Wood pulp is a common pulp type just like straw pulp, bamboo pulp, sugarcane bagasse pulp, reed pulp, cotton pulp, etc. it takes the largest share in the paper and pulp market. Russia is an important producer of wood pulp, export a large amount of paper pulp to different countries around the world every year. In March 2018, Russia exported 189.6 thousand ton pulp (include virgin pulp and waste paper pulp). As a paper pulping machines manufacturer and paper pulp solution provider, today we will analyze the Russian wood pulp from three parts, including primary pulp, fiber morphology, beatability, and paper strength properties.
Primary pulp
Paper pulp contains cellulose chain of various lengths, cellulose, and hemicellulose. In general, the fiber material with rich content of cellulose will have higher strength, chemical, and thermal stability. The hemicellulose is also the vital part of paper pulp, it makes the fiber easy to be swelling and fibrillating. They are good for increasing the bonding strength of fibers and sizing. Based on various materials and pulping processes, different type of pulp has a great difference in chemical composition and degree of polymerization of cellulose. The fiber that has a higher degree of polymerization of cellulose also has good cutting resistance, obtained paper relatively has high strength.
From the view of whiteness, cellulose content, average length of fiber and width, Russian softwood pulp is very close to Canadian softwood pulp. In comparison, Russian softwood pulp has a higher content of pentosan, low degree of polymerization, high content of fines. russian softwood pulp fiber has worse elasticity, weaker cutting resistance, which is bad for paper strength.
Russian hardwood pulp and Finnish birch pulp has the same material and chemical composition. Russian hardwood pulp has a lower length rate and degree of polymerization than Finnish birch pulp, but it has better average fiber length.
Table1: primary pulp analysis
| Russian softwood pulp | Canadian softwood pulp | Russian hardwood pulp | Finnish hardwood pulp | |
| Whiteness of primary pulp (%) | 86.3 | 88.7 | 83.6 | 88.2 |
| Ash content of primary pulp (%) | 0.18 | 0.23 | 0.22 | 0.53 |
| αcellulose (%) | 86.89 | 85.25 | 80.72 | 81.22 |
| Pentosan (%) | 9.72 | 7.54 | 17.37 | 18.19 |
| viscosity | 309 | 711 | 511 | 618 |
| degree of polymerization | 870 | 1030 | 716 | 877 |
Table2: pulpwood of Russian wood pulp
| Russian softwood pulp | Canadian softwood pulp | Russian hardwood pulp | Finnish hardwood pulp | Indonesian hardwood pulp |
| Red pine 70% White pine, larch20% Hardwood10% | Spruce60% Fir40% | Birch90% Poplar10% | Birch100% | Birch80% Others20% |
Fiber morphology
Physical properties of paper are up to the fiber morphology, such as fiber length, fiber width, cell cavity diameter, fine fiber content, fiber flexibility, and etc. generally, thin and long fiber will have better felt properties in the paper and pulp making, so the obtained paper has good strength. But if the fiber is too long, the evenness of obtained paper will decrease.
Table3: features of different fiber material
| pulpwood | Average length of fiber(mm) | Average width of fiber | Thickness of cell wall | latewood percentage (%) |
| Red pine | 3.62 | 54.3 | Early wood3.5 Late wood4.3 | 7\17.7 |
| larch | 3.76 | 45.6 | Early wood4.1 Late wood9.5 | 30.4 |
| spruce | 3.62 | 39.4 | Early wood3.6 Late wood5.9 | 17.9 |
| fir | 3.29 | 51.9 | Early wood3.8 Late wood6.0 | 22.1 |
| birch | 1.21 | 18.7 | ||
| poplar | 0.86 | 21.0 | 3.4 |
From the point of fiber morphology, there are three main factors to affect the paper strength including felt property, combining capacity, fiber strength.
- Felt property of fiber is affected by fiber length.
- Combining capacity and strength of fiber is related to the cell wall width.
According to the data shown in the table2 and table3, the russain softwood pulp has complicated material, the cell wall of larch is wider than spruce and fir, and it has higher latewood percentage, so the Russian wood pulp is hard. The Russian hardwood pulp contains birch pulp and poplar pulp, compared to birch pulp, poplar pulp fiber is short and wide.
Beatability and paper strength properties
The beating curve of paper pulp partly reflects the pulp property. Beating degree is changed according to the change of beating time, at the same time, it affects strength index. Above data can show the pulp beating rate, strength index and so on, so we can judge the pulp quality.
At same condition of beating, Russian softwood pulp has faster rate of beating degree, lower wet weight than Canadian softwood pulp. Because Russian softwood pulp is made from mixing pulpwood, thick walled fiber has large rigidity and elasticity, which result in difficult flocculation of fiber.
In addition, Russian softwood pulp has lower degree of polymerization and wet weight, easy to be cut in the pulp beating.
Table4: pulp strength of different paper pulp
| Russian softwood pulp | Canadian softwood pulp | Russian hardwood pulp | Finnish Hardwood pulp | Indonesian hardwood pulp | |
| tensile index N.m/g | 77.0 | 84.7 | 59.0 | 63.2 | 51.5 |
| tearing index mN.m2/g | 10.34 | 9.83 | 5.12 | 5.39 | 7.61 |
The tensile strength of Russian softwood pulp is better than Swedish softwood pulp but lower than Canadian softwood pulp. Tearability of Russian wood pulp is similar to Canadian softwood pulp.in comparison, Russian hardwood pulp has better tensile property, and Indonesian wood pulp has a higher tearing index.
In conclusion
As given above, Russian wood pulp has similarities and differences in various properties with other types of pulp. To be specific, due to high pentosan content, low degree of polymerization, Russian softwood pulp is easy to be beaten and cut, low wet weight, low pulp strength. But the average fiber length is not short, so reasonable pulp beating can improve the Russian softwood pulp strength. Russian hardwood pulp is similar to the Finnish birch pulp, but they are different in the ratio of length to width, degree of polymerization and pulp strength.
