Simply speaking, wood pulp refers to wood reduced to pulp through mechanical or chemical treatment for use in the manufacture of certain kinds of paper. According to the raw material for making wood pulp, pulping method and the usages of paper, pulp can be divided into kraft pulp, mechanical pulp and pulp refining, etc. At present the use of wood pulp covers more than 90% of the amount of paper pulp. Wood pulp is not only used for the paper, but also widely used in other industrial sectors.
Classification Based on The Characteristics of Beating
According to the characteristics of beating of the wood pulp, wood fiber can be mainly divided into softwood and hardwood categories. The same species can be further divided into earlywood (spring wood) and latewood (autumn wood), because of their different growth rates in different seasons. Consequently, their beating characteristics are respectively different.
Softwood and Hardwood Pulp
In Europe, hardwoods cover 29% and softwoods 71% of wood consumption. For the paper pulp manufactured by the same method, hardwood needs higher beating rate to get the similar physical strength with softwood. However, the fiber of hardwood pulp is shorter, usually 0.8-1.1 mm. It is necessary to improve the beating degree, but also to avoid excessive cut fiber, therefore, hardwood pulp should take lower beating specific pressure, and the higher concentration of beating pulp is appropriate. The fiber of softwood pulp is longer, usually 2-3.5mm. In the production of cement bag paper, it is inappropriate to cut off the fiber too much, however, when used in the production of a tissue, such as typing paper, paper seal and so on, in order to satisfy the requirement of uniformity of the paper, it needs to be cut off to the 0.8-1.5 mm. Therefore, the processing conditions can be determined according to the requirements of different kinds of paper in beating.| Pulp Type | Hardwood Pulp | Softwood Pulp |
|---|---|---|
| Type of Tree | Oaks, beeches, poplars, birches and eucalyptus | Mainly pine and spruce |
| Main Spread Area | birches (found in Sweden, Norway, the UK and Spain) and eucalyptus (found in Portugal, Spain and Norway) | Pine found in the UK, Norway, Finland, France, Spain, Portugal and Greece. Spruce is found in the UK, Finland, Norway and Sweden. |
| Type of Fiber | Short | Long |
| Average Length of Fiber | 1mm | 3mm |
| Features | Achieving bulk, smoothness, opacity | Providing additional strength. Also suitable for writing and printing |
| Typical Products | Writing papers, printing papers, tissue papers | Shipping containers, grocery bags, corrugated boxes |
Earlywood and Latewood Pulp
In the manufacturing process of wood pulp, the proportion of earlywood and latewood is different, thus, the quality of final paper pulp is different even in the same beating conditions. The fiber’s length of late wood is longer, and its cell wall is thick and hard, which is not easy to be destroyed. Late wood’s fiber is easy to be cut in beating process, and it is hard for swelling and fine fibrosis. Therefore, for the pulp with large proportion of latewood, in the middle of beating process, especially in the wet beating, lower specific pressure, higher concentration, successive knife or knife from the beating of successive narrowing are adopted. The fiber of softwood is softer, and the fiber wall is thinner, which makes it easy to be separated into single fiber in beating. Therefore, softwood’s beating process is easier.
