of the vascular bundle, or about 1 / 2 of the total fiber population.

2) The other type of fiber cell wall is very thick and narrow. The inner layer of the fiber secondary wall is mainly composed of two wide layers, and the outer wide layer is much wider than the inner wide layer. From the electron microscopic picture of potassium permanganate staining, this fiber was less than the previous multilayer structure type, and was more present in the middle of the fiber group of vascular bundle tissue.

3) The pores on the bamboo fiber wall are far less than the needle fibers, and the holes are smaller, so the penetration of the liquid is slow. In bamboo, cell corners are often vacant, especially in parenchyma cells.

4. Bamboo pulp fiber beating method

 Making paper with bamboo fiber began in the Tang and Song dynasties, has a history of more than one thousand years, and has rich practical and theoretical experience."Three points of paper, seven points of pulp", no matter what kind of pulp is very important. Bamboo pulp at the beginning of the early wet tensile index and cumulative rupture work, but when reaching higher pulp (5 5  SR), continue to improve the pulp, the initial tensile index and cumulative burst work fell instead, because in the case of higher slurry, fiber is excessive cut off, affect fiber effective entanglement and interweave, cause the bamboo pulp early wet tensile index drop. The medium length ratio of wet paper is due to the elasticity of the fiber network of pulp and the formation of the resistance of fiber slip. It is related to the average length of slurry fiber, fiber curl index and the adhesion force of wet paper amplitude. The average length of fiber amplitude is the basis of the elongation of wet paper. When the pulp is greater than 5 5  SR, the degree of bamboo pulp fiber will be improved.

 With the process of beating, the breaking length, folding resistance and breaking resistance of bamboo pulp are higher, while the tear degree drops faster.

1) The bamboo pulp fiber is fine and soft, which is easy to assemble into a group. Therefore, the length of the fiber should not be too long, and the thick pulp should not be too large.

2) When copying the offset paper, the bamboo pulp fiber should be less than 1 mm, and then the wood pulp is generally more than 1 mm.

3) Bamboo pulp makes cultural paper, paper is strong in ink absorption, and easy to glue, paper tissue is dense, printing is not easy to drain hair. Bamboo pulp has a high tension, can add more filler, and the packing retention rate is also higher, its main disadvantages are high transparency, large expansion.

3) Bamboo pulp fiber is easy to be made into sticky pulp with high hydration degree. The transparency of bamboo pulp is high, which can be used for the production of paper such as drawing drawings, imitation parchment paper.

4) Bamboo pulp fiber is slender and soft, and the surface combination force is large, which can replace some long fiber to produce kraft paper, paper bag paper and other paper with high strength requirements.


3. The production and manufacture of bamboo pulp fiber

1. Chemical combination characteristics of bamboo

1) Bamboo pulp is generally used by sulfate method, bamboo composite lignin less, sulfate method is easier to cook lign.

2) Bamboo has a higher content of lilac basic element structural units than conifers.

3) Bamboo also contains 5~10% coumaric acid and a small amount of ferulic acid, which are ester associated with other structural units.

4) Ester coupling is a bonding bond that can alkalize and break at the early stage of cooking, so bamboo is easier to cook than wood.

2. The process parameters of sulfate cooking are different from the age of bamboo, and the amount of alkali added, sulfide, liquid ratio, temperature and time of cooking are quite different.

1) Base amount: generally 18~23% (dry). According to the characteristics of paper demand, bamboo paper bag pulp of about 16% is about 13%, and special materials reach 26~27%.

2) Sulfide: the sulfide of the boiled bleached bamboo pulp is generally 20~25%, and the boiled natural bamboo pulp is generally 28~30%.

3) Liquid ratio: 2.6~2.7:1; 2.6~2.7:1; 2.5~3.0:1.

4) Cooking temperature and time: bamboo sulfate method, a large number of lignin stage is before the heating to 140℃, heating up about 1 hour can reach 64%, the heating time is 2 hours, the lignin can reach 74%. For the most suitable maximum cooking temperature, when cooking the bamboo by the sulfate method, the temperature rises to 160℃ to reach the fiber separation point, but there is still a small amount of residue. This indicates that the maximum temperature of 160℃ is suitable, but at this temperature to keep warm for a period of time. In the actual production, in view of the close structure of bamboo, and the air retained in the pipe is extremely difficult to eliminate, bamboo cooking needs a long penetration time, the heating penetration time is generally 1.5~2 hours, and the heat preservation time needs 2~2.5 hours. The warming time and the insulation time are complementary.

