Optical brightening agent

Optical brightener

Optical brightener

Optical brighteners, optical brightening agents , fluorescent brightening agents or fluorescent whitening agents are dyes that absorb light in the ultraviolet and violet region of the electromagnetic spectrum, and re-emit light in the blue region...

 is used to make paper appear more white. Optical brightening agents use fluorescence

Fluorescence

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

 to absorb invisible radiation from the ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 part of the light spectrum and re-emit the radiation as light in the visible blue range. The optical brightening agent thus generates blue light that is added to the reflected light. The additional blue light offsets the yellowish tinge that would otherwise exist in the reflected light characteristics. It thus increases the brightness of the material (when the illumination includes ultraviolet radiation).

Pigment

Pigment

Pigment

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s that absorb in the yellow and red part of the visible spectrum can be added. As the dye

Dye

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....

 absorbs light, the brightness of the paper will decrease, unlike the effect of an optical brightening agent. To increase whiteness, a combination of pigments and optical brightening agent are often used. The most commonly used pigments are blue and violet dyes.

Cationic starch

To enhance the paper strength, cationic starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 is added to wet pulp in the manufacturing process. Starch has a similar chemical structure as the cellulose fibre of the pulp, and the surface of both the starch and fibre are negatively charged. By adding cationic (positive charged) starch, the fibre can bind with the starch and thus also increase the interconnections between the fibres. The positively-charged portion of the starch is usually formed by quaternary ammonium cation

Quaternary ammonium cation

Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...

s. Quaternary salts that are used include 2.3-epoxy propyl trimethyl ammoniumchloride (EPTAC, also known as or Glytac Quab) and (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC, also known as Quat 188).

Retention agent

Retention agent is added to bind filler

Filler

In general, a filler is something that is used to fill gaps. Specialized meanings of the word "filler" include:* Filler , dietary fiber and other ingredients added to pet foods to provide bulk...

s to the paper. Fillers, such as calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

, usually have a weak charged surface. The retention agent is a polymer with high cationic, positively charged groups. An additional feature of a retention means to accelerate the dewatering in the wire section of the paper. Polyethyleneimine and polyacrylamide

Polyacrylamide

Polyacrylamide is a polymer formed from acrylamide subunits. It can be synthesized as a simple linear-chain structure or cross-linked, typically using N,N-methylenebisacrylamide. Polyacrylamide is not toxic...

 are examples of chemicals used.

Caustic soda

Caustic soda is added to increase the pH in the pulp

Pulp (paper)

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

ing process of fibers. The higher pH of the paper fiber solution causes the fibers to smoothen and swell, which is important for the grinding process of the fibers.

Sizing agent

Internal sizing of paper, most paper types must have some water-resistance in order to have a specific writing quality and / or printability.
Until 1980 mainly a rosin

Rosin

.Rosin, also called colophony or Greek pitch , is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black...

 in combination with alum

Alum

Alum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...

 was used. When the paper industry started using chalk instead of to china clay as filler, the paper chemistry had to switch to a neutral process. Today mainly AKD (alkyl ketene dimer

Diketene

Diketene is an organic compound formed by dimerization of ketene. Diketene is a member of the oxetane family. It is used as a chemical reagent in organic chemistry. It is a colorless liquid and heating regenerates the ketene monomer...

) and ASA (alkenyl succinic anhydride

Succinic anhydride

Succinic anhydride, also called dihydro-2,5-furandione, is an organic compound with the molecular formula C4H4O3. It is the acid anhydride of succinic acid.-Applications:...

) are used.

Wet strength additive

Wet strength additives ensure that when the paper becomes wet, it retains its strength. This is especially important in a tissue paper. Typical chemicals used are as epichlorohydrin

Epichlorohydrin

Epichlorohydrin is an organochlorine compound and an epoxide. This is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but miscible with most polar organic solvents. Epichlorohydrin is a highly reactive compound and is used in the production of glycerol, plastics,...

, melamine

Melamine

Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....

, urea formaldehyde and polyimines. These substances polymerize in the paper and result in construction of a strengthening network.

Coating binders

Styrene butadiene

Styrene-butadiene

Styrene-Butadiene or Styrene-Butadiene-Rubber is a synthetic rubber copolymer consisting of styrene and butadiene. It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tires, where it may be blended with natural rubber...

 latex, Styrene acrylic, dextrin

Dextrin

Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....

, oxidized starch

Modified starch

Modified starch, also called starch derivatives, are prepared by physically, enzymatically, or chemically treating native starch, thereby changing the properties of the starch. Modified starches are used in practically all starch applications, such as in food products as a thickening agent,...

Pulping chemicals

For the production of chemical pulp from wood chips, following chemicals can be used:

• Caustic soda, Sodium sulfide
  Sodium sulfide
  Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...
  
   for the Kraft process
  Kraft process
  The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
  
  
• Sulfurous acid
  Sulfurous acid
  Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
  
   for the Sulfite process
  Sulfite process
  The sulfite process produces wood pulp which is almost pure cellulose fibers by using various salts of sulfurous acid to extract the lignin from wood chips in large pressure vessels called digesters. The salts used in the pulping process are either sulfites , or bisulfites , depending on the pH...
  
  
• Caustic soda, Anthraquinone
  Anthraquinone
  Anthraquinone, also called anthracenedione or dioxoanthracene is an aromatic organic compound with formula . Several isomers are possible, each of which can be viewed as a quinone derivative...
  
   for the Soda pulping
  Soda pulping
  Soda pulping is a chemical process for making wood pulp with sodium hydroxide as cooking chemical. In the Soda-AQ process, anthraquinone may be used as a pulping additive to decrease the carbohydrate degradation...
  
  

Bleaching chemicals

Sodium dithionite

Sodium dithionite

Sodium dithionite is a white crystalline powder with a weak sulfurous odor. It is a sodium salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water and in acid solutions...

, Chlorine dioxide

Chlorine dioxide

Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....

, Hydrogen peroxide

Hydrogen peroxide

Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

, Ozone

Ozone

Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

Bleaching additives:

• Sodium silicate
  Sodium silicate
  Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...
  
  
• Sequestering agents: EDTA
  EDTA
  Ethylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...
  
  , DTPA