Process of viscose rayon
Process of viscose rayon
Viscose rayon is a man-made fiber. This is a regenerated fiber whose raw material is cellulose. This is made with the combination of some chemicals and cellulose. Basically, we mean regenerated means that the fiber that is generated from cellulose and other chemicals like hydrogen, oxygen, nitrogen, sulfur, carbon, etc. Let's get started to know about the viscose rayon processing flow chart.
The raw materials
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Purification of raw materials
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Conditioning
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Steeping
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Shredding
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Ageing
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Churning
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Dissolving
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Blending and filtration
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Ripening
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Spinning
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Winding
A description of the processes for the production of viscose rayon fiber is given below.
1. Collection of raw material: The main element of viscose fiber is cellulose. This is regenerated cellulose fiber. This cellulose can be collected from various types of wood. In wood, there are 90% cellulose is present. Other elements like lignin are also found in wood.
2. Purification of raw materials: First of all we need to do purification of cellulose that we get from wood. After that, we need to add Caustic soda. Caustic soda reacts with cellulose and produces alkali cellulose. After that carbon di sulfide reacts with this and produces sodium cellulose xanthate. After this is dissolved in non-concentrated caustic soda. In high pressure, the chemical passes through the spinning unit. If we pass through an acid solution then we get reprecipitated fine filament. This reprecipitated cellulose is called viscose rayon. Generally, we use the spruce tree as our main and good raw material.
This tree is cut and makes small pieces size 7/8'' in length and 1/2'' in width and height 1/2''. These small pieces are treated with calcium bisulphide and boiled for 14 hours. Cellulose has no problem but lignin becomes transformed into the sulfonated group that is soluble in water. Sulphonated bi-product is separated and we get cellulose. Cellulose pulp are floating in calcium bisulphide and after that passes through 0.2mm hole and made wood pulp.
3. Conditioning of wood pulp: In wood pulp sheets have 90-94% cellulose. This wood pulp is placed in a certain temperature and moisture to regain moisture. After that, we need to cut sheets by guillotine in a certain shape and send them for conditioning in a room.
4. Steeping: After conditioning the wood pulps it needs to react with caustic soda solution which process is called mercerizing or steeping. The wood pulp must be impregnated well in a caustic soda solution. In this state wood pulp degree of polymerization will be up to 1000 beta glucose units. Conditioned pulp sheets are taken in a steeping tank. Sheets are moved by a steel plate that is perforated. Caustic soda solution is added to the steeping tank. Up to the coming dark brown color of wood pulp, the steaming process is on. It can take 1-14 hours. After that, the Caustic soda solution is out by a drain. The revolving plate also give pressure on the wood pulp to remove caustic soda.
5. Shredding or Cutting: Soft and wet sheets are sent to the shredding machine. This machine has two handles, a bearing, and wings. When the vessel moves then sheets be small to smaller pieces and be like bits. During shredding need to water flows through the outer body of the vessel to control temperature. This process continues up to 2-3 hours and at a time can be cut 200 lb wood pulp into small pieces like bits.
6. Ageing: To get the standard solution to increase the viscose solution quality need to process soda cellulose. This process is known as Ageing. We need to take beets in a galvanized steel drum and continue this process for 48-72 hours. The aging temperature depends on the quality of the wood pulp. In this process soda cellulose's degree of polymerization be down from 1000 to 300 due to the presence of oxygen in the air. For this reason, aging need to do hurriedly. Sometimes aging can be done by increasing temperature and decreasing time.
7. Churning: This process is also called Xanthesion or subsidizing. Small soda cellulose crumbs are taken in a hexagonal-shaped vacuum drum. It looks like a cement mixing machine. This is double-jacketed to control temperature during churning. Carbon di sulfide is added as 10% based on the weight of the crumbs. The mixture continues churning up to 3 hours and 2rpm. Due to this soda cellulose makes a reaction with carbon di sulfide and makes sodium cellulose xanthate. Slowly change its color. First, its color be white and change to light yellow and next dark yellow, and at last, be a grey color.
8. Mixing or dissolving process: The small balls that we get from churning are named sodium cellulose xanthate. These balls are filled in a mixer machine called a dissolver. This dissolver has a mixer. In the dissolver need to add a caustic soda solution and mix for up to 4-5 hours to make the dissolver cool. Sodium cellulose xanthate be soluted and make brown color viscose jelly. This liquor is called Viscose. This contains 6.5% sodium hydroxide and 7.5% cellulose.
9. Blending and filtration: The viscose solution needs to place in a vertical or horizontal mixer. From 8 small dissolvers, we need to bring viscose solution into a big mixer through a pump. Here also need to blend viscose liquor. Need good blending to make good quality fiber. After that need to filter and remove dirt and insoluble cellulose. The full process is done in a vacuum vessel.
10. Ripening: Increasing the yarn-making capability of fiber ripening is very necessary. Viscose solution needs to keep 2-5 days 10°C-18°C. As a result, the viscosity becomes less and comes in the main condition. Then need to filter and remove foreign materials.
After that, we start spinning viscose fiber.
After making the yarn need to winding.
