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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.)
What else can I help you with?
Do clear cases turn yellow?
Yes, clear cases can turn yellow over time due to exposure to UV light, heat, and oils from skin. This discoloration is often more pronounced in cheaper materials like polycarbonate and TPU. Maintaining the case by cleaning it regularly and avoiding prolonged exposure to sunlight can help minimize yellowing.
Why would biurets solution turn yellow?
Biuret solution turns yellow when it is exposed to high temperatures or prolonged exposure to air. This can degrade the reagents in the solution, leading to a color change. Additionally, contamination or impurities in the solution can also cause a yellow color to develop.
What percentage of leaves turn yellow?
On average, around 20-30% of the leaves on a deciduous tree will turn yellow during the fall before eventually falling off. This color change is due to the breakdown of chlorophyll and the exposure of other pigments in the leaves.
Why do gloves turn yellow on sweating?
Latex gloves sometimes turn yellow because of your hands. The oils and fatty acids on your hands breaks down the latex and can turn the gloves yellow.
What is a yellow pigment derived from food that sometimes colors the skin?
Beta-carotene is a yellow pigment derived from food, such as carrots, sweet potatoes, and squash, that can sometimes color the skin. Consuming large amounts of foods rich in beta-carotene can give the skin a yellow-orange hue, particularly in areas with high levels of sun exposure.
When a newspaper is left in direct usnlight for a few days the paper begins to turn yellow The yellow color is evidence of a what?
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.
Do clear cases turn yellow?
Yes, clear cases can turn yellow over time due to exposure to UV light, heat, and oils from skin. This discoloration is often more pronounced in cheaper materials like polycarbonate and TPU. Maintaining the case by cleaning it regularly and avoiding prolonged exposure to sunlight can help minimize yellowing.
Why would biurets solution turn yellow?
Biuret solution turns yellow when it is exposed to high temperatures or prolonged exposure to air. This can degrade the reagents in the solution, leading to a color change. Additionally, contamination or impurities in the solution can also cause a yellow color to develop.
Why did my cucumber turn yellow?
Cucumbers can turn yellow due to overripening, lack of nutrients, or exposure to extreme temperatures.
Why do cucumbers turn yellow?
Cucumbers turn yellow due to overripening, exposure to excessive heat or sunlight, or a nutrient deficiency.
Does polyurethane turn yellow over time?
Yes, polyurethane can turn yellow over time due to exposure to light and oxygen.
Why does the peace lily's leaves turn yellow?
The peace lily's leaves turn yellow due to overwatering, underwatering, or exposure to direct sunlight.
Why do the leaves on my plant turn yellow?
The leaves on your plant turn yellow due to a lack of nutrients, overwatering, underwatering, or exposure to extreme temperatures.
Does silver turn yellow over time?
Yes, silver can tarnish and turn yellow over time due to exposure to air and certain chemicals.
Why has my cucumber turned yellow?
Cucumbers can turn yellow due to overripening, lack of nutrients, or exposure to extreme temperatures.
Why do gardenia flowers turn yellow?
Gardenia flowers turn yellow due to a variety of reasons, including aging, nutrient deficiencies, improper watering, and exposure to extreme temperatures.
Why did my polyurethane turn yellow?
Polyurethane can turn yellow due to exposure to light, heat, or chemicals. This yellowing process is known as oxidation, which can happen over time as the polyurethane reacts with its environment.
