Paper chemicals#Sizing agent

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.{{cite book|author1=Office of Air and Waste Management|author2=Office of Air Quality Planning and Standards|title=Compilation of Air Pollutant Emission Factors|date=August 1977|publisher=U.S. Environmental Protection Agency|location=Research Triangle Park, North Carolina |isbn=978-1-249-50100-8|edition=3rd|url=http://www.arlis.org/docs/vol2/hydropower/APA_DOC_no._1762.pdf|access-date=7 September 2015|chapter=10 Wood Processing|page=419|editor-last=Lahre|editor-first=Thomas |via= ARLIS |archive-date=3 June 2016|archive-url=https://web.archive.org/web/20160603062138/http://www.arlis.org/docs/vol2/hydropower/APA_DOC_no._1762.pdf|url-status=dead }}

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.

File:Florida Pulp and Paper Company mill, Cantonment, Florida.jpg]]

{{Main|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:

• Elemental chlorine bleaching uses chlorine and hypochlorite.
• Elemental chlorine-free bleaching is more environmentally friendly since it eliminates the use of hypochlorite and replaces chlorine with chlorine dioxide or sodium chlorate.{{cite report |url=https://www.akzonobel.com/eka/system/images/AkzoNobel_Eka%20Chemicals_ProductLine_WebRes_tcm56-60891.pdf |title="Performance chemicals for the pulp and paper industry" |date=2011 |page=2 |publisher=EKA Chemicals/Akzo Nobel |location=Gothenburg, Sweden |access-date=8 September 2015 |archive-date=14 May 2013 |archive-url=https://web.archive.org/web/20130514180354/http://www.akzonobel.com/eka/system/images/AkzoNobel_Eka%20Chemicals_ProductLine_WebRes_tcm56-60891.pdf |url-status=dead }}
• Totally chlorine-free bleaching utilizes oxygen and hydrogen peroxide. This is the most environmentally friendly process since it eliminates all chlorinated pollutants.{{cite report |date=October 1997 |chapter=7.3.9. Totally Chlorine-Free Bleaching of Papergrade Kraft Pulps |title="Supplemental Technical Development Document for Effluent Limitations Guidelines and Standards for the Pulp, Paper, and Paperboard Category" |url=https://www.epa.gov/sites/default/files/2015-10/documents/pulp-paper_suppl-tdd-subparts-b-e_1997.pdf |publisher=U.S. Environmental Protection Agency |location=Washington, D.C. |pages=7–26 |id=EPA-821-R-97-011 |access-date=22 May 2016 |url-status=live |archive-url=https://web.archive.org/web/20220123025108/https://www.epa.gov/sites/default/files/2015-10/documents/pulp-paper_suppl-tdd-subparts-b-e_1997.pdf |archive-date= Jan 23, 2022 }}

{{Main|Sizing}}

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,{{Cite web|url=https://www.advancechemicals.in/products/cationic-surface-size/|title=Cationic Surface Size|date=22 May 2021|access-date=30 June 2022|archive-date=15 December 2022|archive-url=https://web.archive.org/web/20221215153644/https://www.advancechemicals.in/products/cationic-surface-size/|url-status=live}} which is applied using a size press. The advantage of surface sizing is that it does not interfere with the backend water chemistry.

{{Main|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.

File:Cationic starch.jpg

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.{{cite journal|last=Fardim|first=Pedro|title=Paper and Surface Chemistry Part 1- Fiber Surface and Wet End Chemistry|journal=Institute of Quimica|year=2000|pages=1–14}} Binders are spherical particles less than 1 μm in diameter. Common binders are styrene maleic anhydride copolymer or styrene-acrylate copolymer.{{cite journal|last=Fardim|first=Pedro|title=Paper and Surface Chemistry Part 2- Coating and Printability|journal=Institute of Quimica|year=2000|pages=1–13}} 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.{{cite journal|last=Granier|title=Adhesion of latex particles on inorganic surfaces|journal=TAPPI J|year=1994|volume=77|issue=5|page=419}} 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.

File:Binder spheres.png

File:Cationic starch.jpgs.]]

{{Main|Filler (materials)}}

Mineral fillers are used to lower the consumption of more expensive binder material or to improve some properties of the paper.{{cite web|title=Market Study: Fillers (3rd edition)|url=http://www.ceresana.com/en/market-studies/additives/fillers/|publisher=Ceresana|access-date=7 September 2015|date=January 2014|archive-date=21 September 2013|archive-url=https://web.archive.org/web/20130921115959/http://www.ceresana.com/en/market-studies/additives/fillers/}} China clay, calcium carbonate, titanium dioxide, and talc are common mineral fillers used in paper production.{{fact|date=June 2022}}

{{Main|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.{{fact|date=June 2022}}

{{Main|Coated paper}}

File:Paper Coating.png

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.{{fact|date=June 2022}}

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).{{cite journal |author=He Shi |author2=Hongbin Liu |author3=Yonghao Ni |author4=Zhirun Yuan |author5=Xuejun Zou |author6=Yajun Zhou |date=2012 |title=Review: Use of Optical Brightening Agents (OBAs) in the Production of Paper Containing High-Yield Pulps |url=http://ojs.cnr.ncsu.edu/index.php/BioRes/article/download/BioRes_07_2_2582_Shi_LNYZZ_Review_OBAs_High_Yield_Pulp/1529 |journal=BioResources |volume=7 |issue=2 |pages=2582–2591 |access-date=22 May 2016 |archive-date=24 June 2016 |archive-url=https://web.archive.org/web/20160624115204/http://ojs.cnr.ncsu.edu/index.php/BioRes/article/download/BioRes_07_2_2582_Shi_LNYZZ_Review_OBAs_High_Yield_Pulp/1529 |url-status=live }}

{{portal|Chemistry}}

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

{{Reflist}}

• [http://www.paperonweb.com/chemical.htm List of chemicals used in pulp and paper making]

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Category:Papermaking

Category:Chemical processes

Category:Cellulose

Category:Pulp and paper industry