Key factors for the tear resistance of brown kraft paper: the influence of wood pulp, recycled pulp and processing technology

1. Wood pulp quality
Wood pulp is one of the main raw materials for making brown kraft paper. Its quality has a crucial impact on the tear resistance of paper. The quality of wood pulp determines the fiber structure, strength and durability of paper. Different types of wood pulp (such as softwood pulp, broadleaf pulp, etc.) will affect the different properties of paper.

Softwood pulp (softwood pulp) and tear resistance
Softwood pulp comes from coniferous trees such as pine and fir. Its fibers are long and flexible and can provide high tensile strength. The longer fibers in softwood pulp can form a stronger fiber web, thereby increasing the tear resistance of paper. Due to the length and strength of these fibers, brown kraft paper produced from softwood pulp usually exhibits better tear resistance and durability.

Broadleaf pulp (hardwood pulp) and tear resistance
Broadleaf pulp comes from broadleaf trees such as oak and birch. These trees have shorter fibers but higher toughness. Hardwood pulp paper has a smooth surface and good water absorption, but its tear resistance is usually not as good as softwood pulp paper. Hardwood pulp is usually used to improve the softness and printability of paper, but if strong tear resistance is required, hardwood pulp alone may not be as effective as softwood pulp.

Fiber length and quality of wood pulp
In addition to the source of wood pulp, the fiber length and quality of wood pulp are also key factors affecting the strength of paper. Longer fibers can interweave with each other to form a tighter network structure, improving the overall strength and tear resistance of paper. High-quality wood pulp usually has higher fiber quality and longer fiber length, which allows the paper to withstand more pressure and is not easy to be torn.

2. Use of recycled pulp
Recycled pulp is another important raw material for brown kraft paper. Recycled pulp is usually made from recycled materials such as waste paper and cardboard through processes such as deinking and washing. Recycled pulp has significant advantages in environmental protection and reducing production costs, but its quality may also affect the tear resistance of paper.

Quality differences of recycled pulp
The quality of recycled pulp is closely related to its source and processing process. Recycled pulp from high-quality raw materials (such as waste cartons, office paper, etc.) usually has good fiber quality, and the kraft paper made from it can also maintain strong tear resistance. Waste paper from poor sources (such as ink printing paper, paper with chemical coatings, etc.) may affect the quality of the pulp, resulting in poor strength and low tear resistance of the brown kraft paper.

Recycled pulp and tear resistance
Recycled pulp usually contains shorter fibers, and its tear resistance is usually not as good as wood pulp. The fibers of recycled pulp will gradually become shorter and more fragile during repeated use and processing, resulting in a decrease in the overall structural strength of the paper. Nevertheless, by optimizing the processing process of recycled pulp and reducing impurities and foreign matter in the pulp, the strength of the paper can still be improved to a certain extent.

Use of additives
During the manufacturing process, manufacturers may add some chemical additives to improve the fiber quality and strength of recycled pulp. These additives include reinforcing agents, cross-linking agents, flexibilizers, etc., which can improve the structure of recycled pulp and increase the bonding force between fibers, thereby improving the tear resistance of paper. The use of additives also needs to be cautious, because excessive use may affect the environmental performance of paper.

3. Raw material processing technology
The raw material processing technology is another important factor affecting the tear resistance of paper. In the paper production process, wood pulp and recycled pulp will go through a certain processing process, including cooking, bleaching, beating, etc. These process steps directly affect the fiber structure and strength of the paper.

Pulping process
Pulping is the process of mechanically treating the fibers in wood pulp or recycled pulp. Through beating, the fibers in the pulp will be further dispersed and elongated to form a more uniform fiber network. In this process, the length and shape of the fibers will affect the tear resistance of the paper. Proper beating can increase the strength of the paper and improve its tear resistance.

Forming and pressing
During the forming process of paper, the pulp will be evenly coated on the screen to form a thin paper layer. During the pressing process after forming, the paper will experience high pressure, which helps to make the fibers more closely bonded, thereby improving the strength of the paper. The pressure and time of pressing also directly affect the tear resistance of the paper. Improper pressing may result in a paper surface that is too tight, making it brittle and prone to tearing.

Bleaching and decontamination
Bleaching is the process used to remove the natural pigments in the wood pulp to make the paper whiter. While brown kraft paper is not typically bleached, even unbleached wood pulp may go through some decontamination process to remove unwanted impurities and resins. This helps improve the uniformity and strength of the paper, making it stronger and more resistant to tearing.