Paper

 

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How Paper is made from Sugarcane

Today we’re in the heart of the KwaZulu-Natal sugar cane fields to have a look at the way in which paper is made from sugar cane. We’re going into the SAPPI paper plant, which is right next to a sugar factory, so all of the crushed sugar cane is sent from the sugar factory straight over to the SAPPI paper plant.

The crushed sugar cane is known as Bagasse. Bagasse is the fibrous matter that remains after sugarcane is crushed to extract it’s juice.

Large stockpiles of bagasse are fed to the Pulp Mill as required.

It passes through a number of washing processes to remove pith, dirt and stones.

The bagasse is cooked in a large digester , a big pressure cooker, to separate the fibres by dissolving the  Lignin in the material.

Lignin is found in the cell walls of plants. It binds the fibres of the sugar cane together to give the cane the strength to grow straight up from the ground. Without the Lignin binding the fibres together, the sugar cane would just flop over.

The bagasse is cooked in a digester using caustic soda, steam and water to separate the Lignin from the fibres.

All of the cooking and refining processes are computer controlled, with all materials being added to the machines automatically.

Here the remaining caustic soda, and dissolved Lignin is washed out of the remaining fibres.

Next a bleaching process changes the colour of the fibres from brown to white as they pass through these three bleaching stages. The first stage uses chlorine dioxide to remove most of the remaining Lignin in the pulp. It’s washed to remove the chlorine dioxide and moves to the second bleaching stage where a hydrogen peroxide and sodium hydroxide solution further bleach the pulp. In the final bleaching stage, the fibres undergo a further hydrogen peroxide process after which they are white and spotlessly clean

The Paper made at this mill consists of a blend of between 60 and 65 percent of Bagasse and various hard wood and soft wood pulps. This blend is known as ‘the Furnish’, and varies according to the type of paper to be produced.

Fillers such as clay and calcium carbonate may be added for opacity, brightness and smoothness of the paper.

Dyes and brighteners can enhance the shade and brightness of the paper.

The furnish is pumped to the paper machine where it is converted into a long sheet of paper. The mix is 98 percent water at this stage. Within the head box it is sprayed onto a wire mesh belt that has very tiny holes in it. The spraying nozzles provide a very consistent layer of pulp across the entire width of the machine.

The paper pulp forms on top of the wire and the water drains through the holes. The thickness of the paper is determined at this stage by the amount of pulp mix that is sprayed onto the forming wire.

The pulp is rapidly de-watered as it moves along the length of the moving wire belt. The fibres begin to bond and a mat is formed which is known as ‘the web’.

The paper sheet passes into the huge dryer in which it will be dried using heat and pressure. The paper web is squeezed between a series of pressure rollers and steam heated rollers to remove water and to dry the paper.

The paper sheet can be dried to very accurate moisture levels to cater to each customer’s requirements.

As the sheet comes out of the machine it’s pressed between two metal rollers to create a smooth surface and checked for thickness and quality by an electronic scanner.

The huge roll of paper at the end of the machine weighs over 6 tons and is called the jumbo reel. As one reel is filled, a new empty roll takes its place. The machine does not stop for reel changes. Instead the paper sheet will be switched to a new reel with the machine in full flight, expertly handled by well trained staff.

The paper now passes through a chemical coating process. Coatings consist of pigments made from chalk, clay or talk which covers the surface of the paper and is bound there by bonding agents. The paper can be polished to a high gloss quality finish if required.

The paper now has all the characteristics required for its end use, but must be cut to the size required by the customer. In the finishing department the jumbo reels are cut into narrower reels by a slitter re-winder.

These reels can be delivered directly to the customer, or can be processed into specific paper sheet sizes and sheets. Modern sheeters not only cut the paper to the desired size, but also check the surface quality of the paper, remove faulty sheets and count the sheets. All offcuts are recycled, with very little wastage occurring in this mill.

The final step is to wrap each reel or sheet stack to protect it from damage on the way to the converter factories. The converter factories will turn the paper into magazines, school books or any other paper product.

Well, that’s quite a process, manufacturing paper from crushed sugar cane, who knew? By making use of previously used sugar cane that has already been processed to produce sugar, this factory produces paper in a very efficient and environmentally friendly way.