Paper chemicals

Paper chemicals designate a group of chemicals that are used for paper manufacturing, or 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.^[1] The chemicals can be defined on basis of their usage in the process.

Chemical usage is not only for imparting properties to paper but to handle the water cycles in the process, conditioning of fabrics, cleaning of equipment and several other applications.

Common name	Scientific name	Chemical formula	Notes
Alum	"Sulfate of alumina"	Al2(SO4)3 · 18 H2O	For alkaline sizing along with rosin[clarification needed]
Albarine	"Calcium sulfate"	CaSO4 · 2 H2O	Building materials
Chlorine dioxide	Chlorine dioxide	ClO2	Pulp bleaching
Chlorine	Chlorine	Cl2	Pulp bleaching
Dolomite	Calcium magnesium carbonate	CaMg(CO3)2	Filler, Coating
DTPA	Diethylenetriaminepentaacetic acid	C14H33N3O10	Used for chelation (removal of transition metals from pulp).
EDTA	Ethylenediaminetetraacetic acid	C10H16N2O8	Used for chelation (removal of transition metals from pulp).
Enzyme[which?]			Used in deinking
FSA	Formamidine Sulfuric acid or Thiourea dioxide	CH4N2SO2	Post deinking bleaching
Guar gum	Natural polymer; no systematic name		Dry strength additive
Gypsum or mineral white or plaster	Calcium sulfate	Ca SO4 · 2 H2O	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
Limestone	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	Na2CO3	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 hypochlorite	Sodium hypochlorite	NaOCl	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		Wet and dry end additive	Consists of glucose units linked together by oxygen bridges called glycosides
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

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.^[2]

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.

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]
3. Totally chlorine-free bleaching utilizes oxygen and hydrogen peroxide. This is the most environmentally friendly process since it eliminates all chlorinated pollutants.^[4]

Most paper types must have some water-resistance to maintain a specific writing quality and 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. At several places AKD (alkyl ketene dimer) and ASA (alkenyl succinic anhydride) are used. Latest development is to use surface size,^[5] which is applied using a size press. The advantage of surface sizing is that it does not interfere with the backend water chemistry.

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.

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, GMAC™) and (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC, also known as Quat 188, Quab 188, Reagens™).

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 promote the binding of pigment particles between themselves and the coating layer of the paper.^[6] Binders are spherical particles less than 1 μm in diameter. Common binders are styrene maleic anhydride copolymer or styrene-acrylate copolymer.^[7] The surface chemical composition is differentiated by the adsorption of acrylic acid or an anionic surfactant, both of which are used for stabilization of the dispersion in water.^[8] Co-binders, or thickeners, are generally water-soluble polymers that influence the paper's color viscosity, water retention, sizing, and gloss. Some common examples are carboxymethyl cellulose (CMC), cationic and anionic hydroxyethyl cellulose (EHEC), modified starch, and dextrin. 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.

Mineral fillers are used to lower the consumption of more expensive binder material or to improve some properties of the paper.^[9] China clay, calcium carbonate, titanium dioxide, and talc are common mineral fillers used in paper production.^{[citation needed]}

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.^{[citation needed]}

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.^{[citation needed]}

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).^[10]

• Deinking recycled paper
• Surface chemistry of paper
• Organosolv (pulping technique)
• Per- and polyfluoroalkyl substances

• List of chemicals used in pulp and paper making