Paper chemicals

Paper chemicals designate a group of chemicals that modify the properties of paper. These chemicals can be used to alter the paper in many ways, including changing its color and brightness, or by increasing its strength and resistance to water.

Sulphite Pulp Mill discharging water waste

Chemicals used in paper manufacturing

Chemicals used in the paper manufacturing process

Common Name Chemical Name Chemical Formula Notes Agalite or Talc Silicate of Magnesia MgO3SI-32%, SiO2-42% It gives paper a greasy or soapy feel. and enables it to take a high finish. AKD alkyl ketene dimer C4H4O2 Sizing Alabaster or Annaline calcium sulfate (anhydrate) CaSO4 Paper loading material alganic acid alganic acid ("Na-alginate") Na-(C6H8O6N Coating and surface treatment alum "sulfate of alumina" Al2(SO4)3.18H2O For alkaline sizing along with rosin albarine "natural sulfate of lime" CaSO4.2H2O building materials. chlorine dioxide chlorine dioxide ClO2 pulp bleaching chlorine chlorine Cl2 pulp bleaching Dolomite calcium Magnesium Carbonate CaMg(CO3)2 Filler, Coating DTPA Diethylene Triamine Penta Acetate C14H33N3O10 Used for chelation (removal of transition metals from pulp). EDTA Ethylene Diamine Tetra acetic Acid C10H16N2O8 Used for chelation (removal of transition metals from pulp). Enzyme Used in Deinking FSA Formamidine Sulphuric Acid or Thiourea Dioxide CH4N2SO2 Post Deinking bleaching Guar Gum Natural Polymer   Dry Strength Additive Gypsum or Mineral White or Plaster Natural Sulfate of Lime CaSO4.2H2O Gypsum board Hydrogen Peroxide Hydrogen Peroxide H2O2 In Pulp Bleaching Hypochlorous Acid Hypochlorous Acid HOCl In Pulp Bleaching Lime Calcium Oxide CaO Alkaline Pulping Process Chemical Recovery, Bleaching Lime Stone Calcium Carbonate CaCO3 To make Precipitated CaCO3, is used as Filler and in Coating Magnesium Bisulfite Magnesium Bisulfite Mg(HSO3)2 Used in Sulfite pulping Magnesite Magnesium Carbonate MgCO3 -100% Filler for cigarette paper Milk of Lime Calcium Hydroxide Ca(OH)2 For causticizing of green liquor Milk of Magnesia Magnesium Hydroxide Mg(OH)2   Oxygen Oxygen O2 In Pulp Bleaching Ozone Ozone O3 In Pulp Bleaching Rosin Abietic Acid C19H29COOH Sizing Rosin Soap Sodium Abietate C19H29COONa Sizing Salt Cake Sodium Sulfate Na2SO410H2O Makeup chemical in sulfate pulping chemical recovery (Na2SO4. ---Na2S) Soap/ Fatty Acid Deinking Sodium Bisulfite Sodium Bisulfite NaHSO3 Used in Sulfite pulping Soda Ash Sodium Carbonate NaHSO3 Makeup chemical in alkaline pulping chemical recovery (Na2CO3+Ca(OH)2---2NaOH+CaCO3) Sodium Aluminate Sodium Aluminate Na2Al2O4 Used in conjunction with alum to control pH Sodium Bisulfite Sodium Bisulfite NaHSO3 An acid type cooking liquor chemical component sometimes used to neutralized residual chlorine in the pulp during the bleaching process. Sodium Chlorate Sodium Chlorate NaClO3 Used to generate Chlorine Dioxide Sodium Dithionite Sodium Hydrosulfite Na2S2O4 Bleaching Sodium Hypo-chlorite Sodium Hypo-chlorite Na2S2O4 Bleaching Sodium Peroxide Sodium Peroxide Na2O2 Bleaching Sodium Silicate Sodium Silicate Na2SiO3 In waste paper deinking for wetting, peptization, ink dispersion, peroxide stabilization. Sodium Sulfide Sodium Sulfide Na2S Active chemical in kraft/sulfate cooking liquor Sodium Thiosulfate Sodium Thiosulfate Na2S2O3 Bleaching Sodium tripolyphosphate Sodium tripolyphosphate Na5P3O10 Dispersant Starch Consists of glucose units linked together by oxygen bridges called glycosides Wet and dry end additive Sulfur Sulfur S To make HSO3f or bi-sulfite pulping Surfactant Used in deinking. Used as debonders in fluff pulp manufacture. Titania Titanium Dioxide TiO2 Filler to increase the opacity and brightness of paper. Used in coating. Anatase Titanium Dioxide TiO2