5) The bamboo slices and cooking liquid must be mixed as well as possible at the beginning of the boiler, which can shorten the cooking cycle and is particularly important for bamboo cooking.

3. Wash, screening, and bleaching of the bamboo pulp

1) Wash

Bamboo pulp washing generally uses vacuum washing machine or horizontal belt washing machine for washing.

2) Screening

Deremover, centrifugal sieve machine and Ball slag remover were used for bamboo pulp screening.

3) Bleach

 The bleaching of bamboo pulp is carried out in the bleaching machine or bleaching tower. Considering the high bleaching rate of bamboo pulp by sulfate method and the bleached pulp is prone to return yellow phenomenon, in addition to strictly controlling the pH value of the final drift above 9, different bleaching methods should be adopted according to the requirements of whiteness. Because bamboo contains high lignin content, it is necessary to combine deep delignification technology and oxygen delignification technology, to control the Kappa value into ECF and TCF slurry (recommended <10), use Eop, acid pretreatment or Eop, and bleach sulfate bamboo pulp to the high white level of 88%ISO. The bleaching performance of different raw materials of bamboo is quite different. With Kappa value of about 11~16, even with the ECF and TCF, the pulp can only reach 79% ~ 185%. Compared with TCF bamboo pulp, the bleaching loss of ECF bleached bamboo pulp is smaller, and the paste viscosity is higher, which can generally reach more than 800 ml/g. But even with the improved modern TCF bleached bamboo pulp, the viscosity can only reach 700 ml/g. Bamboo pulp ECF and TCF bleaching will coexist for a long time, and the TCF and ECF bleaching process can be used.

(1) The use of ECF bleach paste has better pulp quality, less chemical drugs, high bleaching efficiency, mature equipment system and stable operation performance. The investment cost of ECF pulping production line is 20%~25% higher, and the investment of joint pulping production line is also 10%~15% higher. The investment of chemical recovery system is also large, and the operation is more complex.

(2) The use of TCF bleaching technology has the advantages of less wastewater discharge in bleaching workshop, low equipment corrosion requirements and less investment. The semi-closed bleaching system is adopted in the TCF chlorine-free bleaching production line, and the wastewater discharge in the bleaching workshop can be controlled at 5~10m3 / t pulp. The wastewater from the (PO) section is sent to the oxygen lignin section for use, and the wastewater from the O section is supplied to the washing and screening section for use, and finally enters the alkali recovery. The acid waste liquid in Q section enters the effluent wastewater treatment system. Because it does not contain chlorine element bleaching, chemicals are not corrosive, bleaching equipment does not need titanium metal and special stainless steel, with ordinary stainless steel can be, so the investment cost is low.

(3) It is feasible to bleach TCF and ECF to produce 88%~90% fully bleached bamboo pulp. Pulping should use deep delignification technology, oxygen delignin before bleaching, control the slurry Kappa value into the bleaching system, bleaching using three or four stages of bleaching process. It is recommended that bamboo pulp ECF is OD (EOP) D (PO) and OD (EOP) DP; L-ECF is OD (EOP) Q (PO); and TCF is Eop (ZQ) (PO) (PO) and O (ZQ) (PO) (ZQ) (PO).

(4) The chemical composition (especially lignin content) and fiber morphology of different bamboo varieties vary greatly. The pulp and paper performance of different bamboo varieties are systematically studied to provide guidance for the formulation of reasonable process routes and conditions.

4. The advantages and disadvantages of bamboo pulp fiber

1. Advantages of bamboo fiber

1) "Clear water and green mountains are golden mountains and silver mountains" —— Bamboo is a perennial growth resistant plant, planted into a forest can be cut down every year, can be called "inexhaustible" inexhaustible. More sustainable than trees.

