Paper chemicals designate a group of chemicals that change the paper properties. These chemicals can be used to convert paper in various ways, including changing its color and brightness, or by increasing its strength and resistance to water.
Video Paper chemicals
Chemicals used in papermaking
Maps Paper chemicals
Pulping
Pulping chemistry involves dissolving lignin to extract cellulose from wood fibers. The process of making different chemical pulps includes the Kraft process, which uses caustic soda and sodium sulphide and the most common; Alternatively, the use of sulfuric acid is known as the sulphite process, neutral sulfite semichemistry is treated as a third separate process of sulfite, and the most ecologically harmful soda pulping using sodium hydroxide or anthraquinone.
Caustic soda is added to increase the pH in the fiber pulping process. The higher pH of the paper-fiber solution causes the fibers to soften and swell, which is essential for fiber grinding processes.
Bleaching
In the production of white paper, the wood pulp is bleached to remove any color from the amount of lignin that is not extracted in the process of making chemical pulp. There are three main methods of bleaching:
- Elemental chlorine bleaching using chlorine and hypochlorite.
- Elemental-free chlorine bleaching is more environmentally friendly because it eliminates the use of hypochlorite and replaces chlorine with chlorine dioxide or sodium chlorate.
- A completely chlorine-free bleaching using oxygen and hydrogen peroxide. It is the most environmentally friendly process because it eliminates all chlorinated pollutants.
Sizing
Most types of paper must have water resistance to maintain specific writing qualities and print capabilities. Until 1980, the typical way to add this resistance was to use rosin combined with alum. When the paper industry began to use lime instead of Chinese clay as a filler, the paper chemistry had to switch to a neutral process. Today, especially AKD (alkyl ketene dimer) and ASA (alkenyl succinic anhydride) are used.
Reinforce
Wet strength
Wet strength additives ensure the paper retains its strength when wet. This is very important in tissue paper. Chemicals normally used for this purpose include epichlorohydrin, melamine, urea formaldehyde and polyimines. These substances polymerize in paper and produce stronger network construction.
To increase paper strength, cationic starch is added to the wet pulp in the manufacturing process. Starches have the same chemical structure as cellulose fibers from the pulp, and the surface of starches and fibers are negatively charged. By adding cationic star (positive charge), the fibers can bind with starch and thus also increase the interconnection between the fibers. The positively charged portion of starch is usually formed by quaternary ammonium cations. Quarter salt used includes 2.3-epoxy propyl trimethyl ammoniumchloride (EPTAC, also known as Glytac Quab, GMAC (TM)) and (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC, also known as Quat 188, Quab 188, Reagent (TM)).
Power-dry
Dry strength additives, or dry strengthening agents, are chemicals that increase the strength of normal condition papers. It increases the strength of paper compression, explosive strength, tensile strength, and delamination resistance. Specific chemicals used include cationic and polyacrylamide derivatives (PAMs). This substance works by binding fibers, often under the aid of aluminum ions in sheets of paper.
Binder
Binders promote binding of pigment particles between them and a layer of paper coatings. Binder is a spherical particle whose diameter is less than 1 Âμm. The common binder is a styrene maleic stiren anhydride copolymer or styrene-acrylate copolymer. The chemical composition of the surface is distinguished by the adsorption of acrylic acid or anionic surfactant, both of which are used for the stabilization of the dispersion in water. Co-binders, or thickeners, are generally water-soluble polymers that affect the viscosity of paper color, water retention, size, 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 fillers to paper. Co-binders are natural products such as starch and CMC (Carboxymethyl cellulose), which are used in conjunction with synthetic binders, such as styrene acrylic or styrene butadiene. Co-binders are used to reduce synthetic binder costs and increase water retention and rheological coatings.
Charger
Mineral fillers are used to lower the consumption of more expensive binders or to improve some properties of paper. Chinese clay, calcium carbonate, titanium dioxide, and talc are the common mineral fillers used in paper production.
Retention
A storage agent is added to bind the filler 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 speed up dewatering in the wire section of a paper machine. Polyethyleneimine and polyacrylamide are examples of chemicals used in this process.
Coating
Pigments
Pigments absorbing the yellow and red parts of the visible spectrum can be added. When the dye absorbs light, the brightness of the paper will decrease, unlike the effects of optical illumination. To improve leucorrhoea, combinations of pigments and optical brightening agents are often used. The most commonly used pigments are blue and purple dyes.
optical-enlightenment
Optical brightener is used to make the paper appear whiter. The optical pollutant agent uses fluorescence to absorb the invisible radiation from the ultraviolet part of the light spectrum and retransmit the radiation as light in the visible blue range. Optical-lightening agent thus generates blue light added to reflected light. Additional blue lights offset the yellowish tinge that should be present in the reflected light characteristics. Thus increases the brightness of the material (when the illumination includes ultraviolet radiation).
See also
- Deinking recycled paper
- The surface chemistry of the paper
- Organosolv (pulping technique)
References
External links
- List of chemicals used in pulp and paper making
Source of the article : Wikipedia
0 Comments