As we all know, the raw material of paper pulp manufacture can be divided into four types, including wood fiber, non-wood fiber, wastepaper, and non-plant fiber. Bamboo belongs to the non-wood fibers. For most paper pulp mills, the main source of paper pulp production is wood fiber. Because the wood resource is short, at the moment, there are many other non-wood fibers can be used for paper pulp makings, such as bamboo, bagasse, jute, cotton, and etc. With a variety of advantages, bamboo is recognized as a trend of the paper pulp industry. What are the pros and cons of bamboo pulp making?
Pros of bamboo pulp making
The biggest benefit of bamboo pulp making is easy obtainment of the raw material. There are common kinds of bamboo for paper pulp making, include small diameter bamboo, moso bamboo, de-greening bamboo and etc. Bamboo is a common plan in the southern tropics, subtropics area. As a country of origin, China has the richest bamboo resource.
Bamboo is the fastest growing plant in the world and easy to be planted. Every ton of paper needs four tons of fresh bamboo and one acre of land produce about 1 to 2 tons per year. If the bamboo variety is selected, the yield can reach 3 to 4 tons. After successful afforestation, the first harvest requires three years, and then, bamboo can be cut down every year. It does not need to reforest in a few decades with reasonable management and protection, you can protect the green hills and use them forever. The growth pattern of bamboo has great positive significance for alleviating the shortage of timber resources and preserving the ecological environment.
As the raw material for paper pulp making, the fiber of bamboo should be paid more attention to. In general, longer fibers produce stronger paper. Bamboo fiber is thin and long, the average length is 1.5-2.0mm, higher than wood, reed, rice straw and bagasse. Bamboo also has large length-width ratio and good drainability. Bamboo has fewer parenchyma cells, about 20-35%, and higher cellulose content, between softwood and hardwood. The lignin content is between 21-27%. The ash content is 1.0-2.9%, which is relatively low and is mainly concentrated in the skin and nodes, and the content of fiber bundles and parenchyma cells is very small. The fiber cavity is larger than that of wood or grass, and the bamboo can reach 4.55. Taken together, bamboo is second only to wood and it is most suitable for pulp and paper making. Bamboo pulp paper and wood pulp paper have little difference. Generally speaking, bamboo pulp paper is more straight and can be applied to medium and high-grade paper making including offset printing paper, letterpress printing paper, oil seal paper, kraft paper and match paper.
The preparation of bamboo generally include dry cut, screened, then washed, dehydrated, and then sent to pulp cooking, the pulp production is not more complicated than the processing of other fiber materials. In addition to the cutter-type and the knife-roller bamboo cutting machine, there is also a drum-type bamboo cutting machine which is widely used today. The bamboo pieces are generally 2-3 cm. The drum washer and the twin roll press used for washing are closed and washed, but the slag is required to be drained regularly. The cooking process has been improved by techniques, and the cooking yield is about 50%.
Cons of bamboo pulp making
According to statistics from 2010, all pulp mills around the world produces 146 million tons of pulp, including 2 million tons of bamboo pulp. It can be seen that although bamboo has the above various advantages, the current proportion of bamboo pulp papermaking is not very high. Presumably, bamboo pulp papermaking also has certain limitations.
Firstly, due to the growth habit of bamboo, the territorial scope of bamboo pulp making is relatively limited. The bamboo
Bamboo grows well in the place where it is warm and humid, so the countries with more bamboo in the world are concentrated in the tropics, subtropics, especially Southeast Asia. In China, the south of the Yangtze River is a tropical monsoon climate and a subtropical monsoon climate zone. It is warm and rainy enough to produce bamboo in large quantities. Although the bamboo can be planted in the north of China, it belongs to the zone of the continental monsoon climate, the bamboo is used as a landscape bamboo with a small diameter. Growth period is slow, not suitable for industrial use. From the view of the bamboo source, only the bamboo forests in the south are suitable for bamboo pulp papermaking, while the north is greatly limited. Even if the preparation and papermaking can be carried out separately, the transportation cost will increase, so pulp mill is generally chosen to be near the place where produce bamboo in large quantities. Therefore, the regional problem should be the most important factor restricting bamboo pulp and papermaking.
Secondly, the black liquor of bamboo pulp making is hard to recover, environmental pollution is large. Although there are some new technical processes, such as low temperature and high-pressure mechanical extraction, which can be used to extract black liquor, this method has not been well promoted by scientific research and identification. Many places where water bodies are limited are not suitable for the development of bamboo pulp and paper making. In this regard, an environmental impact assessment is also required at the time of construction.
Thirdly, from the view of the pulping process, when the bamboo slices are cooked, the air is trapped inside the bamboo ducts, which hinders the penetration of the liquid. The sand is mixed with silt and gravel, and it is difficult to remove by screening. As a result, increase the equipment wear and affect the pulp quality. In order to solve this problem, some people have proposed the technique and equipment for tearing bamboo into bamboo filament. After cutting the bamboo into bamboo chips by a cutter-type bamboo cutting machine, the bamboo is twisted into bamboo filament by a tearing machine, the washing machine and the depithing machine separate the relatively dense debris such as sandstone and iron block, remove the fine bamboo filament and bamboo pulp while depithing, and dissolve part of the dissolved matter. However, this method complicates the process and affects production costs. In addition, because the bamboo pulp fiber is long, it is necessary to beat to properly cut the fiber, and the wear on the machine during the pulp beating is often very serious.
As a compromise, many paper mills add a certain proportion of bamboo pulp to the wood pulp to increase the stiffness of the paper.
In summary, bamboo pulp papermaking is a non-wood pulp fiber paper with great potential. Despite the limitations of bamboo pulping and papermaking, advanced production techniques can overcome some of the process and equipment challenges in bamboo pulping. Coupled with the cultivation of high-quality and high-yield bamboo forests and the establishment of a bamboo pulp production base integrating forestry and paper, bamboo pulp and papermaking can be better developed.