[/caption]Paper is one of the most important recyclable materials. What is paper recycling, and what is the importance of paper recycling has already been discussed here…” recycled paper”.
The whole paper recycling process can be divided into two basic stages. First one is pre-processing stage [involves collection, sorting and the transportation of the waste paper], while the other one is the processing stage [processing of junk paper to the final products].
Pre-processing stage
The pre-processing stage of paper recycling involves following steps:
- Collection & Transportation:
The paper is first collected and transported to the respective locations.
- Sorting:
The collected paper is then sorted out on the basis of types or grades of paper.
- Storage:
The paper is then stored in the warehouses for further processing.
Processing Stage:
The processing stages are the main stages involved in the recycling of used paper to the manufacturing of newer products. This processing stage involves:
- Pulping:
The stored paper is then moved by the conveyor belt to the “Pulper” – A big unit contains dissolving chemicals and water. Firstly, the paper is chopped into small pieces, then into tiny strands of cellulose because of heating. This mixture of water, chemicals and tiny strands of cellulose is termed as “Pulp”.
- Screening
The pulp from the pulper is then passed through screens of different sizes. The purpose of screening is to remove small contaminants [like glue, plastic, sand, etc] from the pulp.
- Cleaning
The screened pulp is then introduced into large cylinders [cone-shaped], which are set to rotation or spinning [same as sedimentation process], due to which the heavy contaminants such as staples are settled at the bottom of the cylinder, while the lighter contaminants are collected in the center of the cone.
- De-inking:
After cleaning, the pulp undergoes through a pulp laundering process, known as de-inking. Deinking will remove the printing ink and other sticking materials like glue, adhesives, etc. Usually a combination of two deinking processes is used. Washing helps in rinsing the smaller ink particle from pulp with the help of water, while the stickies and larger particles are removed with air bubbles in floating process.
- Refining:
During refining process, pulp is beaten to ensure the separation of large bundles of fibers into individual fibers.
- Bleaching & Color Striping:
The selection of bleaching and color striping process depends upon the type of paper to be made.
If the colored paper is to be produced, the, the color stripping process is used. The stripping chemicals help in removing the dyes from the paper.
Bleaching is used in case of white paper production. Paper is bleached with oxygen, chlorine dioxide or hydrogen peroxide.
For brown paper production, pulp is neither stripped, nor bleached.
- Paper Making
Finally, the clean pulp is ready to be processed as paper in the paper machine. Paper machine itself consists seven different sections, which are flow box, wire, presser, drier, size press, calendaring section and reeling up section.
The pulp can be used alone, or can be blended with newer material [virgin fiber] to add strength and smoothness to the paper. Rest of the recycled paper making process is same as that of the simple paper making process, which can be read here…”Paper Manufacturing”.
