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Why does the newspaper turn yellow on prolonged exposure to air?
Wiki User
∙ 14y ago
Paper turns yellowish or brownish for a couple of different reasons. For example, dust and oil from fingertips will discolor paper over time.
But a big part of yellowing in paper is a chemical called lignin. The amount of yellowing and the time it takes for paper to turn yellow is determined by the amount of lignin in it. When paper pulp is created from a tree, the tree contains cellulose and lignin. The highest quality paper has the lowest lignin content.
So, newsprint is low quality paper. It typically contains 20% lignin or so. If you leave newsprint out in the sun for a day or two, you can see its color changing. The lignin reacts with light and turns yellow.
Typical white copier paper, on the other hand, has less than 1% lignin. It fares much better in sunlight, but given enough exposure it too will turn yellow.
The smell and the yellowing are both mainly due to the presence of hemicellulose and lignin.
Paper is essentially formed from cellulose fibers, which are produced from wood, from cotton or from annual plants like flax (or even from straw). In these plants, the cellulose is generally accompanied by hemi-cellulose (roughly short chained cellulose) and lignin, which both act as binders to constitute cell walls and such things.
Before you make paper, you make paper pulp from these plant sources. Paper pulp is actually "industrial cellulose". There are two main procedures, with subdivisions but also with the possibility of intermediate procedures. They would be classified as mechanical pulping and chemical pulping.
mechanical pulping in its simplest form means that you take a piece of wood (a log actually) and press it against a very wet turning grindstone. The product is also known as "groundwood" and contains not only the cellulose but all of the hemicellolose and lignin. Groundwood used to be the raw material for "newsprint" (= the paper your daily newspaper and similar articles are printed on)
chemical pulping consists more in dissolving and/or decomposing the binders. There are different procedures, some of which give a typical brown pulp (like "kraft"). Very often the chemical pulping is completed by bleaching. Paper made exclusively from bleached chemical pulp is known as "woodfree" even if the raw material for pulping was wood.
Matters are complicated a bit because more and more "secondary fiber" is used nowadays. ("Secondary fiber" is simply a more expensive term for "recycled waste paper").
(see also the Wikipedia article on wood pulp : http://en.wikipedia.org/wiki/Woodpulp or http://www.paperonweb.com/
Anyway, cellulose itself has little tendency to turn yellow with age, UV-light or chemical reaction with acids, but lignin will do exactly that. Up to a point this can be compensated by adding optical brightening agents, which reflect UV light as visible light. And a brown paper may become clearer under influence of the UV in sunlight, (although that would be more the case if the brown colour is due to addition of a colouring agent.)
Wiki User
∙ 11y ago
Wiki User
∙ 14y agoThe basic constituent of paper are Cellulose and water, and which are bleached by bleaching agent, on long exposure to air moisture becomes evaporated (along with bleaching agent) which is a binding force among cellulose units now the original colour of material comes back which is yellow
Wiki User
∙ 14y agoIf you leave Paper in the sunlight for a long time it can be heated in a way. It can become discolored from so much light and heat.
Wiki User
∙ 13y agoa chemical change :)
Wiki User
∙ 13y agono a chemical change
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Which of the following statements indicates the way in which the body's natural defenses protect the skin from the effects of UV damage?
Prolonged exposure to the sun induces melanin dispersion, which in turn acts as a natural sunscreen.
Why do gloves turn yellow on sweating?
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Beta-carotene.
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The yellow color on the newspaper is evidence of oxidation and chemical breakdown of the paper fibers due to exposure to sunlight. This process is known as photooxidation and it causes the paper to lose its brightness and become yellow over time.
When paper turn yellow brown upon exposure to sun light what type of change is likely taking place?
chemical change
Which of the following statements indicates the way in which the body's natural defenses protect the skin from the effects of UV damage?
Prolonged exposure to the sun induces melanin dispersion, which in turn acts as a natural sunscreen.
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why does wheat turn yellow when it grows in the dark
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Why do high-gloss cabinets turn yellow?
High-gloss cabinets can turn yellow due to a variety of factors, including: UV exposure: Prolonged exposure to sunlight or artificial UV light sources can cause the glossy finish of the cabinets to yellow over time. The UV rays break down the chemical structure of the finish, leading to discoloration. Aging of materials: Some materials used in the construction of high-gloss cabinets, such as certain types of paints or clear coats, may naturally yellow or discolor as they age. This can be exacerbated by environmental factors, such as heat or humidity. Chemical reactions: Interaction with certain chemicals or cleaning agents that contain harsh ingredients can react with the cabinet finish, causing it to yellow or change color. Quality of materials: Lower-quality finishes or paints may be more prone to yellowing compared to higher-quality options. Inferior materials may not have sufficient protection against UV rays or may have inherent properties that lead to discoloration. To minimize the risk of yellowing, it is important to choose high-quality materials, avoid prolonged exposure to direct sunlight, use gentle cleaning agents specifically formulated for glossy surfaces, and follow proper maintenance instructions provided by the manufacturer. Regular cleaning and maintenance can help preserve the original appearance of high-gloss cabinets. کابینت گارنی
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Why do gloves turn yellow on sweating?
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