Bamboo Pulp Making Process

cut bamboo for bamboo pulp production

Bamboo pulp is a type of paper pulp with a medium fiber length. Its fiber is thin and soft, with a length between the wood pulp fiber and the straw pulp fiber.

Bamboo Pulp Advantages

Bamboo is the best papermaking material next to coniferous wood because of the superior papermaking performance of bamboo pulp.

Compared with hardwood, bamboo has higher cellulose content and less miscellaneous cells, which makes its pulp index better than that of hardwood pulp.

Compared with the common straw of the family Poaceae used in papermaking, the advantages of bamboo in pulp production include higher cellulose content, less miscellaneous cells, longer fiber length, larger aspect ratio and less ash content. For example, the cellulose content of bamboo is 44-49%, and that of straw is 35-42%; the content of miscellaneous cells of bamboo is 10-16%, and that of straw is 30-60%; the ash content of bamboo is 1.2-1.9%, and that of straw is 4-14%.

The natural color bamboo pulp can be used to produce paper towel, toilet paper, lunch box, packaging paper, etc.; the bleached bamboo pulp can be used to produce writing paper, printing paper, etc.

Natural color bamboo pulp paper product.
Natural color bamboo paper

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The Bamboo Pulp Making Process

Raw Material Preparation

The raw material preparation of bamboo pulp making includes rolling, cutting, and screening three processes: The bamboo is cut into 10 ~ 25 mm long bamboo slices by a bamboo cutter. After rolling, the bamboo slices are smooth, which is convenient for the air in the bamboo to be discharged and the liquid to permeate into the bamboo. The bamboo joint is hard and contains a lot of silicon, so it is necessary to screen the bamboo joint when screening.

Bamboo piled in the paper mill ready for bamboo pulp production.
Raw bamboo material in paper mill

Bamboo Pulp Cooking

Bamboo pulp is usually produced by kraft cooking. The kraft cooking of bamboo pulp is easier than that of wood pulp because of the following reasons: 1) bamboo contains less complex lignin and is easier to delignify; 2) bamboo contains more basic structural units of Syringa than wood, and 5-10% coumaric acid and a small amount of ferulic acid in bamboo are connected with other structural units in the form of lipid, and the lipid connection is the combination that can be alkalized and broken in the early stage of cooking Connect the key.

bamboo pulp raw fibers
Raw bamboo pulp

Bamboo Pulp Kraft Cooking Parameters:

1) Alkali consumption: generally 18 ~ 23% ( to the absolute dry weight), sometimes less than 18%; using continuous cooking method to produce high yield chemical pulp with bamboo chips, the alkali consumption is generally 13%, but can also reach as high as 27%.

2) Sulfidity: generally, the sulfidity is 20~25% when cooking bleached bamboo pulp, and 28~30% when cooking natural color bamboo pulp.

3) Liquid ratio: the liquid ratio varies with different cooking equipment. The liquid ratio of cooking ball was 2.6 ~ 2.7:1, that of vertical cooking digester was 2.6 ~ 2.7:1, and that of continuous digester was 2.5 ~ 3.0:1.

4) Cooking temperature and time: in kraft pulping, the delignification stage of bamboo pulp is before 140 ℃. The delignification rate can reach 64% at an hour and 74% at two hours. The fiber separation point of bamboo pulp is 160 ℃, but a small amount of residue can still exist for a short while at this temperature, which indicates that 160 ℃ is the most suitable temperature for bamboo pulp cooking, but it should be kept at this temperature for a period of time. In view of the tight structure of bamboo, it is very difficult to remove the air left in the pipe, so the bamboo cooking needs a long infiltration time. The time of temperature rising infiltration is generally 1.5 ~ 2 hours, and the holding time is 2 ~ 2.5 hours.

Bamboo Pulp Washing & Bleaching

The cooked bamboo pulp needs to be washed and screened before being used to make paper. The pulp bleaching process is also necessary for making specific types of paper.

Bamboo Pulp Washing:

The vacuum washer or horizontal belt washer are the commonly used equipment for bamboo pulp washing, because they can not only effectively wash the bamboo pulp but also extract the black liquor, which is conducive to alkali recovery. Some small and medium-sized pulp mills without alkali recovery system will also use rotary screen thickener or side press thickener to wash bamboo pulp.

Bamboo Pulp Screening:

The machines commonly used in bamboo pulp screening are knot remover, centrifugal pulp screening machine and Bauer slag remover.

The purpose of bamboo pulp screening is to remove the solid impurities and excessive fiber in the pulp, so as to prevent them from damaging equipment, hindering the operation of the process or causing low product quality.

Bamboo Pulp Bleaching:

The bamboo pulp can be bleached by using disc filter or gravity disc thickener.

Because the bamboo pulp has a high bleaching rate after kraft cooking and the bleached pulp is easy to turn yellow again, it is necessary to strictly control the pH value of final bleaching above 9 in the bleaching process and use different bleaching methods according to the requirements of whiteness.

Generally, the whiteness of bamboo pulp can reach 70% in single stage bleaching, 75% in h-stage bleaching and 80% in three-stage bleaching.

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