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What Is Paper Pulp?

Paper pulp from recycled products might be used to make toilet paper.
Recycled paper, which is made from paper pulp.
A bag made of recycled pulp.
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  • Written By: Paul Scott
  • Edited By: E. E. Hubbard
  • Last Modified Date: 07 April 2015
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Paper pulp is a term used to describe various slurry preparations used to manufacture paper and paper products. The pulps are either produced from wood or cotton fiber, and are made by “cooking” the wood chips or cotton fibers in a solution of water and various chemicals to reduce them to a consistency suitable for the rolling of the various end products. Both hard and soft woods harvested from sustainable sources are used to produce wood-based paper pulp. In the case of cotton-based pulps, raw cotton linters or recycled rag off-cuts are used to produce higher quality papers than those made with wood pulp. After production, the pulp may be used immediately, stored in vats, or dried and packaged for later use.

Most commercial paper products are made from pulped wood or cotton fiber. With both raw material sources, the paper pulp is generally manufactured by “cooking” wood chips or cotton fibers at high temperatures and pressures in a digester to reduce, or break down, the material to form a viscous suspension. The raw material is cooked in a solution of water and chemicals such as sodium hydroxide, sodium sulphide, and calcium carbonate, known as white liquor. Once the cooking process is complete, the pulp typically undergoes several washing and bleaching stages before it is dried and processed.

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Wood-based paper pulp processes start with the collection of suitable wood stocks from sawmill waste sources, forestry harvesting, or thinning operations. These stocks include both hard and soft wood varieties, including pine, spruce, and birch. The wood is then cleared of bark and debris and chipped to produce a fine aggregate. The chips are introduced into a heated pressure vessel known as a digester along with a solution of water, sodium hydroxide, and sodium sulphide, where they are cooked under pressure for approximately 90 minutes. This process breaks down the lignin, or cell-binding agents, in the wood, reducing the chips to a thick pulp.

Cotton paper pulp is produced from one of two raw material sources — raw cotton linters and cotton rags. Cotton linters are long, fine fibers that surround the seed on a cotton boll, while rags are simple garment and fabric manufacturing off-cuts. These cotton fibers are cellulose-rich and have no lignin, resulting in a whiter and stronger end product requiring less bleaching. Cotton pulp is made using a similar process to wood pulp with the fibers being cooked under pressure in a solution of water and chemicals such as calcium carbonate and hydrogen peroxide. Due to their strength and longevity, cotton-based papers are commonly used as archival supports for artwork and currency manufacture.

In both wood and cotton paper pulp processes, the pulp undergoes several washing stages after the initial cooking is complete. In addition to washing, wood pulp is typically also bleached to neutralize any remaining lignin coloring in the pulp. The finished pulp is then either used immediately or may be stored wet in vats, or dried, cut, and packaged for distribution to paper producers.

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croydon
Post 3

It's not that difficult to make paper pulp at home and use it for a variety of different things. I made paper bricks for our fireplace when I was a kid and you can do that with homemade molds. In theory you can also sculpt with paper pulp, although I've never done that.

And, of course, you can make paper, although it's more difficult than it looks to make good paper from recycled pulp. It's definitely worth a try though.

clintflint
Post 2

@umbra21 - Well, not that it makes it any better, but original paper is going to have bleach added to it as well, and in fact will probably be exposed to a lot more of it to get it a uniform color, so it's still better to choose recycled paper if you have to use any kind of paper.

Also I believe there are definitely companies out there who are attempting to make paper in a way that is environmentally friendly. You don't have to use trees to make the pulp, for example and some of them use recycled cotton or flax or hemp fibers instead. You also don't have to use industrial chemicals (is dispose of them in rivers and other waterways, which is the larger concern).

Paper isn't an inherently wasteful resource. It can definitely be made from renewable, environmentally friendly processes.

umbra21
Post 1

The problem with a lot of recycled paper is that recycled paper pulp tends to be a rather murky grey even after it's been washed, because of all the ink and different shades of the original paper and other products. So it requires additional bleaching in order to make it into the kind of paper that people expect. They might add a few additional bits to make it look a little rough so that it's obviously recycled, but that's intentional.

Paper in general is just a really wasteful product, and it's a shame that it's so ubiquitous and taken for granted in our society.

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