Can paper be synthetically produced without wood
Papers according to the fiber composition
Apart from a still small percentage of synthetic fibers, today's paper fibers are almost exclusively of vegetable origin. In addition to straw and some grasses, that forms Wood is the most important source of raw materials. The best is Softwood suitable for fiber production. The breakdown into the individual fibers, also called digestion, takes place either mechanically or chemically.
Wood pulp is the generic term for the various types of fiber pulp made from wood, largely produced by mechanical means. It is subdivided into the purely mechanical pulp: wood pulp, brown pulp and refiner pulp as well as the pulp with thermal and / or chemical pretreatment: thermal refiner pulp, chemically thermal refiner pulp.
Wood pulp (white pulp) is made in a purely mechanical way by grinding coniferous wood, mostly spruce. The wood is broken down to a fineness that comes close to the size of the cellulose fibers. The trunks, which have been debarked and cut to a length of about one meter, are pressed against rapidly rotating grinding stones with the addition of water. Hence often referred to as stone cut. The rough stone surface tears out intact fibers 1 to 4 mm in length as well as fiber fragments and the finest fiber particles from the wood. Wood pulp is a cheap pulp that, in addition to the cellulose fibers, contains all non-fibrous components of the wood, such as. B. lignin and resin. It is short-grained, brittle, hard and, despite its bleaching, somewhat yellowish.
At the Brown grinding process the debarked sanding wood is steamed under pressure for several hours. This loosens the wood fiber bandage and a long, crisp fabric is obtained when sanding, but with a strong and non-bleachable tan. The area of application of this material is significantly restricted and limited to packaging paper, cardboard boxes and cardboard (leather cardboard).
At the Refiner wood pulp the wood is shredded in refiners. The refiner essentially consists of two grinding disks, which consist of profile-equipped segments. Of these, one is usually fixed, while the other rotates quickly in parallel. The disks are designed in such a way that the grinding gap becomes narrower and narrower towards the circumference. This creates a break-up zone in the center, which then merges into the grinding zone. In contrast to stone grinding, the wood has to be cut into small pieces of wood, the so-called wood chips, before it is shredded. These wood chips are fed continuously in the center between the grinding disks, crushed in the breaking zone and driven into the grinding zone by centrifugal forces. A combined compression and rolling effect creates frictional heat, which softens the lignin and enables it to fray. The advantages of this process are that you can process industrial waste wood, sawmill waste and even coarse sawdust. Furthermore, a longer-fiber wood pulp with high strength properties is obtained. The splinter content, on the other hand, drops. The international designation this procedure is Refiner mechanical pulp or abbreviated RMP.
The difference from thermo-mechanical wood pulp (TMP) to refiner wood pulp consists of the thermal pretreatment of the wood chips, otherwise the processes are largely identical. The wood chips are impregnated by means of steam in a preheater, inserted between the grinding disks and cut up. The steaming time is approx. 1–3 minutes at 110–130 ° C and approx. 1–2 bar overpressure. The thermal pretreatment enables a very gentle defibration, whereby a very high quality wood pulp is obtained, which is characterized by many well-preserved, long, supple wood fibers and hardly contains any splinters. The greater proportion of intact fibers is of great advantage for some strength properties. The international designation this procedure is Thermo-mechanical pulp or abbreviated TMP.
At the chemical-thermomechanical wood pulp (CTMP) In contrast to the TMP process, the wood chips are not only impregnated with steam, but also with chemicals, mostly sulfites and bisulfites. This causes the resins and the lignin in the wood to dissolve, which means that the actual cellulose fiber can be partially detached from its association during the subsequent defibration. This type of wood pulp remains relatively long and supple and almost represents a transition to the more valuable pulp international designation this procedure is Chemical-Thermo-Mechanical-Pulp or abbreviated CTMP.
Papers, as well as cardboard with wood pulp additives, are called wood-containing (hin). The amount of wood pulp added can have a positive or negative effect on the quality of the paper.
Positive impact are:
• reduction of the weight per unit area,
• increase in opacity (opacity),
• Increased flexural rigidity, especially with cardboard.
Negative impacts are:
• reduction in strength,
• yellowing and becoming brittle when exposed to light,
• Reduction of the splitting strength with multi-layer cardboard,
• Increased accumulation of dust during processing (cutting, folding).
cellulose is obtained by chemical decomposition of the wood. In this process, the wood chopped into chips is boiled in acids or alkalis at high steam pressure. These liquids have the ability to dissolve those substances from the wood that are disadvantageous in the paper. It is above all the non-fibrous components such as lignin and resins, which are also called incrustations. A largely undamaged cellulose fiber is obtained, the strength of which has been retained. Papers, as well as cardboard boxes that are only made from cellulose, are called wood-free (h'fr). They are very firm, tough, elastic and pliable. They hardly or not at all yellow when exposed to light.
Rag fabrics are vegetable fibers obtained from textile waste such as cotton, linen, hemp and flax. They are long, supple and unwooded fibers of high strength. Rag fabrics are the oldest and finest pulp for paper production. They were already used in medieval paper production and are still used today for the production of high-quality paper of great toughness, folding and crease resistance (e.g. banknotes and document papers).
Synthetic fibers are plastics that are made up of large molecules. They get their fiber shape through spinning or spraying processes. Synthetic fibers have a very high strength, do not absorb water and do not rot. Since they are not made up of the finest individual fibers like vegetable fibers, they hardly tangle with one another, but have to be glued together when the leaves are formed.
Fibers from waste paper: This is not a new fiber material, but fibers that are obtained by breaking down paper waste or used paper (secondary fiber material). Over 40% of the total amount of fiber is already obtained from waste paper. The quality of the pulp from waste paper depends crucially on the previous purpose of the paper. The degree of soiling, wood content and color play a major role. This fiber is mainly used for the production of recycled paper, wrapping paper, cardboard and cardboard.
Paper types: The papers are divided into the following groups according to the type, quantity and mixing ratio of the fibers mentioned:
• Rag papers: Only rag pulp is used to make them. Examples: handmade paper, banknote and document paper.
• Papers containing rag: They are wood-free papers with an admixture of at least 10% rag pulp. The main part is pulp. Examples: high-quality writing and drawing papers, thin and bible printing papers.
• Wood-free papers are made exclusively from pure cellulose, but may contain up to 5% woody fibers. Examples: good writing and printing papers, end papers, lots of cover papers.
• Papers containing wood consist of 10 to 90% (e.g. newsprint) of wood pulp, the rest is pulp or waste paper. In terms of quantity, they make up the largest proportion of paper consumed. According to the wood pulp content they are divided into:
- almost wood-free papers,
- slightly wood-containing papers,
- medium-fine papers (wood pulp content 30 to 50%)
- Papers with a high content of wood (wood pulp content up to 90%).
Examples: cheap writing paper, printing paper for mass printing, magazine and newsprint paper.
• Synthetic papers: They either consist entirely of synthetic fibers or contain an admixture of cellulose. Their mechanical strength is very high; In other words, they are scratch and scuff resistant, very tear-resistant and can often be folded without breaking (high folding resistance). Many types are even waterproof and can no longer be glued with the usual adhesives used in bookbinding.
Examples: ID cards, driver's licenses, long-lasting user manuals, waterproof maps and the like.
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