Pulping

Chemical pulping involves dissolving lignin in order to extract the cellulose from the wood fiber. The different processes of chemical pulping include the Kraft process, which uses caustic soda and sodium sulfide and is the most common; alternatively, the use of sulfurous acid is known as the sulfite process, the neutral sulfite semichemical is treated as a third process separate from sulfite, and soda pulping which is the least ecologically hazardous utilizing sodium hydroxide or anthraquinone.

Caustic soda is added to increase the pH in the pulping 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.

Processing pulp in a Hollander beater

Bleaching

Main article: Bleaching of wood pulp

In the production of white paper, the wood pulp is bleached to remove any color from the trace amounts of lignin that was not extracted in the chemical pulping process. There are three predominant methods of bleaching:

1. Elemental chlorine bleaching uses chlorine and hypochlorite.
2. Elemental chlorine-free bleaching is more environmentally friendly since it eliminates the use of hypochlorite and replaces chlorine with chlorine dioxide or sodium chlorate.
3. Totally chlorine-free bleaching utilizes oxygen and hydrogen peroxide. This is the most environmentally friendly process since it eliminates all chlorinated pollutants.

Sizing

Main article: Sizing

Most paper types must have some water-resistance to maintain a specific writing quality and/or printability. Until 1980 the typical manner of adding this resistance was by using a rosin in combination with alum. When the paper industry started using chalk instead of china clay as filler, the paper chemistry had to switch to a neutral process. Today mainly AKD (alkyl ketene dimer) and ASA (alkenyl succinic anhydride) are used.

Strengthening

Wet-strength

Main article: Wet strength

Wet-strength additives ensure that paper retains its strength when it gets wet. This is especially important in tissue paper. Chemicals typically used for this purpose include epichlorohydrin, melamine, urea formaldehyde and polyimines. These substances polymerize in the paper and result in the construction of a strengthening network.

Cationic starch

To enhance the paper's strength, cationic starch 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 cations. 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).

Dry-strength

Dry-strength additives, or dry-strengthening agents, are chemicals that improve paper strength normal conditions. These improve the paper's compression strength, bursting strength, tensile breaking strength, and delamination resistance. Typical chemicals used include cationic starch and polyacrylamide (PAM) derivatives. These substances work by binding fibers, often under the aid of aluminum ions in paper sheet.

Binders

Styrene butadiene latex, Styrene acrylic, dextrin, oxidized starch are used in coatings to bind the filler to the paper. Co-binders are natural products such as starch and CMC (Carboxymethyl cellulose), that are used along with the synthetic binders, like styrene acrylic or styrene butadiene. Co-binders are used to reduce the cost of the synthetic binder and improve the water retention and rheology of the coating.

Fillers

Main article: Filler (materials)

Mineral fillers are used to lower the consumption of more expensive binder material or to improve some properties of the paper. China clay, calcium carbonate, titanium dioxide, and talc are common mineral fillers used in paper production.

Retention

Main article: Retention agent

A Retention agent is added to bind fillers to the paper. Fillers, such as calcium carbonate, usually have a weak surface charge. The retention agent is a polymer with high cationic, positively charged groups. An additional feature of a retention agent is to accelerate the dewatering in the wire section of the paper machine. Polyethyleneimine and polyacrylamide are examples of chemicals used in this process.

Coating

Main article: Coated paper

Pigments

Paper Coating

Pigments that absorb in the yellow and red part of the visible spectrum can be added. As the dye 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 an optical-brightening agent are often used. The most commonly used pigments are blue and violet dyes.

Optical-brightening agent

Optical brightener is used to make paper appear whiter. Optical-brightening agents use fluorescence to absorb invisible radiation from the ultraviolet 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).

See also

• Deinking recycled paper
• Surface chemistry of paper
• Organosolv (pulping technique)

External links

• List of chemicals used in pulp and paper making