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Food Packaging
Paper is thin material mainly used for writing upon,printing upon or packaging. It is produced by pressing together moist fibers, typically cellulose
pulp derived from wood, grasses, and drying them into flexible sheets.
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Papermaking
- Chemical pulping
The purpose of a chemical pulping process is to break down the chemical structure of lignin and render it soluble in the cooking liquor, so that it may be washed from the cellulose fibers. Because lignin holds the plant cells together, chemical pulping frees the fibers and makes pulp.
- Mechanical pulping
There are two major mechanical pulps, thermomechanical pulp (TMP) and pulp. In the TMP process, wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and fibreized between two steel discs. Mechanical pulping does not remove the lignin, so the yield is very high, greater than 95%.
- Recycled paper
Paper recycling processes can use either chemical or mechanical pulp. By mixing with water and applying mechanical action the hydrogen bonds in the paper can be broken and fibers separated again.
- Additives
Besides the fibers, pulps may contain fillers such as chalk or china clay, which improve the characteristics of the paper for printing or writing; Additives for sizing purposes may be mixed into the pulp and applied to the paper web later in the manufacturing process.
- Drying
After the paper web is produced, the water must be removed from it by pressing and drying. Pressing the sheet removes the water by force. Drying involves using air and or heat to remove water from the paper sheet
- Finishing
The paper may then undergo sizing to alter its physical properties for use in various applications. Paper at this point is uncoated. Coated paper has a thin layer of material such as china clay applied to one or both sides in order to create a surface more suitable for high-resolution screens. Coated or uncoated papers may have their surfaces polished by calendering.
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