2) No bleached natural bamboo fiber, retains the natural lignin pure color of the fiber, and the root eliminates the chemical residues such as dioxin and fluorescent agent. According to the data records, dioxin is a high carcinogen, and its toxicity is 900 times that of arsenic. Bamboo fiber contains "bamboo kun", has natural anti-mite, odor and anti-ultraviolet effect. The bacteria on bamboo pulp paper are not easy to reproduce. According to records, "Zhukun" will die 72-75% bacteria within 24 hours, which is suitable for pregnant women, women and infants.(Except for waste paper pulp)

3) Bamboo fiber belongs to medium length fiber, thick fiber wall, large fiber hole, has good air permeability and water absorption suitable for living paper, pulp molding and special paper pulp fiber products.

2. Lack of bamboo fiber

1) Bamboo is rich in sugar, fat and protein, which is easy to cause moth and rot and affect the quality of pulp.

2) Bamboo has a close structure, and it is difficult to penetrate the cooking liquid horizontally from the bamboo slice. The tube or juice fills the liquid juice from vertically. After drying, the air replaces the liquid juice and remains in the tube. In this way, in the cooking process, the air in the catheter is very difficult to eliminate, greatly hindering the immersion of liquid medicine. The cellulose content is 15% less than the stem, which is more difficult to penetrate.

3) The bleaching rate is high. When the bleached hypochlorite is used alone, the bleached bamboo pulp is easier to turn yellow.

4) Because the ash content of bamboo is higher than that of wood, silicon interference is easy to occur in the process of pulp and black liquor recovery.

5) Bamboo fiber paper products, the paper color is yellow, more particles. And wood fiber paper, paper is delicate, soft, smooth surface, good toughness, high whiteness.

6) Bamboo fiber mechanical properties are poor, lack of certain strength and elasticity.

5. Bamboo storage and selection

1. Young bamboo storage, first in the origin of processing into the green bamboo, remove bamboo tip and bamboo shell, split into not more than 25 mm wide, about 1.3 meters long bamboo, thickness does not exceed 5 mm, into the clear pool soak 45~60 days after remove dry, then bundle, each bundle of 25 kg, storage in the warehouse, warehouse should be tall and spacious, ventilated, dry, bamboo water should not be more than 18%. The bamboo pieces can also be stacked in the open air 0.3 meters high from the ground, the pile can be 6~7 meters high, and then piled into a spire, each pile about 12~15 meters wide.

2. Omanosteen is first bundled, and then like green bamboo pieces in the open stacking method.

3. Bamboo, there are two methods, one is the vertical pile, vertical frame with logs or bamboo, bamboo stacked on both sides of the frame, tilt of about 10~15 degrees; the other is the horizontal pile, namely set up the original bamboo in 100~150 meters long, 8~12 meters wide, pile height of artificial up to 6 meters.

4. Material preparation includes three processes: bamboo rolling, bamboo cutting and screening. The longitudinal penetration of the cut bamboo is faster than the transverse, and the transverse penetration of the heart is slightly faster than the skin, the shorter the better, generally requires about 10~25 mm.

5. After rolling bamboo, the cut bamboo slices have no slope, which is easy to discharge air, conducive to the penetration of liquid medicine, and improve the cooking effect.

6. Bamboo joints are highly lignified and contain more silicon. After the rolling and cracking of the bamboo, the bamboo segments should be sifted to ensure the uniformity of the bamboo slices.

 Vi. Chinese bamboo pulp production enterprises and bamboo fiber development trend

 In November 2021, at COP 261,114 countries signed conventions to stop and reverse the problems of deforestation and land degradation in 2030. Signatories include China, Canada, the United States, Australia, Russia, Colombia, Peru, Indonesia, Brazil and other countries. The 114 countries have signed up with more than 33 million square kilometers of total forest area, or 85 percent of the world's total.

 Thirty banks and financial institutions around the world have pledged to halt their investment activities related to deforestation.

In recent years, China's major forest paper enterprises have started or added bamboo raw materials to produce copies, such as sun paper, Shanyin paper, Chenming paper, River paper and other enterprises.

Specialized in the production of bamboo pulp enterprises are Taisheng Group, Qingshan Paper, Yunjing pulp paper, Fengsheng paper and so on


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