Paper Machine Kraft

Paper Machine Kraft

Kraft paper machine is a complex piece of equipment used to produce kraft paper.

Pulping Process for Kraft Paper

- The kraft process starts with wood chips, which are usually from softwood trees like pine. The chips are cooked in a digester with a mixture of sodium hydroxide and sodium sulfide. This chemical treatment breaks down the lignin that binds the wood fibers together. The kraft pulping process is known for producing strong fibers because it causes less damage to the cellulose during the pulping compared to some other methods.

Stock Preparation

- After pulping, the kraft pulp is washed to remove the cooking chemicals and lignin residues. It is then refined to fibrillate the fibers, which means the fibers are mechanically treated 

to make them more flexible and better able to bond with each other. Fillers such as talc or calcium carbonate may be added to improve the paper's opacity and smoothness. 

Sizing agents are also used to control the paper's water - absorbency.

Paper - making on the Machine

- Formation: The prepared kraft pulp slurry is fed onto a wire - part (such as a Fourdrinier wire). As water drains through the wire due to gravity and vacuum suction, the kraft fibers interlace to form a wet paper web. 

The speed of the wire and the consistency of the pulp affect the formation and basis weight of the paper.

- Pressing: The wet kraft paper web is passed through press rolls. These rolls remove a significant amount of water from the web and compact the fiber structure. 

The pressure and number of press nips can vary depending on the paper's desired thickness and strength.

- Drying: After pressing, the kraft paper still contains moisture. It is dried using a series of steam - heated drying cylinders. 

As the paper passes over these cylinders, the heat causes the water to evaporate, leaving a dry kraft paper sheet.

- Calendering: The dried kraft paper may undergo calendering. Calender rolls are used to smooth the paper surface and adjust its thickness and density. 

This step gives the kraft paper a more uniform appearance and better physical properties for applications such as packaging.

Kraft paper produced by these machines is known for its strength and is widely used in packaging applications such as for corrugated boxes, grocery bags, and wrapping paper.

What are the advantages of using rice straw or sugarcane bagasse pulp in a kraft paper machine?

1. Sustainability and Resource Utilization

- Renewable Resources: Rice straw and sugarcane bagasse are agricultural by - products. Using them for kraft paper production means making use of waste materials. 

Rice straw is the residue left after rice harvesting, and sugarcane bagasse is the fibrous residue after sugarcane juice extraction. Instead of these materials going to waste or being 

burned (which can cause air pollution in the case of straw burning), they can be turned into a valuable product like kraft paper.

- Reduction of Deforestation: By using agricultural residues as an alternative to wood pulp in the kraft paper machine, there is less pressure on forest resources. 

This helps in reducing deforestation and conserving natural forests, which are important for biodiversity and carbon sequestration.

2. Cost - effectiveness

- Lower Raw Material Cost: In many agricultural regions, rice straw and sugarcane bagasse are abundant. 

Their availability in large quantities can lead to a lower cost of raw materials compared to traditional wood sources. 

This can result in more cost - effective kraft paper production, especially for applications where cost is a significant factor, such as packaging.

3. Unique Paper Properties

- Good Printability and Surface Properties: Rice straw and sugarcane bagasse pulps can contribute to good paper surface characteristics. 

The fibers can be processed to provide a relatively smooth surface, which is beneficial for printing. The kraft paper made from these pulps can have a suitable surface for applying inks, 

making it useful for packaging materials that require branding or product information to be printed on them.

- Strength and Durability: With proper processing in the kraft paper machine, papers made from these pulps can have adequate strength. 

The fibers can be refined and treated to form strong bonds, allowing the kraft paper to have properties suitable for packaging applications such as carrying a certain weight of goods or providing protection during transportation.